HEAVY MINERAL ANALYSIS OF SELECTED MONTEREY BAY CORES By William Patterson Hunter * » United States Naval Postgraduate School THESIS HEAVY MINERAL ANALYSIS OF SELECTED MONTEREY BAY CORES by William Patterson Hunter Thesis Advisor: Robert S. Andrews March 1971 Appiovzd Ion. puhtic. nzlza^o.) dUtsubuution u}itimite.d. i 37783 Heavy Mineral Analysis of Selected Monterey Bay Cores by William Patterson Hunter Lieutenant Commander, United States Navy B.S. , Trinity College, 1960 Submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN OCEANOGRAPHY from the NAVAL POSTGRADUATE SCHOOL March 1971 MOHTEBEY, CALIF. W*> ABSTRACT This study was conducted to identify heavy minerals and their changes with depth in three cores taken from different locations in Monterey Bay, California. Monterey Bay provides an area where several different sources influence the sediment deposition. Minerals indicative of the geological formations in the drainage areas of the Pajaro and Salinas Rivers were found in distinctive distribu- tion throughout these cores. Glaucophane, indicative of the Franciscan Formation, was found near the bottom of all cores. The larger percentages of augite found in the core at Santa Cruz were probably derived from the north due to longshore drift. High percentages of garnet and low percent- ages of hypersthene with depth in the Moss Landing Core reflect the influence of the Salinas River. TABLE OF CONTENTS I. INTRODUCTION 8 A. OBJECTIVE 8 B. GENERAL DESCRIPTION 10 1. Geology and Hydrology 10 2. Sediment Transport Mechanisms 13 C. PREVIOUS INVESTIGATIONS 14 II. PROCEDURES 19 A. TEXT URAL ANALYSIS 19 B. HEAVY MINERAL ANALYSIS 19 III. TEXTURAL AND HEAVY MINERAL ANALYSES 31 A. MINERAL DESCRIPTION 31 1. Major Constituents 31 2. Minor Constituents 32 B. QUANTITATIVE RESULTS ■ 33 1. Santa Cruz Area Core 33 2. Moss Landing Area Core 34 3. Monterey Area Core 34 IV. DISCUSSION 36 V. FUTURE WORK 38 APPENDIX A FIELD DESCRIPTIONS AND PHOTOGRAPHS OF CORES 39 APPENDIX B TERTIARY DIAGRAMS 46 REFERENCES 51 INITIAL DISTRIBUTION LIST 53 FORM DD 1473 54 4 LIST OF TABLES TABLE I. RIVER BED HEAVY MINERAL COUNTS 17 II. SANTA CRUZ AREA CORE ANALYSIS 20 III. MOSS LANDING AREA CORE ANALYSIS 21 IV. MONTEREY AREA CORE ANALYSIS 22 V. HEAVY MINERAL CONTENT 26 VI. HEAVY MINERAL PERCENTAGES 29 VII. COUNTS OF THE CONSTITUENTS IN THE HEAVY MINERAL FRACTION 30 LIST OF FIGURES FIGURE 1. LOCATION OF CORES 9 2 . GENERALIZED GEOLOGY OF THE MONTEREY BAY DRAINAGE BASINS 11 3. SOUTHERN MONTEREY BAY TRANSPORT PATTERNS 15 4. SAND/SILT/CLAY COMPOSITION OF CORE 10 23 5. SAND/SILT/CLAY COMPOSITION OF CORE 14 24 6. SAND/SILT/CLAY COMPOSITION OF CORE 18 25 7. FIELD DESCRIPTION OF CORE 10 40 8. PHOTOGRAPH OF CORE 10 41 9. FIELD DESCRIPTION OF CORE 14 42 10. PHOTOGRAPH OF CORE 14 43 11. FIELD DESCRIPTION OF CORE 18 44 12. PHOTOGRAPH OF CORE 18 45 13. TERTIARY DIAGRAM: HORNBLENDE ,AUGITE, HYPERSTHENE 47 14. TERTIARY DIAGRAM: HORNBLENDE, AUG ITE, ZIRCON — 48 15. TERTIARY DIAGRAM: HORNBLENDE, OPAQUES, HYPERSTHENE 49 16. TERTIARY DIAGRAM: HYPERSTHENE, OPAQUES, GARNET 50 ACKNOWLEDGEMENTS ■ The author wishes to express his grateful appreciation to Professor R. S. Andrews who inspired the interest in this subject and provided immeasurable assistance in petrographic procedures and techniques during the progress of research. In addition, appreciation is expressed to T. E. Yancey of University of California for his recent personal communication on further findings in this area of study, to LT. K. J. Hermann, USN, for his previously-conducted textural analyses of the cores used, and to Naval Postgraduate School Educational Media Department for all services rendered . Further sincere appreciation is given to my wife for her critical reading of my drafts. I. INTRODUCTION A. OBJECTIVE Numerous studies have been conducted in order to define heavy- mineral assemblages in the coastal sands of California. These studies have been directed not only toward beach sand analysis but also toward continental shelf sands and sediments. However, few of these studies have been directed toward analyzing heavy mineral changes with depth in a core sample of the sediments with the purpose of defining possible changes in drainage patterns in a given area. Monterey Bay provides a region of interest where several drainage areas may be defined by heavy mineral assemblages. The sediments in the northern part of the bay are affected by the outflow of the Pajaro River, Soquel Creek, and San Lorenzo River (Fig. 1). The sediment deposition pattern is broken by Monterey Submarine Canyon. In the southern portion of the bay, sediments are predominantly influenced by the Salinas River outflow since there has been, at least in recent periods, only minor transport across the head of the canyon. The objective of this research has been to