| EB Me Mm ro HO oe Se Res. Qe TY, S/T ADL. T.M. 40 Pleistocene-Holocene Sediments Interpreted by Seismic Refraction | and Wash-Bore Sampling, Plum TECHNICAL MEMORANDUM NO. 40 JULY 1973 U.S. ARMY, CORPS OF ENGINEERS COASTAL ENGINEERING RESEARCH CENTER Approved for public release; distribution unlimited. or Reprint or republication of any of this material shall give appropriate credit to the U.S. Army Coastal Engineering Research Center. Limited free distribution within the United States of single copies of this publication has been made by this Center. Additional copies are available from: National Technical Information Service ATTN: Operations Division 5285 Port Royal Road Springfield, Virginia 22151 At the time of publication, prices were $3.00 for hard copies and $0.95 for microfiche. Contents of this report are not to be used for advertis- ing, publication or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. The findings of this report are not to be construed as an official Department of the Army position unless so desig- nated by other authorized documents. 0 0301 0089955 5 NUNN N LU UU Pleistocene-Holocene Sediments Interpreted by Seismic Refraction and Wash-Bore Sampling, Plum Island-Castle Neck, Massachusetts by Eugene G. Rhodes TECHNICAL MEMORANDUM NO. 40 JULY 1973 U.S. ARMY, CORPS OF ENGINEERS COASTAL ENGINEERING RESEARCH CENTER Approved for public release; distribution unlimited. ABSTRACT The wash-bore method of soil sampling, which can be employed from both floating and land equipment, was found to be an excellent technique for subsurface study. Seismic refraction is a valuable tool in the coastal environment but phenomena to be considered when interpreting records include a) "the blind zone,'' b) the non-zero time intercept, c) time gaps in the time-distance plots over buried peat, and d) vari- able thicknesses of dry sand layers. The seismic method successfully located Pleistocene and bedrock topography. Dry sand, water-saturated sandy sediments, glacial till, and bedrock provide well-defined seismic contrasts. Glaciomarine clay does not show a seismic contrast with respect to sandy, water-saturated sediments. Topography exposed during lower sea level 10,000 to 11,000 B.P. (Kaye and Barghoorn, 1964) has a dominant influence on modern coastal geology. Barrier-island features became anchored on drumlins and other Pleistocene features as the relative sea level rose. Thick sequences of sediments, including clam-flat facies, channel deposits, and point-bar deposits, accumulated in the estuaries behind these barrier beaches. Major channels of the estuaries migrated landward with the sea-level rise, a hypothesis in agreement with McCormick (1968). A bedrock high beneath the centerline of the barrier beaches on all seismic profiles is perpendicular to barrier elongation. Bedrock topography is extremely irregular and drops over 150 feet beneath the Parker and Essex estuaries. Essex Bay appears to move in deep channels incised in underlying bedrock; two mid-estuarine sand bodies, Essex flood-tidal delta and Middle Ground, appear to have rather stable sedimentary deposits. Although no radiometric dates were determined for samples taken in this study, the sedimentary stratigraphy fits the time frame of McIntire and Morgan (1963) and Kaye and Barghoorn (1964). FOREWORD CERC is publishing this report because of its interest and value to coastal engineers. This report was prepared by Eugene G. Rhodes under Contract No. DACW- 72-70-C-0029 with CERC. It is an edited version of a thesis submitted in partial fulfillment for a M.S. Degree in Geology at the University of Massachusetts. Special appreciation is extended to Miles 0. Hayes, who served as the immediate supervisor of the study from inception to completion. Profes- sors Joseph H. Hartshorn and Randolph W. Bromery provided a constructive, critical review of the geological and geophysical problem. The wash- boring phase of the study could never have been accomplished without the equipment and instruction from the Civil Engineering Department, University of Massachusetts. Professor Karl Hendrikson contributed to the project through the training and advice to the author and the field crew. The author is especially grateful to George E. Butler, Jr. and Richard K. Callahan. In addition, John F. Kick, Stewart C. Farrell and Jon C. Boothroyd gave considerable effort to the field study. Edward S. Moses, manager of the Parker River Wildlife Refuge, obtained approval for field operations on Plum Island. Robert Hebb, Department of Natural Resources, also offered his cooperation for the author's use of the Plum Island State Park. The Trustees of Reserva- tions, in particular Garret Van Wart and Gordon Abbot, Jr., opened the Richard T. Crane, Jr. Memorial Reservation, to both seismic and drill- hole phases of the study. Additional gratitude is expressed to the employees of the Parker River Wildlife Refuge and the Crane Reservation for their help during the project. Vincent J. Murphy of Weston Geophysical, Inc. and Curtis R. Tuttle of the United States Geological Survey, aided greatly in the reduction and interpretation of seismic data. William G. McIntire and James M. Coleman of the Coastal Studies Institute, Louisiana State University helped with geological interpretations. At the time of publication, Colonel James L. Trayers was Director of CERC; Thorndike Saville, Jr. was Technical Director. NOTE: Comments on this publication are invited. This report is published under authority of Public Law 166, 79th Congress, approved 31 July 1945, as supplemented by Public Law 172, 88th Congress, approved 7 November 1963. CONTENTS Io INTRODUGTION “Soest cies) ces IG FEELD) TECHNIQUES 2%) 193%. 3 ike Drill-Hole Study e e e e e e e 2. Seismic Refraction Study... III. SEISMIC PROFILE INTERPRETATION . . » Formulas and Nomograms ... .~ o 6Senlsmble WeiloeiislSS 6 6 6 6 0 6 1 2 3. Graphic Interpretation... . 4. Problems of Interpretation .. Vis DRILL-HOLE INTERPRETATION. . .. © iL 2 Soe LnduratedsCillayarcmel telienollcl elle a Weathered=Zone) « « «© « .«: <<: hele Se Billack. Peat < « << % «@ % «6's 6. Estuarine Sediments. . ... - V. CASE HISTORIES FROM PLUM ISLAND. . Wile DEVELOPMENT OF A BARRIER ISLAND. . Wills (CONG RUSTONS G96 5 665 6 G06 os 6 LITERATURE |GRTED see 6) ole) ele Generalized Stratigraphy .... . Glacial Till and Glaciomarine Clay APPENDIX - SUMMARY LOGS OF DRILL HOLES TABLE Listing of Bore Holes Containing Marine Clay FIGURES 1. Location Map for Study Area. ...... 2. Location Map for Drill Holes and Seismic Lines 3. Drill Rig on Barge Platform. . .......-s 44 18. 19. 20. Oho De DG 24. BDC FIGURES (Continued) Drilling Crew Disconnecting Pull Piece ...... Cathead) Acting asa) Ropes Clutch yoy scien te ean Delevan Ope pel MY 6 5 6 6606606600600 0 WESMNES 6 6 56105 6 6 OF OOO OK OOOO Two Common Samplers and Some Sample Retainers. . . Geospace GT-2A Portable Refraction System. ... . Geophone sini SOs uremic ounces cm u- iran rtm ont Woe 47 Iroilesrosicl \eauikm keeontel 56 6 6 5 06 0 6 0 OO Diagram of Seismic Profile Layout. ........ Offset Distance and Critical Angle ....... . Apparent and True Bedrock Velocities ...... . Determination of Bedrock Relief by AT. ..... . Example of a Non-Zero Intercept. . . . « « « « « e Apparent Sediment Velocities Due to Variable Thickness. oe e e e e ° e e eo e e ° e e e e ° e e e Time-Distance Plot Showing a Time Step for Buried Peat ee e ‘@ |e .0 -e ‘eo ie. ‘0 ‘e) je (e ‘ee @ (‘© jo ‘e @- @ @ ‘e Profile from PI-7 and Drill Hole PIC ....... Time-Distance Plot and Cross Section from PI-17. . Time-Distance Plot from Middle Ground. ...... Cross Section of Middle Ground Showing a Bedrock Hi gh e e e@ e e e e ° e e e e e e e e e e Graphical Explanation of the "Blind Zone", .... Nomogram for "Blind-Zone" Computation. . ..... Transverse Profiles Showing a Bedrock Rise... . vi 2th 28 29 31 32 33 35 36 38 26. Allo 28. 29. 30. 31. 32. 33. 