recede aeene cetaeane ee nase eas oan eR asa aie BLY i Ot Hy St Hash ¢ b9e?TEOO TOEO O “MN 1OHM/18lN avi HA Gin} SUBMARINE GEOLOGY OF SANTA MONICA BAY, CALIFORNIA by Richard D. Terry, Stuart A. Keesling, and Elazar Uchupi A Final Report Submitted to Hyperion Engineers, Inc. by the Geology Department University of Southern California September 11, 1956 ayer ia Oy TABLE OF CONTENTS INTRODUCTION = #999999 9 rr rr rer eee esesses= PREVIOUS WORK=22222 « tan, toute. @etreavY aotst ed? ai. isvel aoe. Yo dixon fevel pez woled teet | | anol dtioned esedur soe? 000,51 am oem @, ote geble srotans bas piredtwon, aad my) Belinea, Ave baiiiatey's> enoaont ax) 1s ei “bex0u? ak nanan oe Mit adiqod tay : VOOO,82 twats mow ay eolognk sot edT fatal oe Cr en tee edt Ot vrotalt okgotoes a oe . “anion od ont 36 Aheiat setae qQeaw: ee ee sag ye dd kw. . Poti? oat eew ita. cog et pay yowollada Bas xowollede to ae Bi scien alineo® | Eats Fada Latnoakines or y drowns weg ant ff vipers bering) data alii eto Beret ti 3) 10 Figure 1. Major land provinces adjacent to Santa Monica Bay. ben} yA soknoM atnsé of tasasl bs se>nbvotdg bend atti Sorprrhyo?A00m SAN FERNAN LANDFORM DO VALLey see “AL ANGELES © COASTAL BOUNDARIES ADJACENT TO SANTA MONICA BAY Smaller features Simi Hills Verdugo Hills San Rafael Hills Repetto Hills Elysian Hills Santa Monica Plain Hollywood Plain Sawtelle Plain La Brea Plain Downey Plain +tMH OQ DOBBE RW Mountains and other major land divisions Baldwin Hills Rosencrans Hills Ocean Park Plain Ballona Creek Gap El Segundo Sand Hills Torrance Plain Dominguez Hill Dominguez Gap Signal Hill Uplift Long Beach Plain SUBDIVISIONS OF THE LOS ANGELES COASTAL PLAIN MODIFIED AFTER POLAND ET AL 1945 & McGILL 1954 BLK ghwhled - x LLL aeroaeBoN w. L alelS gia Geen + Heed elem, ws eLUE base chmpee Le +o REL MNT xt LoS seit * io yiphue tie renin th Gheld daaet aia # a ae parenoe: sateneh ROT Aaa ORR aM ws eT Coastal Plain to the east, and the Palos Verdes Hills to the south. That part of the Los Angeles Coastal Plain nearest to shore can be further sub-divided into the Santa Monica Plain, Ocean Park Plain, Ballona Creek Gap, and the El Segundo Sand Hills (Poland, et al., 1945; and McGill, 1954). Because the topography, drainage, structure, and rock composition in the provinces and sub-provinces have played an important role in the submarine geologic history of the adjacent continental Shelves and borderland, each area is briefly.described. Santa Monica Mountains The Santa Monica Mountains vary in elevation from 1,200 feet in the east to more than 3,000 feet at their western end. The rocks in the mountains range in age from Mesozoic to Recent and the sedimentary sequences total more than 26,000 feet in thickness. Many varieties of rock occur including Slate, schist, quartz diorite, basalt and andesite flows, tuffs, breccias, basaltic breccia, rhyolite, trachyte, sand- stones, shales, and conglomerates (Hoots, 19313; Durrell, 1954; and Bailey, 1954). The complex structure of the Santa Monica Mountains is shown on geological maps by Durrell (1954) and Bailey (1954). The major faults in the Santa Monica Mountains along the northern part of Santa Monica Bay are shown in Figure 2. The Malibu fault trends east-west along the base of the mountains close to the shore line, and crosses the coast west of Point Dume and Las Flores Canyon. From available data (Bailey, 1954, and Hill, 1954) it is believed that the Santa Monica Mountains Anygat ino. tuesatbe oad, +0 ee Rigoioss on} samdag: ‘edt ade - bedihzoash vet obad’ an ‘so bd eBowironod See + mrt (et ‘piosoesm: do’ 236 ‘ck opus pares edt me extgox ‘se 000,06 anit? o10m tase? vasasipes pistaombhoe pat bes sngasi | gnibhetoud : P90 Acer es: neki ebiny nid hagonptotat: wk fost, vewot? ethasbun bite ttaad vatinode eine \teinve hale om Dyraas'2 vetynosts . 42h Lowdy ehooeed' ‘ght haved ask anerd, etited Weer, biaxeed ¢itet 24008) _setanamotgans fas eolede anode C802 wot b ies: Saal ae Cie BoinoM maine eat te bint ootre xelqinos ont PERL) (olket Dik COOCE) Lkepranel ve aqem Indbyotoay 20, mmole, a eat anata enles mom nobioM ptne® sit? ni etived xobsin oct 4 ant. ¢ a i * nwode sam at a okAOM, mrnige 38 ect grb tt som a: tniot te teow pn wit geeaor> bee ‘ei ieee E lee: eal tee sie re ‘a Bocas! ] 12 Figure 2. Major faults in Santa Monica Mountains along the northern boundary of Santa Monica Bay. aah, ay! be Wie Neuen! ded hdeal ‘ ia swat? i Qnole anal: woM eainot atast at atten 048M tee ankooM ange: SNIVLNMOW SAINI NZ SILINTINZ SS NII Sale saves =| INKS) SE (ates) JES aI \ 8 SSPE SS . be SS Q St Ly .Y OE (\ S21IW S ,O€ ail Sv ell (es6/ 773¥9Nd ‘2 4#FL4¥) a em aang RMON. — as = 13 have been uplifted and shifted to the west in relation to Santa Monica Bay. Most of the other faults within the mountains are small and probably have had little effect on the geological history of the bay. Except in the vicinity of Malibu Creek, the slopes of the Santa Monica Mountains adjacent to the bay are steep and in places form nearly vertical sea cliffs. The coast is irregular, being cut by numerous canyons, and is quite rocky; especially between Las Flores Canyon and Santa Monica Canyon. The beaches from Malibu to about Las Flores Canyon are sandy and continuous, but east of this point to about Santa Monica Canyon the natural beaches are small. The earliest topographic sheets of the U. S. Coast and Geodetic Survey, made in 1876-77, show narrow sandy beaches extending from Point Dume to Las Flores Canyon. From the latter point to Castle Rock the shore was mostly rocky. The construction of the Coast Highway and the use of groins has slightly altered the shore, but the beaches are probably about the same as they were when the first surveys were made. From Castle Rock to Sunset Boulevard, the old maps show a beach about 75 feet wide, but from here southeast the shore was rocky for a short distance. From this rocky Shore to Santa Monica there was a continuous sandy beach. Man has altered this part of the shore appreciably in the last 50 to 80 years. From Potrero Canyon to Santa Monica Pier the shore is bordered by a nearly vertical sea cliff which varies in elevation from 60 to 160 feet above sea level. “anwten oat eae aoknon gakell peel ot + satoa Pe aed ei te .. ear we Breede obtigaigoqod. danttra ott | Ateme D318 a8 mn ia woven “wot UTHOTBL mb Shem yyevaue pti 9090 baa 20802 aaiiguy aeeaet ut ot oma vaio no? an aedonod vt ‘ te oa jhaayetond ssenue ot oo etzend toa sta + oa eat aeit sdinok teak oF mona oxsited non x : seb aey doi she Wane goa Emokrx9y Lamon. ae: . pea 80. ar eS ne JLewae age vyode ta91 Oat oF 68 14 Santa Monica Plain Hoots (1931, p. 130) designated the south flank of the Santa Monica Mountains as the Santa Monica Plain. Poland, et al. (1945), on the other hand, restricted the name to the older alluvial surface lying west of Beverly Hills. The underlying platform was cut by marine erosion in Late Pleistocene time and subsequently was covered partially by marine and continental sands and gravels. While the plain and most of its deposits are considered to be of Late Pleistocene age, the surface has been modified in Recent time by erosion as shown by the broad channels and gullies. Later deposition of coarse deposits has partially filled the channels. Ocean Park Plain The Ocean Park Plain is part of the Santa Monica Plain as designated by Hoots, but was restricted by Poland, et al. (1945) to the region “whose surfaces is composed substantially of marine deposits of Late Pleistocene (Palos Verdes) age, and which lies largely in the south-west angle of Pico Blvd. and Bundy Drive.” This mesa extends inland from the coast about 3 miles, is 1-2 miles wide, varies in height from about 125 to 200 feet, and is relatively undeformed. The plain has been divided into three smaller units by Poland: (1) a small bench to the east, about 190 feet above sea level, (2) an extensive central plain which slopes gently southward, and (3) a ridge-and-trench area paralleling the coast, considered to be Upper Pleistocene in age (Hoots, 1931). According to Hoots, part of the western region consists of old sand bars 7 Aaebte oi ot aa. ys. eine “athaogsb art to Feom saul mata ah ania celoveny Ea end atkeogsh se1803. to nots eoasb sae uaasien baw | | | veteoname! 2 Iboteeh i i os te bers vd botoiwape | saw sud a ee dennaatash - Bh ay “feane eat won? bine hank abrstne oasm ein "ovixa = iwods m9 Hitgind old zokasy shew eotin es ek veotha ' nme , tevat’ BOR ovods sept oor tuods teas. yas . buswalt HOR yitnes exqots cea nbslq, tex berehianod teed nat gablotiaxng sors ADE 1 : oF ankbvonon (CLEOL ,at00H) Sae| at snooor nese ened hawt bho to: etetanop apanet msedaew SB. 5 and shoreline bluffs formed at a higher stand of sea level. The material composing these old sand bars is a fine brown thin-bedded sand that has been washed free of all clay material. Ballona Gap Ballona Gap is a terrestrial feature of importance in the study of Santa Monica Bay as large amounts of sediment have been carried through it to the shelf and offshore region. Drainage through the gap has probably played an important role in the history of Santa Monica submarine canyon and per- haps, to a minor extent, Redondo Canyon. Ballona Gap at its narrowest place is 1.2 miles wide where it cuts through the Inglewood-Newport fault zone, and is about 10 miles long in its present extent from the coast to the east end of Baldwin Hills. Bluffs up to 400 feet high were cut by the old stream as it flowed between Baldwin Hills and Beverly Hills. There is evidence that an antecedent stream existed on the surface of Late Pleistocene (Palos Verdes) age before it was deformed. The stream had sufficient eroding power to cut across the warped rocks as quickly as they were uplifted. The ancestral Los Angeles River which formed the Ballona Gap cut a channel at least 50 feet below sea level at Ballona Creek outlet, and 400 feet deep where it crossed Baldwin Hills. Subsequent deposition of gravels am sands has filled the channel at the coast and to a depth of 80 feet northeast of Baldwin Hills (9 miles upstream). According to Poland, et al., (1948, p. 51), the incised stream graded to base level substantially ie cal sosnom ae 7 ae ey fl \ 194 baw noynss sobromdwe salen Peaat, ve leek a (9) att te qad snoktsd .aoynsd obae bes taeda romker # oF ga ie a etd diguotds i> tk sradw obbw pens rae eb poetg eswoa ( (nk gast astin 01 toda ab hme \snos thiet fingwolt-boowsias ‘a siwblsd 20 ‘Dio tae’ ont ot tenog orth not? deetxs tas09%q. F : be } oh: meante. bie. ott Yd two stow dyke toed 008) ot qe eYwta contin De |) eset Jerri ytesved bas ahtil diwbtet nested Bowl?! Han | Bogtiue ont NG Heteixe overt Snabagsime te Pads somshhye) ab benroien aew st oxotad ein (aebre¥ ste) -gieasotets19 otal Yo boquew om Beets: toot EOWKY quihoks faalos? tire bad agoxte, ‘oil a chet tbliqy | Siow! You? ee eitokmp: ea rien pmo Led ads. temo} ree gover euiranaie aot Sader; sa at : ySROL) 4 elt $2) hing to ot aaibroo9a” nee" : wi, Leateatices, Levat vend. os bobaxg mnie! Rola 16 more than 50 feet below present sea level and possibly extended as much as two to three miles seaward from the present shore- line, presumably toward Santa Monica Canyon. According to Layne (1935), the Los Angeles River was flowing through Ballona Gap in 1815 and continued until 1825 (Kenyon, 1951) when a particularly severe flood diverted the river to the south where it joined the San Gabriel River emptying into San Pedro Bay. Other extensive floods in 1862 and 1884 caused part of the waters to return temporarily to Ballona Creek, but since 1884 the Los Angeles River has discharged only into San Pedro Bay (Troxell and others, 1942). The mouth of the stream apparently migrated north and south of the Ballona Creek outlet, for the earliest U. S. Coast and Geodetic topographic maps show the natural outlet discharging at the end of a long sand spit, while landward of the split there was a salt marsh averaging about one mile in width. In 1906 and 1908 the outlet was “fixed”, but in 1936 it was again moved 1,400 feet farther to the north. At the present time Ballona Creek has a drainage area of approximately 131 square miles from the southern slopes of the Santa Monica Mountains and parts of Baldwin Hills (Fig. 3). Since the construction of flood control channels and other works by man, little detrital material is brought to the bay through this course. Probably the most important rifting in the Los Angeles Basin is the Inglewood-Newport fault zone, which occurs in the vicinity of Ballona Creek. Three faults which run perpendicular to the old channel are associated with this a. ee nagto | a id a co aretaw ont Ao. ‘gotogne Rol on ‘38h 2 mae “ofa a. vegaadosht ae ; wi ie | | ASROL “~— a if b, ne ie task tak0 ont ae ote > Aa tiottas aus te bette Lexetan aft worta eqau obdqet ges 2 SbFSboaD bina. : “Buwebiint thin tiga bape gaol 5% bee at te gniaxeit | ftim an0 tnods aalgenova darn tee a enw oped) thtge pa pis ee on st ‘sud “boxe ew tative ads Reser tna 2 B00! at | athe om) ait ton eat of “am apaatsr® aah se enottal emis faoeorg ont $A ; _ RoqokR mretitios soy nos eatin ‘genus yer yistantxoxqgs: jo eLLAH abwisaa te atsaq be anbed awol aobeom soma hi 0 rt atonneda Loxtios boot Jo HOR aYYEnED att somke ake: | Aatgnoxd ob akestae Aetiotsb ettght nam ve. exo aodto I eSOTNOD, id Aevoa ee : | Vth a AE esa diode: 2hox thus) ‘ogee mS | “8 Rea a iu’: Aoietw. etiap) out aK, U7, Figure 3. Drainage areas tributary to Santa Monica Bay. : a ae is S3139NV SO71 QOOMA110H ‘ ' ! ' / O¥6/ NOSNHOF Y#ILIV O09 VOY TVW HOVvV3g OGNOQG3uY a VvSOWY3H a. Hovaa oO NVLLVHNWW + AaY 130 VAV 1d <3 VDINOW ‘ ici i =~ = =" ee BOS \ % : ’ Wires ‘ e-EE\ % aj : : y 1 AVG VWOINOW VLNVS OLNI ONINIVYO vaYdv JO AYVONNOS AUS BIIUOW ULUES 01 AYULNIML Staub JOBUIDYC ly S Q wR ES 9 x A» Ay, G ONYISIY. - 990NI¢ | ‘ ( PS ‘ yy \ \ ! a ae} Se Tr ~w FHV Nee neiwnt ~~~. } Yel : i SvBee me ; dem tct ae — ie a haan ea oo aoe 7 eS 4 ‘4 ine eke a ssn : ; oc ur : Seas | : ae q peat: ra + + sesaeshend 18 fracture zone and are known in the vicinity of Ballona Creek. From east to west they are: the Inglewood, Overland, and Charnock faults. The latter two have only been identified below the land surface, largely on the characteristics of the ground water table. In each case, the western side of the rift has been uplifted relative to the eastern block. Poland, et al., (1948) points out that the transverse profiles across Ballona Creek show that the gravels and sands within the old stream channel dip to the south and frequently are more than 40 feet thicker on the southern side of the channel. This could indicate that a fault partly controls the stream channel, and may also account for the relatively steep and straight bluffs along the Ballona Creek escarpment. The circulation of ground water does not indicate one way or the other whether an east-west fault exists. However, as an alternative to faulting, it is suggested that the stream migrated to the south and as a consequence cut a deeper channel in this direc- tion. El Segundo Sand Hills From the Ballona Creek outlet to Malaga Cove, a distance of 11.7 miles, there are extensive coastal sand dunes which have been termed the El Segundo Sand Hills (Poland, et al., 1945). Merriam (1949) made a comprehensive study of the structure, composition, and geologic history of the sand dunes. She notes that the main part of the sand dunes ranges from 2.0 miles to 4.2 miles in width, while the active dunes, which lie atop the main ridge, have an average width of 0.4 mile ne nen obtevenast 6 ont tadtt tue 9 se 7 “digterte bets qoote vlovisates mg “to Roktsiuorio st: -tnom38989 sony an a fl edt of bataxabe morta ony seme | betas $k +h “eskaten Bi ~99rih REAP sk Ienna da reqeoh a “somateee | rl sre ape tam or dolauo Sae20 snoltedt oat mont 7 Hos tw sone b tatae:, TS PRSOD eviemsixe orth axeatt .eptbe vith % ssda te \hiato®) elit deep obowyet 1a oat bares heed ‘eva ait to YhuTe swiantougae g obsu CORGLD) nai Bese y 3 saveed boys oat) Sd Ciotets, Diem hoeg tas Tr cutouts eon o's o's Lay vee Ve rn ahent nai tat 19 between Playa del Rey and Redondo Beach. The dunes range in elevation from 85 to 185 feet above sea level, and have an estimated volume of 36 billion cubic yards of sand. Vegetation has anchored the dunes in many places so that today running water and wind cuase only minor changes in their structure. Lithologically, the cemented dune sands compare closely with the beach sands now found in Santa Monica Bay. Subrounded sand grains were found to be very abundant in only the larger sand sizes and frosting and pitting, generally believed to result from wind action, occur on about 5 to 15% of the grains. The coarse sands appear to be derived primarily from a granitic source. Reddish=-brown sands, similar to the red sands found offshore, are common in the sand dunes; the color resulting from the presence of iron oxide as a stain on the grains. According to Poland, et al. (1945), Woodring, et al. (1946), and Merriam (1949), a marine platform, correlated with the lowest and youngest terrace in Palos Verdes Hills has been deformed along the Newport-Inglewood fault zone as have the sands of Upper Pleistocene age which were deposited on its surface during a higher stand of the sea. After the deposi- tion of this sand (Palos Verdes formation), a large region west of the Newport-Inglewood fault zone was uplifted above sea level. Nonmarine terrace material of Upper Pleistocene age was deposited on this uplifted surface in the Palos Verdes Hills and various places inland. There is some dispute as to whether the El Segundo Sand Hills are partly offshore bars (Eckis, 1934; Poland, et al., 1948) or wholly of eolian origin (Merriam, 1949), Merriam concluded that the sand hills are : oe Poaet aaa wine i: ehinids ee adds beveited fexeaag phi set te gmt veo: alas! eat. to. HOE oF em a wi ks oe okt haery fellate a df “\GQR22) Ep te aabebaown ene iene hile bot ot oe ey - | Ant ibiw beteisaneo ine trate pith: + shone) maby cbt «ba | y hoot eae 60 asbusy oe ‘ne Laionitand Tyeganey ete tepwol ri sHeoge>: eat bubba ‘bas Attu bree oat on aay 20 composed entirely of eolian sands lying directly on the Palos Verdes sand in most of the area, and that the sand dunes were formed continuously as the sea regressed across the Palos Verdes surface. Zielbauer and Davis (undated) note that the Palos Verdes formation in the Hermosa=-Manhattan Beach region is composed mainly of sands and gravels which are similar to the overlying coastal deposits, except that they occur somewhat farther inland and include calcitic fragments. The formation is absent in some of the region and its absence is attributed to marine and/ or fluvial activity. There is more or less continuous horizon of relatively impervious deposits composed of silts, silty sand Stringers, sandy clays, and clays that lie directly below the sand dune and coastal deposits. This layer, called the “clay cap”, is unusually flat, varying from 10 feet above sea level to about 10 feet below sea level, and reflects the underlying structure which consists of transverse drainage channels. The clay cap feathers out completely at the present strand line, and it is absent in a well 800 feet inland. The drainage of the El Segundo Sand Hills (Fig. 3) shows that only a narrow belt of that shoreline adjacent to Santa Monica Bay drains into the bay. Palos Verdes Hills The Palos Verdes Hills, which form the southern and south- eastern boundary of Santa Monica Bay, are a conspicuous uplift along the southern border of the Los Angeles Basin. For the most part, the hills have a relatively simple structure con- sisting of broad gentle folds which from an anticlinal structure. on juneita ad Anttama’y er c Soa vi dormsintae ak Taree. Bae. exega pny or moat cae 2caveune, ak 199 cashed ‘Sd? es04tton baa Laval ana: welled need Of —— A) cateaneiy spanked oenoveness We iatabe aa | saa tudenag odd Fe vleretgnoa) ines 2h geo ie ee ils shankar tusk GOW Lew gomki times 2k 7h fe: 7 ake : ae, @hLIH noe® obugn® ta wit Jo opsmbea ai Bhi sine on poeta podin veda tna to: ted wove, vA ‘ 00 ey a ‘A Abies aiinsie: ihe: ah ts | i na Vics ott sor, tye 21 There are few major faults, but those that do occur roughly parallel the axis of the hills. The most important fault is not exposed at the surface, but is a major structual feature in the schist basement and the immediately overlying rocks. This fault has been called the "San Pedro Fault" by subsurface geologists, but Woodford, et al. (1954) have termed it the "Palos Verdes Fault Zone’. According to Woodring et al. (1946) the Palos Verdes Hills were uplifted with the San Pedro fault (or the Palos Verdes fault zone) spearating the hills from the Los Angeles Basin. This structural feature conceivably extends far out into Santa Monica Bay (Fig. 4). The exact age of the major faulting along the northern border of Palos Verdes Hills is still unknown, but the zone is probably still active. The strongest deformation in the Palos Verdes Hills took place during the Upper Pliocene. Less marked deformation during the Middle Pleistocene, and still weaker movements occurred near the close of the Pleistocene period. Deformation has been so recent along the northern border of Palos Verdes Hills that the lower marine terrace and its associated deposits have been slightly to moderately deformed. The basement rock is glaucophane schist and altered basic igneous rocks of probable Jurassic age. Unconformably above the basement rocks are several thousand feet of strata of Miocene and Pliocene age and a relatively thin veneer of terrace deposits of Pleistocene age. The rocks of Miocene age are cherty, phosphatic, and silty shales, mudstones, basaltic sills and tuffaceous beds. Pliocene rocks include ile tno wendae somes. omyast, tewivnaye ae iia pase: Pikes tng stegotsketa etbb2e. wit eel prin Sripoosehel4 ‘ef? to seoly ea mee) bins agnsiow a Tome vO | penta zon ett giote toadey oe Meee) ait eRe tod wapriss Sata eH - saweil om Sede annie nvbray Bo let met etoterabon ot ¢itdylte bia ora ethaoaes beeaiooesal aE 22 Figure 4. Block diagram of Palos Verdes Hills and adjacent areas. aur Lanna Pues ” (; ie mn ROMA i esbuoV tolat to nergetb Wools | PLAYA DEE (ee i DOMINGUEZ HILL oO (2) za =) ty og Sy 2 w S> 40 ke Zz aq Ww fo) (a) Zz (e) (a) LJ jag uJ oO Zz © op) ne Q na - wo = 7 or (e) = tt = a Or Cp) (e) ao (a) uJ = ae za a (dp) i. 0’ N BS 74a S— . S DTM ne SEZ 7, \ WSeTRINN S aS SS mail [o) I 16000’ Ane ee oa \ a Claas CVO CHERRY HILL FAULT PALOS VERDES HILLS FAULT ZONE < i BEMES RAE “y WAEs Tne Me AESess SETS 23 bluish gray glauconitic and formainiferal siltstones. Deposits of Lower Pleistocene age are marine marls, silts, and sand, while sediments of Upper Pleistocene age are mainly nonmarine deposits. The shores around Palos Verdes Hills are rocky with steep sea cliffs. The beach sediments are mostly cobbles and only occaSionally are there any small sandy pocket beaches. SUBMARINE TOPOGRAPHY OF SANTA MONICA BAY The bathymetry of Santa Monica Bay has been determined largely from U. S. Coast and Geodetic Survey "smooth sheets” numbers 4559, 4784, 5235, 5364, 5390, 5396, 5397, 5507, 5653, 5851, and 6259. Certain unavoidable errors were introduced when contouring due to survey methods employed by the U. S. Coast and Geodetic Survey. For example, most of the sounding lines, especially those close to shore, were run along lines parallel to shore. As a result, the exact position of the constructed contours are not as accurately positioned as they would have been if the sounding lines had been run normal to the coast. Also, soundings were rounded off to the nearest fathom, and the conversion to feet introduced more uncertainties as to the exact position of the contours. None of the inaccur- acies mentioned are critical and they become less important with increasing depth. Additional soundings by the VELERO IV were used only in the vicinity of the terminal ends of the proposed outfalls and in the rocky area to the south of Santa Monica Canyon. The data gathered by the VELERO IV indicated no significant changes of the nearshore topography so that * a ae sone ster net omen i me _ 7 oe ee “apakt geote mos sre" state, on seats seh itetongee. muit Yo soktieog: Thee. add | ; Sipes ' if pt aa bore Lkteod, yterawann, or “ton Se srvosnes boss ” ‘or Aamion tirk ase’. bait ay chbesie ont 2b Vaile. ehom beoubortak Steet of otazevo00 oa | wawopedd: ons to enol ete 9 yet vest omens : Kee VE OREJEV 9M? ed wanit ii Panolrtbba atgos : eae 0 aba, ae oat Gis be cane ati tals me eiaamsogar « hee i ot i eel i 4 I Darky 24 U. S. Coast and Geodetic Survey soundings were used almost exclusively in that area. Submarine Physiographic Provinces The general physiographic divisions of Santa Monica Bay are: (1) the Shelf, (2) Redondo and Santa Monica submarine canyons, (3) the Basin Slope, and (4) Santa Monica Basin. Shelf For convenience in describing the submarine topography and other portions of this report, that part of the shelf that lies between the two submarine canyons is designated the "outer shelf", or "central shelf projection”. The Santa Monica Shelf extends to a depth of approximately 270 feet. At this depth a pronounced steepening of the sea floor indicates the shelf break. The width varies from a few hundred feet at the head of Redondo Canyon to more than 8 miles between the two submarine canyons. North of Santa Monica Canyon the shelf is very constant in width and the edge follows the shape of the present coastline. From Figures 5, 6a, & 6b, it can be seen that the bottom slopes seaward evenly and has a gradient of about 4 degree. Nearshore, where sandy beaches are present, one or more parallel troughs and ridges are often present. These long- shore troughs and bars are generally transitory, moving up and down in the nearshore zone and their presence, absence, and position depend upon currents, storms, the tide, and wave height. The shifting of sand, and even gravel along the bottom aN xtearnegot solsandue ‘pile gard tes Meds sat Yo taag Sant? ae Pomitontona Yee ‘te ated oat ewe eee. war ‘Me aatheqone | we g word iets atbbw oat “eat ts asthe as taat ened peu Sheds say novned nom ceils wont ni tesos ite od Ye saaran edt anes! ae w200 20 th sande a8 “abitoasd (basa oxoabi axoaaiaait! ea i 1 ramen eneet — mathe ote asgbls wae ave es cm 25 Figure 5. Submarine topography of Santa Monica Bay. MONICA BAY SANTA e iy Ww & . j < = 2) i) pe : foe o “A j j cs) by = Z| 4 ieee = \) is Mk Peeks ayy: ae x ' ey re ie i, ig —s ae 5 , L Ml i) mit (aaa Arle 26 Figure 6. Fathometer traces of Santa Monica Shelf. (a) Location of fathometer traces. (b) Representative fathograms. Jy meee me eA hey nah abies emimgieDe dh ae ication wr Vr Se een rete Bre Wb De y * \ 1 * i . a cat tn Aaah Da deh Casemnn mam wae Fat maen pe phe sadeseewpnlonraampeats Wawe ata eaten wap Slear > alla sicaeriatinsny iain miata La ka i ce ith chit i ean i n Ma th i j “i =f SSA = a ; } t HI 4 Bn Rh wy) a hit aul Lit ai an = Sih 9 ST ED Engs tn as Bo HGR: Bi So 0) OED a Pag Lac om iter 27 May Cause pronounced but local relief within the nearshore zone (Schupp, 1953). The shifting of bottom material in the form of longshore troughs and bars is generally confined to water less than about 15 to 20 feet deep (Shepard, 1950). With the exception of the surf and nearshore zone, most of the shelf is devoid of any significant relief. Small current and wave formed ripples, marks, and burrows caused by bottom dwelling animals may form mounds, depressions or undulations a few feet high. However, these features like the bars and troughs generally are not permanent. A large number of shallow-water fathograms to 300 feet were taken by the VELERO IV over the central part of the Santa Monica shelf. It was observed that much of the shelf had virtually no relief while other parts had significant changes in elevation. Generally, the surface of any continental shelf has small features consisting of mounds, ridges, depressions, or undulations called micro-relief. Features about three feet high are usually the smallest that can be determined by an echo-sounder due to the motion of the ship caused by sea and swell. Ripple marks and mounds formed by organisms are, there= fore, too small to be recorded. A special study of the shallow- water fathograms collected in Santa Monica Bay was made in order to find the extent, type, and distribution of micro- relief on the shelf (Staff, Allan Hancock Foundation, 1956). Figure 7 shows the tracklines along which the fathograms were obtained and studied, and Figure 8 shows the different types and distribution of micro-relief which were then plotted along the trackline. After all fathograms were examined and plotted, ie “anok tativtc 30 or xs “ban bred sat ogatht sensed eee. ve " bad Yess on? Ng soar + Ait ue ‘i aa a om VI, tLeie "ie tonnes faa! Vea bait ertod voehtor ‘stky Wei tes cet (Lineal | pelt tes ono eee se peng AA a BAO a! tw narelaacs donitns? ema a post ‘Soni iaeda evdlet aah Jab ooees i teed bins’ rok ta Lalo | re vil poriandey ac ssn oat tepltnne aust ¥ t Lawed ate, i ae sae m i Donte qi ite ic ae ow aed OY sath > venauees ea | ergdt ae icin alle Ph fuaag? ainyan. baw ataasy ol Lye r swat fads ott? Ae qua Ae aksoge A ibebaebos “vd od xs! gat * ane: bait, enw NOS ep bio agent fee Be bien t Lod TED ay negtudtst kb oan al ¢ tee Pcs ‘oie ——. ; { Aeog t ee 2 ran Me Ae p , 28 Figure 7. Shallow water fathometer tracklines on Santa Monica Shelf. HenLidseit setornudte? setew wetteads [oak wokiom \ \ ZO Y DoVr Wisk Xp Kf \} ; Ee vs 2 S a tat PWD ate N | i if Rie ay a Se Figure 8. Micro-relief of Santa Monica Shelf. 