identify heavy minerals and their respective changes with depth in three cores taken in Monterey Bay aboard the M.V. OCEANEER during the period 28 February to 2 March 1970. The primary purpose of the sampling was to obtain long sediment cores in Monterey and Carmel Bays through the use of a 20-ft hydraulic powered vibratory corer designed by Ocean Science and Engineering, Inc., 8 Long Beach, California. There were several other cores (varying in length from 0.5 to 21 feet) taken on this cruise, but the ones analyzed for heavy minerals in the present study were considered most typically located to define the various sedimentary provinces of the bay. Textural analysis of all of the cores shown in Fig. 1 was performed by LT. K. J. Hermann, USN, as a research project at the Naval Post- graduate School, Monterey, California. B. GENERAL DESCRIPTION 1 . Geology and Hydrology Monterey Bay is located on the central California coast 70 miles south of San Francisco. Its northern half experiences long- shore drift from the north, but at the southern extremity a prominent headland exists. The bay is divided by the Monterey Submarine Canyon which heads nearshore in the center of the bay. Smooth depth contours characterize a great portion of the continental shelf area in the bay except where the Monterey Canyon appears . San Lorenzo River and Soquel Creek empty into the northern portion of the bay. Both of these streams have small drainage areas in the Santa Cruz Mountains of 140 square miles and 25 square miles, respectively (Hendricks, 1964). The Ben Lomond area of the Santa Cruz Mountains, which is the drainage area of the San Lorenzo River, contains granitic and metamorphic rocks as well as Miocene and Tertiary sedi- mentary formations (Fig. 2). 10 : % N scale in miles I 1 10 20 30 alluvium Terfiary undifferentiated ^ ^ Y/////s Middle 0 Miocene ^™, 121° 30' Cretaceous r * r ' /V "i volcanic rocks Franciscan fm and Franciscan type rocks granitic intrusive* and metamorphics "»—•—»- outlines of drainage basins '"""" San Andreas fault zone from Yancey (1968) FIGURE 2 GENERALIZED GEOLOGY OF THE MONTEREY BAY DRAINAGE BASINS 11 Pajaro River flows into the north-central portion of the bay north of Elkhorn Sough and drains a considerable area of the Santa Clara Valley. Pajaro River and its tributary, the San Benito River, carry sedi- ments derived from a number of geological formations. Franciscan rocks are exposed on the west side of the Santa Clara drainage basin (Yancey, 1968) and exposures of granitic rocks are extensive in this area. Granitic or Franciscan rock types everywhere form the basement rock of the drainage area of Monterey Bay, but over most of the area these types are deeply covered by Cretaceous and Tertiary sedimentary rocks. Elkhorn Slough, a salt-water embayment, presently provides little sediment to the bay. Shepard and Emery (1941) suggest that the Salinas River may have emptied through Elkhorn Slough in the recent past. Dorman (1968) noted that prior to 1906, navigation charts showed the Salinas River emptying through Elkhorn Slough. Starke and Howard (1968) reported the presence of a deep buried canyon in the area of Elkhorn Slough extending inland from and aligned with the Monterey Submarine Canyon. Salinas River, south of Elkhorn Slough, drains an extensive area to the southeast of Monterey Bay. Included in this area are portions of the Gabilan Range, Santa Lucia Range and Sierra de Salinas. The Gabilan Range and most of the Santa Lucia Mountains are formed of quartz diorites, quartz monzonites, and metasediments . The Salinian Block which composes the majority of the basement rock is of the same rock assemblage. Only a very small area of Franciscan-like rocks is 12 included in the Salinas Valley drainage basin, and at a great distance from the river mouth (Yancey, 1968). Galehouse (1967) investigated provenance of the sedimentary Paso Robles Formation which is located in the upper reaches of the Salinas River drainage area. He reported the heavy mineral compositions of this formation to be high in sphene, hornblende, garnet, epidote, apatite and zircon. This formation is also found outcropping east of the City of Monterey (California Dept. of Water Resources, 1970). 