34. FIGURES (continued) Cross Section from CB-18, CB-19 and Drill Hole Essex Flood-Tidal Delta Profile. ... .j Sandy Till from Drill Hole CBB ..... Weathered-Zone Material. . . . « » o eo » Sketch of Castle Neck at 10,000 B.P... Sketch of Southern Plum Island at 10,000 and 4,000 Babe e e e e e e e s e ° e e oe Sea-Level Trends for Plum Island Area. . Seamciieyel QUAIE5 6 6 6 660005 00 6 Orel Ge CASIO NES 6 6 6 6 60 0 Oo 53 56 * Pont x Aig it f vr oft) url ae i ee a ar Thy rt i" - 7 4 { mreetere HE if 20) eteeb> a va ite, Tee es etiam Fi eee A HER, PP Raa, ONE, eh at, nf t Yaa i rp a, i. : on . Se, ew ee ee f j msi Py ayer vy tries Phat ; PLEISTOCENE-HOLOCENE SEDIMENTS INTERPRETED BY SEISMIC REFRACTION AND WASH=BORE SAMPLING, PLUM ISLAND-CASTLE NECK, MASSACHUSETTS by Eugene G. Rhodes I. INTRODUCTION The shoreline of northeastern Massachusetts is dominated by exten- sive barrier beaches. This study attempts to reconstruct the three- dimensional stratigraphic framework of these deposits. The Pleistocene and Holocene stratigraphy of Castle Neck and the southern third of Plum Island, the two largest barrier beaches in this area (Figure 1), was determined by wash-bore and seismic refraction methods. Thoreau vividly described this part of the New England coast in the 1840's: "Tt is a mere sandbar exposed, stretching nine miles parallel to the coast, and, exclusive of the marsh on the inside, rare- ly more than half a mile wide. ...The island for its whole length is scalloped into low hills, not more than twenty feet high, by the wind, and excepting a faint trail on the edge of the marsh, is as trackless as Sahara. ...I have walked down the whole length of its broad beach at low tide, at which time alone you can find a firm ground to walk on, and probably Massachusetts does not furnish a more grand and dreary walk. ...A solitary stake stuck up, or a sharper sand hill than usual, is remarkable as a landmark for miles; while for music you can hear only the ceaseless sound of the surf, and the dreary peep of the beach birds." from Henry David Thoreau, A Week on the Coneord and Merrimack Rivers. The 3-mile expanse of dunes and beach south of Plum Island, which comprises Castle Neck, could also have been the object of Thoreau's description. Much of Plum Island is now controlled by the Parker River Wildlife Refuge. Castle Neck is a recreation area held by the Trustees of Reservations, Milford, Mass. Both areas have been subjected to agri- culture and other manmade modifications since colonial times. Yet, today they are two of the least disturbed sand bodies on the New England coast. Much of Plum Island and most of Castle Neck have been allowed to undergo uninterrupted natural modifications in response to the environ- ment. For this reason the area provides an excellent outdoor laboratory for this type of project. HAMPTON BEACH HAMPTON ESTUARY MERRIMACK PLUM ISLAND GLOUCESTER tit IZ Figure 1. Location Map for the Plum Island - Castle Neck Study Area 2 Sears (1905) found the coastline to be subsiding at about 3 feet per century, and noted the various drift patterns of the beach sand. Chute and Nichols (1941) presented ideas on the formation of Castle Neck, and studied the recent geologic history of the area in greater detail than previous workers. Sammel (1963) mapped the surface geology of the Ipswich quadrangle, which includes parts of Plum Island and Castle Neck. McIntire and Morgan (1963) were the first to probe the subsurface with drill holes, and to correlate drill-hole horizons with known Pleistocene and Holocene stratigraphy. From 1965 to 1972, students of Professor Miles 0. Hayes, at the Univ- ersity of Massachusetts, studied coastal processes in this area. Much of this material remains unpublished in the form of theses. A large part of this work has been summarized in Coastal Envtronments, a guidebook for the Society of Economic Paleontologists and Mineralogists field trip, May 9-11, 1969, written by the Coastal Research Group, University of Massachusetts. McCormick (1968) studied marsh stratigraphy in the Plum Island marsh with more than 60 cores, some to a depth of 40 feet. ; Linehan (1942, 1948) was one of the earliest seismologists to do shal- low refraction work in New England. He and others used the method to determine bedrock profiles along proposed highway routes. By this method, the Department of Public Works determined the volume of overburden to be excavated and the nature of the rock topography. The seismic method has been used to locate preglacial bedrock channels of the Merrimack, Connect- icut, and Charles Rivers. In these examples, refraction seismology was used primarily to "see through" the overburden and map the bedrock sur- face. Currier (1960) evaluated the seismic method for determining bed- rock topography under proposed highway and foundation sites. He also discussed resistivity, wash-boring, and core drilling as useful subsur- face profiling aids, but concluded that the seismic method was the most successful. The purpose of this study was to develop field and interpretive techniques for the study of the third dimension in the coastal environ- ment. Plum Island and Castle Neck were chosen for their almost untouched natural state and for the large amount of accumulated information on sur- face processes. An understanding of the types and rates of shore pro cesses aids in the interpretation of subsurface data. Methods and interpretative guidelines developed during thisstudy can now be applied in other areas, perhaps while gathering other coastal data. The result can be a three-dimensional sedimentary model that effectively links space and time. II. FIELD TECHNIQUES 1. Drill-Hole Study Seventeen wash-bore holes ranging in depth from 30 to 100 feet were completed in this study (see Figure 2). This boring program employed an Acker Model RGT wash-bore rig operated by a three-man crew. Figure 3 shows the barge-mounted drill rig at an estuarine drill site. The maxi- mum drilling depth with this equipment is 100 feet. Except where till or bedrock was encountered, the bore holes were drilled to that depth. Bore holes were logged continuously by noting the nature of the washwater. Holes were sampled at 5- to 10-foot intervals, or at every change of sedi- ment type. The wash-boring process consists of hammer driving a casing, washing the inside of the casing clean, and then sampling beyond the end of the casing. This project used an Acker NX flush-coupled casing, which has an inside diameter of 3 3/16 inches. It is constructed of cold-drawn, steel tubing and assembled in 5-foot lengths using couplings with square threads. It is designed to withstand only limited driving, and is not recommended for casing drill holes in sand beyond 100 feet. The casing was driven into the sediment using a 300-pound drive ham- mer sliding on a pull piece attached to the casing, and was retrieved by bumping the hammer against the top of the pull piece. Figure 4 shows the drill-rig crew disconnecting the pull piece and a 5-foot section of casing during casing removal. Casing should be driven into the sediment vertically to eliminate sway in the hammer and prevent metal fatigue near the connecting joints. The hammer was attached to a l-inch manila line by a manila sling, rather than by a chain or cable sling, to protect the threads on top of the pull piece. The l-inch manila line passed through a pulley on top of the drilling mast and down to the cathead on the power unit. Figure 5 shows the manila line engaging around the cathead as the operator applies tension to the slack end of the line. The manila line acts as a clutch, engaging on the cathead when tension is applied and releasing when the operator lets the line go slack. Casing is driven by alternately tighten- ing and slackening the line to the cathead. Figure 6 shows the drill rig and its operation. The number of blows per foot of penetration is record- ed to obtain useful penetration data. The casing is cleaned of sand by a chopping bit (Figure 7) before taking a sample. A high-pressure water jet is used; there is no rotary movement. A working pressure of more than 100 pounds per square inch is developed by a double-action piston pump opposite the cathead. Water is supplied to the pump directly from a pond, estuary, or truck-mounted water tank. A day's drilling, which usually averages 50 feet, requires about 1,000 gal- lons of water. Saline, brackish or fresh water may be used if precautions are taken to retard rust after use. CAMP SEA HAVEN GULF OF MAINE @ BORE HOLE — SEISMIC LINE A A 5 TRAVERSE PROFILES 1000 500 oO 1000 2000 METERS PI-17 STAGE ISLAND POND 1000 500 Oo 1000 2000 (Lene ny J —__J YARDS APPROXIMATE SCALES IPSWICH BAY WINGAERSHEEK BEACH oe 5 be Figure 2. Location Map for 17 Drill Holes and Important Seismic Lines. Seismic line numbers mentioned in text are shown. The Essex flood-tidal delta site is at drill hole ETD (Figures 3 and 27). aN: m j sere Figure 3. Drill Rig on Barge Platform. This site is on the Essex flood-tidal delta where drilling was done at low tide for added stability. The casing is driven through a well in the center of the barge. Drilling Crew is Disconnecting the Pull Piece Before Removing a 5-Foot Section of NX Casing. After removal, the pull piece will be attached to the next 5-foot section and more casing will be bumped out of the ground. *SYBTOM IOTAPOY YFTT ued 3nq ‘ATT IGedes zoumey punod-009¢ & sey }TUN STU, “pug 9014 9Y4} 03 UOTSUS] set{[ddy 1tojeZ0dg 242 UseYyM YOINTD edoy e se peoyieD oYy2 YsuTesy soseSuq out] eTTueW YOUT-[T ou, “Ss ean3TY Figure 6. PULLEY a FOUR-MEMBER DERRICK SAFETY HOOK —————y) SLING I" MANILA ROPE i ENGINE ment, Diagram of the Wash-Bore Unit Used. A 15-horsepower engine powers a clutch unit which in turn powers the cathead and water pump. The pump, a double acting piston type, develops over 100 pounds per square inch. A high-pressure hose carries this water to the drill string. The operator uses the mechanical aid of the cathead to raise and lower heavy objects and to operate the hammer. Figure 7. Washbit