29 30 three types of micro-relief were outiined: smooth, variable, and irregular. A wide belt of smooth topography extends from nearshore to varying distances out on the shelf (Fig. 8). The only distinguishable irregularities within this area are isolated mounds a few feet high. Depressions are conspicuously absent within the zone. Near the edge of the shelf, occasional well- defined terraces or flat areas can be seen on the fathograms, some of which can be seen on the topographic map of the bay (Fig. 5 ), but little micro-relief is evident. An especially well-defined terrace is present at the boundary between the smooth and irregular zones and extends a short distance north towards Santa Monica Canyon. The zone of variable topography is generally seaward of the smooth areas. The offshore limit could not be determined accurately because of the transitory nature of the boundary and the lack of fathograms in this region. Within this zone are broad areas of no micro-relief and smaller sections having low mounds, undulations, and small steps or terraces. Also included in this zone is the sudden steepening at the shelf break and the irregular topography associated with the sub- Marine canyons. Along the edge of the shelf and the upper part of the basin slope, are numerous notches, steps, and small terraces. Closer to shore, north of Santa Monica Canyon, are several gullies 20 to 30 feet deep which are, perhaps, similar to those described by Buffington (1951), and Emery and Terry (1956). Although there are many mounds and irregularities within this general area, none compare in ays gue witeows: ei “ exede2nce oe ‘ebgorss ee ont Shee ay ™ 21 ae ae ihe igen vey ae Xiteisewes eA “ynouibes eh: bit lom-mrokm ina ot ngswe at: usbavois ont? an suseoxa eh spatter ‘bent ot a i300 soasteih rare s ehaenes bees eens ssiugortl haa ity 2 emweeven + coh one ei ugoasts 0208) ie - e) 31 size and number with those in relatively rugged topography of the irregular zone. The irregular zone consists mainly of mounds and ridges which project 10 to 40 feet and occasionally 60 to 80 feet above the sea floor. The flanks of many of these mounds and ridges appear jagged, irregular, and steep on fathograms. The slopes may be locally more than 15°, but generally are less than 1° or 2°. Some of the mounds are connected by low ridges and these also have irregular and jagged sloping sides. Individual mounds are 2,000 to 3,000 feet in diameter; some are smaller or larger, but this appears to be the average size. The area enclosed by the irregular zone is known to have much gravel and some bedrock so that the relief evidently is due to rock outcrops and patches of gravel. Because the micro-relief chart is based only on fathometer traces and not on bottom sampling, and because the fathometer does not necessarily distinguish between bottom types, the limits of the rock and gravel area differ slightly on the two charts (Figs. 8 andi3. Redondo and Santa Monica Canyons The head of Redondo Canyon consists of an amphitheater- like bowl which is located a short distance from the shore. The canyon has a relatively flat floor throughout most of its length, has only a few bends, and has a wide terminal end at a depth of approximately 2,200 feet. According to Shepard and Emery (1941, p. 64, pl. 12), the gradient of Redondo Canyon decreases along its course; being 8% at the head, 2.5% at the “tent 08: b eye an | bes, wba seedt to, Nita: BO Ao etimis odo \ 2eqve vio tod noowred ‘aadbupgiesan vibeasesee pdaads owt ect ho plldehee te toPheb were) ts even bee soon at bre brad? oa gai dota wornet) obacneh 40 snoboonp ast cosy em oe “a ae MR Te ae Beek aati Pe Lil scold ieanieag #ab. : 32 outer edge, and averaging 4.1%. The axis of the terminal end, like Santa Monica Canyon, swings to the south and appears to terminate in a fan or delta (Fig. 9). The south wall of the canyon generally is much steeper than the north side and has local gradients of 25%. Two large tributaries are located on the north flank of Redondo Canyon, whereas only small ones are found on the south side. Shepard and Emery (1941, p.64) compared soundings within the large tributary closest to shore on the north side of the canyon. They found evidence that recent soundings are consistently deeper than the soundings taken about 50 years before which suggests slumping. Figure 9 shows cross-sections of Redondo Canyon taken at regular intervals from near its head beyond its terminal end. Santa Monica Canyon starts at a depth of approxmately 180 feet about 33 miles offshore. Unlike Redondo Canyon, it has a Sinuous course, starting in a northeast-southwest direction, turning slightly northwest, and then south at the outer end. Santa Monica Canyon also differs from Redondo in that it appears to be less rugged and complex, is more asymmetrical, and has only small and few tributaries. The average gradient along the axis of the canyon is 3%. Figure 6 shows fathograms taken across the upper part of the canyon. It will be noted that the canyon has a "V" shaped cross-section at the bottom but the north side flattens out forming the wide north side of the canyon and part of the basin slope. A few terraces along the side of the canyon are also conspicuous. sai -Jnkqmate eteaqaee oben sued ‘piney fe weds: + mans ar to eqat 3 s bz) arnt seus mak hom ssoue | mownune “ort OA aah Pau ptode hie: eat Ria: cis Hivos 198% an feunitvoe- temeniiom a mt gait ete, PatOD euourke s at +t ey te stios ned Sen teeeitcen ¢itiaate gt ine? \woltnealb § 7 - Sbobea ek Bg eae ttit oe by mov. sotto adnne bere sate sith Stom ai ,xotgnas bere boaaws sat od wi era sya td todd ey), ott Pebzeied ixt wor hate t este ttn earl bits tasias oneren | ? i RE ak aoa eld ae abe BET yoo Le THO bare ogereva | toy ott to: tae reaqu itt waetae gsaet enn gosta ewore *] noi! osenna012 bhgetie? ah al ‘git ayaa ond teat ‘beron ad be " ; wet A laats atead oa Yo tn9q bas novo ‘ott we ‘oota 4 Ge even Regaatt 10 is a7 axe ROYABD ot? 30 shbe sets grote | Figure 9, Profiles of Redondo Canyon. 33 Sie Xen NOANVD OCGNOQd4uU H1Ldid ss N SATIN SIE AWEN AES) eae a ae SGvC0 aA =< sae ea 7 n seta apenas I ne : ep endetmy atom. 0 34 Basin Slope Off most coasts the continents are surrounded by a continental shelf and continental slope. The continental slope forms the seaward margin of the continents from which the water depth increases to the abyssal sea-floor several thousand feet deep. Off southern California, however, the continent is separated from the abyssal sea by a series of basins and ridges. The slopes bordering these basins are called "basin slopes" to distinguish them from true continen- tal slopes. The basin slope in Santa Monica Bay is that part of the sea floor seaward of the shelf and terminates on the floor of the Santa Monica Basin. The average gradient is 5° sea- ward of the outer shelf. The slope is broken into several segments as a result of the two submarine canyons. West of the outer shelf and south of Palos Verdes Hills, it is well- defined, but south of Malibu and on the north side of Redondo Canyon the basin slopes are partly the sides of submarine canyons. Fathograms along the slope indicate a generally smooth surface broken occasionally by small terraces or steps. Profiles taken south of Malibu indicate that channels, locally to 60 feet in depth are present. Santa Monica Basin A small part of the Santa Monica Basin can be seen in the lower left corner of Fige 5. The floor of the basin is relatively flat but deepens slightly to the west. Shepard and Emery (1941, p. 64) believe that there is evidence of a | ha exw eo withanddan ows ip es stuns. Pat *f | i ston eh +k Re aabxsl no tat iy iit poe tate Visite, ve | | -phsioten 6 obiks gtx ith to sm to idan fod ay | : | ‘tk epi Ve eine oath rete oy ‘pegote nian ooh . / | iiaseoy « ‘dwerbtaal, agete out Meine Ear tina iigenit pa %e: Mev ait ‘staat! xe etaedina se Ags ee (oheanpite ‘Fett: Stas pee cde “ae by eee rsa? Spee i ebmaet eit 'S 0 i) he, 5) submerged fan off the terminal end of Redondo Canyon, and the profiles shown in Figure 9 confirm that a fan is present. However, there are not enough soundings off Santa Monica Canyon to determine the nature of its terminal end. APPARATUS AND METHODS Prior to collecting bottom samples in Santa Monica Bay, U. S. Coast and Geodetic Survey “smooth sheets" and Shepard and MacDonald's (1938) report were closely examined. Areas where rock and gravel had previously been reported were examined by rock dredges (Fig. 10-E) and in areas where the type of bottom material was unknown or in doubt, an underway sampler (Fig. 10-C) was used. Additional information regarding the bottom character was obtained by the use of a shallow-water recording fathometer, when it was found that extensive patches of rock and sometimes gravel areas could be observed on fatho- grams. After the general locations of rock, gravel, and the finer sediments had been delineated, a snapper sampler (Fig. 10-D) or an Hayward grab sampler (Fig. 10-A) were used for the collection of larger unwashed samples. In areas where the vertical distribution of sediments was of importance, cores (Fig. 10-B), jettings, and samples by divers were obtained. Samples obtained by divers were limited to water less than 150 feet. A preliminary determination of bedrock was accomplished mainly on the basis of the "feel"* of the cable as the dredge was Slowly towed across the bottom. Further criteria used in recognizing bedrock included the freshly fractured aspect pptawessoas: x Ye peu sty vd baci ntde per a woitod a + 7 Mi Badsteg avieas xs jad} Bagel Kaw ot nt Uyeroan ined gin) tin 2 et pene. rei by aSado ed bios dla open abet? em Cea oe Ww \ ae, ergs beable: toes Bi) pRod tia ae Revenoy Haz tO7 1A nina | ai) ‘mpiqase toraagre s atresia ead tod ari omkbee, tint) ‘aes tat, boew been tow (AROt Ry sataione savy tine all oe Ag, soot | ‘gate oraae Bao at a. Wawa roqzet bra) rottoalla | #er08 ,nonadaoant 4) Haw, baMmNE bee iteay | s Daceatde ataw eer sh datgnas = egnkttof Ree) dat past xodiew gz ‘bot hale Sten azavib wt vamiatga bode tundoon bay toanbod ho franc tambo eee in agioat : beet Biseth2o lhe | pmortod os ae apedan % ts rat oat feat net 36 Figure 10. Bottom sampling equipment used aboard the VELERO IV. arn I | a 37 of the rock, and if more than one fragment was obtained, the similarity in lithology. Gravel and rock not in place, i.e., that had been transported, generally were determined on the basis of dissimilar lithology, rounded nature of the fragments, and the lack of fresh fractures. The dredge generally was towed slowly from a region where no rock and/or gravel existed | towards regions where bedrock or gravel was believed to be present. At the first indication of striking hard bottom the ship was stopped and the dredge brought aboard. By repeatedly lowering the dredge and approaching the rocky and gravelly areas from different directions, the general boundaries of these areas were determined. Representative samples of bed= rock and gravel were brought back to the laboratory for later study. Most snapper samples were obtained in conjunction with hydrographic work so that a grid pattern was not used in collecting bottom sediment. However, towards the end of the Survey a number of samples were collected from sparsely sampled areas. Material gathered by a snapper or the Hayward grab were briefly described and placed in air-tight glass jars for later physical and chemical studies in the laboratory. Cores of bay sediment were split, briefly described noting especially changes in texture, and placed in jars and brought back to the laboratory for studies similar to surface samples. Some problems associated with use of gravity coring instruments have been discussed by Emery and Dietz (1941). Their discussion of true core lengths versus collected core length is worth notice. _motiod. brs ao oe _sbasods taywond oat “da bw mot? ort ooo ak Wonk adi ent aeLqmnn z3qqena 120M ae boay fon saw noha i a fda on uow: oscar ek eueestt a pewenteay ri a perentts #3 ‘ 201 anal iduidal ‘beaut md beoaly bite Sediscenk VEekad 9 Oe r) si ng ven ve Denusedt ed ‘ROG 38 A gravity core sample is representative of all depths penetrated, but the in situ depth of a given layer may be as much as twice its actual depth in the core. The difference between recovered core length and the depth of penetration is produced by the thinning of sediments at the cutting edge of the core barrel. Thus, the depths of penetration given for gravity core samples in this report may be up to two times the length of the core recovered. However, since most of the sediment was of sand, or non-uniform sediment, the core length was uSually almost equal to the depth of penetration. Since it is virtually impossible to calculate the depth of penetration because of the heterogeneity of most sheif sediment, the outside of the core barrel was greased to determine the depth of pene- tration. Figure ll shows the location and apparatus used to collect the bottom samples in Santa Monica Bay. Laboratory Studies Mechanical Analysis In a typical sediment analysis, twenty-five to fifty grams of sediment are washed through a 250 mesh screen with .061 mm Square openings to separate silt and clay (grain diameter less than .062 mm) from sand and gravel (grain diameters greater than .062 mm). The coarse fraction is dried and weighed. Gravel (grain diameters greater than 2 mm) is separated from the coarse fraction by screening, and weighed to determine its proportion in the entire sediment. Grain- Size distribution of the sand portion of the coarse fraction “et RotHG . Hetdete exot eroded" | Figure 11. Location of sediment samples. 39 VLS 3903u4qG A/ALESS EItEKO)'S) VLS AVMYSGNN VIS YAaddVNS VLlS EVO GYVMAVH YNOLNOD WOLLOG 14 O0E S3aTIN a3inivis 2 1 te) i Sd IdNVS WOLLOG AVE VOINOW VINVS rit tiie: : sreddeninhte Sr Lab I Tid ase SEeat Hie: rere metal sn opp emt tg) ai ; 7 dai ; i 40 (grain diameters between 2 and .062 mm) is determined using the sedimentation method described by Emery (1938). Grain- size distribution of the silt and clay is determined by the standard pipette method (Krumbein and Pettijohn, 1938, p. 165- 170). The total weight of silt and clay is determined from the pipette analysis. From these data the per cent of gravel, sand, silt, and clay are determined and a cumulative curve of the grain-size distribution is drawn from which the median diameter and Trask's sorting coefficient were determined. Calcium Carbonate In a sediment calcium carbonate is considered to be the material soluble in cold, dilute hydrochloric acid. This value is determined by slowly adding the acid to a dried and weighed sample until effervescence ceases. After this the remaining sediment is washed with distilled water and any remaining acid decanted off. The remaining sediment is dried and weighed to determine the per cent calcium carbonate (dry weight) for the entire sample. Organic Carbon Organic carbon content can be determined by the Allison (1935) method of oxidizing a 500 mg sample of sediment with chromic acid and the excess chromic acid back-titrated with 0.2 N ferrous ammonium sulfate. Under the conditions of the determination, free carbon is not oxidized and carbonates, being already oxidized, are not affected. Although this method is rapid, convenient, and duplications check within one per cent, it is not an absolute method because it assumes “bonberes9d oT ~ sto " ‘ x ; ony od oF Lacuna a ‘vannousaa ates tatanibee é at | ont elas voriA ,e0nees sbieoetvie} te Lid stumes be ght békaes bcdioad Bee) 8 swiss ane me tee ‘thon. F ott te anoke than: ont tobald ote thow jv dmomwa eaoxs9% 4 Lest emotes bia host bie eva ak nodzen: aot? cr : BLax ‘Ayo oh TiA ‘baayatte tag hi: sooth ewan matin dosiio "ano papi tau bad sashes a nomiae ib 41 that all organic matter is in the same state of oxidation. In addition, any ferrous ions present will also be oxidized, resulting in slightly higher values. Mineralogy The percentages of heavy minerals in the sand fraction are determined by heavy liquid separation using acetylene tetra- bromide (C5H5Bry, specific gravity 2.96 at 20°C). Minerals having a density greater than the liquid sink while those lighter than the liquid float. Thus, two different groups of minerals - the “heavies™ and "lights" - are separated and the per cent of heavy minerals calculated. The heavy minerals are then identified by standard petrographic methods. The light minerals can be stained and identified using procedures out- lined by Twenhofel and Tyler (1941, p. 131). Determination of mineral percentages in individual samples is based upon counts of approximately 200 grains. The sand fraction (1/16 mm to 2 mm diameter) of each sample is also usually examined with a binocular microscope to establish sand types and to outline mineral associations within various environments. Sphericity and Roundness Sphericity and roundness are two attributes of particle shape. Roundness refers to the sharpness of the corners and edges of a grain, whereas sphericity is a measure of the shape of a grain as related to a sphere. The sphericity and round- ness of sand grains are usually determined by visual comparison of the grains with charts prepared by Rittenhous (1943) and Krumbein (1941). * i alkane! ao orate eae Oe | freebie baie cute hie A carte auntyroan atkeg ples ‘ oy ; ee elerendy by palin we ents ont vangathaaass hLk@ Dive “bene iatany ant bseed moter ait: -. aio hy, woe low, wok ott. 104 one gp ne ai Balk suaght nk toot | aia poke ons? jet soehows i ketene ton we he setnombhivg | ‘tede q ett f eee Formioqned A wy ‘de, ui aldhiie Etiam, deve vhke, eed ano kta hie bots detae (reve sy Piso Voy pad soe gees oes atnsneyaos) renin Tans GB fae? thom isd oved Oh sayeth al game . ne signs. edt RO FOG tet 210 OF orngoruya. ‘ton | Re bot tienat® a ities we bia douse ay eae #28 yoin oh View: ye bye Ltyitny ms), hier sill eajabade cae . van @e es ay vcibiainiieeadl n ybter. , Ries tis é yaaiebsa ony pome ‘ai 43 Figure 12. Detrital sediment diagram. i1is AGNVS OQNVWS ALTIS Lis AT13AVEYD AGNVS| ATNSAVYESD ALIS T3AAVYS ALMS AQGNVWS CUYAE DS: ; 3 if Sif LA SUYAEFITA 44 Areal Distribution of Sediment Types The least common sand sediment sub-type in Santa Monica Bay is red sand (Fig. 13). This sediment is characterized by an iron oxide staining of all organic (shells) and detrital constituents. Red sand occurs in three small patches near Hyperion, and in a narrow band off Palos Verdes Hills. The sand at the latter location is coarse and contains abundant shell fragments, whereas adjacent to Hyperion it is finer and shell detritus are absent or rare. Similar sands have been reported from many other locations off this coast and Baja California, including: San Pedro Shelf (Moore, 1951), San Diego (Emery, Butcher, Gould, and Shepard, 1952), near San Nicolas Island (Norris, 1951), in Todos Santos Bay (Uchupi, 1956), San Francisco (Bache, 1852, 1856; Alden, 1956), and south of Palos Verdes Hills in the vicinity of the Orange County,and Whites Point outfalls during the present survey. Additional data on the characteristics of the red sand will be found in the section on “Coarse Fractions". Olive green sand occurs in three small patches in the southern part of the bay near Redondo Canyon; in a small area near the Ballona Creek Outlet; and to a larger extent at the head of Santa Monica Canyon. The sand at the head of Santa Monica Canyon is distinguished from the other olive green sand by the abundance of rock fragments, which are rare or absent in the other areas. The greatest areal distribution of olive green sand is in a zone extending from Palos Verdes Hills to Malibu. This deposit is widest near Hyperion and narrows to the south and north. The large deposit near shore 7 7 tae, eras, pone wane, ea kapeo big iio: Beatie ; a val tea nebray eotet vie Tre hee: hte so Dieet | Aiayods: antetios bas, pain, bb oF wets | “Wiha Ta bene “eh eb # nse ot Ho et SS. weber siete E tede . ave ea nest bene ot ie Hpssese: ie watshhh Aha bas’ bee Rae, ‘ahd’ Yo. anntbeont sane ftir tor) sep ognd asad: vCARAL ogoM Phone ogbed aye. equetany mie: ely tae via” | my “4a8n heey i Diaqad bas. yWbwon 4 RRAeIee ore ineey ou kd: atl «bavdsu) yan! neteat ‘wohoT wk it ibe wth ret be “Sirs ek sy roo hh: nnd ‘(kee oeey x fap Ca (G2BL SOME Sito Soacawnia tl, a otek ; - Senet oie te eeinialy ant et ei fer “eobaay OEE tes dines 7: sowie oF nas pitt ae arheiine: enlot wos SEW sine tangd | Ee Daina hey atv to eohtelyaicm yas, att, iad stam tenosT ERR Pie Sewrlearewm 5 ae 2 uy Nok yee od tk pro ae at ‘“ einloi'sa: iiame geal | ee ania be, com BELO, Phe.) Live & ek Bh weno als ter duit or stot att i tg ovate ot 1 save, araset sot tee 5 petano ine eno btw ‘edt 1828 | ; Bete bea’ isnt eat vn: fers get RON? aatiaol shea’ % all ok neha asire att moa) Wpile hregebradly ab ‘lana eri pokswdkese $i leo. Heotn srs, aah, eR aneen oth ah ixoatall raise! go. fail te wabtiaan oo ogy 08 mit cs baal PRP, atte v0] Figure 13. 45 Bottom materials of Santa Monica Bay. BAY SANTA MONICA BOTTOM MATERIAL STATUTE MILES ~~~=300 FT. BOTTOM CONTOUR ea ROCK PSroaI ie Ee SANDY SILTY GRAVEL Fa PS Bi] RED SAND | OLIVE GREEN SAND ee SILTY SAND i] SANDY SILT WO hee « a 46 grades westward into a zone of silty sand which extends from Palos Verdes Hills to Malibu, but has its greatest areal extent in the north. South from the city of Santa Monica to the northern edge of Redondo Canyon, the silty sand is broken by three patches of olive green sand; a large area of gravel and rock; and is separated from the silty sand to the east by an irregular band of sandy silt that extends north from Redondo Canyon. The silty sand in turn grades westward into sandy silt. With the exception of an irregular zone that extends north from the head of Redondo Canyon; this sediment type occurs west of the silty sand where it parallels the topographic trend of both submarine canyons. The finest sediment type in Santa Monica Bay is silt, which occurs in both submarine canyons and along the basin Slope. A large area of silt occurs in Redondo Canyon in the midst of the sandy silt. In Santa Monica Canyon the silt extends eastward coincident with the topographic trend of the canyon. In this same general area, a rather narrow tongue of silt projects shoreward toward Malibu. The effect of the topography on the distribution of this sediment type in Redondo Canyon is not aS apparent as it is in Santa Monica Canyon. The normal decrease in grain size from sand nearshore to Silt offshore is modified by the presence of gravel near the center of the bay on the outer shelf. This grades into a Sandy silty gravel near Santa Monica Canyon. With three vals a 7 Bdiaon whee it eqs tintin ‘oat — lbiea eas huge bas ony ng > snk ned) ia shinee. dake i ae oat ney aad chon eit hit a “Moe worms. Pa ve ee a eo ey ua. oy ‘al. % (5 zeea Seven se $i) meenrg outs s te a oun we ote wobans abe : . Seo dd: hw arog W280 icin wan’ 47 exceptions, most of the samples outside the gravel area between the two submarine canyons contain less than 50% gravel (Fig. 14). Samples collected with the snapper sampler within the gravel area generally contain less than 50% gravel, although those near rock outcrops are composed of nearly 100% gravel. This fact, in conjunction with the abundance of gravel in cores and biological hauls, suggests that elsewhere in the bay the gravel is partly or completely covered or dispersed with finer sediments as shown schematically in Figure 15. In this diagram, a asmouhetical east-west cross-section is shown across the gravel area. The boundaries of the gravel area indicated in the diagram were determined by dredging. Because the gravel is covered in part by finer sediments which are lost during dredging, the uniform distribution of the gravel shown in Figures i3 and i4 probably does not actually exist. Sand, Silt, and Clay in the Sediments In addition to the other charts showing many of the characteristics of bottom sediments in Santa Monica Bay, contour charts showing the proportions of sand, silt, and clay in the sediments are presented in Figures 16, 17, and 18. The distribution patterns of these components are not dis-=- cussed because they repeat information contained in other charts, such as bottom sediment types (Fig.13), and only tend to bear out and re-illustrate those conclusions. Their Main use is as a reference to better visualize the nature of the sediment in each portion of the bay. In this respect, as the charts show. only the proportions of sand, silt, and 48 Figure 14. Distribution of gravel in Santa Monica Bay. We 7 = pea watch arane na lover wi ’ 40S 0$ HOv36e L OQnog3uy |Hovae VSOWY3H HOV3E NVLLIVHNVAN Pee ee eg ee 4 ool 46S OGNNOS3S 13 L Z\ NWHL SS37 ute 1aAvVYD LN3D Yad e | u00u @ ee ee ‘wiS 390340 —=— Sar VAS = ‘VLS LOdS e rlSAVYS LNAD Yad 1334 NI SYNOLNOD WOLLOG ere L S3TIN 3inivis SS) SS € 2 ! to) ' Wea YIOINOW YILNYS lee conconee- =. a “ a 3 “ioral ele ame reich eres ces ONE RE eae 49 Figure 15. Hypothetical cross-section of the rock and gravel area. tn tphawiocy wane Lovszq) ) HYPOTHETICAL CROSS SECTION OF THE ROCK AND GRAVEL AREA JADIT IHTOFYE ” awa AOOR ah Te 50 Figure 16. Per cent sand in the bottom sediments of Santa Monica Bay. 1 ee etnonkhs %. god fod or Hh hope fi cet: «K x XY, CL LLY SBSEBSBN a & KS SIOBOOS I 5550 SSS % KS me rx BES oS O35 % 0, <> <2 Rise < eX 625 \2 x KS ox <5, 2, xz So x SS 5 x Xs 2 eS Se <> oS <> 2. SEK S50 < “ =e scene se &S 3S 8 5S SS aS SHO 05 a SS OO wate Yaa SS SOOO SSS Sere! <9 X % 6S x <> SRK YNOLNOD WOLLOBG 14 00€ ———— Sarin 3inivis € 2 i} ° GNVS LN3O ud AVG VSINOW VINVS O. S585 SE xxxS RRL r®. 2 2: SE OOO 2 SORE Sz Sx SOS x SXNS 2% ox ne % © RS + = nS 50 SL 4 SES * SOK 0.8 x o> ra. LOK 2S x ix S55 SS 52 SSBB SS SARK 2; SEK SOS SOOV 22, <2 aM a > % 2. a x <2 O < es $2505 C8 <5 SS Se 1% me os SS x <0 x 2 sas aX eS oe. sy) x OS 4; QO S2 ras 7 SOS ‘e Soe XS “a see ‘2 SSS < x a “a 0 BER oO <) 0, os ~ DSK <2 or < L205 $5006 e; 0.8 sen = <> Te 6 xs SO 670% Os > 22, OX 4) o ee eX e acereten otaten axe: nS Ke SK SSL SOY 2 S58 SxS oS SRN e; S505 Mek Xs SESS LOO OS SSS SEK SION. x o, $8 525 x2 Sex SS 9.0. xs neces ON S seness @. 