2. Sediment Transport Mechanisms Heavy mineral assemblages are influenced by sediment transport mechanisms in the bay as well as by geological considerations in the drainage areas tributary to the bay. Littoral drift, offshore drift and other mechanisms tend to redistribute sediments. In the southern portion of the bay, Dorman (1968) classified the sediments into five district subregions on the basis of depositional environment. They were: (a) the peninsular region, characterized by locally derived sediments and very little active transportation or deposition, (b) the sandy east coast region, characterized by predomi- nantly southward weak longshore drift transport with heavy wave action and much near shore sediment diffusion, (c) the essentially non- depositional region in the southern end of the bay, with slow water movements and anomalous patterns of bottom type, (d) the confluence region or nodal area, characterized by the convergence of long-shore transport from both north and south and by some offshore movement, and 13 (e) the offshore region with little active sediment movement. These areas are shown schematically in Fig. 3. Dorman further indicated seasonal variation in the eastern longshore drift. Yancey (1968) concluded that there is an eastward flow of sand into the inner portions of Monterey Bay along the north and south margins of the bay as littoral drift, with a section in the northeast sector having a southward drift. Although the Monterey Canyon cuts off a good deal of sediment transport from north to south, some sand can pass the head of the canyon without being lost from the nearshore sand budget. C. PREVIOUS INVESTIGATIONS Past investigations were conducted of the submarine geology of Monterey Bay by Galliher (1932) , during which a general study was made of the nature of the sediments of the continental shelf of Monterey Bay. Hutton (195 9) conducted a very extensive study of the heavy mineral assemblages in the beach sands from Halfmoon Bay to the north to Pacific Grove, located at the south end of Monterey Bay. He directed his study toward the identification rather than the provenance of heavy minerals . Wilde (1965) studied the recent sediments of the Monterey deep-sea fan. He concluded that the sands on the fan were from local sources near the head of the Monterey Submarine Canyon and that the finer sedi- ments were derived locally and from the numerous valley drainages into San Francisco Bay via longshore drift. In addition, he concluded from 14 15 seismic profiles as well as sedimentary analyses, that formation of the Monterey fan began in pre-Pleistocene to post-Mesozoic time and probably in the Oligocene or Miocene. Sayles (1966) undertook a study of heavy minerals in beach sands of Monterey Bay to determine the littoral transport patterns and their relation to present conditions. This was accomplished by grouping into heavy mineral suites those heavy minerals of similar composition/ thereby delineating sedimentary provinces.. In general he showed that Monterey Bay is separated into two heavy mineral suites, hornblende- augite-hypersthene and hornblende-garnet, and that these distinct suites are separated by the Monterey Submarine Canyon. Sayles further con- cluded that no long-term net littoral transport exists along most of the Monterey Bay beaches and that the pattern observed today has carried over from the last period of lowered sea level. Yancey (1968) studied extensively the sediments of Monterey Bay and divided them into five heavy mineral provinces. Table I lists the heavy mineral composition near the mouths of the streams flowing into Monterey Bay. Other samples further up the streams were analyzed by Yancey but are not included in Table I. Two of the provinces were traceable to the Salinas and Pajaro Rivers, while the other three were not traceable to any single source. He noted that the Salinas River sedi- ments had a high garnet content while the minerals glaucophane and lawsonite distinguished the Pajaro River sediments. The San Lorenzo River sediment has a mineral composition that is high in garnet but low 16 Table I River Bed Heavy Mineral Counts* Mineral Sample Name and No. San Lorenzo Soquel River, Creek, 1915 1929 51 30 1 6 5 7 25 28 9 23 Green Hornblende Brown Hornblende Oxyhornblende Augite Hypersthene Epidote 2 Garnet 4 2 Sphene 3 2 Zircon Apatite Clinozoisite 1 Glaucophane 2 4 Lawsonite 1 *from Yancey (1968) Pajaro Salinas River, River, 1949 1972 41 56 13 4 1 27 8 15 3 4 1 9 3 5 3 1 17 in augite. This composition does not extend far beyond the mouth of the river. He delineated sediment types in the bay which occur in three widespread bands that are aligned subparallel to the submarine contours. The sediments vary in age from a relict deposit of Pleistocene age in the outermost band at the edge of the continental shelf, to a middle band of Holocene age in the middle continental shelf, and thence to an inner band along the shoreline part of which may be mixed in age and part of modern origin off the mouths of the Salinas and Pajaro Rivers. Yancey (1971, personal communication) stated that the mineralogic trends near the mouth of the Salinas River that were outlined in his 1968 paper con- tinue to the south in parallel alignment. He also stated that the beach samples from the Monterey Harbor area suggest a distinct mineral suite that is different from the Salinas River mineral suite. 