Used for Cleaning the Casing Before Sampling. This is a chopping bit, and jets water from both sides. The pencil locates one jet. Water is pumped through the center of either E (1 5/16") or A (1 5/8'') size drill rod by a water swivel on the upper end of the drill- rod string. This swivel allows rotation of the drill string in the hole without twisting the hose which carries the water from the pump to the drill-rod string. When drilling in sandy material, wash water is no longer returned up the hole as the washbit passes beyond the end of the casing because of the porosity of the sand. The drill-rod string is removed from the hole in 10-foot sections, and a sampler is lowered into the hole by reassembl- ing the drill string. A sample is taken beyond the end of the casing before advancing it 5 more feet. Samplers are of several types. The type to use depends on the sedi- ment being sampled and the preference of the operator. Figure 8 shows two more common samplers used in shallow holes. The split-spoon sampler is used in sand, clay or till; the Shelby tube works best in silt or clay. A variety of sample retainers are used in the shoe of the split spoon. The more successful ones are also pictured in Figure 8. The metal spring fingers with the plastic bags surrounding the fingers proved most depend- able. Prophylactics of latex rubber are far superior to the plastic bags sold as retainers, and are a recommended substitute. When working in clays with either the Shelby tube sampler or the split spoon, no retainer is necessary if the ball check valve in the head of the split spoon and the Shelby tube is kept free of sediment. The ball valve should be flush- ed clean with water before sampling to prevent sediment from being driven into it. Unless a heavy-duty, split-spoon sampler is used near gravel or till, metal fatigue caused by forced penetration of the sampler will result in a lost sampler. The presence of clay or fine silt the entire length of a drill hole eliminates the need for casing. Clay is self-casing and retains the hole even if drilling is suspended overnight. Many crews use a drilling mud to case sandy parts of a hole, because mud mixed with water fills the pores of the sand and causes the hole to retain its shape. In very porous sand, this process may be tedious. Here, the choice between drilling mud or steel casing depends on the type of equipment available and the preference of the crew. The use of mud simplifies drilling deeper holes as there is no casing to be retrieved. However, certain pumps cannot handle the clay-water mixture. A common problem results from sandy till or gravel under a thick layer of glaciomarine clay. Because the clay part of the hole is not cased, and could be cased only with great difficulty, there is a water loss when the washbit passes from the clay into the more porous material beneath. This usually blocks further drilling, and is one of the more difficult problems of using nonrotary, limited-capability equipment. ‘atqepuedep jsouw oy ST 3UTIOAOD 3eq ButTads oy, “peTqmoesse ST 3T ueym uoods 31Tds 9y2 UT posetTd sZoutTezeL oTdmes snoTIeA 9Le WO2}0q 9Y} IV “ABD UT 389q ST oqnz AqTous 9Yi ‘szUcMTpes Fo sad} [Ie UT [NJssaodons st uoods 31Tds oul “TeTLe.eW peepTToOsuocUH UT peasy Si1oeTduwes UOMO) OM] Ss SME 0 NOOdS LIIdS °g emn3Tty SUANIVLAY YTdWVvS 12 An experienced crew can drill up to 50 feet per day. The early ap- pearance of clay in a hole allows speedier progress. A crew can occasion- ally drill and sample a 100-foot hole in one long day. But usually, it takes 2 1/2 to 3 days to do a good job on a hole. This includes setup and takedown time for the rig and transportation from the previous site. Estuarine (barge-mounted) operations are slower, but unlimited washing water (over the side of the barge) is an obvious advantage. Anchoring a rig against tidal currents is not too difficult. Drilling is then done through a well in the center of a barge with the casing extending up to deck level. This casing not only facilitates re-entry but also helps to anchor the barge. A site on an intertidal bar is desirable because drill- ing can be done at low tide while the drilling base is grounded. 2. Seismic Refraction Study Seismic refraction principles were used in earthquake seismology before their application in shallow refraction surveys. The principles of refraction remain the same whether the layers being studied are thou- sands of feet thick or merely tens of feet thick. Refraction surveys en- able the scientist to gather data on the geometry and composition of sub- surface materials. The simplest case is a two-layer problem consisting of a high-speed layer overlain by a low-speed layer, such as crystalline hedrock overlain by glacial material. In the simple two-layer case, a seismic wave is generated at the sur- face and travels away from itspropagation point in all directions at a velocity unique to the upper layer. On crossing the interface with the lower layer, the wave moves at a higher velocity and overtakes the surface wave. Geophones placed in a linear fashion away from the point of energy propagation measure the arrival time of the direct (surface) and indirect (subsurface) waves. A time-distance plot of these arrival times will determine when the indirect wave overtakes the direct wave, allowing determination of the depth to the subsurface layer. The field techniques of the shallow-refraction phase are'similar to those of the drilling phase. In both phases, equipment must be transport- ed to sites not easily accessible. Dependable four-wheel drive vehicles and rugged boats are needed. Seismic study requires the use of bulky, but delicate, rolls of wire and explosives; both can prevent transportation problems. The seismic work was done with the Geospace Model GT-2A portable re- fraction system. This unit works well near the shore because it is weather- proof when the instrument cover is closed, and is rugged and dependable over a broad range of temperatures and humidities. All time records are taken on type 47 Polaroid film, allowing rapid review of seismic results in the field. Figure 9 shows the recorder with its Polaroid camera in position for recording. Figure 10 shows the geophone attached to its cable takeout. Phones are always planted in holes below the vegetation or loose soil layer. Figure 11 is a typical time record as shown on the type 47 film. Time breaks are usually sharp due to the excellent shock- wave transmission in water-saturated sediment. The Geospace refraction system used yields 12 recording traces and one time break. The recorder provides 100 hertz timing lines (10 milli- seconds) on the record. Recording time of the instrument can be selected as .2, .3, or .4 second. These times allow bedrock deeper than 500 feet to be located, assuming a two-layer case and speeds of 5,000 and 15,000 feet per second for the upper and lower layers, respectively. Lightweight Geospace geophones with a maximum sensitivity of 14 hertz were attached to the takeout cable at 30-foot intervals. The use of slip- on type connectors required preventing sand grains from being stuck between the connector and the takeout on the wire. Whenever lines were run on dry sand or salt marsh, it was necessary to dig the phones into more com- pact sand or peat. On the low-tide terrace, or beach face of the barrier beaches, and on the intertidal bars and tidal deltas, the phones could simply be pressed into the sand, and with this efficiency as much as 1 mile of beach can be profiled in 1 day using 30-foot phone spacings. Figure 12 is a diagram for a typical seismic refraction line layout employed in this study. Two 12-phone takeout cables were laid down with a two-phone overlap. By convention, phones are numbered away from the center of the spread. A shot is made at the shotpoint with phones on section A. Then the phones are moved to section B and two more shots are made. This yields a total of four records, two representing sediment returns with a shot near the "12-phone" end and two representing bedrock returns with a shot over 330 feet from the "one'' end. When plotted, two times are common to each pair of records; this duplication allows for corrections due to loosening of the sediments surrounding the shotpoint. Amplifier potentiometers are adjusted on the recorder depending on the gain setting required to eliminate background noise. Background noise includes vehicles, wind, pedestrian traffic, and the surf. A heavy surf can seriously affect coastal seismic operations. This gain setting varied with the proximity of the phones to the shot hole. The GT-2A system has an individual gain control for each channel; phones near the shot can have decreased gain on their amplifiers, and more distant phones can have in- creased gain on their amplifiers. Problems were encountered in the intertidal area where the insulated parts of the phone takeouts or connectors touched the wet sand. A phenom- enon known as "shot feed'' almost obliterated most time traces where several connectors touched the wet sand. This is probably caused by the electric blaster current (90 VDC) being conducted through the salt water in the sand 14 Figure 9. Geospace GT-2A Portable Refraction Recorder. Records are made on type 47 Polaroid film in camera at center. Knobs on upper half of panel control the amplifier pots; OPERATE, TEST, and SAFETY switches are closest to the operator. Recorder is wired for cap detonation (lower left) and connected to the jumper cable (right side). 