0; O% RS Vg "9% o, eo, at 0% RU, ee Se bee aoe DRS KY Co SoS SSS POOL EK ¥ Ne, KS S ~ 6% R : ESET fe ee ‘ 4 i . z3 ink ey staal a ell a ae bicrystal eT ine nee) aor, ihe cEML Pivinse Sa 0 at. q 3 7 51 Figure 17. Per cent silt in the bottom sediments of Santa Monica Bay. osnstateh marateraterararsbaccte heist ote, o ore e, Seegeteretat atecscy . ore rate Ss ee LS ~%, > SS, x ay aN YNOLNOD WOLLOG 14 0OE——— saz" 3inivis € 2 ' o 11S 1NaD Yad AV@a VSOINOW VINVS 1¥ WOW vB i & a viene seiner Rika «Al 52 Figure 18. Per cent clay in the bottom sediments of Santa Monica Bay. PAN icra Saye wv —— YY LIES 4 tag 4 OK ely 4 [SKE XOX, 6% LSE OOK, ELIE > AEB se SOX LN XY a € 2 AW1D .LN39 u3d AV@ VOINOW VINVS OCI SE OV . A 53 clay, they should be used in conjunction with Figure 14 which shows the location of samples containing gravel. Gravel percentages were not contoured, as the samples with gravel are few in number, and the extent of the distribution is not as general or as well-known as that of the other sediment components. In addition, much gravel apparently is distributed over the entire bay at various depths below the surface sedimentary cover. Coarse Fraction Properties of the sand fraction of sediments, such as mineral assemblages, distinctive minerals, content and type of organic remains, size, and shape can be used to gain an understanding of the depositional history and source of sediments. The sand fractions of all sediments collected in Santa Monica Bay were examined with a binocular micro- scope. From the mineral assemblages and distinctive minerals or components, the following six distinct sand types were established: (1) fine quartz-feldspar sand, (2) rock-fragment sand, (3) glauconite sand, (4) phosphorite-glauconite-shell sand, (5) shell sand, and (6) red sand (Fig.19 ). As the classification into types is often based only on distinguishing components, the areas of occurrence are not considered mineral provinces, but rather as areas having accumulations of dis- tinct minerals or mineral assemblages. aa ievass agua peda ae, Areseumos + aoe Cyelorr ediqae: proksaw te bs autre vi Tie pat ehh eeey ef 28 RNS, itewtaont Pee son ta at nobt ange seanag an. ene artienipea te istioast sien ght i sal aqugo nt | ae eave bay faetoos patarpecie reapenssake 2590 Winger Lexonka te, pais: ow balan i eas ogeds: iia casbe | ie eae, nionere., te, ) ‘edruow pee yseteis Lone toaegsh) SHE te ozbast era imghed tox ettombhies ile to aan ka EY bags aa _wateeatk Bow | 7 kent tehunachth is daky necking as dad vom aningy staat ak Miments eyirans PT RED tm 2: iyakuneeey TwVshka: at ney, cagone| Verew eeqyt imen sonkveth thn gukwqituy, oat ER OOgMOD 100 jremgerttnatairs (5) , tee sieht ten ayy ‘wh +t} ‘boda Lede aiae tietie ethane: Lg- 93 Luodasoily (hy: Bria we Pidoe ala (e) hee enh aA; ae te. who) tven bes Ce) er yeti htode Ate, ORE: ast aeenten eh 29g ithe sodas thkbaal hers hom Sere ataneh Jo wa gamete: ie ewe. aut} 4 even skp to. nies tadeinian.s gquived aiivun ee eodta Tog) weonked spaldnsesk Lnarwel er to stash Yok 54 Figure 19. Distribution of coarse fraction types in Santa Monica Bay. ovine | ° 118307 T ISA NTA MONICA BAY {o} ' 2 STATUTE MILES BOTTOM CONTOURS IN FEET DISTRIBUTION OF COARSE FRACTION TYPES CR acacia can a e ry x —-SHELL ~ SAND S EL SEGUNDO MANHATTAN BEACH a PHOSPHORITE -GLAUCONITE-SHELL \ SAND HERMOSA BEACH REDONDO BEACH q Be 4 SAND PALOS VERDES HILLS 26 EAA NG a ce) AS SS SS ISAN PEDRO™ — AG ey, ~ Me TO ai ent C20RH RAY Abra ed ae 55 Fine Quartz-Feldspar Sand Description The fine quartz-feldspar sand is a fine or very fine angular sand composed primarily of quartz and plagioclase, with orthoclase and heavy minerals making up only a minor portion of the sediment. There is an average heavy mineral content of 2.4%, and a range from 0.5 to 6.7%. The most abundant heavy minerals are augite, hornblende, epidote, biotite, and magnetite (TablelI ). Biotite is exceptionally prominent in the offshore silts and sandy silts where it is the most abundant heavy mineral in the sand. The primary light minerals are quartz and plagioclase, with quartz making up 49% of the fraction and plagioclase 42%. Orthoclase averages 9%. The range of values for light minerals are 49 to 60% for quartz, 30 to 49% for plagioclase, and 2 to 25% for orthoclase. Authigenic minerals are rare. Glauconite, when present, is restricted in areal extent and limited to amounts less than 10%. Phosphorite occurs only in traces. The most abundant organic constituent of these sands are Foraminifera, which are present in all samples in varying amounts. On the outer slopes of the bay, Foraminifera comprise nearly all the calcium carbonate in the sediments. Here, the percentage of calcium carbonate approaches the percentage of detrital material until in some areas, the sand grades into Shell sand. Other organic constituents of the sands are Radiolarians, diatoms, and echinoid spines, which in all cases are minor in occurrence. Naan rshastdasod ott ou ftavoni vy Seanad ae diistelall ee | bane wad ak taiabt ipebesid pos tute: foe oh ical ace: etzeep 9 Se ahasonin fgg qunmaad att gee’ Sgalooigaig bie aoktonst ald tn Fee: cr qsieiaw ‘edna: div q ievents tight wat eau tiv Ye mE es ont ie Senet vn ven tooitt3g) hal 1 bee: Ib binesNeuisauaton 79, POR os Ear matt ene a re oh. 218 } aaa | | yee bebe a4 sa ee aes ae) a Cala steamed / | i meet ay oboe Ay brabhes pirtig Tes Inet and bat okereon | etl iWoowny We white etaout a Eroaqaode POL: nat ee ehris 4 sacdt Tih Pinta 2 a een siadare Sid Png teen oat ve ariy2ay at Rohgae2 tis. ae disenay wen oie vote had 7 “pekrame axe tiaimenah Dill ‘ont es eagote x Hey, oat 7. | etaaot eer e.havoms book: ‘bide rik aY chow AED mikobed oul ve oka Wi ind 0s , oa) voiteas rite atasodtas nekotna: te wt oak bith aca wen, ety sca wi Lb yaw’ Kaban , ny Fon eae a bane silt Be weaniie by aneot ‘ShdaGote| one x ‘ a tte ab, det senate bkowbany bits emote APA Sediment Type TABLE I 56 MINERALOGY OF SAND FRACTIONS OF TWO SEDIMENT TYPES Fine quartz-feldspar sand Rock-fragment sand (ave. of 16 samples) quartz 51.6% plagioclase 40.4% orthoclase 8.6% Per cent of total sample of specific gravity less than 269 augite 30.2% hornblende 28.6% epidote 15.4% biotite 9.3% magnetite 4.9% zircon 1.7% topaz ele less than 1 per cent chiorite ilmenite apatite garnet collophane titanite actinolite fluorite glaucophane spinel anatase barite kyanite tourmaline hypersthene rutile andalusite glauconite rock fragments basaltic hornblende Per cent of total sample of Specific gravity greater than 2.9 3.6% (ave. of 4 samples) quartz plagioclase orthoclase hornblende rock fragments epidote magnetite augite less than 1 per cent zircon ilmenite topaz garnet actinolite tourmaline hypersthene enstatite Oh bias pales nasteeaat \ Sakis Re eiques } To .eva)y er ere eee y >in oe y bs 1% / aaa fou tunly . i SEAL ROT 49 ) Wi | ae ene vw ‘aBy ey ih Ma iene toneeetancan es aceieendeancanemeneeen el abinetdin roi | at re, WR ey siyis 26S) Btusmyan? tone) i ; alien dhs 8 et eee |. @ atc oagsn Srince andes Bs BS a By weet cae at et | i Ee ts STE eMBS f ES | 4 tt” mi) ee ea tote ake Ord t ay} ; sis sly ey Sak cena. | peerage ts STR Ao acy at | cae si ten hos GRETA LL » | oil > Colt fo Brew Oy DB uit ant ae en fre ee: Be same yy St The rounding of the detrital quartz, feldspar, and heavy minerals of these sands is 0.1. Sphericity of this material ranges from 0.70 to 0.80. Organic debris and authigenic minerals are well-rounded and highly spherical. These characteristics are inherent from their mode of formation. Broken shell material is generally angular and exhibits low values of sphericity. Occurrence Fine quartz-feldspar sand is the most widely distributed sand type in the bay (Fig. i9). It covers most of the area of the shelf and forms the major coarse fraction of the sediment deposited in the two submarine canyons and on the offshore slopes. Even in areas designated as glauconite sands, as much as 70% of the sediment may be of the quartz-feldspar type, and where the content of calcium carbonate increases by an abundance of Foraminifera, the detrital mineral grains are mainly quartz and feldspar. Again, on the offshore slopes, where median diameters are small, the coarse fraction of the sediment is generally fine quartz-feldspar sand. The physiography of the shelf areas where this sand type occurs is generally an area of smooth micro-relief. Rock-fragment Sand Description This sand is medium grained, subangular and contains rock fragments that generally are particles of dark schist and fine-grained igneous rock. The rock fragments are acces- sory, however, for the bulk of the sand is made up of quartz eal. ae pea Ys nsktoart as 'g a Saletan waht 58 and feldspar. The average heavy mineral content of these sands is 6.2% with a range of from 2.6 to 21.3%. The most abundant heavy minerals are rock fragments, magnetite, horn- blende, and epidote. Proportions of quartz, plagioclase, and orthoclase show fairly constant relationships with an average value of 50% for quartz, 49% for plagioclase, and 1% for orthoclase. Foraminifera and shell fragments are present in these sands, but are not abundant. Rounding of the grains shows a wide range, with the larger particles generally showing some degree of abrasion. This characteristic is a distinguishing feature of these sands. The range of rounding is from .10 to .60, and the sphericity ranges from .70 to .80. Occurrence Rock-fragment sand occurs in linear patches nearshore between the Hyperion Outfall and Santa Monica, and on the north side of Redondo Canyon where it lies in a depression trending north from the canyon. The largest occurrence in areal extent is on the outer portion of the shelf at the head of Santa Monica Canyon. This accumulation covers the entire head of the canyon and extends south into an area shoreward of the gravel and rock on the central shelf pro- jection. Deposits of rock-fragment sand result in high median diameters and in sediments which have 80% or greater sand content. en questa “4 . ae sbentdot nets aie o = oe os ‘melanie 42. orgs ee Bitsy vhtex 023 9 gry oeomty cf guuract soditukegas? st) 6 a oktals wi a | oe. a pene ‘ett Bann’ 208. oF Oh, Wout ai tara ‘we. spars - Saidataae Sto? ne thaw? 2 edad > i kn ote. ng ‘bas peoktio’ 23 ng8 hin thatawe pose mei old wt id | uaigesnqn® a a) aatt +f aha ORES cea. te abia: Be 03 wh asia 302.20 feenrnl ss Haan: sti rn afzou pata nie oft itis hE wiiz, nat Jo nine Paes carne ott fo 8h) tnetas J | oie erates saab ere an eat ‘hoynes: ihn wttae, Yo | BDIh ta ates iitgoe aio oa, aoynna laid wr, a vf i 2. “GG Hsu Kp yeuen matt (ty aes bia beepzy oat to | xe gather sha ne oe betes hea vieation *~” shea yi ‘ . D 59 Red Sand Description The red sands are coarse and subangular with a characteri- stic red stain on the grains similar to that on the fragments of some present day dune or beach sands. The mineralogy of the red sand is similar to that of the rock-fragment sand and the range of heavy mineral percentages is from 1.3 to 8.8%. The red sands nearshore south of Redondo Canyon are different in appearance from those north of the canyon. The former characteristically have a brown color and a considerable amount of shell fragments. In the northern portion of the bay, a reddish color is more apparent and shell material is generally minor in amount. Shell fragments occurring in both areas show some signs of wear and the rounding of all frag- ments ranges from .20 to .40. The sphericity coefficient ranges from .70 to .80. Occurrence Red sand in the northern portion of the bay is always associated with rock fragment sand where it occurs as small isolated patches. It is nearshore in all cases except for one occurrence where red-stained minerals were recovered from the offshore deposit of rock-fragment sand. South of Redondo Canyon the red sand occurs in a large linear deposit which parallels the shoreline and lies close to Shore. i oe easier: sontin, oat, 2 SRI “ape Ba eu eh ‘base Tahrgast~ ino) wily a 40h ye Sakints. 2f), 1 ay ee a. ete BoM h) BL eset: % aynnke, Wy; ial wan tox ca) £y ARON TO Nias Kpomsanon SRL i ‘atone dD oh? Yo td eer] See noes 9 PRE Te a fps ae “eidesobkarins & bie (20a apd @ ret wi Aoekt Pest aa wentey zoma0% eB: ® Oo SoSH Gg westd2oh ody HPs Les owmpant Liens to taucms | ai Seketan Phewe ‘bak Wipes skeen, Modan Re WOson ek psec is wed | diod wi Rae eshowe! ints) fede indeme ne série yl texas | 1 j : : e) feet ita te Sus hinray ot) te Bae lo Base Mirae! mone asta y Sneks BLitsoa YPto tir4ay vy a. ae ae gina “ehesm! “yt OS “amtin segue, “pons 4 * éyaw te ef: Yad iY OR Oe aa: Geo exit wit) 7h DASE bare | i lea or gassed sh eratw bhes Hawa? daa ew Gat ane pa tqnony eee tia. he S2One ae Be ee BO Oa Letatoe bes svenee Sta ele lat. bes tg ghee ts ib eactte i onertwAne. bias PrsGes a ioe ’faoded siredetioe eat esebeg. Drmem Dog. © : ict vives | to ti08 et oe ee PHOS ap cit ad 1a um q ete ini 2 Hizogeh, 60 Shell Sand Description The shell sands are designated as those primarily com- posed of shells or shell fragments with fine quartz-feldspar sand as the host sediment. Sands with abundant shell material and associated authigenic minerals are excluded from this type. The organic remains, generally tests of Foraminifera, are often broken. The roundness of the shells ranges from 210 to .40, depending on whether or not they are broken, and the sphericity ranges from .70 to .80. The accessory detrital material is angular. Occurrence The shell sands are limited to patches occurring at the outer ends of the submarine canyons. They represent the accumulation of shells as the coarse fraction of sediments in offshore areas where the supply of coarse detrital material is small. Phosphorite=-Glauconite=-Shell Sand Description The composition of this sand is extremely variable, but the association of phosphorite, glauconite, and shell fragments is so distinct that it warrants classification as a type. Quartz, mica, and rock fragments occur in the sand as detrital particles in minor amounts and the average heavy mineral con- tent of the sand is 2.5%. The minimum percentage is 0.6% and the maximum is 6.7%, as glauconite and phosphorite generally as hacia’ ut we bare f aoaigt + maison Date x ptt ge gebrawb20 5 nontorrag n? bosieed? igh bare tt-adn oat ‘aa fume s2y97 ¥ of BAOY He ait brain: ons ‘ wines. 9100 “plat bye ‘Te Ket} neat eunang emt a gh toute te vo ita Lome a a Siivetan tha Abh gestions do kine eat ee hee siodetie® ak “ohlgae ay riak | iade~ot haugelOary orosqeadt Hyd Oheahaey, ch bwninkaee Aa tthe reer Yo soit keoga ott \eehemedtt iteds bag , eo tnoous ta , ot ¥ adil pany ie nobastooaean’ one area’ 6 Rs bod ined dunn eh eRi wane Th: tanta yemiderd on fetistoh eh bees of RE ‘game eter T / hoes, beg ok ms 9 ‘betonke wor ord suerte. wily form adele aa ‘ronéw ad ak , Rei ASLO Wh, Shad aeeey’ wuakuie ait sth 5 ak bnee pine | Ri Laver a at Svemeeorta, wins i eae uci ati an, 61 separate with the light minerals. The shell material present has fragments of the larger shelled animals in addition to the tests of Foraminifera. The phosphorite shows a wide range of rounding (.50 to »80), as do the smaller grains of glauconite (.70 to .80). The sphericity of both minerals is from .80 to .90. Shell fragments are angular, generally with rounding values of -10 and a sphericity range from .70 to .80. Tests of Forami- nifera which occur whole, are well-rounded. However, when the tests are broken, their rounding is in the same range as that of other shell fragments. Detrital minerals in these sands are generally angular. Occurrence Phosphorite-glauconite-shell sand is found covering the entire shelf projection between the two submarine canyons (Fig. 19). They are associated with the area of rock and gravel and also occur as the coarse fraction of all the silty sand and sandy silts on the outer shelf seaward of the gravel areas. A small area near the edge of the shelf south of Redondo Canyon is also covered by this sand type. Glauconite Sand Description The proportion of glauconite in this sand type ranges from about 20% to nearly 100%. Even though the quantity is highly variable, all sediments in which glauconite is a prominent constituent are included as glauconite sand. The thE a at dam04 Pg sient OB: es Let ‘agen ype cae ig A ee o *, ‘sat widw aavengh ta ad ore Fs ene pies be ites Eaten area) pnts as pees smal igh ne ak water peas notord avn ota] -pbaae sands ak abavontm tule ed . fi rem i fode! ae Wi pMelasne yt! axeeey pee od gat tSvoD bow ah haee ft Lbetien be Linco tyne t ~ipel Lent) _ el il wep tno eet PAT ce: itt jee it et ienelore btu che ouitag bts totasy Ses thos To eete eee Ww Pegetigras ote Pads 8 1; Ree aaa Eis gr hielo monte Aro ody. ae wwo39 ola J (Pass soneen HS ep: Fie TTAte “satire adh 5 Kt ee whe obhaotes ty Shedd ties se Aw sebe ot aha eo te bie ooiet fede Shih vd te soten eats et ae eee ih Wale Pe a RoR? Se? he a he: a bob ai A to at #109039, wet ab ye hinaap, ody Miia sane RODE einan@ 0d 08 suede re S Oh y es isle ra rei ae ay: sesabbon, ta! : 1 4 Ree vt tis als 62 accompanying detrital material is generally fine-grained and cannot be differentiated from fine quartz-feldspar sand. The average heavy mineral content is 2.4% with a minimum of 0.9% and a maximum of 4.5%. Shells and shell fragments included in the sediment are generally the tests of Foraminifera. Phosporite may occur, but it is limited to trace amounts, probably because the sediment is fine-grained. The glauconite is dark green to light brown in color. It has a globular form, often with surficial suture-like markings which allow recognition of either internal casts of Foraminifera or coprolite casts. The glauconite grains range in roundness from .70 to .80 and in sphericity from -80 to .90. The associated detrital material is angular as are shell fragments. Whole shells, on the other hand, are well-rounded. Occurrence On the shelf and slope north of Santa Monica Canyon, a large patch of glauconite sand occurs in which the glauconite represents 20-30% of the material; the remainder being fine quartz-feldspar sand. On the basin slope off the outer shelf, glauconite sands virtually ring the entire area of phosphorite- glauconite-shell sand. Here the sand contains the highest amounts of glauconite and some of the sand fractions are composed almost exclusively of this mineral. A small accumulation of glauconite sand occurs along the outer edge of the shelf and on the slope south of Redondo Canyon. The sand on the slope has a low glauconite content and is, therefore, similar to those sands on the shelf and tens. owapaat aati ~ ane one pakae soindounts ett pahag et htipage» zo # vee td saa > etd radio ant mo yet Tate skedw ae Lge # 928) or - area ‘a ok veo wtoad. a dono sleek i! be Lede od, is oink ‘noted AA Geko adt jbsbwetnes att> Li oemOe 3 fade: RPERO: ond, Yin eola hve sad ott Orne sagabisi-nds ORs teri ea Ne oy onbe et one pits Elieurgayv 2 hea, on | seoryal gate emhatacs ike Sed 9xeh . bees t toenba i , ee Oe, TO omoR Gas ee, Loose nig, ipa 63 slope north of Santa Monica Canyon. The sand on the shelf south of Redondo Canyon contains a high percentage of glauconite and is similar to the material on the slope off the outer shelf. The accumulation of glauconite sand is limited to the zone of variable micro-relief on the outer edge of the shelf and on the basin slopes. Median Diameters Definition and Significance The median diameters of the bay sediments have been deter- mined from graphs of the cumulative frequency by weight of the diameters of particles occurring in the sediment samples. The median diameter is the diameter of the central grain separating equal weights of particles coarser and finer than the median grain. The median diameter can be used to determine the manner of formation of a sediment as it relates to the strength of currents which transport and deposit the individual particles. However, transportation and deposition of sediments are complex procedures with many variables, and the relation be- tween median diameters and the agencies of transportation and deposition are too little known at present to allow rigorous analysis in this fashion. The main use of median diameters is to indicate the relative size of the sediment for mapping purposes, and for the determination of the distribution patterns which can be used in conjunction with other components, such as composition. In this manner, known processes in the ocean environment can be related to the occurrences of different tvpes of sediment. seston tosnites st ni meme aatoa sig io te a0 ry “stavazore iis) miraitbeinn sh ji, okt ra ‘ ‘a “aM nokta tee st betas eos BW a a Ruse. | twonosis, wail te ee, weed a cont sister on? ous _eiptomalh mt: hcl oni Aé.g3 ae, 64 Distribution of Median Diameters, An isopleth map of median diameters of the bottom sedi- ments in Santa Monica Bay is shown in Figure 20. In con= structing this map, information from samples obtained with an underway sampler was not used, as the finer portions of material collected with this device are partially washed away during the sampling process. Samples of sediment collected while dredging for rocks were not used for the same reason. Results of the analyses of cores were also not used for this map. Elimination of the foregoing types of samples left 364 samples available for the preparation of this chart. There are important limitations in the interpretation of the contoured information in Figure 20. The first is that \ the contour interval is geometric, rather than arithmetic, \ using boundaries of Wootworth grade sizes as the contour values (2, 1, $, a ete. mm)3 and, secondly, there is a decrease of i the number of samples with increasing water depth. In Figure | 21 is a cumulative curve of the percentage of samples with | depth which indicates the sparsity of samples at the greater depths. Seventy one per cent of the samples were obtained from the sheif at depths iess than 300 feet and the remaining 29 per cent was from depths greater than 300 feet. Thus, the contours of the median diameters are based on successively decreasing amounts of information with increasing depth. Median Diameters of Sheif Sediments Offshore on the outer sheif, median diameters are relatively high and have an irregular distribution. This portion of the Shelf contains extensive rock and gravel (Fig. 13) which are also Figure 20. 65 Isopleth map of sediment median diameters. f een ni tat i , " 1 a | e I we YNOLNOD WOLLOB 14 O0E-----—... S31IN 3Zinivis € 2 ! fe) ' WW NI YSLaWVvid NVIGSW JO dVW H1L31d0S! AVE VOINOW VINVS oe se OE Bil COMLORE: == fie ~ <3 = # PET tke ne re nana PENAL I ERE Wt Sok Tye at seh wane one nee yiesase A 66 Figure 21. Cumulative curve of the percentage of samples in Santa Monica Bay. —— ) SeLhgaas to eye ta a09 SOEMOM u2 et = uJ J re z as fe a uJ (a) fo) 2) AN33583d SAILVINWNS i Lt A tsrmghs 67 contoured. However, these contours are based on only a few snapper samples. Cores for foundation studies indicated that the gravel extends a considerable distance towards shore, but lies under the band of coarse sediment inshore from the gravel. This coarse sediment is a thin cover, 6 to 10 inches thick, over the underlying gravel. From the sediments collected by a snapper sampler in the rock and gravel area, it is evident that at least a portion of the zone has some fine sedimentary material mixed with the coarser fragments. Due to the variabi- lity of sediment in this zone, and the paucity of samples, the exact sedimentary pattern cannot be completely defined. Inshore from the central shelf projection, or the outer shelf, the sediment is roughly banded parallel to the coast. The outer band of sediment is coarse and extends along the head of Santa Monica Canyon and across the inshore side of the outer shelf. Shoreward from this is a pattern of finer sediment extending northward from Redondo Canyon. North of the tip of this deposit there are patches of fine sediment which bridge the gap between the southern zone of fine sedi- ment and a tongue of this material which projects towards Santa Monica on the shelf off Malibu. This fine-grained sediment covers most of the northern shelf, except for a zone with slightly coarser fragments nearshore. South of Redondo Canyon the sediment also occurs in bands parallel to shore with very coarse sands close to the Palos Verdes Hills Shoreline. To break this parallel pattern, between Venice and Hyperion close to shore are several tongues of coarse material which project seaward. | takes end oul OE od. a never abe * ‘eh aoc htoea oases. ne | (ian noite oat seve taobive at th +BoRF covery bina sax a itr welqmae seqgane s “a assatiog atnenthse eat tart Whe tate bee Snk? stoe. Bat oeras ate Ae pris soq 6 baeel, a seat | * esi $n¥ o4 ob .ahaseyert seeiens galt stew Po ae Entrstad | ‘ould eotqmae to yitovaq att baw aoe abate ik Seabee” Yn vat | i sbentted vistelqmes ad ones weetiiad (et em bee ‘¢oune | i aetto na) to ~nokvowp ou Plode Lageesa: ott word snorteasy. ee 7 tage edt ot | botasd vi itu #2 Peni ben Sah ¢ Thee | 4 OOF nao ls shastxe bus se2zs09 ak Yaemebea Yo bees tha out? ty Shit sxodend ett seevde tee govnns en kaolt ata te ned | whigis ating ott te. Aia9k, .fovnsD ohaobed nas yg rye LOR gritnstae trombone i tank) te weetiao = 2) ahite nde besa sods PeemiBer anli jo esdotet. san Guesd? Skuta ere? 1 dit, ot ekbse sak? Yo aus maddie: ott seowisd’ gay itt onhind tem Caivetin shiek ke orgaot a barn ebynwet SIRS hog Ho Lite bsakaaeomnh? Rise vebt Deke to? Liege mt ae. avkaoN. araak 6 20% FgeeRe Viteds ossdivan eae) te Peom REOVOO PME, : fh ty ddnok ,srotieradn erunngart LsMOD vivagets it bs oF Lollaszeaq ebnad gi eniiie ocls spemkbaa oa? nove nap SLT aeabiey sola att ea Reeth: Sirae dich i i hake tbe ontaey neswisd , ested ses ociasati afar danad | ot aveoe 1 avugaos fuxewoe ah pangs. pt _paote 68 The gravels of the central shelf projection are relic and were deposited during a lower stand of sea level. However, the finer sediments occurring on the outer shelf are probably a recent sediment cover. The coarse fractions of this finer covering sediment contain authigenic minerals, such as phos-= phorite, and abundant shell fragments possibly indicating an environment of non-or slow deposition. Often this coarse fraction material is in the size range of granules and pebbles (2 to 64 mm in diameter). There must be sedimentation of fine-grained material here as in other portions of the bay, or at least over a portion of this area, but it ae be slow enough to allow the formation of phosphorite and to favor the abundant growth of shelled animals. It is also possible that the phosphorite and shells are relics of a prior environment and are now being covered or reworked. Then too, the topo=- graphy of this area consists of small highs and depressions of low relief (Fig. 8). Gravel and rock may be exposed at the highs with sediment accumulating in the lows. The high areas may be the loci of formation of phosphorite and the places of growth of shelled animals which are subsequently Swept away and added to sediment accumulating in depressions. The coarse material at the head of Santa Monica Canyon and on the shelf behind the central projection has been identified from its coarse fractions as being mainly relic sand with a low silt and clay content. This sediment is probably an old nearshore deposit in which some silt and Clay accumulated with the sand. The tongues of coarse material nearshore in the vicinity of Venice and Hyperion “ gndvaciint iidkeeog. a ste a Powtaw: te has ina eR teoD, tink! ego .gok keegan ime ip! hehe T6 tmooraskvnS ti, . Gaciad bon, ealwha tp Io. S300) HRD, ‘me seat tehxotsat nok tuaNT | eto dekiarnemé bas, at Seem Svar het ar te, tent Pade bide i 1 res, ‘edt lo enottrceg. tonto) Ba alega ve some porkaamslet woke ed Fp bk Died 2 wide te: soit te 5 olen.” nash te oy | ‘ety sovat of haa “tk se dophshey te wo tac gate watts of dyna | | “tons pidiaeog Gh Re) FT sotining botitgdd! i idtyrony Sanborn , Sieeadatttrs tr ane '& tea Bok Ten ork ébeouts ove ota dqeadg ont | nagot WEF tor gat?’ , beheoway 44 ‘ns sv0%, tee wor wa! ca ‘ eiok RasTde hy Aira a pat! aie ote 8 APN, means Rae to Tie PaAchtaigee et ysm. Ae aah Lenya ie ele . BAS? Foks or won): 30ul | Ayia iT: Jtwol ody od pnbre tains: Hiabhee tite ody. ait outs Diss whkuodqaarty té fis ad aliens: ty kettey 2 ats ad | ek ag Vitwerpsatves azn doidw elemies titrate Yo AHO 9g Yo! event tno kamsiqed ea Shes whine (weastea of bebbas baw che KORRES wD.cm eee es: “Yo hned! att 9s’ Ladyotam sRi8O9 ocr aged. xed take dnt. © ag iwerdnsd: ade me ned Voids ont te Siion tiitem BAPE BeGaght>ax) shang atk moad) partes . ‘ee Perse, Pee eat. at ats ag ge ee ike wed dul cst hyo hn ¢r he Bees cotati te Be ciah nial outa natal te 69 also have coarse fractions which have been identified as relic material. These are likely old beach ridges or near- shore deposits associated with a rising sea level. The intervening band of fine grained material which has a coarse fraction composed of fine quartz-feldspar sand is evidently sediment being deposited at the present time. This sediment has either filled in a low area behind an older deposit farther out on the shelf or has been deposited across the variable topography of an older series of deposits formed by an encroaching sea to create the smooth topography of the shelf (Fig. 9). The inner shelf appears to be a depositional apron, apparently formed by filling in of irregularities and making a smooth plain since the last lowering of sea level. Fine material is kept from being deposited in the near- shore zone by the action of waves. The patch of fine-grained material near the Hyperion outfall, reported at this location by divers, is probably due to the deposition of sludge from _the outfalls, which is relatively rapid so that all of the fine material cannot be removed. Normal deposition of fine-and medium-grained marine sediments is taking place on the shelf off the Malibu coast and the median diameters decrease outward as a result. A clue to the areas where marine sedimentation is taking place at present is offered by a graph of median diameters related to depth (Fig. 22). In the depth interval from 125 to 175 feet, which is the depth range of the band of fine sediment on the central shelf, and also the depth range in which NR I a RT A a aonsten’ ahr "6 RRS dupe ahah aR | op ve Bitivonss Ree es ie seein | Sadie ‘eebto, ner ‘pa keiaer Aaera wa * i heli he wats ‘eof eat sisieiatl ba? beugee Fgh ie ae i panes: rot oO ate abaya bems03, aeksoqeb) 20! sohuas: subd aa ay itgar gogos otdaknay jl XO) yaiqe gnoged Aracura wih ena of ew gai como tomate xa aad of riceggs Liwite wenn oe wee ood? dbsie ode : Ay, Gl get let sof banks): braille ehoaan indott keoa st bast! atid ODER BE REG toa: pe sabotage ne oir retwgomth | ptever see Ly ackiswodil + be OBL oh bot bagTsh’ grind er 39 ist Bt Laetyvedten oak ue Boakeia-enl? Jo Mateq edt |). cerew Fe Meboe one yd! anos “—<— ' nohtsoud ahatt fh) Kevacges Chetan ebesayN bA Sa08 Labeotin ose we hese ho nor haere with a ae Kidatiot ek anys bbe widt Yo tis doit os Giga vlaviterss ee fie kidei in ! hihiteiys if tesruad teases ae ork Les bedbecden thom Hivesewl) iy noredooga TeRegn | ‘teased editim aap Pe, Rkdate. aah inc ane ld BASRRE ae asnont | A Ovttokes Ba bikawebaie Bee ae eee eo Sh Dem Se HOME UHL Ae st) Oe she aba ene ine ats wed sige #5958 ie hate 70 Figure 22. Graph of median diameters of bottom sediments plotted against depth. ao a Ho ee he doe tea HIGHEST VALUE — \ ARITHMETIC MEAN 3L3aWITIIW — a a uJ 2 < > bE 2) uJ > (e} J \ \ .008 DEPTH INTERVAL IN FEET ait Te material of similar size range occurs on the shelf off the Malibu coast, the median value and the arithmetic mean of the median diameters are almost identical. Also, the range of values for this parameter are not extreme. However, the values for sediments in other depth ranges are widely diver- gent, where considerable relic material is known to exist and where there are abundant organic remains. The effect of relic material is not evident in the depth range of 125 to 175 feet as it is in all other depth ranges of the shelf. This, then, is the depth zone on the shelf where sedimentation is probably taking place at the present time and where this Recent material has covered older deposits. The coarse sediment occurring nearshore on the shelf south of Redondo Canyon has been identified as relic red sand which is possibly a submarine outcrop of the Palos Verdes formation. This may be kept free of Recent sediments by currents which flow from the center of the bay impinging against the coast in this area or by the action of waves in shallow water. The outer portion of this shelf is evidently an area of deposition. The sediment there contains coarse fractions of authigenic minerals and shell fragments similar to the coarse fractions of sands on the outer shelf. Currents Sweeping over this portion of the shelf may create conditions of slow or intermittent deposition and a removal of fine- grained sediment similar to that postulated for the central shelf projection as discussed later in the report. oN vravemolt omoxted rn nares tae oF eoutay te Apel ¢ishiw ate asia, sitaeb ‘tains ot Wwe the La Died an obi Widexoniauen. oxi witha | a ook af watt ealeews ahaa Hieehinice o4R s19ah ened, ‘ban iNet) Ded: te Sanat isqan gts ae, pebeve ton at Labvotam oktos » tisda oat 4) Regie? iran hie Wie at eh tho ees tos) Oe “‘tlolistnonibse o2erty \texta att ise sios: pat oid 2d, yea ett aks waite, bite, owbs. seonielail ete ae ede hy poled ridugord a8] whiesase iwike Dados eat Leta ore tral trate ony ao nionedsen whet hOds top bs « a27 400 itt” ber ailer ay ben iliwelbrt mead aml goyesd ohhober 46. 