18 II. PROCEDURES A. TEXT URAL ANALYSIS From the previously-conducted textural analyses performed by Hermann (unpublished data), a sample was taken of each sediment type or at each textural change in the core. Where no changes were readily apparent, samples were taken at least every meter down the core. These samples were desalinated and disaggregated. The coarse fraction was separated into 0.5 4> intervals and weighed. Statistical parameters were computed for each sample and these appear in Tables II, III, and IV. Lithologic logs and photographs of the cores analyzed for heavy minerals appear in Appendix A. The sand-silt-clay relationships for each core are shown in Fig. 4,5, and 6. B. HEAVY MINERAL ANALYSIS From the group of aforementioned cores, Stations 10, 14, and 18 were selected for heavy mineral analysis, and samples to be analyzed were taken from the top, middle and bottom of these cores. The samples were split where necessary, prior to heavy mineral separation, in order to insure that the total weight of the sample was less than 2g for ease of handling. The heavy minerals were separated out of the fine and very fine sand sizes (2 .5 to 4 . 0 ) in 0.5 4> intervals using bromoform (specific gravity = 2.85) (Table V). The samples were then mounted in Lakeside 70 on a glass slide for analysis with a petrographic microscope. 19 * c o u CO CD Q (0 •—I o 55 c fO CO T3 C (0 CO C rd CO C (0 CO T3 C fO CO CO CO CO CO XI c CO T3 c a CO CO r-. CO CO CD (O tD CO Ll") in CM CD -sT CO LO <— « CO CM CO CO >— I t— I c fO CO S5 CM CD CM CM r>* 00 CD cd in t** in in r>. r^ CO fO H CO CO is <0 C < CD u O U fO CD N 3 o (0 ■M c rd CO * co f-i co O £ * co co CD C £ CD J* CO * a o i-< +-» (0 1-1 > Q) Q * c to CD r*. in co co cd lo co r>» CM LO CD 00 CM ^ C^ CO O >— I O O r~> CM co ^r CO CM CM CO CO i-H CD CD o r^ in o o CO CO 1— 1 CD CD t^. m CD CD r*. m l-H o i-H o cd co oo in tv. 00 O "^ O CD CO CD tv. ^ CM r>» CD CO CO CO CO S-i CD CD C_) £ CO u (0 D. r-. 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CO a o CO * * 22 PERCENT 4 0 6 0 SAND ■ ■ ■ ■ ■ '■ SILT CLAY FIGURE 4 SAND/SILT/CLAY COMPOSITION OF CORE 10 23 2.0 PERCENT 4.0 6C SAND SILT C LAY INFERRED FIGURE 5 SAND/SILT/CLAY COMPOSITION OF CORE 14 24 SAND : SILT CLAY FIGURE 6 SAND/SILT/CLAY COMPOSITION OF CORE 18 25 Table V Heavy Mineral Content Core Sample Sample Depth (cm) 10A* 10B IOC* 10D 10E 10F 10G* 14B* 14C 14D- 14E 14G* 100 200 300 400 500 600 620 0 100 150 200 340 Phi Size 2.5-3.0 3.0-3.5 3.5-4.0 2.5-3.0 3.0-3.5 3.5-4.0 2.5-3.0 3.0-3.5 3.5-4.0 2.5-3.0 3.0-3.5 3.5-4.0 2.5-3.0 3.0-3.5 3.5-4.0 2.5-3.0 3.0-3.5 3.5-4.0 2.5-3.0 3.0-3.5 3.5-4.0 2.5-3.0 3.0-3.5 2.5-3.0 3.0-3.5 2.5-3.0 3.0-3.5 2.5-3.0 3.0-3.5 3.5-4.0 2.5-3.0 3.0-3.5 3.5-4.0 Percentage Light Heavy 94.88 5.12 95.86 4.15 97.12 2.88 92.74 7.26 98.60 1.40 98.00 2.00 89.00 11.00 98.10 1.90 98.51 1.49 NO DATA 98.16 1.84 98.42 1.58 90.78 9.22 96.77 3.23 98.21 1.79 91.44 8.56 98.41 1.59 98.50 1.50 89.85 10.15 97.49 2.51 98.19 1.81 61.23 38.77 79.39 20.61 43.45 56.55 74.85 25.15 91.45 8.55 74.47 25.53 88.15 11.85 86.57 13.43 64.17 35.83 95.13 4.87 96.74 3.26 95.10 4.90 26 Table V Heavy Mineral Content (cont.) Core Sample Sample Depth Phi Size Perce ;ntage (cm) Light Heavy 14H 400 2.5-3.0 96.94 3.06 3.0-3.5 97.34 2.66 3.5-4.0 91.32 8.68 141 500 2.5-3.0 96.83 3.17 3.0-3.5 96.38 3.62 3.5-4.0 92.41 7.59 14 J* 628 2.5-3.0 97.72 2.28 3.0-3.5 97.69 2.31 3.5-4.0 93.51 6.49 18 A* 0 2.5-3.0 85.64 14.36 3.0-3.5 88.27 11.73 3.5-4.0 73.18 26.82 18B 50 2.5-3.0 89.35 10.65 3.0-3.5 94.37 5.63 3.5-4.0 93.12 6.88 18C 100 2.5-3.0 92.27 7.73 3.0-3.5 89.46 10.54 3.5-4.0 89.55 10.45 18D* 210 2.5-3.0 96.82 3.18 3.0-3.5 88.81 11.19 3.5-4.0 78.90 21.10 18E 300 2.5-3.0 97.09 2.91 3.0-3.5 91.81 8.19 3.5-4.0 82.97 17.03 18F 335 2.5-3.0 95.50 4.50 3.0-3.5 91.70 8.30 3.5-4.0 84.78 15.22 18G 400 2.5-3.0 97.42 2.58 3.0-3.5 87.72 12.28 3.5-4.0 81.73 18.27 18H* 550 2.5-3.0 96.57 3.43 3.0-3.5 85.59 14.41 3.5-4.0 86.83 13.17 ♦Samples analyzed petrographically, 27 One hundred nonopaque, nonmicaeous and noncomposite heavy mineral grains of each sample fraction were counted by line count method (Table VI). Mineral grains identified in a scan of the slide which were not among the 100 grains counted were listed as trace minerals. Mica, opaque and composite grains were counted and tabulated separately (Table VII) . A recount was made of all the samples at a later time to assure accuracy of the initial counts. An attempt was made, by use of tertiary diagrams, to determine whether distinctive relationships between mineral amounts could be recognized for any of the cores. No distinctive mineral suites were identified. The tertiary diagrams are shown in Fig. 13, 14, 15, and 16 in Appendix B. Mineral identification was accomplished by optical means using a petrographic microscope. Color, pleochroism, crystal habit, cleavage traces, extinction angle, relief, birefringence and interference figure were all utilized in order to identify mineral grains. In all cases, the counts tabulated represent the 3.5 to 4.0 size sample. The 2 . 