15 Geophone Planted in Soil Below the Sod. in under dry sand where a hole 8 to 10 inches deep may be nec- essary to place the geophone spike in more compact sand. On water-saturated sediments the phone spike can simply be pressed into the ground. Phones are also dug Figure 11. wT. “J NV ONS SO, She FOS 4 Bo GIG a Gs Type 47 Polaroid Film Record. The sharp breaks are typical of good energy transmission through water-soaked sediments. The vertical lines are spaced 10 milliseconds apart. The 13 traces include one shot break and 12 geophone channels. Arrivals can be picked to the nearest millisecond. With the exception of the ''-4" at the left of the caret, the handwritten numbers are the arrival times in milliseconds. The "'-4"" is a constant indicating the shot break's relation- ship to the initial timing line marked by the caret. Arri- vals are timed from the initial time line and the constant is then substracted from raw times to give real times written on the record. The almost simultaneous arrival of the last five phones probably indicates rising bedrock. qynoke] S[TZJOLg ITWSTeS FO weIseTq “ZT eIn3TY d SANOHd Neb Lee v J Ge Ole Michie 3YIM ade : j 3YIM LOHS YaqyOosY g S3NOHd NOWWOD v € cd jurod joys 3YIM Yadwar ane SYIM LOHS Y3AquOoSsY 18 and upsetting the galvanometer whose geophone connector lay in the water-saturated material. This can be avoided by placing connectors on the head of the geophone, off the sand, or by using waterproof connectors to the takeout cable. Seismic energy was provided by 60 percent gelatin explosive detonated by an instantaneous electric blasting cap. Blasting caps of the seismic variety are recommended due to the larger amount of current required to fire them. Amounts of explosive varied from 1 ounce to 3 pounds; the smaller amounts were used in areas of shallow bedrock and on clam flats; the larger charges were required in dry dune sands. Blasting caps alone or sledge hammer shock sources will not work in coastal sands. Explosive charges are always buried as deeply as possible to improve energy transmission. This usually means a shovel-dug hole 2 to 3 feet deep on the beach or a bar-punched hole in the marsh peats. The charge should be placed in or near the water table because this allows a reduction in the amount of explosive employed. Dry sand is an energy absorber which sup- presses energy propagation unless the explosion can be coupled to the water table. The ecological effects of explosives in the shore environment require some comment. No more explosive should be used than is required to yield a sharp time break at a particular gain setting, determined by existing background noise. Therefore, three variables are related: background noise, gain setting, and amount of explosive. They should be considered in that order. Naturalists will often express a fear of large scars left by explosion seismology. Such fears are unnecessary because charges up to 1/2 pound can be detonated 3 feet down in marsh peat without disturbing the surface. Seismic charges in dune sand or other dry vegetated areas cause little or no disturbance. Even the larger charges required to pass energy in the loose material rarely leave a scar. Seismic profiles sea- ward of the high-tide mark on beaches or on intertidal sand bodies without shellfish can be run without undue concern for amount of explosives used. The incoming tide erases the craters. Shellfish flats do present a problem. Shell fishermen should be in- formed about the nature of the work. Profiles should be located over areas of sparse shellfish population; gain is then increased and charges as small as 1 ounce can locate a bedrock profile as deep as 40 feet. Safety is always foremost when using explosives. Only qualified ex- plosive experts should handle and load explosives, or wire the shot holes. The crew should be large enough ta keep onlookers from the blasting area, an acute problem in popular beach areas. Blasting caps and dynamite should be stored and transported in separate magazines. If possible, these ex- plosives should be transported in a vehicle used solely for that purpose, rather than in one carrying personnel or seismic equipment, particularly sparking (iron or steel) tools. III. SEISMIC PROFILE INTERPRETATION Although time breaks on the type 47 Polaroid film records can be picked and plotted in the field, it is necessary to replot these data at a larger scale in the laboratory. Time breaks can be picked only to the nearest millisecond. A plotting scale of 10 milliseconds per inch on the vertical axis and 50 feet per inch on the horizontal axis has proved to be a conven- ient layout for the time-distance plots. After plotting the time points, a line (or series of lines) is drawn by visual fit through these points. Velocities for the various layers are computed from these lines. Velo- cities can be computed to a high degree of accuracy and later rounded. When drawing these lines through the data points, slopes should be con- structed on the time-distance graph in accordance with reasonable seismic velocities. Topographic relief or subsurface irregularities occasionally will cause unusually high or low velocities. 1. Formulas and Nomograms Selection of an appropriate interpretation method for seismic refraction data has long been discussed by geophysicists. There is a choice between two formulas: the critical-distance formula, and the time-intercept formula. The critical-distance formula is an excellent determinant for the classical two-layer system. However, this formula performs poorly in the multilayer situation common to the shore environment. The time-intercept formula (there are several variations) has significant shortcomings, but is more successful in multilayer situations. For this reason, it is used most frequently in data interpretation in this study. Nomograms for both critical-distance and time-intercept methods were obtained. When results were checked, the calculated thicknesses and depths usually agreed within 5 percent. In addition to the nomograms for depths, a nomogram was also used to compute offset distances and critical angles. Refraction geo- physicists are concerned about the appropriate location of the depth that has been calculated by the formulas. An offset distance was calculated as a function of velocity and depth, then the calculated depth was placed away from the shotpoint by an amount equal to this offset distance. Figure 13, a sketch of a typical two-layer case, shows the offset distance with respect to the overlying shotpoint. 2. Seismic Velocities When determining intercept times or the difference of intercept times for use in the time-intercept formula, apparent velocities should not be confused with true velocities. Velocities associated with water-saturated sediments tend to cluster around 5,000 feet per second with a plus or minus deviation of about 300 feet per second. Velocities other than those centered around 5,000 feet per second can be related to the degree of satur- ation or to the texture of the sediment. Apparent sediment velocities also may be created in much the same manner as apparent bedrock velocities. This situation will be discussed later. Apparent and true bedrock velocities 20 "90UbISTP OSFFO pue SSouyoTY} ,,9UOZ-puTTG,, o3ndWOD 0} pesn st o[Bue sTYUL ‘*UMOYS ST PT oTSuUe TeOTFTIO Oy FO UOTJETNITeD pue UOTIESOT OY, “SOETJTOOTSA pue sxLoAeT BUTAT -zepun 03 yydep Fo uoTOUNF e& ST UOTITSOd JOSFFO OYL “pa YedTpuT st souoyd Fo Aerze Tetzzed e ATuQ *.UTOdAOYS 9Yi 03 JOedSeZ YIM UMOYS ST 9DULISTP 9SFFJO “FT GansTy ‘op Yoo TITH 9}UD} Z=b -MeINOW £(796T) NIYAOd wWosrz SJONVLSIO L3S4340 f <________ Avy 3NOHd039 ———_> LNIOdLOHS NOILISOd 13S4I30 2 | must be separated strictly by statistics and a knowledge of the approximate configuration of the bedrock surface gained from drill-hole study. Bedrock velocities vary over the study area, but most are between 15,000 and 19,000 feet per second. The 19,000 feet per second velocities are in the Castle Neck-Essex area. The bedrock is largely Salem Gabbro Diorite and Cape Ann Granite (Clapp, 1921). Seismic velocities can be summarized as follows: Material Velocity (feet per second) dry sand 800-2500 water-saturated sediments 4700-5300 (sand, gravel, and sandy till) compact till 6000-9000 bedrock 15 ,000-19 ,000 There are situations where a continuous spectrum of velocities exists from the driest sand to the most compact till. For this reason, it is difficult if not impossible to ascertain