208 borhan ‘ent Bo eS hag, Sneha 8 Widitesd eh iby: pase Neinahtss Tiayen Dey oot) esa ad yam einr uo tt aan} eebag Boagnogak vad wit So xsaneh si es? wort mokuw dtmaeeune nk envew t goktou oft Vd ee aias RLdS Fi deeod off Tanke ee viinehies 2h ie he 22 elif My oharted xnetwo efT 4 sataw wal ire hte aetah, do ase S27 0od SERIO oxeelt dosmifex oaT Selems & ermedaanl | thee ye tlavootm sigge tatu 20: dag ttom ah 1 RIMS PUI ede Pele C82 BO HRMS to ate kT et seme pal AOE ios steers Pan Wee, ont Io wohwsoq hes xev0: qnige waite t te tsveinoa y ‘bas holt teogeD Ig ht bosch | cum woke, ' Lerties: aly yet eda Shae want pelimie tapmbbes. bos ae Foils aie ity eb: Gawea! brie nak ga _pobtoatong ie op rity 72 — -_ lo On the offshore slope below the shelf, basin slope, ,there is a fairly regular decrease of median diameters with depth. Isopleth lines of median diameters usually show the same general pattern as topographic contours. However, this pattern is interrupted at places by small patches of sediment which are coarser or finer than the surrounding sediment, which are the result of slumping on these slopes. Emery and Terry (1956) have shown that the topography of the basin slope of the Palos Verdes Hills is made up of innumerable small landslide scars, and that the sediments themselves on the slope and at the base of the slope show evidence of slumping. The same pro- cesses are undoubtedly active on the basin slopes and the slopes of the submarine canyon in Santa Monica Bay. The sand fraction of the sediment on the slope off the outer portion of the central shelf is a phosphorite-glauconite- shell sand, the same as the sand portions on the shelf above. Thus, it evidently has been derived by slumping of material or iS winnowed from the outer edge of the shelf. The same sand fraction is present in the patch of coarse sediment in the bottom at the mouth of Redondo Canyon. It is also similar to the material occurring on the shelf above. Isolated patches of fine material on the slopes may be areas where fine sediment is building up under conditions of normal deposition. The submarine canyons generally contain a tongue of fine- grained sediment along the axes of the canyons. This is particularly true in Redondo Canyon where fine-grained sedi- ment lies close to shore in the upper end of the canyon. The vig ay, i fr , a ily ha i ; i Chae Fr ; a " i | oes aad aise aoveyeh set m Ragersiegot va penis Dect ye sinkd dl eae Of eae di boandn'n ae i ant? ye betes och ite. dummies Me dey coktoead Gene OND | Sit bender y-orbsoiiqeery B Py tee Loa ae, with 24 nn kt ud ant v ig arriieteh Wont # Ot KO. aaetPyog wre ao em Hien elle 7 howe af ; PRA Ri A: RET ha eS eRe eT haat Yee none wen ae ; a ere ae ts an bits pike tie ‘ih gO Sage, GUT a9 + erie el 4 ab eco eto PRK) bib ddan if, eT Me Megaerg OF not sont " Lhe Hate Bk hE ak abirnted lo sivem. sant) te wetted: ‘ort bate bee. downity Pe hee tee: Ran weet twkentau ett eich 3 wir eiha' aaant ee ht Beyots ot oo Le loot aaa io 9 bikeogen). £ aang 0 epee ryan ) ape ae ome Em a Ee SPT wi aka Lies pray COTE R ove amen uct ra) & fa) vhewReD ; Ret (A Se a Oa, nnd taomiton Seiten a ane? weaili ) wesc pind bai ak ae wa lesa Be) ane a us neq ody sik. ere S water in submarine canyons below the surface of the surrounding shelves is relatively quiet. Here, fine-grained sediments can accumulate. Coarser sediments that are transported across the shelf also have a tendency to accumulate in depressions such as these canyons. Along the axis of a canyon, finer material is often interspersed with coarse material that has slumped down the canyon walls or has been trapped as noted above. This is the case in Redondo Canyon (Fig. 13). Fine-grained deposits in the submarine canyons may be carried there by density currents. The axis of the pattern formed by the median diameters in Santa Monica Canyon is shifted to the north from the topographic axis of the canyon. This may be due to the fact that the south wall of the can- yon is steeper than the north slope, resulting in considerable Slumping of material from the south slope, but allowing sedi- ment to accumulate normally on the north side with a minimum of movement by slumping. The expected pattern of sedimentation on a continental shelf, and to some extent on the steeper slopes at the edge of the shelf, is that median diameters will decrease with depth. This is due to increasing distance from shore, the source of the detrital material, and to a reduced competency of trans- porting agencies with depth. Thus, an ideal isopleth map of median diameters in this environment should show them decreasing with depth and more or less closely related to submarine topo- graphy. Detrital material of sand size which is moved by traction and saltation should show an offshore decrease, _aweeita: beter: ida beagaee avec, yeas Ce aah ty rte weet oat te alxn one . -seneiy yhboo e sande meee ek moraKD eokeoM ctiet ak dat | | stloxnas ae) ag hme eiseargodot xt ut Liha “hehe ee bettate sinks wee "to Liaw lidwos pat, +40 1 i wh ah s¢, vain & suegnely OL A ciphiaute omineter ii wis mee: x8qorhe abe fomtnin thw ohie avon Bee “ap eke o¢ yt ane ee oft Pe Sa) Tee J mam wut | | ‘BIORo) be auatenat9 spivey dog Kntaeaktaes, B ixe nol ietasmbbon an WSs ong bar oes, pat is. agus. HM te Raye tw aoueed a MIP Pavia Oe bans. ef hepa: MT Roe gusexesh Ciiw eet eigia cai baw bane eh 3iode to SER Oe wee Reo os) eomAteee jx hesetork wr) “pas ake ipkseat he Toneregiee Dedies py ad tien. yh eva eee Laseuees te ‘das abut ayn tw “es ittqeds Chiw ise 74 whereas silt and clay which are mainly carried in suspension should increase in an offshore direction. There are certain known factors related to the composition of the sediment which will disturb this theoretical gradation.. These are:(1) the occurrence of authigenic minerals having sizes Het related to depositional mechanics of the host sedi- ments, (2) shells and their fragments occurring in a sediment which are formed by local organic processes and bear no relationship to the transported detrital components where they occur, and (3) relic accumulations which were formed during a previous depositional period, usually that of a lowered sea level, and have not been covered or removed during subsequent periods of sedimentation. The distribution of relic sediments, authigenic minerals, rocks, and organic remains in the sediments of Santa Monica Bay often causes a general offshore increase, or a local in= crease in grain size aS compared to the surrounding material. The relationship of these factors to the general pattern of sedimentation of the shelf and slopes is shown in Figure 23, which is a graph showing the variation of median diameters with depth. The diagram consists of the arithmetic mean, median, and highest and lowest values of median diameters of the deposits in each of a series of depth ranges. It should be noted that the axis of this diagram indicating size is logarithmic. The deeper depth intervals were made greater than those at shallow depths to include a comparable number of samples because of the decreasing proportion of samples with depth as noted earlier. The arithmetic mean is the # Anonibos rs nk sniiuosg pecan ston ties ‘ehbaite & sy. vende Me ot zed bike 2oKes 20%") ite, eve: vid pemtod 238 otiin ‘a eat onde atesnognos: tasks be tang antueh bento). exow Hobita a... mhiow €e) bok ee S92 bovewet) 2. to Pe vi abdings (bob aoy, Phe hh keogel nuokwant! a Insupeedod ae Bevonss 4d betaues! naad Jon vad Iie «howe . | | | eo ait thes te: abokasd. i yeknenabn: DRADER (RISE Oe) apne TO aM tieds ated b: ath Coe apdaolt SPE Ta ar iventh| 2 wots gh aes ‘a sean bre , eknot) “oA | tamat Bh SBS aur k droite 2% her suns os bik, cae i taivoten sicker ssa edt oF heanquos as ote. nase ak vane 10 aseiar Iexon4g sit of Ragteed weeds ky qidenokan ton) ES) sawgtt Bh isis ne Megode bde tiads adit too nekteraomk avai pmakb read bein hy moldy sae ons wstwoda iqaag a ak dake ¢ haem Bi toudy tos, ‘outt Ae ated eitos Wie ea ee te ert witgob, to e1stemaih dedhem Woorawley Suswoh aus seedgkd been (ited biworte +1 2988 Higal Ae aiptoas a te eons nb etheoqab a i ak anke naditsbebed Ange a ial ts ekne ont, fasts baton toteong ‘shmm aso: atavavdas sake regosd, oar cuba sy medics ok | eh agus end ee rt Linnie wi hoa, ae Sood? 2) average and the median is the central value of all median diameters in the depth interval. In each interval, the mean usually becomes greater than the median as the spread of values larger than the median increases. The median and mean of median diameters increase with depth in the interval from 25 to 100 feet. Also in this interval, the values greater than the median are spread considerably more than those that are smaller. This increase with depth and exaggeration toward high values is due to the fairly large amounts of relic sediment, particularly coarse red sand, which occur in this depth range. From 100 feet to 175 feet the median diameters show a decrease. In the range from 125 to 175 feet, the median and mean values for the median diameters are almost identical and the highest and lowest values show a narrow range. These depths correspond to the most widespread areas of fine-grained sediment on the shelf and the change of character in the curves indicates present day sedimentation and contemporary covering of older deposits as has been discussed in preceding sections. The effect of relic material evident in other zones is not shown in this depth zone. From a depth of 175 feet to 300 feet, the median diameters show a general increase and a wide spread of values higher than the median due to the occurrence of relic material, authigenic minerals and rocks, and coarse Shell fragments in this depth range. The coarse gravels, indicated by dredging, cannot be shown on this diagram, since complete samples were not retained for analysis, but their effect would be generally to cause a high maximum value of SE re: anexoat wisrnenltl ahi: Me, ewanr bee abkbee at : i pane oy oaka tet ned iad ieee davrseind) eit) mk oot oa besaqe O48 asthe ‘a0 . snonont abot sroldewe aod tna geaita seit som «ideo PkIngr beni aeh etolage! poet bien te aidaora ee tala aH ot raat NCE ec (egaes ahiab, eae Aine dod tw bia’ ba | ‘e3n07 oat a ss8ugsGeb ih We ki a9 Heid ex toon ott dood ev | | gait Od Moulav wage her nek hoe one liad BYS oF eet nox? | sty FRetere 9F. dag, \Leoatioins Showin 6rAa ot etomede nakoond Saoney tien ‘sai qeh seott ‘OOM? WRUKOD 6 worle eon ter Teqwok| “wae a0, dopmkbod ban huaat WARY, Tet eanwenm Putten) ws had Fae aa?! staat’ aavane sty wk +otoai dale t ogardo ad? bas Ito dab tebbaieeaerics Wak Lovbarlbensd oe ses Hott etmondthee {ab tae 1 wath beau owe guthosHxg ns Daaagoato sand ans ee a> eos iets Pogo) eae “ERT ue Seve: Lake deo ok ton), to, toe tie ($09? QUE ot teed 29% Woo weqab & mest. cane Uihgeb wate Deon nbkw oe Soca sane stk Sansney 4 mods sod ame Bi nb bag Io! Pome Roe ONT ua! Be tal bem S19) ants) rondyla eowiay wkssoo Dw (eee Baw efed ont Deo Kapa a tabeet ae phe Stave p dence Set eaes agoh. eke yd atnengua? rt gankis Clio Ah what ee One ay tetaed dau anoaah 4a votagk ane ‘in ‘ai Laie 403 Senate sani aw patie: 5) 76 median diameter in this range and increase the arithmetic mean while the median and low values would remain almost the same. Below the shelf break the effect of slumping is clearly Shown. The values show a decrease to a depth of 500 feet and in this range there is still a wide range of maximum median diameters. In the interval from 500 to 1,000 feet there is a Slight increase in the median value and the mean shows a sharp rise. This shows clearly the effect either of coarse material which has slumped into Redondo Canyon in a zone of generally fine-grained sediment and the median diameter of the samples of this slumped material forms the high maximum value in this range, or the possible effect of organic contri- bution. At depths greater than 1,000 feet the median diameters show a sharp decrease and the mean and median are nearly the same. Also, the maximum and minimum values are evenly distri- buted about the median. This indicates the existence of normal sedimentation in this region without visible effects of Slumping. Undoubtedly slumping occurs, but is out of the range of delivery of coarse sediment from the regions of the shelf near the break. The slumping is probably of sediments of Similar size ranges and its effect is not evidenced by any apparent anomalous pattern of distribution of sediment. Sorting Definition and Significance The sorting coefficient (Trask, 1932) is computed from the cumulative curve of grain-size distribution. By definition, —~ a taweta ae yatgeote. to ~~ i “bas test 08 2 qed a: of Hi ie ewer reo odd) bak ‘ankey. + al» dl ait seasaant, Lange’ ere Ao: aaidtis ryote et ‘eiswets: ew [ fe ends x nt covneD otaobed oltad “begmate anit okay tatsetan Re xotomed mgktom ont pi iin Be bontaxg-onk® wet s1908y mtd ges ig dat att auise® tebzoton: Dongen 4 adh) ty to eelquige ety ey ‘whatnos ‘ghewsze to. taeite aidhaeng, sat 40 DRPAT eras at out | im , anvtemath nip best any 1293 O00, £ Rent totanty acitasb tA) no kted yy cts utceon Std telbom bap asad? Dae segoaonl iol # woite a stxraty, Vhwsvs 928 vowled aitwhebm dae. muhese odd: outa 9 Sra i ‘eek: od tuods ‘bet Has dons étdinty Trodtiw netyhr eisit wk rok tation bon feuton ae pane set? te too. ME Fad baa betzogemay fest eved dobtin somos staat eeavong: ay baw acai | Yat avtaoM adap? ni admamébe® Jo 4 nk owode ek yad svinoM sinse nt crnemeded to guktros oat betiaog Liew. ak tami ood gk to eet tt thers oct 0) «AS oes ' of seols iremk hee betsau-y lotey stom te euiniekal ewe sebeeV 2olat. oat bas ste caddy “1 et f te ytininty ‘edt ak eat ao Br ING see ondainialy boeiye any kaoog busy iotenahelt HHS Os fr stisnssct ait owt raya 89 inom. asa 80 Figure 24, Sorting of sediments of Santa Monica Bay. >» oon bl Ww Ya OoOoOv7v< OS) LN3WIGSS s G3LYOS ATNOOd 40 SvaUuV ae \ \NS \ ONILYOS Ava VOINOW VILNVS 81 be among the coarsest on the shelf, and (2) moderately-and poorly=sorted sediments occur among the relic sands and sediments containing an abundance of authigenic minerals and shell fragments. The nearshore relic materials, which are both red sands and rock fragment sands, often contain significant amounts of gravel or silt and clay. Both cause a wider spread of the grain-size distribution and create the areas of moderately- sorted sediment. The moderate sorting of these sediments caused by gravel is inherited from their original period of deposition. The sorting value resulting from the silt and clay may have either originated during the last stages of deposition, or as a result of the accumulation more recently of a thin cover of fine-grained detritus over the relic material. Moderate and poor sorting in the offshore sedi- ments containing relic sands or gravels are probably due to the same reasons. Poorly=-and moderately-sorted sediments on the outer sheif have coarse fractions composed of authigenic minerals and sheli fragments and a patchy distribution similar to that observed in sediment size. Any processes which tend to concentrate coarse material, such as winnowing away of fine material or removal of this material from highs and subsequent deposition in depressions, create “depression” sediments which are poorly-and moderately-sorted, and "high"? sediments which may be well-or moderately-sorted. The intervening purely detrital sediments on the central shelf and those on the shelf off the Malibu coast are all well-sorted. bi ale vst een. abies oat r8¥6 eetbarsy sonic fai hank ames amin att, HE ankeaos 3605 bag eral 82 Areas of poorly-or moderately-sorted sediments on the basin slopes below the shelf are more widespread than on the shelf. Here the moderately-and poorly=-sorted sediments are generally in the areas of the finest sediment. Slumping and sliding are important here and probably are responsible for the existing sorting. The accumulation of Foraminifera as the coarse fraction of sediments may alter the grain-size distribution enough to cause moderate to poor sorting. In addition, silt and flocculated clays may settle out together, and yet represent a wide range of particle sizes. Sediment along the courses of the submarine canyons is usually moderately or poorly sorted. This may be caused by the movement of sediment through the canyons by slumping or Sliding, both along the axis and down the side slopes. Relation of Sorting to Depth Figure 25 is a graph of the average and median of the sorting coefficients by depth intervals. The variation of the sorting of sediments with depth is similar to that of median diameters. Generally, the arithmetic mean of values in each depth range is greater than the median, which indicates a wider spread of values toward poorer sorting. A peak occurs in the curve in the 51-75 foot range where patches of moderately-sorted sediment are located. From this depth to 175 feet the curve is fairly uniform. This depth range is over that portion of the shelf where most present- day sedimentation probably occurs. Another peak is noted in the 226-250 foot interval. This is due to the poor sorting fae ‘Sit408 am ote : “a Huo 3 Manges wei to ee neds ad. yam ener sborada ae si My, to mei | | 30 wakemute yo exormao tt agaorith ean iw one icciahahegi ceieeiadiesdimeatbaa adh pet ahtal oe te aadboe thikis suatews wel he Aqusy # ‘a et one “a he meks okany ‘oar Jatarietad giqet eo asastoi Tees mn 0k fie to doe ‘of tlints ef stad HRW etmembbes Er andazoe hy “seutey Ye Mie airendstxs adh eyttiened “azatinn ta a @lad moet. bodenet nan Shen this beonoe=y ister bom! gttgeb eka? eager aw, ehike? el) ovis eek tee ar . tase eg Deon one, hiode ante 36) moi aq da 48 nk Daron ak Apa reittons Jasusoe Sarsind 83 Figure 25. Sorting coefficients plotted agains depth. tga achege beiteta « 00S¢2-1002 00S1-I00I MEDIAN = W my rs é Z > fv WJ = é x - a uJ (a) ARITHMETIC MEAN SNILYOS 84 in relic sands and gravels, and in sediments containing authigenic minerals and shell fragments. There is a tendency for the sediment to become better sorted at 300 feet which is approximately at the shelf break. This may be due to turbu- lence at the edge of the shelf which would tend to create a better-sorted sediment. The curve is fairly uniform to a depth of 1,000 feet and then has another peak due to the relationship of poor and moderate sorting to fine grained deposits on the outer slopes. Calcium Carbonate Origin of Calcium Carbonate It is believed that all, or practically all, of the cal- cium and magnesium carbonates in sediments are due to the accumulation of shells. The examination of sand fractions of the sediments from Santa Monica Bay indicates that the most abundant organic remains are the tests of Foraminifera. How- ever, in some areas, notably on the central shelf projection and the shelf south of Redondo Canyon, fragments of larger shelled animals constitute a considerable proportion of the sediment. Distribution of Calcium Carbonate Percentages of calcium carbonate in the sediments are shown in Figure 26. The percentage increases in an offshore direction, being low over most of the shelf and slightly higher on the offshore slopes. The exceptions to this distri- bution are the extremely high percentages found in the patches i Hear ma “e sides | bane % Aa as ‘dare sem 0 a ay tas nateckin att wba pase 0? » tum Poeun, eee | ees ne -egore Kpearhaee os. pay ag siete seater aie ) 85 Figure 26. Calcium carbonate content of the sediments of Santa Monica Bay. Se Or Sv T S771H_ s304N3A OS J —jos HOvV3e Oagnogs3uy lise VSONYS3H | ‘| HOV38 NVLLIVHNVYN 1¢s OGNNO9A3S 13 V-Oa ee SLVNOSEYVD WNID1V9 IN39D UY3dd 1334 NI SYNOLNOD WOLLOG S21IW_31nivis Wd i . Seco nee ee = 2 Of SII SE OY a Se ral rey rome hl lv al me WN pas =A ; h | i if ) ae a yes Q | ——— a Se - ; n agg feelin gtr a Ri api re : H ime as wah pel A i Me ays neva cea latest ne RO wala yer th Moet an vascartineg spe pore titidakes tii ecn cpenores 86 on the outer shelf between Santa Monica and Redondo Canyons. This is illustrated in Figure 27 in which average values of calcium carbonate percentages in each of a series of depth intervals are plotted with increasing depth. The great increase of the average percentage in the 201-300 foot depth range is due to the large amounts of calcium carbonate occurring in the sediments on the central shelf projection. ‘The high concentration of shells on the outer shelf is due to (1) ecological conditions which are more favorable to the growth of shelled organisms, (2) winnowing of sediment finer than the shells, (3) the low supply of terriginous sediments in this area, or (4) nondeposition in this area. As pointed out elsewhere in portions of this report, this region is probably an area of nondeposition or very slow accumulation of detrital material. The main cause for the increase in the percentages of calcium carbonate then is due to winnowing or nondeposition of fine material. Since the shells are relatively coarse they can accumulate in abundance and thus constitute a high proportion of the sediment in this area. The high values of calcium carbonate on the shelf south of Redondo Canyon result from the red sand which contains a large number of shell fragments. This sediment is possibly a submarine outcrop of the Palos Verdes sand, an Upper Pleistocene age terrace deposit which contains a great quantity of shell debris. The general offshore increase in calcium carbonate in the other parts of the bay is due to the diminishing supply : of ntossors? pao ote bee job | tenttoe ae ‘yyekwonrne ce) ea s tuoatalator te rg ‘sod wt Cy habteate oats noth : yet, aber ab Relittommbaos. cad ee ee is E 7 vel, ww wai dina “a Leb aay taba tm ai “amt a ote ehmnade n> nich aban 19 ) eaneaapreg itt ok vente ~— pou tanga aah te in to ahaa oladteneg ak daaabbee abst -soqql na huge patie ao bes es tp qoxotuo oe Saudi» & ‘eniatana Hote taggin sonemey ‘og ) Figure 27. Graph of CaCO, versus depth. 87 Sle yg fA 30 AIN3983d 00Sc-I00I OOOI-I0S 00S -IOE OO0€-ISe 0S¢-10e 002 -IS| OSI-101 OOI-IS os-O DEPTH INTERVAL IN FEET 88 of coarse detrital material derived from the land areas; therefore, there is less dilution of calcareous material offshore. Thus, the amount of CaCO3 is inversely propor- tional to the supply of inorganic detritus at any point on the bottom. The size of calcareous material is not dependent upon currents and turbulence to the extent that terrigineous sediments are, so that skeletal remains of sand=-size and larger may accumulate where currents are very weak. Con= versely, the coarseness of some of the shells allows this material to accumulate where fine grained material cannot, i.e., in regions of strong currents and turbulence. In deeper seaward areas, shells (primarily the tests of Forami- nifera) form the major portion of the coarse fraction of the sediment, probably as a result of a small contribution of detrital material which in other areas would normally dilute the organic contribution. Organic Matter Almost all elements found in organic compounds are also found in inorganic material. As a result, it is difficult to separate pure organic matter. Since carbon is the princi- pal constituent of organic matter, it is generally used as an index of the amount of organic material. The abundance of organic carbon varies between 50 and 60 per cent in organic debris and if the total quantity of organic matter is desired, the per cent carbon must be multiplied by an appropriate factor which varies between 1.7 and 1.9. The choice of the factor is difficult to make because the value depends upon i Ad , oy San anaanioine | ‘a tees ‘ott ett xiomita) mt pede ieee a i oar a boas) PRABOD oft we no kineg vote att Tle a eh i | “ranks: ee n eludes a ak) wT OES as rhoriig sit ¥ Redan ROWE! “ie ssa a ovalvqasyge | it 0 both ost te ooktis watt 89 the environment under which the sediment was deposited and the type of plants and animals from which it was derived. Furthermore, sediments containing appreciable quantities of sewage may require an entirely different factor than those given above. For these reasons, the per cent organic carbon is used in this report to discuss the relative amounts of organic matter, and these values must be multiplied by some factor (such as the above) if the total quantity is desired. Source of Organic Matter. The source of organic debris in the ocean is both the land and sea. However, since the amount of organic matter brought to Santa Monica Bay by streams is negligible, it can be neglected. An important local source is the sewage discharged into the bay, but the most important source is phytoplankton which is the basic nourishment of all life in the ocean. Only a small portion of the organic material from the water survives the fall through the water or escapes consumption on the bottom by scavangers or oxidation. Sverdrup, et al. (1942, p. 929, 938) estimate that between 495 and 990 grams (dry weight) per Square meter per year of organic production takes place in the waters off southern California. Emery and Rittenberg (1952) estimate that less than 1/16 of the organic matter produced at the surface of the sea escapes destruction during its travel to the bottom of the basins off southern California. Trask (1939) suggests that only 2%, or 20 grams per square meter per year of organic matter is deposited annually of an original 1,000 grams produced near the surface of the sea, and that under natural conditions sediments that have been ae ai tll BP Oitganhsd: 192 tem w10 YD) 1 5 i ae sf Waid ue ; if iS: re kee thet Ry iv > HO baer gre i rae rou ay! phaergye 90 buried to a depth of one foot, on an average, have lost about 15% in organic content. The rate of destruction varies accor- ding to the rate of sedimentation. Thus, when deposition is slow, oxidation can be almost complete,, whereas when sedimen- tation is relatively fast some of the organic matter escapes decomposition and is buried. This, of course, assumes that there is an adequate supply of oxygen and that aerobic con- ditions are present at the sediment-water interface in both instances. Distribution of Organic Material in Santa Monica Bay. The highest values of organic carbon in Santa Monica Bay are found beyond the shelf break and the lowest occur near shore (Fig. 28). There is a general increase in organic carbon with increasing distance from shore and with increasing depth. Exceptions to the offshore increase are at the head of Santa Monica Canyon where the organic carbon is low, and near Hyperion outfail where it is higher than the average in the nearshore region (Fig. 29). There is also a correlation between the organic carbon and submarine topography; the organic carbon being low in regions of elevations and high in depressions such as Redondo Canyon. The organic carbon content for 155 samples ranges from 0.13 to 2.76%, averaging 0.59 for the shelf and 1.52% for the canyons and basin slope sediments. The overall average for the bay is 0.96%. Emery (1954) reported that the average organic carbon content for the continental shelf sediments off southern California was 0.44%, and 1.56% for the basin and canyon sediments (Table II). These values are similar oil ara, sotyhe we hl paid: tnete rR! oo & wath Ha roy tes, ‘ue iokged” ; wnt! Retaeesewt nick cates ‘bm acre atrente ‘one 91 Figure 28. Organic carbon content of bottom sediments. Oe Se los|- GFF TWAYALNI YNOLNOD 1.so YNOLNOD WOLLOB 14 00€ —~—= S3TIN 3inivis € 2 1 [-) ! INSLNOD NOSYVD DINVOYO AVE VWOINOW VINVS | __0e isa Oe. 8il SE DP DU Yaast ne: Perauis Be 92 Figure 29, Distribution of organic carbon with depth. RE RosC BING ORGANIC CARBON (2) 7) > <= U ia m 7) + > at O ZL W 4 e =< tS AY a. mm f 1a 5 lt > 4 S ipa uu ; Fi mE Se aT) i i i news riverine aerate mal tenet amet ing melt yerilaaha ve f hy i 4 -* va Rah omens BROS Nae Se ried 6 , — } a 93 TABLE II COMPARISON OF ORGANIC CARBON IN SEDIMENTS OFF SOUTHERN CALIFORNIA Bay Mainland shelves 0.44% 0.59% (av. of 22 samples) (av.