5 to 3 . 0 and 3.0 to 3.5 4> samples were used for initial identification of common heavy minerals in a slide, for ease in identifying the minerals in the 3.5 to 4 . 0 sample . Kerr (1959) presents a useful series of keys for identification of heavy minerals, and Hutton (1959) considered local variation in charac- teristics of some heavy minerals examined in this study area. 28 Table VI Heavy Mineral Percentages Mineral Sample No. (Depth, cm) 10A IOC 10G (100) (300) (620) Andalusite Apatite Augite Clinozoisite Epidote Garnet Glaucophane 30 Brown Hornblende Hypersthene Kyanite Rutile Sillimanite Sphene 15 Zircon 25 24 TR Green Hornblende 41 36 38 21 15 TR TR 14B 14G 14J (0) (340) (628) 23 13 13 TR 39 43 14 13 38 10 18A (0) 12 13 18D 18H (210) (550) 18 17 30 26 Note: TR (trace) is less than 1.0% of heavy mineral fraction. 40 TR 1 TR 11 21 40 TR 29 Table VII Mineral Opaques Composites Biotite Other Micas Table VI Total Count Counts of the Constituents in the Heavy Mineral Fraction Sample No. (Depth, cm) 10A IOC 10G (100) (300) (620) 26 13 23 16 29 45 21 20 100 100 100 223 153 143 14B 14G 14J (0) (340) (628) 22 23 21 10 28 24 13 100 100 100 183 159 133 18A 18D 18H (0) (210) (550) 16 24 17 8 25 68 19 17 25 23 11 100 100 100 216 186 157 30 III. TEXTURAL AND HEAVY MINERAL ANALYSES A. MINERAL DESCRIPTION 1 . Major Constituents Hornblende, augite, hypersthene and garnet represent the major constituents of the heavy mineral fraction. Hornblende was found extensively in all the samples examined. Green hornblende predomi- nated over the brown variety. Both varieties were observed to exist as irregularly fractured grains, the brown being slightly more rounded. The green variety showed well-defined striations and varied in color from medium to dark forest green. Pleochroism was very marked in the green variety. Coloring in the brown variety varied from light yellow-brown to deep red -brown. Augite was well distributed in all the cores. The grains were colorless to pale green and usually clear and free of inclusions. Nearly all the grains examined had numerous needle-like or spear- shaped endings indicating solution alteration. Hypersthene was identified in all the surface samples but varied greatly in quantity with depth. In all cases, the distinctive pleochroism from rose-pink to pale green was evident and was the major identifying characteristic. The grains varied in shape from a columnar habit to a semirounded shape, with numerous grains showing spear- shaped endings as in the case of augite. A distinctive change of 31 habit from columnar with slight end alteration to semirounded habit was noted with increasing depth in all cores. Garnet was found in moderate amounts, which generally increased from the Santa Cruz core to the Monterey core. The grains were identified by their distinctive high relief and semi-conchoidal fracture surfaces. Two pink garnets were found in sample 18A, one in 14G and a trace in sample 14J. The grains were predominantly sub- angular to sub-rounded with high sphericity. Inclusions were present in most of the grains. 2 . Minor Constituents Small amounts of apatite were identified in all samples. The grains were colorless, clear of inclusions and euhedral in habit. Sphene was found in varying quantities in the cores and was in all cases yellow-brown in color with slight pleochroism. A few grains showed incomplete extinction, and a good interference figure was ob- tained in only one case. The main identifying characteristics were the high-order yellowish-white interference color and the high relief. Epidote and clinozoisite appeared in all samples. Epidote grains were both light and dark green in color with only slight pleo- chroism. The surface of the grains was very granular. The clino- zoisite grains were colorless and exhibited a very low extinction angle. Zircon, although found in small quantities, was distinc- tively characterized by cigar-shaped smooth grains with very high relief and common inclusions. Anomalous biaxial interference figures were obtained in several cases. 