the texture of underlying material by simply determining its velocity. So Graphic Interpretation Interpretation techniques and procedures were standarized during the reduction of the study data. Interpretation of dipping bedrock was studied in detail. A back projection (on the time-distance plot) from the first phone showing a bedrock return, using the true velocity of the bedrock, yielded the time intercept used in the computation of depth. On every time-distance plot with arrival times from both sediments and bedrock it is usually obvious which phone received the first bedrock arrival. The bedrock returns lie along a line of flatter slope, and are usually scattered about this line in a more random fashion than the sediment arrival times. In homogeneous sands, it is not unusual for the arrival times to lie pre- cisely along one line. When in doubt about which phone carried the first bedrock arrival, it is acceptable to choose the next phone from the shot- point as the basis for the back projection. Figure 14 shows a back pro- jection of true bedrock velocities on a time-distance plot that might otherwise be difficult to interpret by the time-intercept method. This technique can also be used for a dipping till-layer that is yielding an apparent till velocity rather than a true one. Irregular bedrock surfaces are a problem. Relief on bedrock topography can be computed by a method presented by Meidev (1960) and reproduced in Figure 15. Empirical results for this study area suggest that use of 1/2 AT rather than AT may yield better estimates of bedrock relief. Dipping and irregular bedrock surfaces caused a lack of agreement between adjoining seismic lines. Seismic lines which share a common shot hole should yield depths of close agreement. However, where irregular bedrock surfaces pre- 22 -yadep so uotzeutxoidde pood e spretA sout, sututofpe worz ejep YIM uoTzoOuUNfuod UT 3nq ‘UOT ZduMsse 35e1L09UT Ue SaUlT}JeWOS ST STYL ‘“SUTddtTp Jou st 9deFzaINsS yoorpeq eyi suoyd yoozpeq ySITZ oY2 pue yUTOdJoYs oY. UseMZeq ey Opeul ST UOT duMsse auL °[eBATIZe yOoIpeq e BuTMOoYSs ouoYd YSATF OY} WOLF STXe OUT} OY OF YOeq UMeIp oe SOTIIOOTOA ONT], *Szded19RUT SUIT] SUTWIE2Eq 03 PpesM oq JOUURD SOTITIOTEA YIOLpog quozeddy ‘pt o1n3ty Bujoods 4004-O¢ ‘Y3EWNN 3NOHdOS9 2 2-lb 20 6S. °S 2 Be coe SG See oe al Ol O02 23 AjoojeA ens} WOss jdeosejul eu O€ Ajo0jeA ens} wots jdaosajul ew) spuosesiiw ‘WIL fe) + OS SOI}ID0|EA yooupeq juesnddy *FOTTOL YOOIpsq FO soezewtiss 19330q septa -o1d IV Z/T 3ey2 e3eOTpuT vere Apnis STY} OF Si[nsoexr Teotatdug *(a) 201d soueqstp-owTt? e 03 eaToeuutd e zo dtysuotzejter syy pue (vy) dzeos e 1aA0 i0T[d 9due STp-oWT? 9Uy SMOYS YDI0AS ‘e[nuUTOZ ydod103uUT ~9uT? 942 UT pasn pue AATIUeNb ydedI10eqUT-oUT, & se poqeer ST LV "20d S9UBISTQ-SWT] SY? WoTy LY FO asM 942 Aq (zy) AYyder3odo]) yoor -peq FO epnittduy ey Fo suotzeutw1ze.0q ayy persessng (0961) ASpToW ‘st ean3Ty S3STOTSAydosy uotie10Tdxq JO AYOTIOS £(096T) AACIAW wosz dominate, it is not unusual for depths to disagree by 20 to 30 percent particularly if the lines are oriented at right angles to one another. 4. Problems of Interpretation The line connecting the travel times for a seismic wave in the first layer rarely passes through the origin on the time-distance plot. Figure 16 is an example of this non-zero intercept; the figure is a reproduction of the time-distance plot of seismic line CB-8A east of Crane Beach. The location of this intercept on this time axis closely matches the depth to the water table in the sand over the seismic profile. A comparison between the penetration drill-log for the nearby drill hole CBD and the time-distance plot showed that the water table is about 3 feet beneath the surface. The first segment of the time-distance plot intercepts the time axis at about 6 to 8 milliseconds. Assuming a velocity in dry sand of about 1000 feet per second for the seismic wave, it can be proven that this timelag represents a 3- to 4-foot overburden of dry sand. Previous discussion of the slower velocity of the seismic wave in dry sand suggested the complications in placing a geophone spread over dunes. Problems of interpretation can be greatly reduced by seeking a level route through the dunes for the seismic line. In addition, a sketch of dunes should be placed on the field notes if the seismic line is not surveyed. A thickening or thinning of this upper dry layer yields an apparent sedi- ment velocity which can be confusing. Figure 17 is a sketch showing a 3-foot thickening over a 330-foot geophone spread. This thickening can change the apparent velocity of (5000 feet per second) water-saturated sediment lying underneath this dry layer. Sediment below the water table rarely yields a seismic velocity less than that of the range 4700 to 5000 feet per second. If a lower velocity is found, a situation similar to that in Figure 17 should be sought as an initial explanation. Occasionally there is a velocity variation beneath the water table which can be attri- buted only to sediment texture or to the environment of deposition. Such a horizon could be verified only by drill-hole correlation. Pium Island seismic lines PI-7, PI-8 and PI-9 and the nearby drill hole PIC suggest another problem common to seismic work near the shore. Apparent attenuation of the seismic energy takes place along this profile due to a possible thickening of a peat sequence beneath a dry overlying sand (Figure 18). The resulting time-distance plot is unusual (Figures 18 and 19). The presence of peat under a refraction profile does not always create a time-distance plot with a step-like appearance like that in Figure 18. Recent work by the author on Cape Cod beaches near Brewster, underlain by marsh-peat sequences, shows that these layers have little effect on seismic transmission. In the area of Plum Island and Castle Neck, the presence of these step-like breaks in the time-distance plot strongly suggests that a nearby drill hole might show an energy absorbing layer, such as peat, near the surface. 25 *yaoz ut yydep eTqez-1907emM au s[enbe ATTeENsN spuodesT{[TW UT OWT} ydodTeIUT OY FO FIVY-9UN “oSoPFANS 9Y1 MOTEq 390F p 02 | SBM OTGeI LOZEM OY 9ZeOTpUT STOY TTTIP Aqieeu & IOF SpLOdeI UOTIeIJOUSg ‘“oTGeL 19IeM eYyI 02 YyIdeq oY eUTUIEIEq 02 PSSf] 9q UBD 32} ydeoD1ejU] O1EZ-UON 94 SMOYS Y8-d) SUTT ITUSTES FO JOTd SDUBISTQ-OWTL “OT oin3ty Buiopds j00os-0€ ‘Y3SSWAN 3NOHdO39 Zi Salle EOlE GS BO" Zs o OSS eb. ee eee | Se ee er Ss Ol jdedsaju! + 010Z-UON 02 = = m oe - 3. ay @® 2) ° Ov a 7) Os 09 26 East West Shotpoint Shotpoint DRY SAND JUue SUS WET SEDIMENT Figure 17. Cross Section Determined by Nearby Drill-Hole Data Explains Apparent Sediment Velocities. The wet sediment has a true velocity of 5,000 feet per second. However, with a dry sand overburden of variable thickness, apparent velocities are indicated on the seismic record. A high velocity appears when the shot is fired at the east end and the seismic wave travels upward through a progressively thinner dry sand as it propagates westward. However, a shot at the west end of the profile, which places energy in the wet sediment, rec- ords successively longer times on geophones toward the east due to the thickening of the dry overburden. The two appar- ent velocities and the respective direction of propagation for the seismic energy are indicated on the cross section. 2 ( 70 60 50 aS (e) TIME, milliseconds oO Oo 20 | 2 Sit c4 5 6 7 8 9 oe | 2 GEOPHONE NUMBER , 30-foot spacing Figure 18. Time-Distance Plot for Plum Island Seismic Line PI-7 Shows Time Steps that Indicate a Buried Peat Layer 28 West ‘drill hole Figure 19. Spent East Shotposnt So DUNE SAND rs, i oy* ve WET . BEDROCK fi Cross Section from Seismic Data Like that in Figure 18 and Drill-Hole Data from PIC. Energy transmission is slow and poor in the peat. Arrivals below the time step on Figure 18 indicate energy transmitted by sediment above the peat. Arrivals plotted above the time step indicate energy taking a path down through the peat into the clay and returning through the peat from the lower strata. A low seismic velocity of perhaps 1000 feet per second would introduce the time gap indicated by the time-distance plot. (as) Vincent J. Murphy, of Weston Geophysical Engineers, Inc., (personal communication) mentions similar phenomena in other areas. A condition known as "velocity inversion", where a lower-velocity layer is sandwiched between two higher-velocity layers, is the best description of the causative situation for the steps in the time-distance plot shown in Figure 18. The velocity inversion causes the layer with the lower velocity to be hidden. In addition, an error in computing depth to the underlying layers results. The surface wave reaches a limited number of phones in regular succession, and then attenuates, causing succeeding phones to await the arrival of the wave which must pass through the deeper sands and their overlying peat layer. Time-distance plots for the remainder of the study area show this