-of 150 samples) Basin slope 1.56% 15526 (av. of 30 samples) (av. of 50 samples) - Te 94 to those of Santa Monica Bay, suggesting that the effect of sewage discharge has not appreciably increased the average quantity of organic matter in the bay except near the outfall. The distribution and quantity of organic matter in any region depends to a large extent upon the movement and physice- chemical nature of the overlying water, and the balance between organic and inorganic deposition. For example, the main cause for the offshore increase in organic carbon is the change in the texture of the sediments in a seaward direction. This is illustrated in Figure 30 in which per cent organic carbon is plotted against median diameter. The diagram clearly illus- strates that as the grain size of the sediment decreases, the percentage of organic carbon rises. This relationship is so well established that Trask (1939, p. 434), knowing the type of sediment, has utilized empirical constants in order to make rough determinations of the percentage of organic matter in the sediment. Detrital sediments and organic debris having the same densities will accumulate together. In the regions where sands predominate, i.e., in the nearshore zone, currents and turbulence usually are strong enough to wash away fine silt anc clay as well as organic matter which is fine grained and is relatively light, so that it is easily transported by weak currents. Even if large fragments of organic debris were deposited in the nearshore zone, decomposition by oxidation or bacterial action would slowly break down the material into finer and finer particles which would probably be washed seaward and deposited in quieter water. The large by : tideree: ‘ye ; Fa ow 95 Figure 30. Per cent organic carbon plotted against median diameter. oO ae) wadoma to oe IN MM. fac LJ be LJ = < O Zz = O LJ 2 se) aN) INOS aD) SIINI\/ Sel) AUN BID), ta) Ble a ee k i ‘4 ee 2 Eas MPnenremenee Nee i aces Oe ee aE eek 96 pore spaces between sand grains in the nearshore region allows water to circulate with little difficulty and as a result, oxidation of organic matter occurs to considerable depths below the surface. The relatively low values of organic carbon in the nearshore region, therefore, are the result of an abundant supply of oxygen and associated bacteria that can penetrate the sediments, together with shifting of sediment by wave and current action. Such conditions facilitate decomposition and transportation of organic debris. Organic matter having a density slightly greater than sea water can best accumulate in quiet waters where silt and clay particles are also being deposited. Fine-grained sedi- ment also aids the preservation of organic matter because it is difficult for water to circulate through the small pore spaces of silt and clay particles. It is noteworthy that the proposed discharge location is in the general region of nondeposition of sediments so that there probably is considerable motion along the bottom. This may have two important effects on the sewage: (1) redistri- bution of the sewage, and (2) faster oxidation of the organic matter. The distribution of organic matter in sludge or effluent after it enters sea water at the point of discharge will depend upon: (1) the rate of flocculation or sedimentation, (2) the direction and velocity of currents and turbulence, (3) rate of decomposition, and (4) slumping and submarine landslides. If the organic matter, largely in the form of Sludge but also suspended in the effluent would flocculate i” ‘pkaay20 to eoot ae ead ps i to Hanoy at ome, : on oronat ean “ptaybtton? acakstngd sow ‘ae | Lindh atnagse 0 shoe: oktets | oe $L2a ons thw sash ‘tatup me el t : ie peadatarontd | bet ivogah sels vate ad vote Risa Haine ots ityerornet? caniiane nk aotew aot htonk 5 eetghtrsy yen bis tthe ‘Yo! a ‘ pone ns as rey bade’ ur 4 +0 miat ane it elope. iottem obeny afstoaoaty, Starg femur th ott, ae 97 immediately upon contact with sea water, the organic matter would initially be deposited over a relatively small area. Experiments have shown, however, that sludge generally does not flocculate immediately, and being lighter than sea water tends to rise. Several observations have been made during a number of experiments on the reactions of sludge in sea water; namely, (1) sludge in the form of large “giobs” rises towards the surface, but begins to disintegrate after rising only a short distance, (2) after the “globs™ break up into smaller par-= ticles there is a tendency for the smaller pieces to settle very Slowly towards the bottom, (3) colloidal (and perhaps clay size) particies do not always flocculate, but form a residual turbidity which lasts in quiet waters for periods in excess of 48 hours, (4) several experiments in which Simulated thermoclines were used, indicated that the thermo- cline may not suppress the rising organic matter below the thermociine = apparently no matter how much temperature difference exists between the boundary layers. The tendency for the sludge to rise in the experiments was due in part to the lighter density of the sludge, but it was also probably due to gas trapped in the large "“globs”. Once the gas was released by disintegration of the “globs", more surface area of the sludge was exposed which facilitated better flocculation. The above laboratory experiments may or may not simulate actual conditions in the ocean; however, the experiments did show the necessity of eliminating as much grease and gas from the sludge as possible. | at ‘abaswot ebay! eco eect " = i vino gakets otha’ v9 Mik: i oun ° “aad asians otnk qu ‘degnd: rede. ial oa , a sities of nevetg wadione ont ‘so yonsbast ‘s a ona | egadaes bist) tabhotion Ch). me tod od ebuwwo? ein # mnot ted ,ptsiasnoit acawde. Jot: oh eslodtieg ome - ebotieg so) exatew teivp wk atmal, sisi yrthkdaos Wey doditw mk ‘wigemkreqee Lexeves Oh) epstion BN fy. momo pit tedt betes khoy ibe anew sanhseies an Laneyal cynbiaed: on agowt ott niekne etaomtzaqxs. odd th PaEx oF onbuke ott tot vonsbas?: ‘ iT +h tud wabote’ eth%e wie ena rottigs t ‘od of aa ak 98 Cores Coincidentally with the collection of snapper and Hayward grab samples, a number of cores ranging in length from 14 to 68 inches were obtained in several localities. A total of 15 cores were collected along the proposed out- falls and at the head of Santa Monica Canyon. A description of the cores is given in the Appendix of this report. Most of the cores along the traverse from Hyperion to the edge of the shelf are uniform, but marked changes in lithology occurred in some (Fig. 31). Close to shore the sediments are generally composed of sands and silty sands. In a few cases some shells mark the only vertical changes in lithology. Farther offshore the sediments are predomin- antly sandy silts, but gravel and other coarse sediments sometimes occur. The two cores at the edge of the shelf and on the basin slope contain sand and silty sands which are overlain by gravelly silty sand, sand with shell frag- ments, or by gravel. These cores on the outer shelf and on the basin slope are therefore unique since they have abrupt changes in lithology. Two cores taken along the axis of the Santa Monica Canyon (3342 and 3345) have gravel and sandy gravel, but the other three are rather uniform in texture. Gravel, sandy gravel, and shell debris are common in all of the cores taken from the head of Santa Monica Canyon. Additional cores and jettings were taken elsewhere in the bay and close to shore, near Hyperion. An examination of the logs show that the lithology varies greatly in a vertical y : | venithiasot puke ak bentats | xtap bevogerg sdt noite 2 | “oktqizazed A snowad | a 1G peer obs iss. “8 prode of sant IE) oe Sv sien ose etnonibes arty rode. searant ghvemkdoe sesnoo Ed sine Loveng te worth a | Mone eits to sabe Sih. Fz | soxee ‘owt iT vate: re ahese hhbe bias powe’ nkataon sorte setae odd | eg at ben est Shede dtkw ticen , hing yelie yitovexe td ixks | pine : no ban Made theo ect ao 29203: ‘some fevers xe ye 428 ; y ‘sentto ont duet atevers yices bas foveaa vad c COREE | ae ; bee been vbane Shahin aati! mh maot Lad beat ’ ous Figure 31. Lithology of gravity cores. 99 v¥ivery Yo yRolodtil an nis ES 1iis aanvs FE Hid 3d anvs Arts[_ | SINIWOVES 113HS % GNVS ALIS 1334 NI GNVS ALTIS g A113Av4u9 & SLIN3NOVES W13Hs [2 3 GNVS QNVS SIN3IW9OV YS T13HS HLON3AT 3405 NI 13aAVvVYe9 Sees ALIMIS AGNWS 13AvYNo AGNWS Bass 1 z 9) =r m w r iH 1 1 tr AUTH ssc iii IZee Wut Wit 2vgEe SV9E 9P9E LVg9E 7 1 ba qaawuo fic] = ‘WLS 3YO0D 0 SJTIW 34iNivis 4 ! Oo ! S$3Y¥0D ALIAVYDS JO ADO IOHLI AWE VOINOW VINVS Nhs a Nb v) gee i 5 he. bi) y = ls a lke ania ih worn neler 100 direction over most of the bay. Except for the uppermost few inches, or feet in a few logs, most cores do not show good core=-to-core correlation. It is obvious that great variations in sedimentation have taken place over most of the bay. Some of the factors effecting the sedimentation in Santa Monica Bay and the significance of these changes in deposition will be discussed after considering the geologic structure and the source and transportation of sediments. ROCK BOTTOM AREAS The rocks of Santa Monica Bay can be divided into three groups; rocks in place (or bedrock), transported rock and gravel, and authigenic rock. Rocks in Place The rock outcrops rise as irregular and scattered mounds on the outer shelf south of Santa Monica Canyon, and occur in an elongated tract close to the Malibu shore as shown in Figure 13. The Appendix lists the samples of rock believed to be in place and describes their lithology. In addition to the samples obtained during the present survey, Emery and Shepard (1945) obtained a few samples of rock from the walls of both submarine canyons. The U. S. Coast and Geodetic Survey "smooth sheets" show rocky bottom along the Malibu coast and off Palos Verdes Hills. Johnson (1940b) made a detailed chart of the rocky (bedrock and gravel) seafloor in the nearshore zone along the coast of Malibu and Santa Monica. No rocks were dredged along this part of the coast during the salt ‘t BASOS pene, gaeud ocowaie oe ots seed maou 4 astqass 9 ‘ehtaw 6a moe) aoe Yo welemns, wad a ‘benkstdo R80), - ghtebos® tate tno 62.0) eR -bwoyass: ontiemdye udiLail od anon, ttos tots yaaa. ‘wont Nedooia 101 present survey, but Schupp (1953) studied the gravel that periodically washes up on the beach in this area so the general lithology of the material is known. Siliceous and non=-Siliceous shales were the most abundant rocks recovered from the offshore area, followed in importance by mudstones, siltstones, and sandstones. Emery and Shepard (1945) recovered limestone and red rhyolite from Redondo Canyon, and dredged conglomerate, rhyolite, andesite, and granite from Santa Monica Canyon. They date the granite as Jurassic (?) on its lithologic affinity to granite outcrops in the Santa Monica Mountains. At least one sample collected by the Hancock Foundation (station 4321) was positively identi- fied as being Upper Miocene in age (Lower Mohnian) and several other samples were dated as probable Miocene. Emery and Shepard also found rocks containing Foraminifera of Miocene, Pliocene, and Pleistocene age,in a conglomerate dredged from Santa Monica Canyon. A large amount of shale (both siliceous and nonsiliceous), mudstone, and siltstone was dredged from the rock and gravel area on the outer shelf. Many of the fragments were nearly covered, or bored through, by organisms such as pholads and echinoids. Few of the sedimentary rocks had diagnostic Forami- nifera. Since pholads and most other rock boring organisms are generally restricted to the littoral zone, or relatively shallow water, where current and wave action is quite vigorous, the abundance of borings indicates that this area was at one time close to sea level. > bans outed. xovengie sanctions eB) bated ona suigunen “esnen0nM 6 arotinkmsro4 virkabet og Bide bave? oats ia vitega sxbe! stnompes? eth We i Mena aetow ast bis ebslosty #2 lowe: aime & es 30 wo sAgisonut: berod 20 Eraser okteongn thy Gad loon wu tenh bee ole Ao. wet anekna yo yibret soon matte tem Pises iwenseses eons 102 One dredge haul (station number 3268) made on the outer shelf contained schist. Since the fragments were large and freshly fractured, it is probable that the dredge struck bed- rock. This dredge haul was somewhat unique in that all other hauls from this part of the shelf recovered only sedimentary rock or well-rounded gravel. None of the gravel was composed of schist, but occaSional small fragments of schist were found adhering to pieces of shale. Gravel Most of the gravel on the shelf is well-rounded and ranges in size from granules to cobbles. It is composed mainly of igneous rock, but metamorphic and sedimentary rocks are also represented. The Appendix lists the transported rocks according to lithology, and Figures 14 and 32 show the areal distribution of gravel recovered from the surface of the sea floor. Most of the sampling in the bay was done with a snapper sampler which gathers about two to four cubic inches of sedi- ment. The Hayward grab, used for obtaining biological speci- mens, collects up to three cubic feet of sediment. The material collected by both sampling devices appeared to have similar characteristics, but after screening the samples obtained by the grab, there frequently remained considerable quantities of gravel which was not always recovered in nearby snapper samples. Most of the gravel does not exceed a few centimeters in diameter. Gravel is evident in the wash=borings made along the proposed and old outfall lines shown in Figure 31. From ie abet ele oabesh, edt ie ids > ratio. can andd nk ouphan redwe xeqqaria a lalate snob zaw yee att mk. gnitqnse ent. ‘to teoM ~kdo2 30 eotook otduo awet of ows twoda exettsg all ~koegqe taokgotoks gituteddo ot base date buswy el, sf? Pt era sat «thpekbee Xe F462 aidus souls 0Ot w wioel : antinke oved: ot bors eqge zenkweb aabignne dzod pai: 103 Figure 32. Lithology of bedrock and gravel in Santa Monica Bay. OC Sil Sr6l wis GuvVd3HS 8 AYSNA YILsVMWVLS 34000" WLS 8VYD GYVMAVH o “WLS YAIDNVS AVMYZONN & YAddVNS @ 1Y3HD 9 SLVY3AWOTSNOD NO IS NOIL3YDNOD BNOLS3SWIT D1 A3NOLS3WIT S71 INSSIH LAY) 3LINOHdSOHd SNOLSI1IS ANOLSGNW A1NVHS sno 3zoiis 31VHS SNOLSGNVS -VLIN WS J3NOLSONYVS AG). Z1iyvNdD ZD 3LIZLYVNDd aivis LSIHDS VOIN 3LIYOIG SLIYOIGONVYD JLINVYS SSISND JLINVYD LiIvsva BLISSONVY NV SLITOAHY HY G3LYOdSNVYL G dOYDLNO HS aN a947 HNOLNOD WOLLOG 14 00€=~— ST‘NI ‘49 Saw ZIIE(MIEVALS al AQOIOHLIT ae WE VYDINOW VINVS \ fe 7s OE ore ° | oe i= G - = rap gecesi a ite A a RA mh SANs soe iepeeete; 104 these considerations, gravel may be more widespread than is indicated on the surface sediment charts, but below the depth of penetration of a snapper sampler. The gravel could either have been derived from outcrops on the outer edge of the shelf or from the land adjacent to the bay. The fragments are too large to be carried by present day currents or waves in overlying shelf water, so they must have been transported by streams or surf action in some previous geologic time of lower sea level. This conclusion was also reached by Shepard and MacDonald (1938, p. 213). The restriction of large patches of gravel to the outer shelf suggests that this may be the source area. However, the great diversity of lithology of the gravel probably indicates that streams carried at least part of the material from some inland source having a complex geologic structure. Whether the gravel was derived from erosion of the rock area on the shelf or by erosion of the uplands and transported to the area by streams during a lower stand of sea level is problem- atical. There is evidence, however, that the gravel is a relic sediment that was deposited in the early part of Recent time or in the Pleistocene period (Shepard and MacDonald, 19383; Revelle and Shepard, 1939). The large size of some of the cobbles and rock fraenente: abundant pholad borings, high concentration of CaC0O3, and the attachment of coral and bryo- zoans are taken to mean a long period of stability in the Marine environment since the material was deposited. Ain | se oe at “mt aro ania hadi aie, et, vom okst an: a seteaatad reads: gent + es. caotonken Me ¥t Lesovkh mos C ay moe) Laban wit iy Rout eae ks ti bud tan wate wedton copa Rae S ad Hat iy Percy eae zai oorwae! Sas m8 ozs does areal te oidoxs: wren bawiicals: ea foray sae ot Pensryeonss them hea ait wy nokaaxs, a rr n estes ae evat eon Yo te nee xeus 4 en cise ye | wee Kepaah on? KGET? eee temant “ae dat ad: ek ort | bs: ‘\aiteson Ley Tre izes ald ; Wed eeoged’ eatte bane Soramd bee hf sbinnedase tas Brags: iy ; ae oneoctere ha afl, at a0. i mck Te halt wuans ‘ue x CREED. sbraqata bee others “Yue e | May kat: «mgd ee bea hua Matec Stal ai Hoe bes ‘esrades 9 4 “eid tab Less te Hoviits Soha aah bane 1 ea 49 nobtash 105 Phosphorite The only authigenic rock occurring in the bay is phos- phorite. Almost every sample collected from the rock and gravel area on the outer shelf, as well as samples from other parts of the bay, contained phosphorite (Fig. 32). The phos- phorite generally is in the form of nodules ranging in size from less than 2 mm to more than 10 mm. Some phosphatized mammal bones and shark's teeth were also recovered (Fig. 33). Dietz, Emery, and Shepard (1942, p. 929) report that the only shelves off southern California having phosphorite are off Santa Monica and San Diego, although it is common on banks and topographic highs far from shore. They report that the shallowest sample of phosphorite obtained was from the Santa Monica shelf in 240 feet of water, but one sample recovered during the present survey came from 140 feet of water. This may have been transported following formation, however. Dietz, Emery, and Shepard (1942), and Dietz and Emery (1942) have shown that the phosphorite found off the coast of southern California is formed in situ by chemical precipi- tation of phosphate from sea water. They also note that Foraminifera of lower Middle Miocene age occur in large nodules on the outer shelf in Santa Monica Bay, and in others from the same general area there are fossils of Middle Miocene age (Luisian or Relizian). Significance and Origin of Phosphorite Phosphorite forms by the chemical precipitation of tri- calcium phosphate from sea water. The precipitation depends leas eaoaiey nee i a cot 4 ahi asi ‘pr my Me oak pe ae at) be: evonsx eat wen Ra | noe boa, eno % oe ott tage damage, OM it pEeOn brains iia 3a “Yo rp wy Prodgiedny dhVeit i ids tat pints ec, Voie “baa! wined a0 mee ek ae Parent ss one ‘canis bisa arta “pet tude taoges Waitt kes tie Mig an ake aitigh obngas a eins? ot ont aa trypek 6 0 aan’ | W, stings : ow ; ‘derarooss otguan tints oe an pe ‘leat Dh ae Mana as (eet a ta toa) ‘én ne) ‘sine Senne: saan | at yal is A a tavonit HOR Ms er10! vere A ita bikapqeninss wad avait peat: Bi 9 tte of MNO LD tiga bre eran. eared ee reso: wat 044 haved): «Fz 1 cosh eM al Pay, swe ala oxad Ch shaboere: tabbmsss OM ait Sy" Be Port of a fireeilt Eo t L +sar atm Gals % oad eihaiee aie aoe sHadyeond to earl | ngzat ne Sebi cee yet Per i othibay awit me! ntatinke f azaitto aut ein ee wets bHe pacag nit Vieda soni. ba te \ baa0hK mihi 2s, atinad? ones apni aoe jatsagy, ames ‘orth ; ‘an | hhgisblaR: 70. Psy oe ea FG 4 106 Figure 33. Photograph of phosphatized mammal bone. i =e 72 ie es << a —— = wus Siw, 7S Se ma ee he ] we mi i ee A ga : ma Se See ataealeta tai DBO RO 107 upon the saturation of phosphate in sea water, which in turn is a function of the pH. Apparently slight changes in the physical=-chemical or biological conditions near the bottom may cause a saturation of phosphate causing precipitation. The formation of phosphorite is apparently a slow process and consequently its presence indicates slow or negligible detrital deposition in the region where it occurs. Since some of the nodules in the bay area have grown to considerable size, they must represent a reasonably long period of nondeposition. The phosphorite generally occurs on the surface, not buried so that its occurrence here is indicative of either nondeposition or very Slow sedimentation Most of the nodules collected by Dietz, Emery, and Shepard contained a predominance of Foraminifera of Miocene age, and at one station a mixed fauna of Miocene and Pliocene ages. In several other samples, separate nodules and phos- phatized cement of conglomerates contained Foraminifera of Quaternary age. These authors concluded that while a small proportion of the phosphorite must have a Quaternary age, the bulk of the phosphorite was formed during the Miocene period. There are at least two ways in which the phosphorite could have formed during Miocene time and still be abundant on the sea floor: (1) the phosphorite formed during the Miocene on submarine highs which have been neither eroded nor covered by later deposition, (2) the nodules on the present sea floor may have undergone residual concentration from Miocene rocks. Dietz, Emery, and Shepard (1942, p. 841) point out some of the difficulties of both hypotheses. In the first Anabmods od Like ton mk) aavoodt ae at eH paw some ¥ bso aif ack lea tt ane at Lepnsaiggr t teoe to anit bias age By, 108 case, they believe it to be inconceivable that the Santa Monica shelf and canyons were eroded during the Miocene period. How- ever, both the shelf and the walls of the canyons contain Foraminifera of Miocene age enclosed in nodules, and Miocene age rocks are on the shelf and probably in the canyons. The second hypothesis = residual concentration of Miocene age phosphorite nodules = perhaps is a better explanation, since it would account for the abundance of phosphorite on the Santa Monica shelf and in the wails of the canyons even though each may have been cut in relatively recent time. Neither hypothesis adequately explained the existing conditions; there- fore, the authors presented two alternative possibilities to account for the Miocene age Foraminifera in nodules of Quater- nary age: (1) phosphorite deposits formed by infiltration of phosphatic solutions into porous Miocene age formations with the replacement of some of the Miocene age material, (2) the phosphorite deposits may have been formed by enclosure of reworked Miocene age Foraminifera in nodules formed during the Quaternary. Thus, they tentatively conclude that possibly the nodules dredged off southern California were deposited on the present shelves, banks, and in the canyons during the Quaternary and that previously an abundance of Miocene age Foraminifera had been eroded or weathered out of the Miocene age formations and concentrated on the sea floor surface where phosphorite deposition took place. No additional age determinations of the phosphorite dredged from Santa Monica Bay have been made so that the determinations by Dietz, Emery, and Shepard are the only i aw tEd “at Heke CRE et | i} \ Wa £ Sah +a “6 Tee 1 er et ae rae 7) i in bite k Kamas y Oh Ey Ty ae ay eS ou 109 ones for this region. It is known, however, that rocks of Miocene age are on the outer shelf, and there is evidence that most of Santa Monica Bay was formed in relatively recent geologic time. Character and Origin of Nondepositional Surfaces From a theoretical point of view, there should be an even gradation from coarse to fine sediment when moving from the shore seaward. Numerous investigators, however, have noted the common occurrence of coarse sediments near the outer edge of shelves (Fairbridge, 1947). In addition, there are any number of places where bedrock crops out on a sea floor which, according to theory, should be covered by sediment. Many of these areas of nondeposition are known off the coast of southern California, so that surfaces of non-or slight deposition in Santa Monica Bay are not unique. However, even though many such submarine surfaces are known in many parts of the world, little is known of their origin. There can be no question that in most cases, sediments are transported at least as far as the nondepositional surfaces, but then either by-pass the surface or are deposited and later resuspended and carried away. The following criteria are used as evidences of non- deposition: (1) rock outcrops exposed on the sea floor; (2) gravel at considerable distances from shore. Gravel intro- duced by streams cannot be carried far beyond the littoral zone. In fact, gravel frequently migrates shoreward if it is in the zone effected by wave action. Therefore, gravel in yon ote) suede Hoke ebb al cee. oie xiao esy: Y dost. oot? neds ag duo: eqns vouhoe saad esdalg to 38 F Shhnael paaaibee, we betsvos wd nla saiaicall ot gn nee ea atae cove wont caikghxe abot + ene ae ae i “Kes 2) Be taael te badxogeos 6i2. ‘ome aineuttur, ,esene $eom | oF sat eeaqeed sont do HAgt fed poets, tanoktttocebaas 98 Pcmictinad bes. Tame ptrese weteh Dee aati sts oe oO reasek Cerety , esoste: ea) osoaor ehh s 9. 