32 Glaucophane was distinctively pale blue in color with pleochroism to violet. These grains exhibited the typical amphibole habit with cleavage traces prominant. Rutile was distinguished by an adamantine luster under reflected light and very deep red-brown coloration which almost quali- fied the grains as opaque constituents of the sample. B. QUANTITATIVE RESULTS Heavy mineral contents tend to decrease with depth in all three cores (Table V). Hornblende, augite, hypersthene and garnet accounted for 75% cf all the samples. Hornblende alone accounted for approximately 30 to 50% in all cases, except in samples 18D and 18H. Augite maintained a relatively constant percentage except in sample 18H. A general in- creasing trend in garnet was noted toward the south of Monterey Bay with the exception of 18H. Hypersthene remained substantially constant in all samples except for notably lower percentages in 14G and 14J and an extremely high anomalous value in 18H. Cores 14 and 18 were garnet rich, while cores 10 and 18 were hypersthene rich. Glaucophane was found in all cores below the surface sample. 1. Santa Cruz Area Core The distribution of heavy minerals in Core 10 is substantially uniform with depth. In general, the distribution compared closely with that found by Yancey (1968) in his Province 4, except for slightly 33 higher augite percentages. Glaucophane was found at the bottom of this core in small amounts. Biotite and other micas as well as opaques generally decreased with depth in this core. Core 10 was visually uniform in composition, a poorly- sorted sand or silty sand, except for the surface sample which was moderately-sorted sand. 2 . Moss Landing Area Core The surface sample of Core 14 differed slightly in heavy mineral composition from the deeper samples of that core. Augite and hypersthene percentages were notably greater at the surface, while the garnet percentage was less at the surface. Small amounts of glauco- phane were noted. This core was somewhat richer in garnet in compari- son with the other cores. Biotite and other micas as well as opaques decreased with depth. Core 14, composed of moderately- to poorly-sorted sand, varied greatly in appearance with depth, as can be observed in the photograph and field description (Appendix A) . 3 . Monterey Area Core The percentage of heavy minerals in the 3.5 to 4.0 range was notably higher in this core than the others analyzed. The total amount of hornblende decreased with depth. A large difference in the relative amounts of garnet, hypersthene and augite was dramatically evident in the bottom sample of this core. Augite and hypersthene together composed 80% of this bottom sample. 34 Garnet decreased from a constant percentage near the surface to a trace in the bottom sample. Hypersthene showed an anomalously high per- centage in sample 18H. Glaucophane occurred in small amounts in this core. Mica decreased in percentage with depth. Sample 18H was noted to be anomalously poorly-sorted (Table IV) relative to the rest of the overlying sediment in the core, which varied from well-sorted to moderately-sorted sand. 35 IV. DISCUSSION The heavy mineral distribution with depth in the various samples could not be classified into any distinctive mineral suites. The samples containing glaucophane were in part derived from the Franciscan forma- tions of the Pajaro River drainage area. The Salinas River drainage area, on the other hand, contains small exposures of this formation so that the amount of glaucophane transported to the bay is probably not signi- ficant due not only to the small size of the Franciscan formation areas in proportion to the whole Salinas River basin but also to the extreme distance of these formations from the bay. Sediment samples derived from the Salinas River contain minerals common to all drainage areas (Table I) and, if mixed with sediments from another source, the relative amounts of garnet and brown hornblende needed to distinguish the Salinas source would be reduced. The distribution in the Santa Cruz area core was not indicative of any one source area but most probably was a locally derived mixture with some augite enrichment by longshore drift from a northern province found to be augite-rich by Yancey (1968). The presence of glaucophane at depth in this core may indicate the influence of the Pajaro River source area at a prior time, although Yancey found small amounts of glaucophane in almost every sample in the northern part of the bay. The Moss Landing area core showed influences of both the Pajaro and Salinas Rivers. The small amounts of glaucophane noted were 36 indicative of the Pajaro Paver outflow. Relatively larger amounts of garnet with depth may be indicative of the period of influence of the Salinas River flowing out at Elkhorn Slough. The decrease of augite slightly with depth again may also be indicative of the prior influence of the Salinas River, which is low in augite relative to the Pajaro River (Table I) . The varying compositional textures indicate multiple and dynamic influences on the deposition in this area. Core 18 is located in an area influenced geologically by both the Salinas River source and the local granitic sources on the tip of the Monterey Peninsula. The influence of the Salinas River sediments can be distinguished