step- like arrangement appearing in other localities where extensive peat deposits could be present, especially interior depressions in the barrier islands which now contain brackish or fresh water marshes. Figure 20 shows a time-distance plot and its associated cross section near the Stage Island Pond on southern Plum Island. Peat deposits apparently are associated with the brackish pond and swamp since early stages of the barrier. It is likely that barrier sands now overlie a predune marsh associated with a lower sea level. This is an example of how seismic profiles and nearby drill-hole logs complement each other. Plum Island seismic profile line PI-17 (transverse profile, Figure 20) is tied to seismic profiles that run parallel to the beach. This arrange- ment of profiles is desirable wherever possible, because tying three geo- phone arrays together at a common shotpoint with a right-angle relationship between two of them provides an excellent check on the continuity of seismic returns. In this example, Plum Island lines PI-17, PI-18 and PI-19 are tied to a common shotpoint on the beach. Till was calculated at a depth of 90 feet on profiles run parallel to the ocean, but was found between 75 and 80 feet on a transverse profile. The time-distance plot also shows the characteristic time steps due to the buried peat. Glaciomarine clay deposits are extensive beneath Plum Island. Their presence was known before this study, in part from a study (McCormick, 1968; McIntire and Morgan, 1963) of previous work in the surrounding areas, and from the occasional outcrop of similar clays in the Ipswich quadrangle (Sammel, 1963). Sj8gren and Wager (1969), Swedish geologists, discovered a velocity contrast between thick clay sequences and overlying wet sand sequences during a preliminary engineering study for foundation construc- tion on fjord and river deposits in northern Sweden. Although velocity contrast was expected between glaciomarine clay and wet sediments in this study area, none appeared, even in locations where impressive clay thick- nesses underlie estuarine and barrier sands. For example, Figures 21 and 22 show one of the seismic time-distance curves and the cross section from the marsh-capped Middle Ground in the Parker River. Sand deposits greater than 60 feet thick overlie glaciomarine clays that extend to at least 100 feet, the point at which drilling ceased. The time-distance plots show no 30 100 3 TIME, milliseconds oO o re) ro) £ oO Oo (e) 12 I 10 9 8 7 6 5 4 3 2 GEOPHONE NUMBER ,30-foot spacing POND DEPTH,feet a ro) {o) (e) 3 80 Figure 20. Time-Distance Plot for PI-17 Shows the Time Step Probably Related to Buried Peat. In addition, till was found in drill hole PID, and was located on the adjoining seismic profiles. Till was calculated at a depth of 75 to 80 feet on the transverse profiles; profiles running parallel to the beach located till at 90 feet. 3 *yoorpeq aze[nserit Aq pasned ate puodes zed 3093 00S°ZZ FO ATOOTOA YBTY oY puke puodes sod y90F OOL‘IT FO AZTOOTOA yooLpeq MOT ey *yOoLpog oy. BuTATIOAQ TeTLeeW 9Y43 TOF AZTOOTEA OUQ ATUO SMOUS PpUNOID SLPPIW UO SOTTFOIg ITWSTeS sy} FO 9UQ LOF JOTq 9dUeISTQ-OWT]L “TZ ein3Ty Byjods 400}-OF ‘YIGWNN 3INOHdOI9 wrodjous g 2 I Vv juodjous (Sel =e Olt 60 a) Se ee Se: ol ¢ » ¢ 9 pe 6 Oo H 2 5 * BINIL . P 90874, 00s - s oo 06 32 *sqZUsUTpas Jo 49003 C9 seddn 242 ovsodwod spues auTZenjse pue ast yOOIpeq sty} IeAO pedeap st ABT) ‘Apoy puvs 94} JO 9[PPIW 942 Lepun osTYyY ydOLpog 3Y3TIS B SeqBoTpUT BB] STOH-[[T4q pues ITWstas YOY WOIZ pUNOIN o[PPpIW JO UOTIDeg SsoIy ‘*7z eAN3TY J1VIS 1WLNOZINOH SSS SSE OOSI OOO! OOS SEARS | og vo) @ $993 “H1d3d 09 Op aNvs -02 BS. 3 3 i Bats O ae é ajOU jj! |SOMUJJON punos9 eIppIW VOW 104 Il4d soayjnos 33 velocity contrast for the glaciomarine clay. The plots show apparent sediment velocities that are probably due to a thickening of the peat sequence towards the center of the sand body. Middle Ground has a bedrock core that rises to within 100 feet of the surface and then drops away to greater depth beneath the present estuary. Leet (1950) and Hawkins (1960) presented nomographs for the determina- tion of thickness associated with an arrangement of velocities and depths known as the "blind zone'' in refraction seismic work. Because it is cus- tomary to base interpretation on "first breaks", or first arrivals, of seismic waves at a geophone, there is a subsurface zone in the three-layer case which is not represented on the time-distance plot. Figure 23 is a graphical explanation for the travel times of a three-layer profile, in which the sediments have velocities of 5,000, 8,000 and 15,000 feet per second. These three layers are shown as a bedrock surface overlain by a till layer which is in turn blanketed with a water-soaked sediment layer. Seismic wave rays that take a path through the intermediate layer do not contribute to the time-distance plot. The arrival that took a path along the deeper but faster bedrock surface registers at the geophone before the arrivals that traveled through the intermediate layer. The thickness of the "blind zone'' is dependent on the respective veloc- ities of the three layers (Figure 24). [In addition, the amount by which V3 (velocity of lowest layer) exceeds V> (velocity of middle layer) is prob- ably the most significant relationship. Figure 23 shows that 50 feet of 8,000 feet per second sediment can be masked beneath 80 feet of 5,000 feet per second sediment if the bedrock has a velocity near 15,000 feet per second. According to Leet's nomogram, a maximum factor Y, where Y = Hp (thickness of middle layer)/H, (thickness of upper layer), equal to -85, can be achieved with this velocity distribution. In other words, as much as 68 feet of till could be masked from the seismic record by 80 feet of overlying sand. Thus, the presence of a "blind zone" could explain the absence of a discrete velocity for the clay sequence beneath Plum Island. It appears unusual that data were gathered only from locations where this "blind zone" could mask a higher clay velocity, but it is a possibility due to the thick blanket of uniform sand that almost always covers the clays. Drill-hole control linked with close interpretation can often help to reduce errors. At locations where two interpretations are possible due to a possible "blind zone", only an additional drill hole can answer the question. Interpretation of bedrock configuration remains the same even with a "blind zone". Only the relative depth of the third-velocity surface changes, not its configuration. A recent seismic reflection study (Duane 1969), performed by CERC to find available sand for beach nourishment also showed the offshore bedrock 34 JNOZ GNI198 *yDoLpeq ay} worZ asoyi Aq poyseu ere LoAeT T[T2 eYi WOIZ STeATIZe ‘eLozetoy, -yyed s3t UT YOoI1poeq popnt> -UT YOTYM OABM B BATOd9I 2x puokoq souoyd ‘pues 9M 9Y2 Y3n0IY aAeM D0ATP @ OATEIEeT x uUeYyI JUTOdJOYS 942 03 IesoTD seuoyd TIy ‘*y0Lpeq Ieisez oy? UT TOABL} OF TIT} 942 pue pues 942 YI0q Yysnozy2 passed yey. AB1oUe ay. se oT owes ey? je ouoyd owes 94} Je SeATIAZe T[T eYy2 OJUT pue pues 942 Y8nor1y) YIed Ae e soye, yey AB1eue ITWSTeg ,,°9U0Z pUTTg,, 942 JO uoTIeUeTdxg Teotydesy9 eR ; 3 aa 30 neN UNOS /0 0.2K: L- AQ ae EEN LS vba Sf? ONO): SS 1d) ReKay Sees ATS ow VOLE b= : =~ OKO OCA: Pee 0 hy A LENG SOOO MRE NOFA" Bo \ OS CON Soi Jeter Ase Sues Oe Oops OAC GA Vase t 988/43 OOOS 0Oee = °x Buioods jooj-0¢ ‘ApssD euoydoeg °¢Z ain3sty AV wa? RE! jujodjoys Sh BOOT OH DWAOBAVAVIsaIO Sere aoD = =a 7 RNIN EAS SS = ees AS =o 60 = SANA SSSR PRN Saws WINRAR ra SORINEUNITN 5 ESSAI Saas SA PSU SOB! LESTE Ae! Cae ee Gn Ss Se I IV 4ONG RSA NIRNR 20) a ae ae a a a ANTON RANA CaS a a ee I I GND. ALN UA ST AON ANIA Mt ie | -2-S = ee OSES BIBI ES SUN 0:1 NUT ANG INUINTN NS BSS AT IN TAT NUIAAOIY LAAUULNETN, DSN TK NAD NWT INTCATUSWUR NUNN NN YEN AEN ANIANTY 12 AM BBGE SHRI BO STIB NEY SEs! UN INING : MUR APRA ANH SN ASNT Ps AAT AGS SORBET SHIT ARSON gb a P-Amaae AULT a SAN nl 8 = | \ eee la 7 , A: (| eas (oan Ew BH SNNSI OUSRUTIBSOA TCC OG 10n 6 7 8.910 12 14 161820 25 30 3540 5306 90 bo3 from LEET (1950); Harvard University Press Figure 24. Leet (1950) Presented a Nomogram to Determine the Maximum Thickness of an Intermediate Layer that Existed as a "Blind Zone.'' The nomogram is entered by any two of the three critical angles involved in a three-layer case (see Figure 13 for explanation of critical angle, i,). From the nomo- gram, a Y factor is determined. The thickness of the upper layer when multiplied by this Y factor yields the maximum possible thickness for a "blind zone." 36 topography from Plum Island to Castle Neck, The results were successful, but Duane found that sand bodies might occur in patches because of the unusually rugged bedrock topography, and a more detailed coring program would be necessary to evaluate further the potential sand deposits in the area. Although insufficient transverse profiles were run to prove the matter conclusively, it appears