110 deep water probably represents a deposit laid down in the geologic past; (3) The occurrence of rocks bored by organisms gives strong evidence of a littoral or shallow water environ- ment at the time the rocks were inhabited by animals. If the depth is now considerably greater than the depth-habitat of the boring organisms, it must be presumed that sea level has risen and that little sediment has subsequently accumulated} (4) the presence of coarse terrigenous sands separated from the shore by finer sediments probably indicates at least two periods of deposition; (5) the presence of glauconite, phos- phorite, and high percentages of CaCO3z are indicative of slow or no deposition. On the other,hand, much of the area in Santa Monica Bay which exemplifies the above criteria also has up to 30% silt and clay in the sedimentary material. Deposition, then, does occur, but is either extremely slow or is intermittent with a periodic resuspension of the material. As pointed out by Fleming and Revelle (1939), and Revelle and Shepard (1939), the primary force necessary to transport sediment is the “static bottom friction" on sedimentary par- ticles. If some force lifts a sediment particle even for a brief moment, then any resultant force (current or turbulence) acting in a constant direction, no matter how small its magni- tude, will effectively transport the particle. On a topo- graphic high, the net result would be a winnowing of the detrital material of a size determined by the force which is competent to put the particle in suspension. Thus, the sedi- ment would be transported from a topographic high area to a > sie an fast smug a ‘ea inne | tena, raaakaneinty fo ade v tei. hp bt bach ‘eye ‘ mela Re srbianibnt ota sisi ne oommanial ae boa) aes ristanihaine nai Mamiernta “mig tsod akbar) py a ato} sme | Coons ladges qm Seusiecan) ono? Pantleass ee sald ‘Ya ae aot eve’ ‘ots aie teoumihaw ew eeTEI Cp argu abd. Siseen “ye Awbam aR antenodhh pestis: bt aan Bore: ohhen att RR: notin a ads pi tah lower part of the sea floor by currents, turbulence, and gravity. The settling velocities for very fine sand (0.1 mm) at 20°C is 0.778 cm/sec. and for clay 0.000892 cm/sec. Since the settling velocities for particles of these sizes are low, they could be carried far before settling. The distance of transport would depend on the height above the bottom and the velocity of the transporting current. Turbulent motion may be caused by waves or currents. In Santa Monica Bay convection currents resulting from the distri- bution of density are too small to produce any significant turbulence near the bottom. Revelle and Shepard (1939) believe that the chief transporting forces must be tidal and non- permanent eddying “slope” currents resulting from wind action. Although these currents produce no net transport of water, they are rapid enough even at considerable depths to generate pronounced turbulence. Turbulence thus produced tends to be strongest over banks and other obstructions. It is likely that such turbulence exists on the outer shelf in Santa Monica Bay. Current measurements and the analyses of slope currents at depths of 100 to 180 feet show that velocities of as much as 0.2 knot may occur on occasion. The only data known concerning threshold velocities is the work by Hjulstrom (1939) and Inman (1949). The minimum threshold velocity necessary to erode sediments already deposited on the bottom finer than silt (1/16 mm) is about 35 cm/sec. (0.7 knot). It has been noted by several sedi- mentologists that particle sizes of about 0.18 mm (fine sand) require minimum threshold velocities, and that the threshold 7 ation ha, rrodunset bom Hi denna erketing. seat; roads | “vince OF) patqut alanasilenylr te neve Hye bhgam aa “wd G8 \ebeg? deauiers 0d sino ivgabT eatatnbae bam etoaes: at ” @itatod? joan teed vadto tutw eatenbe savy "bina wea a bheia 42106 ot’ Ae arabe sonetndas! Age atusyie se: agente: to wergtads oat. bie oi gira aaetheh ae + ; iu ne le aabtivotey dusts: wortier, aed OME: ot wor oi | mmareal En ket ott casety mare) Eaten, roeeea ) sera { heres, snk?) We $1.0 sued, i ene eel hlognersa digi dmett, bap, cedistogah 112 velocity increases for sediments both finer and coarser than 0.18 mm (Inman, 1949). It takes a current velocity between 0.5 cm/sec. (0.01 knot), and 20 cm/sec. (0.4 knot) to keep sediment finer than silt in suspension, but if the velocity falls below about 0.5 cm/sec. the material will be deposited. Shepard (1948, p. 63) made 14 to 21-hour current measurements in Santa Monica Bay with a tripod resting directly on the bottom. Three current meters were superimposed on the tripod at 21, 51, and 126 cm above the bottom. He found few measure- ments over 10 cm/sec. and the maximum was 15.9 cm/sec., 84 cm above the bottom, One series showed extreme variability and the other series in the same general locality showed less variability but equally low maxima. Bottom current measure=- ments by the Hancock Foundation over most of the shelf generally were between 0.1 and 0.4 knots. Consequently, if Hjulstrom's values are correct, then fine sediments should be deposited. Since the fine material is not continuously deposited, some mechanism must operate to keep it in sus- pension and carry it beyond the shelf. Inman (personal communication) has theorized on the possibility of "beat™ effects resulting from the impinging of waves on the adjacent shores aS a possible mechanism. Shepard (1941) has discussed some of the possible explanations of nondeposition on the sea floor off southern California and covers the following possibilities: (1) effect of waves, (2) tsunamis (tidal waves), (3) tidal currents, (4) non=-tidal currents, and (5) mudflows or submarine land- slides. —. wat: dass 5 ; ‘ gubaed md | eae ‘to poke aa ” 7 _ a eae . Ra. eave Y mintaae: way be, Lahn os 7 ve at bowoiti atten hese ig set ab dovivn's stoma asians wot poe: itd ayten itt «supe deer rhs a Mane By Rh TOR ero nod wham, divoaestt att rs Aas (ab dawupsiesnd rind (Pyb bbe J) npaiead oaawogd in btnote: Sthamivon hy “yeniie (sonttheit. ig eoartane Stina t “ehmiuala207 yur 22-28 ror sell ‘some, oar : ~ mete ms ay ll ed) ‘ a-ha ba insatDen agora gta r amon tng) ree ine pit bitay ad ‘+a, enang mee hh oasa® ty. qakgiale tam wth ho wom teat ott (nok | wake mats t aribhuans' ia sae sidieaeng: at amin on aaieoog sie Re Hibs taanpavineiehly ail: LIMORY: ‘oexeeyiit oni dapiiteos 0 saghh AOR ADE tz nal eogataan, Re wok hae hme bn wad ea) ‘wee, De ae haink. yoekty Ly, Vhabt 2 teaibanoR pokwntig’t aelt aaevRD nce eae igen peep iabha: 1) i aaview pabin ): enon 8) whines eka banc. 40. art Ban a) bo isl j ba a caf Thee Pen 113 Effect of Waves Vening Meinesz (in Kuenen, 1939) reports that submarines are moved considerably by waves at depths of 60 m (200 ft.) during rough weather and he showed how waves approaching shelves have their energy concentrated near the break in Slope. Kuenen, therefore, believes this accounts for the common concentration of coarse sediments at the edge of many continental shelves. Dietz and Menard (1951b), in discussing the origin of continental shelves and slopes, state that “effective erosion" does not exceed 5 fathoms (30 feet). Buffington (1956) takes exception to this view and gives information collected during more than 5,000 dives by Geological Consultants of San Diego. He says that when a diver moves from a depth of about 150 feet to water 90 to 100 feet in depth, there is little or no evi- dence of disturbance caused by currents or waves. The only exception to this is around headlands and points where bottom currents are occaSionally observed. At a depth of 70 to 80 feet there is frequently a noticeable bottom water movement. or surge. This implies that bottom motion extends to a depth of at least 80 feet and perhaps occasionally to more than 200 feet. Long period waves or storm waves may generate sufficient bottom motion to carry sediments off the shelf. These waves arrive so rarely that they have not been observed in Santa Monica Bay directly. However, bottom photographs taken off Osborn Bank near Catalina Island show a series of large partially destroyed ripple marks. These ripple marks were r ra er aod. ‘te women is mor nih nevih # wedw, sas : Mawr ae atpak eh spate a0 0 ak torey rrr 6d) iradenait wheat i a ee ane Suet mectzoth ite ania: apts nd heen | _Mamob? tealtobnon Mor wk atte me Le ‘pies gino ok weenalls : “eax Aiinatng £0 Yo ve aia 0 api. fakdw a batkenats ribet hed: tauy raha ene rst a: aye le mi webbtiatey hippies: nr as? btoo nokecdaeHe! ic Sonn wlaw Inti medearia BRR babi ioutay bse | a ibe leseeueinien) eukt iengatt oo Ryteoag are orn} ait) Com ‘pt ately od sane tee oa asitghaonaa re co ae : amt tis. wauanid anusri99: newt "9.2 | ‘aed ak _ esate ota He oh: 116 bed, and (2) there appears to be no relationship between the observed current velocities and the type of bottom. For example, the strongest current was found on the slope off Palos Verdes Hills where the bottom is covered with mud. Cores showed that mud was deposited to a considerable thick- ness in several localities where currents were relatively high. In addition, two water samples taken about 3 feet above the bottom during the time of maximum observed currents failed to show any traces of suspended sediment. In both cases, the bottom was covered by silt and fine sand. Mudflows and Submarine Landslides Shepard (1941) points out the importance of submarine Slides as a cause for nondeposition on some surfaces. While these slides may be important in some localities, such as the head of submarine canyons, the relatively horizontal surface of the outer shelf in Santa Monica Bay probably cannot have Significant slumping. Perhaps the exception to this is along the northern boundary of the rock and gravel area where it borders the southern part of Santa Monica Canyon. Parts of this sediment cover may possibly slide periodically off into Santa Monica Canyon. Sliding also takes place along the basin slope, but the study made by Emery and Terry (1956) along the Palos Verdes Slope indicates that considerable thicknesses of sediment can accumulate before the sediment becomes unstable and slides take place. ‘gohuat. asia bavabees srw 4a uns one antaal d mit yenene #498, at “ tasikhicow bares Ae voor! re iy : | " x Co earl fie ithe pe tease i | “entrants to ener one coe Hernion cass baa are i‘ ohEAW sheoaltoe or ind oytehaaatinets lame sire . oa eet ae cou ‘gaeUny tases onde a iid acca ad a n aN: “gah #1, kat a bso be nay. Wile raided A anzgunts dias + wrt eons. taveny Bere COD R Sae to, eels axadtyag to uditg® emonTAD, sie hapobt aiged Yo rind aratttuae oar ak | oa eV abe bie phi te idk euin Raw eves santos Rah qe: iy wa eal ah ae bik LE, vO EER einon wii ene Caner) earet ita, Waet yd sbam tae) Ml fe suo itl “idevahhenos’ tats ait ob tesh its ns eataat bitch sit 117 Relation of Bottom Character to Surface Currents Shepard and MacDonald (in Revelle and Shepard, 1939, p. 278) report that during a period of calm weather near the head of Santa Monica Canyon, they observed a surface current set to the southeast during the flood tide, whereas there was no appreciable current during the ebb. The same phenomenon was observed during the present survey, but the currents were always weak. Shepard and Revelle state that if the south- east current also exists on the bottom it might carry material to the canyon from the northwest, dumping its load in the canyon so that the water would be relatively free of sediment when it approached the shelf on the south. If such a net current flow exists, there is no reason to believe that the current would drop its load when it reached the canyon. Also, the nondepositional surface extends a considerable distance landward of the Santa Monica Canyon so that if such a current were Carrying sediment, it would not cross a depression before reaching the rock and gravel area. Furthermore, the net current flow along the bottom varies through the entire east quadrant and may at times have a seaward set. Conclusions The presence of rock outcrops, abundance of phosphorite and gravel, the great number of borings made by pholads and echinoids, and abundance of CaCoz are indicative of nondepo- Sition. However, the presence of some fine-grained material indicates that there is some deposition, although it may not be permanently deposited. The origin of non or slight vm vert sisetsnta ep ben aihsiae at ae ; 9 Bid sae tab tse “a est ony ieee SiQusendenes | re ties. esata piruestite | noe at “i * Htoera 3 Patt oe lions cna arma’, ‘out Wet or Oe! baaiwana ot BuOE ey Emires) stixodqeodtg 4s oanabaod aoasine: ao ho. ‘svesonen iene af bone. shalong xa oben gato’: te Porc bhi nt 118 deposition surfaces is not yet clearly understood, but it is known that in most cases it is due to by-passing of fine sedi- ments by currents or turbulence, If Hjulstrdm's calculations are approximately correct, then the average velocity of the bottom currents on the outer shelf is not sufficiently strong to cause erosion in the area nor prevent the deposition of fine sediments. This does not mean that strong currents or turbulent action do not, at times occur. There are insufficient data to determine whether the sediment by-passes the region of nondeposition or is deposited and periodically removed by occasional strong turbulence and current action. Since much greater velocities are required to move sediment after it has been deposited than to transport sediment in suspension, it might be reasonable to conclude that the sediment by=-passes the area. Turbulence resulting from internal waves and eddy currents are possibly the cause in this case for nondeposition. However, it is also possible that occasional storm waves, shore wave reflection, and to a minor extent tidal currents may be impor- tant. SOURCE, TRANSPORTATION, AND DEPOSITION OF SEDIMENTS IN SANTA MONICA BAY Source of Sediments The principal sedimentological studies undertaken during the course of this survey have been descriptive in nature. As a result, the discussion of sources of sediments is primarily based on published and unpublished data. My iH ao ¥ a ‘Soi Ye fason taed soni — toou re i 0a # | it 100 die et if, it oe wane wid ie o ys aan site core + z rt 119 Much information on the general nature of the source rocks can be determined from the mineralogy and organic con-=- stituents of sediments. For example, the presence of Forami- nifera of Miocene or Pliocene age in rocks of Recent age would indicate that the contributing sources included rocks of the older ages. Mineralogically, suites of heavy minerals, including minerals typical of igneous and metamorphic rocks, would indicate the relative importance of these sources. For the purposes of tabulation of sediment contributions and losses, a general budget has been noted in Table III. Of the listed contributing items, it is possible to indicate those of least importance. Gains from wind, chemical precipitation, organic production, sewage and industrial wastes, and artificial fill can be regarded as minor. Erosion of sub- marine rock outcrops is also probably relatively unimportant due to the restricted area of such outcrops in areas of active erosion by waves, and currents. Wave erosion of sea cliffs is not known, but papers by Revelle and Shepard (1939), Grant and Shepard (1940), and Shepard and Grant (1947) would indicate that this contribution is minor. It becomes evident that the major contributing sources are littoral drift and stream-carried sediments. The relative importance of drift versus stream trans- port is not well-defined at present. The effect of Point Dume as a sediment transport barrier to the north is controversial, for example : [rask. (1952), Handin. (1951), Trask. (1955). At the northern end of the bay the evidence leans tovard a southerly movement of sand around the Point Dume area of unknown volume. i ra : coat oy en eh ek at r aa Pe Fee SME TDS SRR ROY! Tare GR Oy See FeO. 4 fae ‘ 4 ih Sgt Te ees beet eet pe ne 120 ' TABLE III SEDIMENT BUDGET FOR SANTA MONICA BAY (beaches and shelf ) Gained Erosion of land within Santa Landward transport of beach Monica Bay tributary sediment. drainage areas; sediments transported to the sea by Transport of fine sediment streams and rain wash. beyond the shelf by currents and waves. Transport of sediment into the bay by littoral currents from ||Periodic slumping or submarine the west and north. landslides carrying sedi- ments on the shelf, basin Wind transported sediments. slope and in the submarine canyons seaward into deeper Erosion of sea cliffs. water. Erosion of the sea floor. Chemical precipitates from sea water (phosphorite, etc.). Organic debris (shells and shell fragments). Sewage, industrial, and shipping wastes. Artificial fill; artificial nouri- shment of beaches, dumping of sediments along the coast for highway construction, etc. rod: : Shahi | ue TD ‘3 + ag MAY Bb oh ‘an hh a ae Se 121 The movement of sand along the central bayshore has been the subject of several investigations in past years. Asa result of these studies, it seems probable that the bay acts as a trap for most of the entering sedimentary material coarser than fine silt and clay. Such a conclusion indicates a negli- gible transport around Palos Verdes Hills coast. This is likely true because of (1) the probability that most of the sediments carried to the south by littoral currents are trapped by the Redondo breakwater or are carried into Santa Monica-San Pedro Basin through the canyon; (2) observations by the U. S. Army, Corps of Engineers (1955) indicate that there is a pre- dominant downcoast drift of sediment to Redondo, and a net up- coast drift between Clifton and Rocky Point; (3) Johnson (1940) noted that between 1939 and 1940,370,000 cubic yards of sediment accumulated on the south side of the Redondo breakwater, but very little on the north side. He postulated a southeast source for the sand drift. It may also be, however, that conditions are such that the sand is by-passed around the breakwater and deposited on the southern side, thus originating from the north; (4) bottom samples close to shore around the Palos Verdes coast indicates rocky bottom and little or no sediment cover. Only small pocket beaches of locally derived composition occur along this rugged section of the coast. Most of the shore consists of rock platforms and cobble beaches; (5) wave refraction dia- grams in the southern part of Santa Monica Bay show that a northward drift near Rocky Point would be accomplished with greater ease than a southeast drift around the Palos Verdes Hills; and (6) more or less permanent rip currents occur in the rrr. N om ri bat w cnabiorsete ts nana aa ates fer aa cone te a ataos ag Pe eE tS r eee cen sa ie os 0s en Pe is io spetaeweintnt Cee itil! aot Yo ht weer! ol 16) badn tateatheamehte @ hint etis¥ ou,‘ wl) i : im ee te 00 vou a i de ait nae ebrioa yt. aed r (phibe kexed2tii, auth Bere . eno2 edt aoded. Mba, Slecusie tay) ahi gt spel won phe een? Oreo! Nicautition oat a ya lol mat hou een “phos thiben Gok leer Bil: Sen iecrerty qibaoe t., te esdvend iatoog 1 ayehanoy avai” iat Lo bigeeat' 3 igs pets ve one Rene apes ait obtonyiex min ise) peade ond asdios Beis = oe | 122 vicinity of Redondo and Clifton and indicate a convergence of littoral currents in this area. Therefore, the sediment within the bay probably represents all sediment contributed by local stream drainage plus littoral drift contributions from the north minus the loss of fine grained sediments to the offshore area, and the loss of coarser sediment down the submarine canyons to the basins. Some losses, although very minor, also can be charged to wind drift from the beaches inland. Drainage Tributary to Santa Monica Bay Figure 3 shows the boundaries of the drainage areas and the streams bordering Santa Monica Bay. Table IV lists the areas and characteristics of the various zones. It can be seen that the Santa Monica Mountains comprise the major element. The area southeast of Santa Monica Harbor is mainly coastal plain, while that northwest of the harbor is primarily mountainous. Inland from Malibu several water supply dams have been built which cut off much of the coarser sediment from the bay. As this watershed alone constitutes 58% of the drainage in this area, the remaining smaller watersheds have been lumped together. Rate of Sedimentation It is difficult to calculate the rate of sedimentation in Santa Monica Bay for several reasons. A number of the problems concerned with source areas are obvious. The volumes 188 sobnowt amar oo ne sere satan ot te eepreen suit avoda C fe ie ae dhdat {ya8 sotqott esya? anbyobrad se Mbp tT “anion apokier sar Ye ‘eobvetzets feLan ont wake’ ahha tie: no kaon otaaé esd 4 | wae. ek godten soknem wife le teaadtooe neta om: | baer ee esac! edt io teewmpoe tats ‘ore ema aged ovad net yiguee stan ibseves wot Lats wor desta on o¥ad ony aout Sramtboe Aegaeud off to some 3te ues rca | 1. 2. 36 123 TABLE IV DRAINAGE AREAS OF THE SANTA MONICA BAY AREA Total Area: Area Area Mountainous region (elevations to 2,500* )------= 217 ‘sds Coastal plain region (below 500° )--------------- 120 Areas adjacent to coast without well developed drainage -------2---9- 9 999 9 nn 10 TER SE I I IO 347 sq. Southeast of Santa Monica Harbor: Ballona Creek Watershed ---- -----92----- ---=------ US SGie Kenter Canyon Watershed ---- ---9-- --9--29-9-9---= 10 Sand Dunes and northern Palos Verdes Hills------ 19 Total -9 en wn rn a en rr rr rrr err ee err senna 160 sq. Northwest of Santa Monica Harbor: Malibu Creek Watershed ----= ----=9-----9--------- 109 sq. All other smaller watershedS---<--~-----------<--= 78 Total ---- 22 on on nn rn rrr rrr errr srr 187 sq. mi. mi. mi. mi. mi. mi. : . Se ee ee aeda on if rae ual Yeo of 2 ohn is ia Seat iy Ah weed Er hota’ avenition bon, Bw j ‘ ya pe oat ernie erennaneeneninnenanwnmainienantinnn LAO Bs rte ae atuat 9 + RSW ad ee ae 1 eed ae hi satel $ Bie fe » ay A adi ialteaisaabcoiieet alah aha Pee Mee wm tr P . donee "4 AD De, Rd hak be eg cy) A WR ate ee pela 124 of sediments calculated by various authors are based upon conditions existing at the present time, but the volume has varied greatly. Numerous natural and artificial changes in the drainage areas have taken place within historic time which have greatly altered the sedimentary regime of Santa Monica Bay. The following is a partial list of some of the most significant changes: 1. Construction of storm drains and debris basins which have greatly altered the former natural drainage and as a consequence, the amount of detritus reaching the bay. 2. Construction of the coast highway which has prevented cliff erosion. On the other hand, large quantities of sediment have been dumped along the coast in order to widen the highway. Davidson (in Cong. Docs., 1897) reported that in 1872 when traveling in a wagon along the northern part of Santa Monica Bay, the cliffs came so close to the shore and the canyons were so steep, that he could only pass this region at low tide. As proof of former erosion of the cliffs in this region, Davidson says: "At Point Dume a very fierce westerly wind Sprang up and retarded my operations so that in returning to Santa Monica I was on the beach through two low waters. I found the beach torn away along the whole shore line, and met with rocky obstructions which in some cases had been wholly uncovered by the washing away of the sands. As we approached Santa Monica the evidences of this destructive action became more and more marked, and for the last 2 or 3 miles the beach was torn away from 10 to 12 feet in depth.” 3. Urban development has stabilized erosion over most of the coastal plain and parts of the Santa Monica Mountains. 4, Widening of beaches by artificial nourishment, con- struction of breakwaters, and by the use of groins and jetties. The construction of coastal engineering structures above Pt. Dume has also cut off large amounts of sediments that may have reached the bay in the past. 5. Beach erosion by the construction of breakwaters, i.e., downcoast from Santa Monica and Redondo breakwaters. 6. Stream piracy of the westward flowing Los Angeles River, and also the changes made in Ballona Creek outlet. 7. Construction of reservoirs which have greatly reduced the quantity of sediments reaching the bay. At the present time only very fine material is washed over the dams and reach the sea. The following are the most important ae nk gognasto petits. aie | sae amt } oinorake nee Al ; © esr Nel aed er baa anene ‘Kay. PI eM ees "ae bite: hora Lewrten. ot 2th, beset ts itsoxs se “ree ent poigirdad pon bs ‘Sitp ed doz dy binary br og | “ssttitaaup Firstar Attend sotto aes | “bedsoas G0 (99 at aut * a Baie teal heey a | - vedas au dalle boast sine r} inoue eke.) $A% Re reigns o8 endsiaziqe Ya bebredas tea opr’ pra : : oh MC oI hirygd ot Qnknweter Bb 17) ae my se: seats baw? # sate wor owe agua rad pron erie Pde i lh ga eee “athiw. #8 pital ree eens, AD es 1) Oneal ae te oie Asoltowsidty botoox aittw bem Bra on i) ode WH beasvoon Viloty seed Ded teen. pmGm 7 \) ot Qe. ow ah ~etten od? Yo vaws erkitesw 0) ee rowaktean aii Yo esunebive ott aphooM, stnag oo Oe | Bite ,devttem cise: bes saan amassed molias, a ‘yaa HOF tow doood Ho) aolin ©. 30) 8 Feed. obs 10) * avqem oh Seok SP of OF richieg \ 1av0 ro bieetais DWKELats aat toomqotaevab nada ee Aree ines saitieinvoMm soko wieke eae “bo after bas skehq evesoo, ett ae nO. 4 tele keodt Fim bagelowlea yd sodased Fe ale DeW') @mcuy: Aekiiel Soa untowg 36 way os ed bas ,exerawleagd te pti a svods sosutouvte pobroeniune Leteson lo aoEfonete “evad yaa bast etosmh hee teeta gow aga Tie pl Osta ee ; -o#aq oft oh Wed ern : peahmnlagud to okt wevedOo edt vd goksoce Moses serstetsord ohaghat hae cokonw wines moa ee, asieygd ‘ecl gniwotd, beawhtew edt, to yoreka aaase Coo Ghee, Teo Be ed, stank eRe, et ae Piper titi ova dabte Brive eews to per eich wih Ye nh seedoeon eevomsbee Te yeatieeD sons it rove chediebi Gk Le kia elm obenk whee el katate Tet ssn OF8 nana) eitt 125 reservoirs and the date of their construction; all are in the Malibu Creek watershed: Rindge Reservoir (1925); Craggs Lake (1913); Malibu Lake (1923); Lake Eleanor (1881); Lake Sherwood (1904). Other questions arising when calculating the rate of sedi- mentation in Santa Monica Bay (specifically the shelf) are the following: (1) How far are the sediments transported before they are deposited? (2) Are the coarse sediments deposited close to shore and most of the fine material carried great distances, i.e., beyond the shelf, before being deposited? (3) How much sediment is carried seaward along the floor of the submarine canyons, especially Redondo Canyon? (4) How much sediment is deposited along steep slopes or at the head of the Canyons and later slumps into deeper water? (5) What volume of sediments is winnowed from the shelf and carried beyond the shelf before being redeposited? (6) What effect do animals have on breaking down sediments thereby producing finer material that may be winnowed away? Theoretically there should be an even gradation from coarse to fine sediments in a seaward direction. In general, this theory applies to Santa Monica Bay although there are several parts of the bay that appear anomalous. Some of the abnormal regions are due to quiet water close to shore (Redondo Canyon) which allows the accumulation of fine detritus. One of the major causes of the peculiar sediment distribution undoubtedly results from the superposition of present day sedimentation on top of a surface formed largely in the geologic past. For example, the rock and gravel area on the outer shelf is believed to have formed in late Pleistocene or early Recent time. Thus, wbith VEesiny ot Hob tent pecs who? : id Laxsyen! one oust Mouddtle ‘yao: cubed bet oF oaknya! : fanronds out ta sa02 Cr aia sins wade Aid ‘att Yo. Goran ohaotest):| s a to ‘peo aus ‘ath elbesdivo ony pair ‘ vc no btatneni tse van a : me “oT staaq ago kos poate sae pe bovaliad et Wega ie: sid pede i i ‘ ew 126 a general seaward decrease in texture exists, but it is modified by (1) the presence of sediments deposited in the geologic past, and (2) submarine topography which in part causes deviations in the sediment distribution. Probably most of the clay and a large portion of the silt originating within the distributary drainage area is carried beyond the sheif and deposited in the offshore basins. It is likely that bottom scavengers break up sediments into smaller particles, but there are no quantitative data on this process. It is probable, however, that beach sand does not become appreciably broken down by transport along the coast by littoral drifting (Mason, 1942). Since littoral drift along most of the shore is southeast- ward, and meets northward drifting sand at Redondo, some of the sand must go seaward = presumably out through Redondo Canyon. After the construction of Redondo breakwater, much of the south- ward drifting sand was trapped by this structure. Prior to the construction of the breakwater, however, a large amount of sand may have been lost through the canyon. According to Mr. William Herron, Army Corps of Engineers (oral communication), a con-=- Siderable quantity of sand is lost seaward between Santa Monica and Redondo, and at the present time it is possibly as much as 150,000 cubic yards per year. Although sediments may accumulate on slopes and later slide off into deep water, this does not seriously effect calculations on the rate of sedimentation on the shelf. More important, how- ever, is the amount of sediments deposited and later resuspended and carried in a seaward direction. The more or less continuous - beiaaan ab 938 a oyeniasd er if aera a a seatned rode Tio -.. sottongeo a a ay onak staontboe aw dee does ereyasvece noted 48 i a i Duenras abet Coe iad Pes sanmieer ‘on ene sua aad ray th dt io: bona anititad baswldsen etoem bee ae cae sont 40 ¢idamare gag = brawsae 03 taunt b va if | cere | sith te oom oe ohnebal to coktowst amo odd, hi Lind ne siti wnt ef gaesoosit storys oat saver 3 02 hte: ae uanoy ae ‘ebay | Ohi be ‘gotat Deve angola a0. » Satucwods eel alot bed an wut gear aye ar , beinoqenzy: vibe bun bovdeoge “stuomidee te tuowabigoa enol 26 os0m a : : iii ctup sot ey M 127 redistribution of sediments makes it difficult to determine how fast sediments accumulate at any*particular point. Sedi- ment traps have been constructed by Emery and placed on the sea floor off southern California. Apparently, most of the sediment collected in the traps is the result of the movement of sediment along the bottom. A number of investigations in various parts of the world have shown that in relatively Shallow water, where the investigations were made, there is an almost continuous change in the texture of the sediments. Thus, the median diameter, or per cent sand, silt, and clay vary greatly over relatively short periods of time. It can only be assumed that sediment movement along the bottom is zero at any particular time when the calculated rate of sedi- mentation is made; or in other words, the sediments are in a "steady state condition”. Assuming that 80% of the sediments are deposited within 8 miles of shore or over an area of 200 square miles, and the estimated volume of sediments is 478,000 to 650,000, then the rate of sedimentation would be between 0.02 and 0.03 inches per year. Thus, even if the calculations are off by factors of 2 or 3, the overall rate of sedimentation is slow at the present time. While it is not possible to quantitatively estimate the rate of sedimentation over a long period of geologic time, a few conclusions can be reached on the relative rate of sedi- mentation and to changes in the depositional history of the Day. ner youre sang a ees wee jen ou Ve Bobet Eiki evhiahen ste: ater betel “1 pei a! ; seh heron 207 6a, | heaaiinedeek oath ct 128 Natural or artificial changes in the tributary drainage areas and changes resulting from other works of man, are indirect evidence that the sedimentation in Santa Monica Bay has varied. In addition, it can easily be shown that pro- nounced changes in sedimentation have taken place by exam- nation of the sediments in the bay. There are a large number of cores, jettings, and borings taken in various parts of the bay and on land close to shore. They show that numerous textural changes occur in a short vertical section