in the relatively high garnet content of the upper two samples. The high amount of hypersthene indicated a source of igneous or metamorphic rocks. In this area the Santa Lucia granodiorite , which outcrops along much of the Monterey Peninsula, could have contributed to the quantity of hypersthene but probably not in this large a percent- age. A large source of metamorphics exists in the nearcoast portion of the Salinas River drainage basin. Considering both the depth of the sample in the core and the water depth (146 ft), a possible source of the high pyroxene content (augite and hypersthene) in the bottom sample could be a relict beach deposit from a period of lower sea level. Glau- cophane in small amounts in this southern core suggests transport of the Pajaro River sediments to this area. 37 V. FUTURE WORK This study, of necessity, has been limited in scope and has not covered the entire spectrum of compositional changes in heavy mineral- ogy with depth in the cores examined. More complete studies of these cores, correlated with similar studies of other cores taken in this group would yield not only more knowledge of the heavy mineralogy of the sediments but would lead to a better understanding of the sedimentary processes in Monterey Bay, both now and in the recent past. In order to further delineate the heavy mineral provinces and the origin of sediment suites in the southern portion of the bay, a large number of core samples should be obtained and analyzed. 38 APPENDIX A FIELD DESCRIPTIONS AND PHOTOGRAPHS OF CORES 1. Fig. 7 Field Description of Core 10 2. Fig. 8 Photograph of Core 10 3. Fig. 9 Field Description of Core 14 4. Fig. 10 Photograph of Core 14 5. Fig. 11 Field Description of Core 18 6. Fig. 12 Photograph of Core 18 39 SAMPLE FIELD DESCRIPTION OF CORE NO. BREAK M E T E R S BREAK Greenish fine sand - IOC --> BREAK BOTTOM - 10A 10B - 10D — 10E k 10F 10G CORE NO.: 10 LATITUDE: 36° 53.97' LONGITUDE: 121° 59.49' WATER DEPTH: 118 ft CORER TYPE: VIBRO CORER TOTAL LENGTH: 17 ft 6 in REMARKS: Bottomed in sand. Penetration of 22 ft. Uniform core of greenish fine sand. Core taken March 1 , 1970 Core cut May 5, 1970 after Andrews and Hermann (unpublished data) FIGURE 7 FIELD DESCRIPTION OF CORE 10 40 • J FIGURE 8 PHOTOGRAPH OF CORE 10 41 SAMPLE NO. FIELD DESCRIPTION OF CORE 0 i r- 14A, 14B M E Buff pebbly coarse sand Very coarse sand" Medium sand 14C BREAK Very coarse sand Medium sand with pebbles Very coarse sand Medium sand Pebbly coarse sand '^Basjal conglomerate" _ 14F Oxidized greenish tine sand Black fine sand - 14G Black mud Black fine sand BREAK BREAK BOTTOM - 14E - 14H 141 14J CORE NO.: 14 LATITUDE: 36° 45.63' LONGITUDE: 121° 48.72 - 14D WATER DEPTH: 106 ft CORER TYPE: VIBRO CORER TOTAL LENGTH: 21 ft 2 in REMARKS: Bottomed in fine sand. Penetration of corer undetermined . Sample 14A is large shale rock. First 3 meters appear to be beach sand. Core taken March 2, 1970 Core cut May 5, 1970 after Andrews and Hermann (unpublished data) FIGURE 9 FIELD DESCRIPTION OF CORE 14 42 / FIGURE 10 PHOTOGRAPH OF CORE 14 43 SAMPLE NO. FIELD DESCRIPTION OF CORE -18A 0 - Buff medium sand CORE NO.: 18 """ r] Green-black medium sand -18C LATITUDE: 36° 38.12' 1 - Dark-buff medium sand LONGITUDE: 121° 51.75' (grading down to grey WATER DEPTH: 128 ft fine sand) CORERTYPE: VIBRO CORER r* BREAK - 18D TOTAL LENGTH: 18 ft 1 in 2 ■ M Grey-brown shelly REMARKS: Bottomed in E very fine sand medium sand. Penetra- T tion to maximum extent. E 3 — -18E Core taken March 2 , R S Rounded granules _ - BREAK -18F 1970 Core cut May 21, 1970 i i — - 18G after Andrews Reddish-brown fine and Hermann (unpublished data) sand I BOTTQ1 18H FIGURE 11 FIELD DESCRIPTION OF CORE 18 44 FIGURE 12 PHOTOGRAPH OF CORE 18 45 APPENDIX B TERTIARY DIAGRAMS 1. Fig. 13 Tertiary Diagram: Hornblende/Augite/Hypersthene 2. Fig. 14 Tertiary Diagram: Hornblende/Augite/Zircon 3. Fig. 15 Tertiary Diagram: Hornblende/Opaques/Hypersthene 4. Fig. 16 Tertiary Diagram: Hypersthene/Opaques/Garnet 46 AUG IT E HORNBLENDE 25 75 50 50 75 25 HYPERSTHENE FIGURE 13 TERTIARY DIAGRAM HORNBLENDE/A UGITE/HYPERSTHENE 47 AUGITE HORNBLENDE 25 75 50 50 75 25 ZIRCON FIGURE 14 TERTIARY DIAGRAM HORNBLENDE/AUGITE/ZIRCON 48 OPAQUES HORNBLENDE 25 75 50 50 75 25 HYPERSTHENE FIGURE 15 TERTIARY DIAGRAM HORNBLENDE/OPAQUES/HYPERSTHENE 49 OPAQUES HYPERSTHENE 25 75 50 50 75 25 GARNET FIGURE 16 TERTIARY DIAGRAM HYPERSTHENE/OPAQUES/GARNET 50 REFERENCES California Department of Water Resources. 1970. Sea -water intrusion, Lower Salinas Valley. Progress Rpt. 1968-1969. 28 p. Dorman, C. E. 1968. The southern Monterey Bay littoral cell: A pre- liminary sediment budget study. M.S. Thesis, Naval Postgraduate School, Monterey, Calif. 234 p. Folk, R. L. and W. C. Ward. 1957. Brazos River Bar: A study in the significance of grain size parameters. J. Sediment. Petrol. 