that a bedrock rise occurs beneath major features such as Plum Island and Castle Neck and smaller forms such as Middle Ground. Figure 21 shows the rise under Middle Ground. Figure 25 summarizes two additional traversesthat indicate the possibility of bedrock rises. McIntire and Morgan (1963) found that the northeastern Massachusetts and New Hampshire beaches are anchored on both bedrock and glacial deposits. The shallower bedrock depths at Crane Beach allowed determination of the shape of that bedrock surface in greater detail than elsewhere. The surface is cut by preglacial depressions and channels into which glacio- marine clay was deposited apparently before the existence of the barrier island. Figure 26 shows a cross section from data of seismic lines CB-18 and CB-19, with the accompanying drill hole CBG. Figure 27 shows the bed- rock configuration beneath the Essex flood-tidal delta. This large sedi- mentary body is apparently sited on bedrock at a shallow depth. Hydro- graphy of the nearby Essex Bay between the rocky headland of Wingaersheek Beach (locally called Coffin Beach) and the southern tip of Castle Neck, indicates that the location of the main channel is restricted by bedrock topography. In addition, the bedrock surface deepens beneath the channel that separates the tidal delta from Castle Neck proper, indicating that this sediment-filled depression once might have contained a deeper Castle Neck River. Seismic profiles over the swash bars offshore from the Parker River inlet indicate a deeper bedrock horizon. These profiles are without drill-hole control, but even with the possibility of a "blind-zone" error there is unquestionably a great deal of recent sediment without a bedrock or glacial rise on which to anchor these sediments. Profiles such as these on intertidal sand bars in the nearshore zone suggest that seismic refraction methods could aid in the data collecting for a sand inventory program. In addition, sedimentary horizons detected by seismic methods in deeper water could be correlated with similar horizons beneath inter- tidal and exposed shore formations. 37 “sUOTIBIO[ IOF Z OANBTY 9eG “SLoTIIeg oy} Lopun osTY yOoLpog & 9IOTPUT SeInjeey TeTIZeg oy} UO SeTTFOIg SSLOEASUPLL TBUOTITPPY “SZ oin3t 4 93S/L4 Ni NSAID 3YV S3ILIDO13A 31V9S 1WLNOZINOH a ae so | > 1333 00S fo) q meta AV19 JANIMVWOIDV19 fe ONIATH3AO0 ONVS eral tf oh Ww ft $28) “Hid3ad Oo wo ie) NU ee 6 <2 0G6 QIFs:K ey: azecOSP Sle S SPO Suey. Sal OO0ES OOl og. 9 m z Os - o CY G2 O > & % & A x = 38 949 STOH TITId pue 6I-d) ‘8T-d) Woz UOoTIDEg ssoIQ “97 aINTTY J1VIS IWLNOZIYOH 13343002 OO! O 09 0g 4 #244 oONdaE' A NaEET NO SEEENE bos Op Oo SD) 4983 “H1d3d o¢ 4: = O02 O WN Ol © ee e ee e e ee PER PRT Peet Or PO te fe) e staconeee Peece gg? ° © Pe, 0% 0% « Or ee ° OO OP oO Og w 0 8 oo 0% 00 8686" O COR RI Lvad | NY3COW | : JSOMULJION ve jsDayYJNOS 29 48a) oS ‘Zz ean3ty uo GLA eTOY TIT4Ip 3e st attzord aul “YystH yoLpeg Be uo peLOYouy st Apog pues STY2 IeYI SMOYS ITEC TePTL-POOTH XeSSa eY2 SSOLOY eTTFOId “LZ oanBTd 93S/L4 NI NSAID 3YV S3ILIDOTSA 31V9S IW.LNOZIYOH 1334 002 001 0 0g Oo nN $02} ‘H1d3d JSOMULJION ysDeu;NOS 40 IV. DRILL-HOLE INTERPRETATION 1. Generalized Stratigraphy Sampling techniques have been discussed in Section II. Samples were given a preliminary inspection in the field upon removal from the split- spoon sampler. This allows the driller to make decisions about sampling interval and perhaps estimate the proximity of a significant sedimentary change. The Drill-Log Appendix summarizes the preliminary field observations and later binocular microscope analyses of the samples. Using the binoc- ular microscope, estimates were made of grain size, sorting ,roundness, and gross mineralogy. Examination showed a distribution of sediment that closely agrees with previous work of McIntire and Morgan (1963) and McCormick (1968). . This study went beyond the depths of the McCormick study and added to the interpretation of the geological history of Plum Island. The pale- Ogeography suggested by this study fits well with the ideas about submerged relict dunes expressed by Anan (1971). McCormick determined seven stratigraphic zones by analysis of marsh cores. His generalized column follows: High salt-marsh peat Spartina alterntflora peat Western fine-grained facies Eastern coarse-grained facies Black peat Weathered zone Blue clay McCormick's samples were studied by x-ray and grain-size analyses. Such analyses were not made in this study, because it is more concerned with the large-scale, more obvious, correlations. For example, results of this study allow broader correlation (extension deeper and further seaward) of such horizons as the weathered zone, which overlies the glaciomarine clay sequence in McCormick's column. 2. Glacial Till and Glaciomarine Clay Overlying the igneous bedrock surface is glacial till, which varies from highly compact drumlin material to extremely sandy till beneath some of the beach deposits. Figure 28 is a photo of this sandy till from hole CBB. Identification of this material as till is sometimes dis- putable; the possibility that it is outwash or an ice-contact deposit is acknowledged. However, the material is poorly sorted, angular, and the pebbles have a silt cap-evidence that indicates till. The 4\ "sqseTo oy? jo eoezins roddn oy} 0} Sutzoype tokeT AeTO “ATS SuTYy? e ST ded 4I[TS y *setqqed ey} uo yuesead skempe st ded [Ts y “°sazoeTdwes oy ut dn iyYsno1g TeTLoyeW TeTOe[D eszvo) oy? Fo TeoTdXk] st qq) SLOH TITId wWorz TITL Apues S hy | bo es: eee e ee °8z ean3Ty 42 compact till is identical to that of the major drumlins in the area. Coarse material is tightly packed with a matrix of fine silt-clay-sized particles. In fact, without the coarse angular pebbles, the fine part of this till could be confused with the glaciomarine clay when viewed in a small quantity in a sampler. The absence of glaciomarine clay overlying the sandy till in some drill holes (CBC, CBD and CBE) suggests that the clay was never deposited here, or that if deposited, it was eroded during a later transgression by the sea. I believe that the clay was deposited on top of glacial mate- rial as found beneath Crane Beach, but was removed by erosion. Perhaps the sandy till, which is so common in the Crane Beach drill holes, is simply the compact till reworked by the sea and mixed with coastal de- posits. If a deeper drilling had been possible, the sandy till might have turned out to be a veneer over the more compact till. The glaciomarine clays were deposited during a high stand of the sea in a blanket of variable thickness over existing topography, lapping up on the sides of drumlins. The presence of glaciomarine deposits in a steep bluff at the southern end of Plum Island above sea level, and at elevations higher than 40 feet near Ipswich, contribute to the uncertain- ty about how these deposits were superimposed on the topography. Glacio- marine clay usually appears at depths below 50 feet (see Table); the same clay outcrops are throughout the Ipswich quadrangle (Sammel, 1963). This gap between surface outcrops and the 50-foot depth may be an ero- sional situation. More observations of buried clay horizons are needed to determine the configuration of the top of this deposit. 3. Indurated Clay An indurated layer is found on top of the clay layer (see Table). Five of 10 bore holes containing marine clay showed an indurated layer. This layer is a hard cement-like material that is 3 to 10 inches thick. Once the material has been loosened by the chopping bit it closely resem- bles the softer clays below. The layer is located by the difficulty of drilling through it. The hard clay is washed up the holes in chips or lumps, and becomes softer as it is mixed with water. Such a layer may be dewatered by compaction. This is a common phe- nomenon, especially in areas of artificial fill overlying clay deposits. Induration may also be due to exposure to subaerial weathering. An alter- nate mechanism, secondary precipitation, has been suggested by Coleman and Ho (1967). Coleman and Ho studied recent sedimentary sequences in the Atchafalaya Basin, Louisiana. They obtained undisturbed cores of 120-foot borings near the Mississippi Delta. The age of the deposits ranged from 10,000 B.P. to present. This extensive study determined that increase in com- pressive strength and decrease in water content in sediments in this area was partly due to the presence of cementing minerals such as iron hydrous 43 TABLE-BORE HOLES CONTAINING MARINE CLAY Depth in Feet Indurated | Sandy Till Layer Encountered | To Clay| To Clam Flat |} Total of Hole 44 oxides, calcium carbonates, minor amounts of siderite, manganese oxides, and manganese carbonate, with additional strength contributed by accumu- lation of fine clay fractions after burial. A similar process may have affected the Plum Island sediments. The possibility presents a question that could be answered by further study. An undisturbed core of the indurated layer is needed. Although the ce- menting agents mentioned may be present deeper in the glaciomarine clay sequence, it is possible that there is a zone of greater accumulation at the top of the clay. Unquestionably, carbonates exist in the blue clay sequence, because calcite nodules can be seen and a positive carbonate reaction to hydrochloric acid is common. 