of any random core or jetting. Thus, there are distinct beds or laminations of gravel, silt, sand, clay, silt and gravel, beds of shells, and even layers of vegetation. Although cores that are close together may show some correlation, there is in general a poor core to core correlation. The pronounced alterations in texture can only be explained by changes in the competency of the transporting agents(waves and currents), and to variations in the supply of detritus supplied to the bay, and/or to alternate cutting and filling of the nearshore shelf sediment surface. Rain falling in the tributary drainage areas can have several different effects upon the supply of detritus to the bay, depending upon the amount and distribution of the preci- pitation. If the rainfall is small, only silt and clay will be brought to the bay. If there is slightly more precipitation, considerable amounts of coarser sediments, especially material of about fine sand size may be washed to the bay. If a flash flood occurs, material ranging in size from clay to boulders ‘i yaktnds Yo. bed «tovann naw 1125) ihis shaten: hl quel esaob aquodtia anita To gewad i terenny wk ak gees smn yeteertion vamer wai rae asta s82 0 pasmiaesy wa owntiqlsxdog shbe. ot at dao on ot soghage ye Genkatqus avin: lal ; “4a “bes Cetasaws bis Savon has eh Bek omer ar wal ot pabladhe txts eb te ae eines att: Hes . “ sxotenson ea. wD. ae ELLY Ste gaenids abated ta o's . YR Bl Lenslann thpadho'tt vena eet oKeas saenierh vietpaahe wo aE anasialt) sa at nk ert eae Hey eae Hip ‘abontts sao rs ~theng eas te: pokyuaharest tame Naser it” meee et “Ebbw (als* bas: 2ibaiphao” .L pig #8 Eta Nicka lovbtareghiesg. sae" vba te ee ‘wy i Rares i: rue tetistem a tabgeqes! “bbe Le a eto is » Goa 4 tad out or taanow wea ibe | 129 may be carried to the sea. If there have been several years of only small rains, the stream may have built up to a thick deposit of sediment in its channel. Then when a flash flood occurred the sediment in the channel may move out into the bay as a plug of sediment (Revelle and Shepard, 1939). Under such circumstances a great heterogeneous mass of unsorted fragments will be deposited in the bay. Waves and currents may then redistribute the sediment over a larger area. The presence of considsrable quantities of coarse sedi- ments, especially gravel, over a large part of the bay probably indicates that sedimentation in the past was faster than now and the source of sediments was much greater. The volume of sediment brought to the bay during periodic storms must have been great. Cores taken far out on the shelf generally do not show many distinct beds of gravel, but gravel is widely distri- buted over most of the bay as was shown in Hayward grab samples. This distribution may be the result of extensive reworking by marine processes after initial deposition. Distinct and correlative beds of clay are conspicuous at the site of the Santa Monica breakwater and farther to the south. Clay can only be deposited in quiet waters which are not disturbed appreciably by waves or currents which would wash away the clay, nor can there be a large supply of coarse detritus. The thick deposits of clay are therefore difficult to explain unless it is assumed that one or more offshore bars allowed fine grained sediments and vegetation to accumulate in the quiet water behind the bars. These hypothetical offshore bars migrating landward might have been the major source of \, ua ON ir ah eed Pye CH he's 7 Poo, 130 sand in the El Segundo Sand Hills. Several geologists who have studied the sand dunes have concluded that they might be the result of offshore bar migration. The above discussion is sufficient to indicate that con- Siderable changes in the depositional history of the bay have taken place, and that on the whole, the rate has decreased in historic time. The changes are attributed largely to alterations in the tributary drainage areas and to the work of man, but climatic changes may in part be responsible for the decrease in the rate of deposition. Deposition in the Past Two Decades A comparison of Shepard and MacDonald's samples with those collected by the Hancock Foundation reveal that nearly all of the samples collected in the 1934-38 period or earlier were coarser-grained than those pp eared approximately 22 years later. There are several possible explanations for this: (1) Shepard and MacDonald used a pipe dredge to collect their samples and some of the finer sediments may have washed out during the dredging operation. Dr. Shepard (personal communication) reports that a piece of cloth was used over one end of the dredge, and that once the dredge was full little washing took place. (2) The mechanical analyses made by both collectors were different. The samples collected by Shepard and MacDonald and the Hancock Foundation used standard sedi- mentary techniques. However, the Emery settling tube was used to analyze the coarse sediments at Hancock Foundation, whereas the earlier samples were analyzed using screens. The th) De: fy! a AT: Pures (ek AY NS 1 CA a et a eth ih ¥ ts J vil Hh n, au 5 my bs ae eat if Loa Be) Leiter ® os wo: Pity T, ie Pp eee 2 Pgh RE 131 settling tube technique is comparable with analyses made by screens, so that no difference should have resulted in the sedimentary parameters from these practices. (3) There has been an increase in the percentage of fine sediments, especially silt and clay, since Shepard and MacDonald collected their samples. It is known that the volume of sediment reaching the bay has decreased in historic time. It might be reasonable to conclude that there has also been a decrease in grain size. In other continental shelves and submarine regions where sediments were collected again after a lapse of time there frequently are pronounced changes in texture. In some areas where sediments have been collected only a month apart the various sediment parameters may differ so greatly that there is little similarity to be seen. Although an attempt was made to quantitatively measure the rate of sedimentation by comparing Shepard and Mac- Donald's samples with those collected by the Hancock Foundation (Table V), the results were inconclusive because it was difficult to accurately estimate the sediment thick- ness represented by the samples. The only conclusion that can be drawn from the two sets of samples is that most of Santa Monica Shelf appears to be accumulating material finer than prior to about 1934. “seats staat at i \ ne > privenon’ Lildsasea hoc’ et wien rn) tqnetts shit. ‘i “Dam, bane’ Beeqede: yet akqno’, ve subsedmemt ties ho 6 ‘‘tkooodeh Bett eel borastdes: wigult it ew eotamee = sens p¥kevtonoon | Sty et trap way ay tga) sakokel “treads edt syewi ies tisha vow of ‘Hie ot YD fait cokeirtono Wha hort meer ‘edt ‘vd be | teow tna leon ‘cen te ater owt aut moa | 132 *xtT pusddy aes UOTLEOOT JOF yx °(SE6T) PTeuCgoeW pue pIedeysg ses UOT}EOOT JOG »x 9° TY b°ss £90°0 OTVE 6°ST T° v8 LL0° d O°Se 0°s9 060°0 9CCE Vaabe 9°82 Z0T*O ZEE 8° 6 c° os €90°0 TSTe v°Ttv 9° 8S 290°0 TEV b°ss 9° VY 8s0°0O vvce c°Se C°¢L eZ0°0O 6TE 9°77 p°scl vIT’O C6EE GL $°?6 0L2°0 CLE 0°os 0°os 290°0 OSEE ees L° L6 TOT’O CCV 6°€9 T° 9€ €£0°0 COTE v°?e 9° L6 090°2 LOT S°cs S* LE c720°0 cOTe COLE 8°c9o vl0°O 99T 69S 6°SL wu O£0°0O ¥*TOEE 9°60 v°Os wa €90°0 xv CT A®TD Taz,oOWeTG ACT) 8 Ia ,OwWeTG TES % pues % ue TpeEN “ON UOTZEIS TTS % pues % uertpon “ON UOT}EIS AdaImMsg yUSesseIg ; prleuoqoew pue predays AVG VOINOW VINVS WOU SHIdNVS LNAWIGHS dO SLHS OML AO SLINSHY AAILVUVdWoo A FIaveL 7 me Se ‘TMaMIOSe sc rae owe 70. Aa SOFA ATVAS — es a A TS £33 Other changes appear to have taken place since 1934-38 in the bottom sediment distribution. The most outstanding is the lack of evidence of a rocky area reported by Shepard and MacDonald to be one to two miles offshore between Playa del Rey and Manhattan Beach. Shepard and MacDonald stated that part of their data was based upon aenerts by fishermen and also bottom notations by the U. S. Coast and Geodetic Survey. It is possible that this region was delineated largely on the basis of scattered notations of hard bottom that actually may have been gravel, since it has been found that gravel is wide- spread nearshore. At that time extensive patches of coarse gravel perhaps were exposed at the surface and these were taken to indicate rock. Nevertheless, there is no indication of rock bottom in this region so far as could be determined during the present survey, and either no rock exists here, or it has been covered by a considerable thickness of sediment since the earlier report was made. The submarine topography gives no clue, for the micro-relief in this region is very smooth. Submarine Landslides and Slumping While the vertical changes in lithology over most of the shelf are explained by variations in the quantity and quality of sediments deposited and also in part to oceanographic conditions (waves, currents, etc.), the frequent textural changes in cores taken in submarine canyons are due largely to an additional factor - submarine landslides or slumping. ree 0. asdo?ag ovtanodxe ekEt ‘tae: th a o19W otodt fave ooat we per de DAROGLD ousw ae mobteabbak 6a et sxsd? aks tadion vet Ja90% eiaahtak ot tinteneteb od blwoo as wei o# aoiged: abit ak siotied hs VAD jedod atekxe door os 2edtia dos ,yerien tasen3g: oft gab: aie train bse Ww spon bit Sides ashi xaos ayo beseves iad — pakqmol? hay subitaoned smtramdue oadt te teow tere Yaolods +t ah ewpiedy Lankiree sa: ork whi Earp tera bl i J ont at aro kee Lae “9 backetaxd wie oltyexgenseag od fxs nit conte. ba) Detinogab: % Eesutest raoupaat ONT 4 3x9 spinoymra ee 134 Sediments accumulating on a slope are unstable and the stability of the deposit in general depends upon; (1) the size and sorting of the sediment, (2) water content, (3) the degree of compaction, and (4) the angle of the slope. Loose, fine- grained sediment having a high water content and Aecunulatine on a steep slope is unstable and eventually slides off the slope into deeper water. | Shepard has shown that slumping and submarine landslides are common, especially when the canyons are close to shore where there is an abundant supply of sediment. No quantitative data exist on the periodicity of slumping, but it is likely that the sediments are unstable on the slopes of submarine canyons, and that slumping takes place fairly often. A detailed study of a slope off Palos Verdes Hills indicated that appreciable quantities of sediments may accumulate on a slope before slumping takes place, but evidence was presented that indicated slumping very probably did occur (Emery and Terry, 1956). Benest (1899) pointed out the difficulties that resulted from placing telephone cables across submarine canyons, and the difficulty was not remedied until the cables were placed on the shelf well above the head of the submarine canyons. The cores taken in Santa Monica and Redondo canyons indi- cate that slumping and sliding probably takes place, parti- cularly in Santa Monica Canyon. dace asbhllw (castes ehittwt ec 28! i | ie is, sted ew teqgtins : -abbite baat sn bukmcie bine: wee ia pula tadt swore came on f ramede of geo tine anoymns Oat siti ybikoses, ‘yA " sm tvbtedtinaup ou. isn 10 oe fy qe { oui tidierite ge ais | 7 yhnwet ab ti tua pn Raggi te v tio keen ak? ne) hekies vebsancuy te wpyots at fia often) ote arasni bbe : A ~n23t6 yet? oate ented ‘garkqenn t= test wan bas “Seater thai «iil achiev eorut Yio: Soke a ae youse 8 m0 Stadnarsae > xn atedattea iyi cadtbenkop eidags botasaord ehw ttanstive suit ete, euat A ad a0 290) baa yremh), two0e0 62» ridadend yiev yabgmete bstnobbad f | Pad aottiuskPeo ov: tow emailing: (o08L teband B2Ok yy ©: oy ,2moy nes setzamine “etono« 2vides i a gntontg wor? bette 7 bevala Si9W asigad bt fi tiv bie. afb ton aw crt Sk hy ode | _Baoynes ‘enbnaeies 7b) 46 bed ott erode: Etane itsde eit? a “bol anoyns> ohaotell! tao cotnoM aimee me aeatet ssx00: af - is oe Dae es este? yidedo on wobbita bis gobgeals sail te ‘ . us ie “so aH: abel —— ts te + W'S GEOLOGICAL STRUCTURE OF SANTA MONICA BAY Seismology The seismological data used in the preparation of Figure 34 have been taken from the California Institute of Technology, Seismological Laboratory, Bulletin on Local Shocks. The four types of “Quality” shown in the legend of the diagram refer to the accuracy in location of the epicenter. "“Magnitude™ ("M" on the chart) refers to the relative movement of the ground using Richter*s scale (Gutenberg and Richter, 1942). The magnitudes range from O to about 83, the latter being the largest shocks recorded anywhere in the world. A brief comparison of magni- tudes and their approximate extent in damage are listed below. Magnitude Effects 0 Slight shock = probably imperceptible to humans. 1 Slight shock = possibly felt near epicenter. 2 Very small shock = felt slightly over a small area of a few miles in radius, 3 Small shock = felt sharply over a small area, but incapable of causing any but insignificant damage. 4 Moderate shock = may cause considerable minor damage near the epicenter; felt to a distance of about 45 miles. 5 Minor shock = may be destructive near the epi- center, with damage over a larger area; felt to a distance of about 125 miles. 6 Major shock - a strong destructive earthquake. 7&8 Progressively stronger destructive earthquakes. The Long Beach earthquake of March 10, 1933, had a magni- tude of about 6.3. The last series of major earthquakes in southern California of comparable magnitude were the Kern County shocks of July and August 1952, which had magnitudes of 7.6 to isthe oe a ¥. eA DRS ONO RA Aa ha ey 7 : i : 7 ene Lobe cir vibe bey ott 3d YoU OU oor A oe ease) tiie ie ets! ° % be nga j Lyris a 136 Figure 34, Distribution of epicenters in Santa Monica Bay. Soi - STH S30¥3A SO 1VWd Ste OQNOQG3uy cl &2 + 22e@ yc? HIV38 WSOWYSH HOV3G NVLIVHNVN —— 9'2@ OGNNS3S 13 a2 t ree Sze B6ze ee — IN € NIHLIM AlgvdOud-9 NON — G3LVOILS3ANI ATIWI93dS - V W | =7'C AaYy 130 YVAV 1d \ Zo HONOY AYaA-G ; % pe ee 9%, ey 2€—"IW O! NIHLIM A1@v80ud - 9 \ i vce 7 ze vze 0Fe HHH fa nN 9 SIO INESES a 009” | Se 1 P SHA LNAOIda ° HO NOILLOGTALSIC le VOINOW VLNVS SYALN3ADd3 JWYWVNOHLYVA © 1334 NI SYNOLNOD WOLLOP L S37IN- 31nivis € 2 i ° 1 [ INKS| VYOINOW VLNVWS a ee [acest Es eer Se L377 All shocks, including aftershocks, from 1934 to April 1955, are shown in Figure 34. The shocks are located to the nearest minute of latitude and longitude, and the qualities on the chart are shown by the varying style of lettering for the magnitude number. It is difficult to make definite conclusions about the relationship of earthquakes to the geological structure of Santa Monica Bay for several reasons; (1) most of the shocks are poorly located (2) statistical studies of the earthquakes are not possible due to the inaccuracies in location, and (3) in most cases, earthquakes do not originate at the surface, but at a depth of several miles. Most earthquakes in the California region are associated with faulting. Numerous large faults and countless small faults exist in the vicinity of Santa Monica Bay. The largest and most important fault in the region is the Newport-Inglewood fault zone, which originates in the Santa Monica Mountains near Beverly Hills and continues more or less uninterrupted to Huntington Beach where it goes out to sea. The faulting in this zone is not one major fault, but is composed of numerous short overlapping faults. Other fractures that may be of importance to the geological history of Santa Monica Bay are the Malibu fault and the San Pedro or Palos Verdes fault zone. All of these have been discussed to some extent earlier in this report. The Palos Verdes fault zone is known to leave the coast in the vicinity of Redondo Beach, but just what happens to the fault after it reaches the bay is somewhat obscure. Some 1 tases tad SoTaom areas Te Gua pitt rh ae Roowete 1 xoque Ga ah ne ac a Viens: rad toaae : . eke tsi, Rokivom 6 eae eAelg a A 4 eit Re bee daikaw eoI0S) th ne a vobarnievaknw wens sich eink eae Fos ng ‘etniy yield 3 : | ibe ge gion sat eet ye A038 +i anad, done ‘notaoitn acre Ie OweanMdy bi tod \o tied ape $10, Pour at ‘sn9m 2 84 We od can’ Ha ieaatine) ean smarts ® tolaget tao ne Ty a8 asknolt Eee Ge yoda Tek Be horn cot 6 Ob ob ie somate qth | hos SLared epbeey ented £5. Ob Capt a eet ‘ek hea mia th coke tee ey eae! ov bsumges a8 wsied oad wands to : | | nbtod onde add avael OF into ai ones sta goby noled ‘oat 138 geologists think that the fault turns west or southwestward down the axis of Redondo Canyon. However, there seems to be more evidence that it may continue in a northwestward direction. The following information perhaps supports this theory: (1) num- erous 0il and gas seeps are found at the head of Redondo Canyon and farther to the northwest, (2) the large grouping of earth- quake epicenters in the vicinity of Santa Monica Canyon (lat. B2057" 5 lone) 1189388"), C30the general pattern of the submarine topography suggests that faulting perhaps has played a role in its origin, and (4) the discovery of schist on the outer shelf appears to correlate with the schist in Palos Verdes Hills and the basement rock in the Los Angeles Basin. Clements and Emery (1946) plotted epicenters for the off- shore area in southern California and found them to be grouped along straight steep slopes which they believed to be of fault origin. No such groupings occur in Santa Monica Bay so that the relatively steep slopes are probably due to other factors, or the faulting that may have been important in the formation of the slopes is now inactive. It is noted that Redondo Canyon has the appearance of fault control since it is deep, has steep walls, and has a straight longitudinal profile. However, if faulting played an important part in its formation, it must have been in the geological past since there is no seismological evidence of faulting at the present time. The only earthquake in Santa Monica Bay that has received special study occurred on August 30, 1930 (Gutenberg, Richter, and Wood, 1932) and was located in the area where a large 139 number of shocks are reported in the northern part of the bay.” For more than three years prior to this shock there were numerous small quakes which were felt in the beach cities. The main shock had a magnitude of 5 followed by 16 immediate aftershocks. Ioseismal lines (lines of equal magnitude) indicate that the shock was felt more than a hundred miles away. It was calculated that the shock originated at a depth of 6 to 9 miles below the earth's crust in bedrock, probably granite. Thickness of Overburden Thicknesses of unconsolidated sediment in several parts of the bay are shown in Figure 35. Thicknesses of less than 10 feet are found in the rock and gravel area on the outer shelf, off the Malibu and Palos Verdes coast. U. S. Coast and Geodetic Survey charts and a chart prepared by Johnson (1940) also show rock off the coast of Malibu. The overburden increases eastward from the outer shelf, and reaches a thickness of 500 feet within one mile of the rock and gravel area. The scattered patches shown in Figure 36 are geophysical anomalies and probably are due to irratic or scattered patches of gravel, except some of the nearshore ones which may be rock a short distance below the surface. *This shock has not been shown on Figure 34 because it took Place before 1934. Prior to 1934, earthquakes were not system- atically recorded. They were largely “eye-witness™ accounts and have little scientific value. Rh 8% a ‘Pel. ees 140 Figure 35. Probable thickness of overburden in Santa Monica Bay. aioe k ° 1830’ 25° AF ra T T 7 Isa NTA MONICA BAY ° ' 2 3 STATUTE MILES BOTTOM CONTOURS IN FEET PROBABLE THICKNESS OF OVERBURDEN (PLEISTOCENE AND RECENT) LESS THAN 10 FT EL SEGUNDO MANHATTAN BEACH HERMOSA BEACH h \ A LS 2 REDONDO BEACH ) ) { / / i t ! it { | i Remrerty opel “ 7 1 eran caren Da aces oe 141 Figure 36. Areas of anamolous seismic data in Santa Monica Bay. j ™ zis att 7 ts? ave ° 18 30° 25° T oT re T T T =T T SANTA MONICA BAY | ° ' 2 3 STATUTE MILES BOTTOM CONTOURS IN FEET AREAS OF ANOMALOUS SEISMIC DATA BO SS ———— — ~ “ AREA OF ANOMALOUS SEISMIC DATA, MAY INDICATE GRAVEL BURIED BY FINER SEDIMENTS EL SEGUNDO MANHATTAN BEACH HERMOSA BEACH REDONDO BEACH PALOS VERDES HILLS ‘ a $45’ ) y, ~ ™~~ — AS EIT ee is 142 Structure Figure 37 is a generalized diagram showing the lithology of the upper few hundred feet of sediments near the shore. The impervious clay cap in the upper part of the San Pedro formation is believed by ground water geologists to extend only to the shore in the region shown by the diagram. However, a similar clay cap was found at the site of the Santa Monica breakwater and also along the old Hyperion outfall course. In the latter case, however, the clay in the cores may or may not be the same clay cap identified on land, but at the Santa Monica breakwater the clay cap was found in every core, at or very close to the surface of the sea floor. The “Silverado zone" of the San Pedro formation probably extends only 2 to 3 miles offshore, but the other formations lower in the geologic section may extend far out onto the shelf. Two geologic formations in the Los Angeles region may be correlative with the schist cropping out on the shelf; the Catalina schist and the San Onofre breccia. The San Onofre breccia is Middle Miocene in age; the Catalina schist may be pre-Cambrian or Mesozoic (Jurrasic ?). The Catalina schist underlies almost all of the Los Angeles region and crops out in the Palos Verdes Hills. The San Onofre breccia was formed by the erosion of the underlying Catalina schist, and consists of angular blocks up to 10 feet in diameter (Woodford, et al., 1954, p. 71). Even though there is a significant difference in the age between the Catalina schist and the San Onofre breccia, it is difficult to assign a definite age to the schist fragments found in Santa Monica Bay. rate a LG ‘mat ‘ 3 Stains hay ate ad - aids Mv 143 Figure 37. Geologic cross-sections in the Santa Monica Bay area. ew De te ie Bs 5 aot ge) Ase . 7 ~ LSTHIS RSS d ZNVISIINVYS assvanr S><3¢ QOORS = SSS —————————— ——== LINV es : : LS/HIS ors s vy \ ® OGNVS TYSVE ILVYFINOTINOD LSIHD INFDIOIW YIdd 13A37 Va4s INIIOIW AYIdIN Wedd T INI LY INFIIOIN YIdGIN a7at4 110 t oannoas 143 vauv T3AVYD F WO0u Aa) ALY fyrZ Or ine et OF 2) m fun LNIIIYX 8 INFIIOLSIFTd ; 14 110 jOGNND3as 13 2 I € v S 9 I sawn SLtNtvlts — a 4 0 q op He 2 a 2201S) ~“g¥9 VNOTIVE ooz+ O s77!#8 GNVS&S v > f= Oo Iw r rm YD o m we NIV1Id Wuvd NV Ame: 144 Perhaps only a small number of schist fragments have been found in the region because the original outcrop had been covered by Miocene and later sedimentary deposits and only recently was partially uncovered by erosion. Since Pliocene age Foraminifera have been found both to the east and west of the rock areas and only Foraminifera of the Miocene and Recent periods in the rocky area, perhaps erosion in post=-Miocene time carried sediments from the topographically higher rocky area leaving only Miocene and Recent age rocks where rock is now exposed. If this is true, then the rock and gravel area has suffered deep erosion, including deposits of the Miocene, the Pliocene, and perhaps Quaternary periods. If deep denudation took place in this part of the bay, the gravel might be a residual deposit brought about by erosion and winnowing of fine material. This process is similar to the accumulation of "lag gravels” in desert regions in which the wind removes fine-material and leaves a residual deposit of coarse gravel. In the El Segundo oil field, the Franciscan (?) or Catalina schist is overlain by a schist conglomerate and nodular shale at a depth of 7,000 feet below sea level. The conglomerate in this oil field was formed by the weathering of the underlying Catalina schist. It is conceivable, therefore, that the schist fragments and the gravel on the outer shelf have a similar origin. A possible argument against this theory is the almost complete lack of schist fragments or gravel composed of schist elsewhere in the region, In addition, the gravel is not restricted to the rock and gravel region on the outer shelf, but is found in scattered patches over the entire bay. oe vr ‘- Bictars eka ‘Mayle seat ‘ono i aie a | 1 tale ate a pe 9 tribilaaabe ak 7 ; oldie a if ‘mallee, eS ai) 1 ine wach iat Se me ieoran one san nia ! 145 The schist cropping out on the sea floor may correlate with the Catalina schist assuming that the equivalent to the San Onofre breccia never was deposited on top of the Catalina schist in this area or that the schist breccia (or conglomerate) has been almost completely removed by erosion. Since the schist outcrop on the sea floor is a topographic high now, and probably was a high area when it was buried during Miocene time, it may be reasonable to assume that no significant quantities of fragments of schist could accumulate. Fragments of schist that might have broken off during weathering prior to burial would have accumulated in low areas, but a few fragments of schist might have been incorporated into the overlying shale. Although the difference in geologic time between the Catalina schist and the San Onofre is very great, sedimentary rocks of Miocene and more recent ages frequently rest directly on the basement rock. Therefore, whether the schist dredged from the outer shelf is basement rock or its weathering product is not too important. Rocks in the El Segundo oil field located approximately one mile east of Hyperion range in age from Recent to Jurassic (7). Pliocene and post=Pliocene age rocks having an aggregate thick=- ness of 5,700 feet are composed largely of alternating sands and shales, except the lower 450 feet which is composed of shales alone. Sediments of Pliocene age are underlain conformably by 1,300 to 2,000 feet of Miocene shales. The basal section of the Miocene is made up of a nodular shale, and a schist conglomerate. The Catalina or Franciscan (?) schist of Jurassic (7) age : a i He seine irwtisame cai ramon ‘ent to, GPO rest pasina eo wet alte sgnose ) wae peut) pa Tacit ahstby: *: oi waeibeat i) bs icra riiees 3 ohan 146 unconformably wnderlies Miocene age sediments. The stratigraphic section is shown diagramatically in Figure 37 in which two possible interpretations of the structure between the El Segundo oil field and the outer shelf are presented. The fossiliferous shales and mudstones dredged from the rock and gravel area on the outer shelf are Upper Miocene in age and correlate with the shales in the El Segundo oil field. The schist recovered on the outer shelf is, therefore, correlative with either the schist conglomerate or with the basement schist. The structure between the outer shelf and-the shore can be explained by one of two theoretical structures or perhaps by a combination of them. They ares: (1) A very gentle dipping syncline or trough exists with rocks of Upper Miocene age and possibly the schist basement exposed on the western limb of the syncline, and Plio- cene age rocks in the central part of the bay are covered by sediments of the Quaternary age. Sediments derived from this island and from land to the east eventually filled the trough. (2) The Palos Verdes fawit zone extends northwestward from the Palos Verdes Hills and has uplifted the outer shelf several thousand feet. Rocks younger than Miocene have subsequently been eroded away leaving only Miocene and perhaps basement rocks on the outer shelf. The Palos Verdes fault dips steeply to the northeast along the north side of the hills, but it would have to have a relatively low dip to account for the changes in the thicknesses in overburden on the shelf. It is noteworthy that Corey (1954) and Woodford, et al. (1954) show a continuation of the Palos Verdes fault across the Santa Monica shelf, | ‘ oe ettitos figmeens eat seetime lynne Stier 4 Bonin lexs 26 mao Stode sith. bina Asie satie0 ver opewees _ Rolisaidaos s ‘ah baseless 0) ieeiaaiaaal tones ovoaite oe ; tabace. ont Yidkzeoy Daw sg0 ‘ua ‘xg ie tine a or" binds inioaosiicctatid ad} Yo. elon S invatwow ‘on ie basaqe “ahah nee? horiaab bonsakiet sos veneer’. elt sm | paloos ree ey eqedasy ture pdt 2.4 ab, entvead amet oh | eatt e+ ¢lasode: ecpdite eat: eebrey vo kgt met! , MH eitta: astuo® ovad brow $2 td ,@hhs oot Xo wade Aixem ony yaots t | eat md, Kagrads nen fect Hegre oF gets wot peeve a ty: Tone bila lava oh hil are iad ae sabato nk 147 It would appear, therefore, that on the basis of available data there is a considerable thickness of sediment between the coast which probably becomes thinner towards the outer shelf as shown in Figure 38, Although sedimentary rocks of various ages may be covered by only a thin veneer of Recent sediments in the inner shelf region, it is highly improbably that basement occurs at or near the surface anywhere in this area. A detailed study of fathograms taken over most of the shelf indicated that most of the inner shelf out to a depth of about 170 to 180 feet is a depositional plain. This suggests that deposition of sedi- ments has covered a large portion of rock of Pleistocene age and older