27: 3-26. Galehouse, J. S. 1967. Provenance and paleocurrents of the Paso Robles Formation, California. Geol. Soc . Amer. Bull. 78(8): 951-978. Galliher, E. W. 1932. Sediments of Monterey Bay, California. Calif. State Min. Bur. , 28th Annual Rep. State Mineralogist: 42-79. Hendricks, E. L. (Ed.) 1964. Compilation of records of surface waters of the United States, October 1950 to September 1960, Part II, Pacific slope basins in California. U. S. Geol. Survey Water- Supply Paper 1735. 715 p. Hutton, C. O. 1959. Mineralogy of beach sands between Halfmoon and Monterey Bays , California. Calif. Div. Mines Spec. Rep. 59. 32 p. Kerr, P. F. 1959. Optical mineralogy. McGraw-Hill Book Co. , Inc. New York. 442 p. Sayles, F. L. 1966. A reconnaissance heavy mineral study of Monterey Bay beach sediment. Univ. Calif. Hydraulics Lab. Tech. Rep. HEL-2-16. 20 p. Shepard, F. P. 1954. Nomenclature based on sand-silt-clay ratios . J. Sediment. Petrol. 24_: 151-158. Shepard, F. P. and K. O. Emery. 1941. Submarine topography off the California coast: Canyons and tectonic interpretation. Geol. Soc. Amer. Spec. Paper 31. 171 p. 51 Starke, G. W. and A. D. Howard. 1968. Polygenetic origin of Monterey Submarine Canyon. Geol. Soc. Amer. Bull. 79J7): 813-826. Wilde, P. 1965. Recent sediments of the Monterey deep-sea fan. Univ. Calif. Hydraulics Lab. Tech. Rep. HEL-2-13. 153 p. Yancey, T. E. 1968. Recent sediments of Monterey Bay, California. Univ. Calif. Hydraulics Lab. Tech. Rep. HEL-2-18. 145 p. 52 INITIAL DISTRIBUTION LIST No. Copies 1. Defense Documentation Center 2 Cameron Station Alexandria, Virginia 22314 2. Library, Code 0212 2 Naval Postgraduate School Monterey, California 93940 3. Asst. Professor R. S. Andrews, Code 58Ad 5 Department of Oceanography Naval Postgraduate School Monterey, California 93 940 4. LCDR William Patterson Hunter, USN 1 1309 Baltic Avenue Virginia Beach, Virginia 23451 5. Department of Oceanography, Code 58 3 Naval Postgraduate School Monterey, California 93940 6. Professor W. C. Thompson, Code 58Th 1 Department of Oceanography Naval Postgraduate School Monterey, California 93940 7. Mr. Thomas E. Yancey 1 Department of Paleontology University of California Berkeley, California 94720 8. LT Kermyn J. Hermann, USN 1 Key West Test and Evaluation Detachment Operational Test and Evaluation Force Key West, Florida 33040 53 Security Classification DOCUMENT CONTROL DATA -R&D ,Security classification o( title, body of abstract and indexing annotation must be entered when the overall report is classitied) I originating activity (Corporate author) Naval Postgraduate School Monterey, California 93940 2». REPORT SECURITY CLASSIFICATION Unclassified 2b. GROUP 3 REPO R T TITLE Heavy Mineral Analysis of Selected Monterey Bay Cores 4 DESCRIPTIVE NOTES (Type of report and.inclusive dates) Master's Thesis; March 1971 9- iu TMORIS) (First name, middle initial, last name) William Patterson Hunter 6. REPOR T DATE March 1971 la. TOTAL NO. OF PAGES 55 76. NO. OF REFS 14 •a. CONTRACT OR GRANT NO. 6. PROJEC T NO. 9a. ORIGINATOR'S REPORT NUMBERI3) 96. OTHER REPORT NOISI (Any other numbers that may be aaslgned this report) 10. DISTRIBUTION STATEMENT Approved for public release; distribution unlimited. II. SUPPLEMENTARY NOTES 12. SPONSORING MILI TAR Y ACTIVITY Naval Postgraduate School Monterey, California 93940 13. ABSTRACT This study was conducted to identify heavy minerals and their changes with depth in three cores taken from different locations in Monterey Bay, California. Monterey Bay provides an area where several different sources influence the sedi- ment deposition. Minerals indicative of the geological formations in the drainage areas of the Pajaro and Salinas Rivers were found in distinctive distribution throughout these cores. Glaucophane, indicative of the Franciscan Formation, was found near the bottom of all cores. The larger percentages of augite found in the core at Santa Cruz were probably derived from the north due to longshore drift. High percentages of garnet and low percentages of hypersthene with depth in the Moss Landing Core reflect the influence of the Salinas River. DD,f.°o"v-..1473 IPAGE " S/N 01 01 -807-681 1 54 Security Classification A-31408 Security Classification KEY WORDS Geological oceanography Heavy minerals Monterey Bay sediments Sediment cores Sediment size analysis Petrographic mineral analysis DD .'•" .1473 S/N 0101-807-6321 BACK) 55 Security Classification »- 3 I 409 28 Jan. <82 INTERLIBRArTToAiT U.S. Geological $Urv Menlo Park, CA 126472 H952 Hunter c.l Heavy mineral analy- sis of selected Mon- terey Bay cores. 28 Jan. '82 INTERLIBRARY LOAN +36472 Hunter Heavy mineral analy- sis of selected Mon- terey Bay cores. thesH952 Heavy mineral analysis of selected Monte 3 2768 002 13278 9 DUDLEY KNOX LIBRARY