which possibly at one time were exposed at the surface. However, some areas, such as the regions where red sand occurs, and at the head of Santa Monica Canyon, relic sediments have not been covered. Since some of these relic sediments do not have any discernable relief, they must be at equilibrium with the present depositional surface, and as sediments are spread evenly over the entire region they will be covered. This assumes, of course, that most of the shelf is undergoing aggradation, and there appears reason to believe that this may be partly true. No definite statements can be made for most of the other parts of the bay since data are lacking. Nothing is known concerning the age of the rocks beyond the shelf break, but a large variety of rocks have been dredged from the submarine canyons by Emery and Shepard (1945). A few of the rocks had a possible age of Pliocene, but it appears as if the bulk of the rocks should be dated as Miocene. No schist has been found in the canyons. This imposes a very interesting question: If the “battetsb A. ee ait mb $5; nat . : | fade betaskbak Bede ‘ody: to tran apr, aatkint enpayontat tes co vat ot ove duds to, odalah os $9) eve. nes oa | ape aasccrntois te xaos: Wh notes sve a on a —- te besogxs stow emit ono te ytdkesoq dokitw sab) | «bqwo90 Dane: bor oaniw cooknot edt widows yedens mmon ¢ “toa: wend etnsmbbor okies yooynad sotnol atne2 Lo. Saod edt) \-gyait toh ob stncukbye Sites ‘seeds 40 sMoe souk? -bexsy09 “i red | q este wy bw wurbadLt hope Pe Vodd. Tebien ofdens ‘ . o ae. bavage ona #Inemcbee oa iin yeaa isnoktheaqeb: | = “a sPonudee skit .oer9ven on thew ‘vent aaihgore eatin ont > ° | aerial eh gnuteat faveses oan: etak sous ot oar ace z sted heed Biod a ate" thsderie set. sino oft to sae emt 3 it of sere scammer pat nes) teahoah oad oven etaom, Da: tesa | nes edpor salt Re wa? a yereed) banqene ‘baw Rene Ye ont Ao Lut edt 7 ay pcan tk weed pT 148 Figure 38. Hypothetical cross-section across Santa Monica Bay Shelf. V3aY¥vV T3SAVYHY9D F WOON 149 schist on the outer shelf is basement or near basement (San Onofre), then all rocks below the schist must be basement also}; which means that all rocks found in the deeper parts of the bay should be composed of schist or at least basement rock of some kind. Thus, if schist occurs on the outer shelf at the surface, then only schist or basement rock should be found in the Santa Monica Canyon. This is not the case since most of the rocks dredged from the Santa Monica Canyon were Miocene in age. One way to explain this anomalous problem is by assuming that an east-west trending fault separates the rock and gravel area on the outer shelf from the region north of the submarine canyon. Such a fault would tilt the region north of the axis of the submarine canyon downward, and uplift the outer shelf. In this manner, Miocene and post=Pliocene rocks could still be present in the canyon, but have been largely removed by erosion on the outer shelf. Another alternative is to assume that the schist dredged from the outer shelf is not in place. Third, the schist and gravel area of the outer shelf may represent an eroded dome- like structure. Poland, et al. (1948) mentions that the Ballona escarpment along the southern boundary of the Ballona Creek has character- istics which suggest faulting. For example, the escarpment is more or less straight over most of its length, but more impor- tant is the fact that the gravels in the old stream channel are thicker on the south side. The thickening to the south can be explained by tilting of the land area to the south and by assuming an east-west trending fault at the southern boundary of the stream channel. It is possible that the faulting and ‘tphiioe i boat | co eo. fever baz to07- ws sores sa acthuoas t Ay Tk Oise dag soaker a9oela wk ton + Made s0tv0 at ni recomg tages whol tat ear a elt) ato tema coer, de a. od. seo thwor eas of pales ott = eon Adm + 7 at 150 tilting proposed by Poland, et al. also is responsible for the tilting of the northern flank of Santa Monica Canyon. A large percentage of submarine canyons have streams or former streams entering into the head of the canyon. No problem is involved in the origin of Santa Monica Canyon since Ballona Creek is known to have flowed into the bay until 1825, and probably flowed directly into the head of Santa Monica Canyon when sea level was lower. Redondo Canyon, on the other hand, has no historic, topographic, nor sedimentary record of a former stream landward of the canyon. The only evidence known which indicates that the region at the head of Redondo Canyon may have had a stream is the existence of marsh or lagoonal deposits at about sea level one-half mile inland. Although faulting may have played some role in the control of Redondo Canyon, some additional agent is necessary to cut the gorge. Two theories which are most commonly argued for the origin of submarine canyons are; (1) subaerial erosion by streams, and (2) erosion by turbidity currents. A detailed discussion of these theories and others are unnecessary here3 however, it is necessary to briefly state the turbidity current hypothesis. Sediments accumulating on the shelf or in the upper reaches of the submarine canyon periodically slump or Slide into deeper water. The material that slumps has a very high water content and travels at a high velocity which is assumed to have the power to erode the bottom and walls of the canyons. It is obvious that there is no apparent abundant source of sediments which could form turbidity currents; therefore, both f pala eat my “nox sages al sme Kasred ats i . te: broset ‘exataamibae ana yabdgavaoqes. jon: é “ennedive viao edt sxoteaeds tina Tavel ave oF waste us aty teott 25k. a nosd o ie ~ escormo qribidx? xo} atnsaibee te soisttoaup ops saa | an vs snoqnes ett Yo nigise sit anti iat ® : abst toes sins tata: semaine Yo Sell - WW lak SesxD stobTnd ehsawak spyned phnodes to pote nibzen sa edecgave 2beT ae puote sa dnote st GLEE Yai Teansce menate poe nbdqeigentsoe sagesan Yo \Fkeoqeb tnembhee Lstabideaee ath jerneukoee 36 adiivdEenahd Sit? vo soneat ink wa sval Hoke . eaistudien tite edt ot betaiog Daa Boeset emor 207 8 ize 152 SUMMARY The Geologic and Geographic Setting of Santa Monica Bay Santa Monica Bay is bordered on the north by a mountain range that has been uplifted along east-west trending faults. On the southwest, the Palos Verdes Hills have been elevated during relatively recent time. The north side of the hills is separated from the Los Angeles Basin by a fault trending in a northwest direction. This fault probably extends into Santa Monica Bay and has played an important role in its structural history. The relief in the Los Angeles Basin was formed largely in Late Pleistocene and early Recent geologic time and the tectonic forces responsibie for deformation probably have also affected the submarine geology of the bay. Thus, the structure of Santa Monica Bay is more related to forces active in the Los Angeles Basin and Palos Verdes Hills than to tectonic activity in the Santa Monica Mountains. Earth- quakes on land and in the bay, and other lines of evidence indi- cate that deformation is still taking place. The major drainage into the bay is from the southern slopes of the Santa Monica Mountains, while there is little or no drainage from the area south of the city of Santa Monica. Prior to 1825 Ballona Creek drained a large inland area, but since that date only a minor amount of material has entered the bay through the Ballona Creek outlet. A variable amount of sand comes into the bay around Point Dume, but probably no material finer than beach sand comes from this source. | ietaven ry 1 ve iy08 ait ao Piyreod ad at watack shana? - : . oe gaitmeat teserteag guoky coi qu’ heed sad sah osu | ie baravels aned ovat ernst mabe’ sa bal seht temuttuoe say a etka ort te ebée st3a@ tr «MES hese ylovetaten | a ius | gaibasat tigal s yd meet antioycn ost aah mo'xd bedaragee i | Ofat ehasixe | idaduxg +tea’ oh rth : hnsaah *emultron a noe i 7 eth: me! Bfo2 inet xq ie bay ats eel: Rosh ad psknolt a ‘ a naw akend aofoyah el ody nm doi Loa Sey riotabd tatan me y : . “plystony teeo88 qines hig satis. occ Cl stad ab qisgaad’t ae thes nodtanw2eb 10? shdtemoqe:: cassel skeen 09s aut tan: snct F ved out te THOLOeD pritemdvs oct) bstostis vain oved yid sow - ; ot botetox Broo at wea aoliow slam ¥ Port ours sat eae he eres sabrs¥ mole? hos nieul, enlageh aod sdf at aviton, pee ie? Pat “9x08 , tis En rw ‘eokaoM wion? of? Bh Yo lritos obnotaes, ors a ; a, yy r oh ~ & - } f hy an L bb haha ‘-b.4 it . £ 158 topography and sediment size indicating that organic particles are selectively transported from nearshore and the topographic highs and deposited in deeper water in the same manner as detrital sediments. The high values near the Hyperion outfall indicate that here there is a faster rate of deposition of organic matter than can be oxidized, removed, or masked by detrital sediment. Cores and borings, especially those close to shore, show extreme vertical variations in texture. These variations may be due to many factors, including (1) fluctuations in quantity of sediment reaching the bay from the watersheds and other sources, (2) redistribution during periods of especially strong turbulence in the bay or in periods of calms, (3) the deposits may be related to former positions of sea level, (4) formation of special topographic features or changes in bottom topography, such as offshore bars, which may allow the accumulation of unique deposits, and (5) slumping of sediments. It is likely that many of the textural changes in the cores from the submarine canyons are the result of slumping. The clays and vegetation found in cores nearshore and also in borings made on land close to shore are believed to be due to deposition behind offshore bars. Landward migration of sand from these bars may be the source of the sand in the El Segundo Sand Hills. adie ‘bak abadesotam itt ape , ets. nel | “yilskosges) Ye ivobyeq pekaiet Aobiucix athoa: a) 9a 8) eemles te whokesq af aoqed wa he gemeanel 3 oy ers, “ytoves HD, te maz kt hao ote} 6? bete Catt ad tom ae nz eogandy 70 eowtset Dkiqninogey cekoag ‘ jn et wolfe Taw elo kab yezad aexomeily ap toe aridaatgoqoi oy aamakbea Ww sige CU) baw eben supple to 0 ‘A ‘bens snoiterses 2908 th ey aoktat Rey baa cate oft neue ipoey ani! buawhnal ame eaeie tie han A nobtizoas ot ‘seb edt ak Dane oat Fe sutwee: © 159 Relation of Transportation and Deposition of Sediment to Discharge of Sludge into the Bay Existing patterns of sediments in Santa Monica Bay indicate that oceanographic conditions which cause the deposition and transportation of the sediments may fluctuate enough in some areas to create a condition of intermittent deposition and removal of fine-grained material. This con- dition seems to be especially true near the head of Santa Monica Canyon and along the inshore side of the central shelf projection where sands and silty sands are composed of a relic coarse fraction plus a fine fraction deposited from suspension. The preservation of relic material in these surface sediments indicates that although the fine silt can deposit here, often the sediments are reworked and most of the fine material resuspended. This area is in the vicinity of the end of the sludge outfall. Currents in this portion of the bay flow toward shore during most of the year. It is evident that particles of sludge emanating from the end of the outfall which go into suspension will move shoreward as they settle. However, it is also important as a result of information collected on sedimentation in the bay to recognize the possibility of resuspension and further movement toward shore of any sludge accumulating in these areas of the shelf. Thus, there is a distinct possibility that sludge accumulating near the end of the outfall and at a distance inshore might be carried pro- gressively toward shore by repeated resuspension and current motion and form a sludge deposit at a point intermediate between the end of the outfall and shore. ae elias na Sa, . allie hO st @ oa +i ., ie ia 1a! eee eee a tea alt a ae Le ig wean: nee iia bait he spas, oes A 160 Areas of Rock Bottom Rocks occurring in Santa Monica Bay are classified into three groups; (1) bedrock, (2) gravel (transported rock), and (3) phosphorite (a chemically precipitated rock). Bedrock The major area of bedrock exposed on the sea floor occurs on the outer shelf pro jection between the two sub- marine canyons, and rocks that are believed to be in place occur off Malibu and the Palos Verdes Hills. The major rock types found on the outer shelf are shales, but mud- stones, siltstones, and sandstones also occur. Some of the rocks have been dated as Miocene in age. Fragments of schist recovered from the outer shelf are either basement rock (Jurassic or older) or from a Miocene=-age breccia. Other investigators have dredged rock from the Redondo or Santa Monica Canyons. Gravel There are extensive patches of gravel in the nearshore region, off Palos Verdes Hills, and near Malibu. Gravel in extensive quantities is known to underly finer sediment in other parts of the bay, but the full extent is unknown. Some material of gravel size also occurs in the fine sediment of the bay, but is widely dispersed. The gravel fragments are primarily composed of igneous rocks with lesser amounts of metamorphic and sedimentary material. The major gravel deposit far offshore is surrounded by finer sediment, indi- cating that it is relic and was not transported to this ee tare LOC atie ZF ‘ RY wits ry lt Deel oy gel ba) a SP ae han d maewolerg Wace ‘ ny) ; hes ot Le Bae Tye uel 7 - : Ph in, th ren B Lela Lee Aa pin ein Yaste. ce Gob eo hat ona i eR i oh} Yee aa ke. a ee | > end by. pons Ma a aah hich Nsae 36 Bipot Comte 161 location during the present cycle of sedimentation. It was probably transported and deposited in the littoral zone during a Pleistocene lowering of the sea. Its source was the bedrock outcrops nearby and/or fluvial transport to its present location by streams flowing from the east - presumably Ballona Creek. The gravel is flanked by coarse-to medium-grained sand containing a great proportion of rock fragments. These rock fragment sands are thought to have been deposited at the same time as the gravels. Phosphorite Phosphorite occurs in the sediment over the outer shelf and on the outer edge of the shelf south of Redondo Canyon. The presence of phosphorite is indicative of slow or non- deposition of sediment in these areas. Geologic Structure The increase of the thickness of overburden in a shore- ward direction from the central shelf projection indicates that the bedrock area is high and that a trough exists near- shore where great thicknesses of sediments have accumulated | Two theories are presented to explain the geologic structure of the outer shelf; (1) a continuation of the Palos Verdes fault zone into the bay in which the outer shelf has been uplifted in relation to the nearshore area, or (2) the underlying consolidated rock dips gently toward shore with bedrock exposed on the outer shelf. The absence of schist among the rocks dredged from Santa Monica Canyon by other investigators may indicate that the 4 it A an ange a snoie moat 7 _" cpt Gps o k & td otqodee | neuode ke ab msbardxov0 Yo oer std ‘0 paiee oor ; aey eo bat pobsestio-ny Stene tentape git 90) woktverkb: baa ) mqner etetke Agnes w Pode bow alt eb aene aooxbed! nt ith botalvnvons owed etmomhiog lo weapentokat: teary oisdw “a atyolosg rr a migtaxs OF De ie@ery ose ao iroote owt: (tole sdt to rokteuaetdnd a CL) 7 ebede etuo vote to’ onutoogte 1 tad dtede totue. ett abbas ud yad edt ofad oune stents asbuey ‘ adr (8) 20 ees MaReMAbe sdt OF eobtaew ab oe sittw anode bsaves, ites eqih faon) beta bktokmoy | iiehinaat | | tate rete a? mo bee | ston tee heybisx aa oo% ate. gmoma, teidne be ose tat disei sel Yam “azovepliaaymd xoitto 162 area north of the shelf projection has been down-faulted, or tilted to the south. The geologic structure of the bay is not considered to be unique and faults are probably as numerous as on land. In addition, it is likely that faulting is as active in the bay as elsewhere in the southern California region. Although there is no topographic expression of faulting on the shelf, data strongly suggest one or more major faults. It is not known whether the outfalls cross active subsurface faults. However, since there is no surface expression of faulting along the proposed outfall route, it may be presumed that no vertical displacement will occur even if the faults are now active. Earthquakes resulting from movements along active faults, either within the bay or elsewhere in the region, should be regarded as probable. A long rigid outfall on unconsolidated sediments may then be subjected to considerable stresses. “4 Motte aie 0 5 edd twe'l Yo! wae zes aksgragoge? ‘ alice. tom wh eT > yettwe? rotamr 3am 70 0 Toog eee at eet toe pow Fasadie ovktaa ‘anarcy Mela ot eat “on ants: Siecccyi atonal twos tuk tae wae in atm ads 1 ween uEe tke o ; ay Bs eat SS 7 itive ovEton groks etapmovon not ttt navn “aateepainat od Biugda ymalQos wht nt wrndwenty wa vaet ott mitt bw: “ betabksouanoeu as bia Lowe :bighs wt A sidadoag 6a rs sesneate biderebhenn2 op hetooldee ed month xual . 163 REFERENCES Anonymous, 1916, Shore at Venice, California, best protected by permanent sea wall and low groins: Eng. Record, ve 73, no. 2, pe 36, 51-54 (rept. of Leeds and Barnard, engineers). Anonymous, 1917, Experiment with groins at Santa Monica Beach successful. Wood and concrete structures are effectively building up sand deposits: Eng. Record, v. 75, no. 13, PeESOlasoa. 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Coast Survey 1856, app. 16, p. 119-120. Bailey, T. L., 1943, Late Pleistocene Coast Range orogenesis in southern California: Geol. Soc. America Bull., v. 54, Do 1549-1568. Bailey, T. L., 1954, Geology of the western Ventura Basin, Santa Barbara, Ventura, and Los Angeles Counties: Calif. Div. Mines Bull. 170, Map sheet no. 4. Bailey, T. L., and Jahns, R. H., 1954, Geology of the Transverse Range Province, southern California, in Geology of Southern California, Chap. II, Geology of Natural Provinces: Calif. Div. Mines Bull. 170, p. 83-106, 14 figs. Beach Erosion Board, 1938, Beach erosion study at Ballona Creek and San Gabriel River, California: Cooperating agency State of California acting through the Los Angeles Flood Control District. Se : taisetona ‘teed skego tea. — da. rion 2101 200m econ {owoet oases sq Weel ban t Layr 882). BS req uth - ‘ poe bes tte ‘ a 98 i ie Pian hae ‘dpoott ‘pont pene } indeed og susan 4 Wut be Science ereL. mist 0 f Bow Das boow “Hee aoe oc lgaataiaa hitee = ae a ioe | te wend srninlaest Rolin ie ea eee: a OMY w& in wae to. ug Siro ead are hed fo tts0000 008 ae FER xe » tale a Kebmoii ts? -¥si oodtgnar ee Bats aOS. «Gis Stee % Dials: ek ae oe nods#s ‘Line pinegr? gine «i: whit : eat oq ae aw grit fig 2 ion obmoaiy ee ote’ errors | Sat ad sated SEB ey A ia f ae abebight ae qnisates no apse ger at hte od yao ian ae 7 i Te ote: upce att eh : amolcat b es: eke Py ¢ Qs GL of a rag int ue Ne es Baaqhae ben Gs smal, ; eat waoud * | vee eS ne 4 Ee i pore oat eid maint Pian Sirs 168 Emery, K. O., and Foster, J. F., 1948, Water tables in marine beaches: Jour. Marine Research, V. 7, P. 644-654 Emery, K. O., and Rittenberg, S. C., 1952, Early diagenesis of California basin sediments in relation to origin of oil: Am. Assoc. Petroleum Geologists Bull., v. 36, pe 735-806 Emery, K. O., and Shepard, F. P., 1941, Lithology of the sea floor off southern California: Geol. Soc. America Bull., ve 52, Pe 1899-1900 (abs. ) Emery, K. O.,y and Terry, R. D., 1956, A submarine slope of southern California: Jour. Geol., V. 64, P. 271-280 Emery, K. O., and Shepard, F. P., 1945, Lithology of the sea floor off southern California: Geol. Soc. America Bull., Ve 56, Pe 431-478 Fairbridge, R. We, 1947, Coarse sediments on the edge of the continental shelf: Am. Jour. Sci., V. 245, p. 146-153 -Fleming, R. H., 1937=38, Tides and tidal currents in the Gulf of Panama: Jour. Marine Research, V. 1, P. 192-206 Fleming, R. H., and Revelle, R., 1939, Physical processes in the oceans, in Trask, P. D., Recent marine sediments, Symposium pub. by Am. Assoc. Petroleum Geologists, Tulsa, Okla., p. 48-141 Frasher, C. McL., 1943, General account of the scientific work of the VELERO III in the eastern Pacific, 1931-41; Part III. A ten-year list of the VELERO IIIcollecting stations including an appendix of collecting stations of the Allan Hancock Foundation for the year 1942; Los Angeles, Univ. Southern Calif. Press, Allan Hancock Pacific Expeditions, V. 1, No. 3, p. 259-431, incl. 15 charts. Goldberg, Jo, 1940, The geological significance of the coastal terraces of the Santa Monica Mountains: M. A. thesis, Univ. Calif., Los Angeles, 133 p., 18 pls, 3 figs., Grant, U. S., 1938, Geological problems involved in the conservation of beaches: Pacific Southwest Acad. Pub. 16, p. 27-28 Grant, U. S., 1943, Waves as a sand-transporting agent: Am. Jour. Sci., V. 241, p. 117-123; Shore and Beach, V. 11 pe 46-48, 52. Grant, U. S., 1946, Effect of ground-water table on beach erosion: Geol. Soc. America Bull., V. 57, pe 1252 (abs.). Ay ray Ee, okie 1 iy Grant, Grant, Grant, Grant, Grant, Griffi Gutenb Hall, Handin Handin Heck, Hill, 169 U. S., 1955, The relation between amount and character of beach sand and denudation rate in source areas: Pacific Petrol. Geologisit, v. 9, nos 5. U. S., and Shepard, F. P., 1937, Changes along the California coast: Geol. Soc. America Bull., proc. for UOSGy Wie c4Sig GD OK), Cabs! >’. U. S., and Shepard, F. P., 1938a, Short-period oscilla- tions of southern California beaches and adjacent sea filloor: (Geol sec. America Bull.,, proc. for 1937, v.49, pe 84-85 (abs.). U. S., and Shepard, F. P., 1938b, Magnitude of some shore processes in southern California: Geol. Soc. America Bull, proc. for 1937, v. 49, pe 239-240 (abs.). U. S., and Shepard, F. P., 1946, Effect of type of wave breaking on shore processes: Geol. Soc. America Bull., Wo Sly M5 se (Goose ps n,:D.,R., 1944, Coastline plans and action for the development of the Los Angeies metropolitan coastline: Los Angeles, Haynes Foundation, 38 p. incl. illus. Cre enichiten Celis s)anGdmWood), Hi.) Os ihOS2)suhe earthquake in Santa Monica Bay, California, on August $0, 1930: Seismol. Soe. America Bull., v. 22), p. 138-= 1S. pS. Wh, ie, Je Ve, Jre, 1952, Artificially nourished and constructed beaches: U. S. Army, Corps of Engineers, Beach Erosion Board, Tech. Memo 29, 25 p.; Third Conf. Coastal Eng., Berkeley, (1953), p. 119-136.. » Je W., 1949, The source, transportation and deposition of beach sediment in southern California: Ph. D. thesis, Unive.) Calitvy Eos Anreles, Ou7sipe, L2 eplisas UsS Army, Corps of Engineers, Beach Erosion Board Tech. Memo. 22, Gost) LZaokp. sine 2 etablesh. 2) plist. nie We, and) Cudwaick, jin) GC.) 1949),) Accretion) of beach sand behind a detached breakwater: Scripps Inst. Oceanography, Submarine Geology Rept. no. 8, 15 Pe, 1 pl., 1 fig.; U. S. Army, Corps of Engineers, Beach Erosion Board Tech. Memo. 16 (1950), 13 p. N. H., 1947, List of seismic sea waves: Seismol. Soc. America Bulll., v. 37, ps 269-287. (First pub. in Internat. Geod. and Geophys. Union, Comm. pour. 1'Elude des Raz de Maree, no. 4 (1934), p. 20-41). M, L., 1954, Tectonics of faulting in southern California: Calafiy Divo Mines Bull.) 170),. Chap. IV; .p. S=13% 1 mde probe eagait i arias ca Bao A Tt we bane tna ei ets) hited Reeeps: an. | buy en 908 loge, Biome ri wh ESBS, aia gi th a pap resece ‘wo es Saad anew «tine bisa =f ie + 1 ye a Ae a fae a : oe ae we hig et’? aie is i oe acabier ee tose Peres Cary e16Fe. Ais] gas cease y ies ha BO i ‘; Weeden) BC WE) Mt hs 2 Stil do a bas, aawiquealtesed $40; wpe won Aap ei odo og Fe eel sh? te rasmye, 7 ate 4 See aq ot Lg hint F SH apcvall 2 otagnk aod ae ett Ged | re San Ada Bons yatuad ended WB a 57) ge MTOR Ta. eyed | woke) Pinas wok mhepaeas tet i “a bee ‘ev yokes jeak weak 90. .lumetee, OnE LOE’ ie me eel, bein 2 oa bntninecr, gi tees REPT (SEC daly ae ath tial, a aeee angen ee. to eo) To a Thiel aa i ‘cape Sani bain te RS NS oul anal: baaodt one Mig ME RPL op y KORA? » eRe peel tn, nobieinog gh (warios atts OROL oth i v athe F anaclaei Siete ) -Bsesyeee ne ‘ch ih Bode aaaad 3 2 5 4 tora: B igs push iy nen “BUE seeieanh PET 5 5a th ERO oeen ; ae ee dee? beped soieo 7a pits salen / ose tga Yo EOD © om aay Fi ea art his mks a We bead: bS sae ae baat ae) ft ame habe: rR My - bodied se) ae) ee ‘Aina a. Heed nwasesd heiipareb a, Da kdew bine ih ag Awan iond stktandee re iii 9 nly ey or een) ae ees Ae dse eal 6 4 ry ee ae ae ; eae eee) al .emekl. Maae band ia tae sia ee tome bed, ABA TR BOF wiwed ek dee ern she. ae oot geht: Pea ROU NSS 05S og ORE pw ee Ltue ep preset a shorete’ shee emt. peo ro at Hiei aa HSK. DOR ot ; of ihe 0S: hich ent Pi3 Re anes paonee, obs y ey Re Oey.) ee » aleweyee ovata stl dist! he: witunooee: ie RI SS WWE be Oty ie aease 170 Hill, R. T., 1928, Southern California geology and Los Angeles earthquakes: Los Angeles, Pub. by Southern Calf Acad. ocinnecoce De, Lllus., 4uplsi. Hjulstrom, F., 1939, Transportation of detritus by moving water, in Recent Marine Sediments, pub. by Am. Assoc. Petrol.eGeole., tulsa, Ola. pe S—Sai. Hoots, H. W., 1931, Geology of the eastern part of the Santa Monica Mountains, Los Angeles County, California: U. S. Geol. Survey Prof. Paper 165-C. Inman, D. L., 1949, Sorting of sediments in the light of fluid mechanics: Jour. Sed. Petrology, v. 19, p. 51-70. Inman, D. L., 1952, Measures for describing size distribution of sediments: Jour. Sed. Petrology, v. 22, p. 125-145. Inman, D. 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Calif., Berkeley, p. 271- ple, GS esterC\, Kelley, V. C., 1932, Geology of the Santa Monica Mountains west of the Malibu Ranch, Ventura County, California: Master's thesis, Calif. Inst. Tech. Kenyon, E. C., Jr., 1951, History of ocean outlets, Los Angeles County Flood Control District: Firs Conf. on Coastal Eng., Berkeley, p. 277-282. le oy + 4 * ia witest L) ten er oo eae OEP Lc, By A ; oh es 4 an i ae i L f, i” “7 erie HOH? Cea tag itA, ay . 1 7 . Voy W) oehcx pene ivis*es che v4) : OY V8 ee ats a af py oa <4 d L My y 7 « b Bult. ¥' a TRS 1.8 4 4 a9 j - é - a +e « r y “—.h fies aie / ; - an + * ea) uf Py ve } t oo et i * 7 " fi ; y. ‘ i a 5 ya) an s i Hh: 2 : \ 5 hf * i °. | , ney 7H 4 - ” i 171 Kerr, A. R., 1938, Littoral erosion and deposition of Santa Monica Bay: M. A. thesis, Univ. Calif., Los Angeles, 49 pe, anew. tables. SO) pls. Krumbein, W, C., 1941, Measurements and geological significance of shape and roundness of sedimentary particles: Jour. 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Banat: aM Bria. 3 oll spas atargetosd musiostst -a0atA WA Eekasetifed . st 2 500K 7 ab LEMS NS ma | ae av -s ite cae ehasthiss. aft be. ayeltav sxicengue sit S00 ,.T 2 take 804-0Td ~q ~S8o som ger .v ,SDGBESS + 2a 805 Tyee madian aitoat lar ties e644 90. yactosd. cee0l aX af 982 4 bra setit .Yudl «ities svintes eaisaca 204 . an tap auom : SOBLMLEL od, feiaoleranie Stet? .rqah Aree 3 Tao feed ad ao wastdoe eh; bem nottewids Stel notsiqar® teint 728eD risdtuce ,onilssovte votaal~ olin clare omar ee veg LOL 2 5hogns. sal ,. tile vba ,eteat? 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SEV E | meet axel ome SOV4 Lien each .va Bible 2ektrt0 tk ist eyentuee 7. q 7 6% £ wom shane hh bere rane ak ie edeodty Sees eee ts0 pita ,.0 ot. Disxaree Qidnyeat2a8W ‘yorrde toed .& ae, eaboadidiad noe eee ; sBobdes Sh wy #2 Ch. 6 eke OF ene COE Phe rsyad Lvbybe Sc: @hORSM. . Eee god a eo) OE ee storm athe ee errs ti wall x20) fy eter $y wambbee . ; sie yyot Bowes 2eket to Edepwthes afi 62° iat § yaeesn aieie7 {souaull dahoneenen vMugum, LopixeM pee ae SE : Aunpisat Sithes ade td selog gear , Ther 44 Tall oh roma ee TEE , cups oul |, Thedt ke: 2K tetipssawee ngkee? .tooL,axoonigcd) Ie egsod Yee © aeeesOutine: ,tetian Ateae abucben so} nylesh. Lersued iWortteib esisana 200 peta ins beet. ,gaudats 64 soy tate tram sa uyawtst aw .cry ahesigitl fe sino, Sonenyd aise jo ybots Pspome Ae (eure a acs a ae 2 0 beeen sil ao, *O206) ~F Satee #4o5D oG- bh , 22 .on rsqeq |, 27SsRRgae ee phates reeeM, < preset EY wioats j2 ¢nomiwegxd eyewwstal ge #9970 englisé is eaten socacotentad W yhote LebeM ,80vE (vO. .oi > aire sas et RTT TS ,soliaeY ,isiguw f oe | gow! Tig senoee way aly Gores Psrdse tf ides -AXSGl patueh eXtSs2okF wrghes Ts Sk! . eee he. Stiag ikTze05 sragak Bod a> 3 -. Bip 7 = oe 3 re ‘ y mae tue 7 Eso il oed Siete kere S22 ton _y2erkt ,eecl . Ft am isto tied Teears Beloysd eot sar On eaeetsa seh SR I a ees 10% .oerg ,, fiSe weargeee ao08 - LT Wheeler, G., 1936, Davis's study of California marine terraces: Union Géographique Internat., Comptes Rendus du Cong. Internat. de Géographie Varsovie, 1934, Travaux de la Sect. Gy) pe 26t=552i. Wood, H. O., 1947, Earthquakes in southern California with geologic relations: Seismol. Soc. 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