4. Weathered Zone The weathered zone above the glaciomarine clay is believed to rest on a surface of deposition on which clastic materials were deposited during a low stand of the sea. This weathered zone is composed of coarse, poorly sorted and highly oxidized sand and gravel. Figure 29 is a photo of this material from Plum Island hole PIG. These clastics could come from nearby drumlin tills, ice-contact drift, or stranded beach deposits of earlier sea levels. 5. Black Peat The black peat here is likely a correlative of the black peat found by McCormick in his drill holes further north. Johnson (1925), Davis (1910) and Bloom (1968) all recognized this peat in New England marshes. These investigators agree that the black peat represents an accumulation of fresh- and salt-water plants deposited in the zone of transition from salt marsh to upland vegetation. The peat is a highly organic compacted layer. Its dark color is probably due to a reducing environment estab- lished after transgression of the sea. Its silt content is variable. It ranges in thickness from 1 foot to a few inches, and is totally absent in some of the more seaward drill holes. The black peat does not overlie clay everywhere, because this transitional situation probably could not develop in lower or more seaward locations. This peat layer commonly lies directly under a thick estuarine sequence of either channel, point- bar, or low energy mud-flat deposits rather than a marsh deposit. It is found directly on the weathered zone when all of these layers are present. 6. Estuarine Sediments The sands that overlie the glaciomarine clay sequence and its capping weathered zone represent various environments of deposition. Most of the Subdivisions grouped under the heading of estuarine sediments that are only drill hole horizons, not seismic horizons. Occasionally the seismic record shows a horizon within these sediments, but detailed stratigraphy can only be accomplished with closely spaced drill holes. 45 *poqios ATtood st Tetsroqew ay, “Le~nsue 0} popunorqns oze satqqed sy], “LoTo) peuteqs-uory ue Se 1eYy 91N}IXTW [OAeIDN pue pues e Fo posoduoy st suoZ poroyieoM "62 omnsTy 46 Clam-flat sequences overlying the clays are often thick (see log for drill hole PID in the Appendix). The clam-flat facies are identified by a large accumulation of clam shells and by an extremely silty to muddy nature. Figure 30 is a sketch of the study area near Castle Neck as it might have looked before the readvance of the sea over the glaciomarine de- posits. Stranded beach ridges probably contributed the material to the weathered zone that appears over the glaciomarine clay. Glacial material provided topographic highs on which to anchor the modern barrier sands. It is suggested that the Essex Bay flowed in nearly the same channels as it does at present. This suggestion is supported by the fact that the Essex flood-tidal delta is anchored on bedrock. The bedrock topography is glacial or preglacial, and this tidal delta has apparently been stable throughout the sea-level rise. The existence of a deep bedrock low be- tween the Essex delta and the modern Castle Neck suggests that a deeper. relict Castle Neck River might have flowed in this preglacial-bedrock low, and built the thick sequence of sediments presently filling it. Gla- ciomarine clay is found in the bedrock low at the margins of the modern Castle Neck. Its depth varies between 50 feet (log of CBF) and 70 feet (log of CBG). An extensive clam-flat sequence overlies the clay horizon in drill hole CBF, which suggests a fringing clam-flat environment behind a topography of glacial material during the low stand of sea level. Other drill holes support the scheme in Figure 30. For example, drill hole CBB bottomed in till at 60 feet. Directly on top of the till is a brown clay that grades upward into a blue-green clay before becoming a brown clay again. It is presumed that some weathering changes have been preserved in this record. A highly organic, perhaps fresh-water, black peat overlies the clays. Coarse sand to fine gravel predominates in the section upward from this point. Drill hole CBB is on the Ipswich River west of Castle Hill. It is one of the more inland sites, and its record suggests that much geologic history could be discovered by a comprehensive deep drilling program in some of the more protected or inland marshes. Drill holes at such areas could sample the black-peat horizons for age dating purposes and deter- mine more closely the sea-level curve for this coastline. V. CASE HISTORIES FROM PLUM ISLAND Extensive sand deposits underlie the Parker River estuary. For ex- ample, the log of wash-boring MGA (Middle Ground) shows more than 55 feet of sand on top of the clay horizon. Only the lower 10 to 15 feet of sand is thought to be clam-flat deposits. The upper part of the deposit, fine quartzose sand interspersed with organic layers, is thought to have been deposited on sand flats dominated by strong currents and rapid sediment transport. Shellfish do not thrive in such environments on the modern 47 THH J1LSV9 *pezoysue ouledeq LaTilieq ULOpow oy} YOTYM yYsuUTese systTYy ITYder30d0} peptaoad Tetzezyew Tetse[TH *(*d°d OOO‘OT) T9AST BOS PaTOMOT BUTINp poyYooT oaey 2U3TU 4— MOY SMOYS STU] “BOTY YDON 9TISeD 9Y LTOAQ PIeEMZSeOYINOS BUTYOOT YyDIEey¥S “OES eANBTY 4 v4 Y3AIY Les SS Ava 48 Middle Ground (Boothroyd, personal communication, 1971). Therefore, Middle Ground had its beginnings as a clam flat on a surface of glacio- marine clay, which is anchored on a slight bedrock rise (see Problems of Interpretation, Section III, 4), and changed to a rapidly accreting mid-channel bar as the estuary continued to fill. Drill hole PIF shows a thick sequence of estuarine sands from -65 feet up to a buried peat layer at -28 feet and then general coarsening from there upward. The stratigraphy determined by McCormick (1968) agrees with this sequence. McCormick found that the western fine-grained facies (a fine, mud-flat sediment) has been replaced and overlain by the coarser eastern coarse-grained facies (a coarse channel sediment) as the estuary migrated landward in response to barrier transgression and sea-level rise. Between about -38 feet to -48 feet there are alternating sandy and muddy layers in drill hole PIF. The coarser, more angular, more feldspathic sediment above the peat layer perhaps represents a higher energy environ- ment, that is, the encroachment of the major channel of the estuary. The drill hole is located on the eastern margin of the estuarine channel where the marsh peat is eroding in response to the meandering of the Parker River channel, which apparently moved westward over this spot centuries ago. Cottages on the channel are rapidly losing their foundations. His- torical accounts by previous inhabitants affirm the modern eastward move- ment of the estuarine channel. Drill hole PIF went to a depth of 65 feet. No clay was found, but nearby drill holes indicate that clay should not be far below the 65 feet horizon. Deeper bedrock topography probably accounts for the lower clay horizon. Insufficient drilling depth left a small, but perhaps sig- nificant, question unanswered. Drill logs for holes PIA and PIB are nearly identical. In both holes, grain size varies upward from the clay horizon. PIB shows a coarse gra- vel or weathered layer above the indurated clay; the weathered material probably became the floor of the developing estuary. The alternating Silt and sand layers noted in PIF are also present in PIB, confirming that the main channel of the estuary migrated back and forth significant- ly through time. The peat layer at -11.5 feet in PIB is probably salt- marsh peat that has been compressed by advancing barrier dune sand. Figure 31 is a sketch drawn from seismic data and drill-hole logs of holes PIC, PIE and PIG. These drill holes were selected for correlation due to their proximity and interrelated depositional sequence. It is Suggested that during the low stand of the sea, after deposition of the glaciomarine clays, the estuary maintained a major channel east of its modern change. The original barrier then was farther seaward (Anan, 1971), and the estuary surrounded the drumlins at the southern end of Plum Island. McCormick's map of sediment distribution agrees with a more eastward location of the younger estuary. Clams flourished in the low- energy fringing mudflats along the irregular drumlin shoreline. While 49 *puod ystyoezq & ollo0deq LojeT [TIM JuUoUXequa sTY], "way? puTYeq JUeUXeque T[eUS 94} UT BUTdOTeAep ST YysZeM e se BUTpore oe SUT[UMZp OU, ‘g'g 000‘y Ioqe 1e TEAST ves smoys Ied LOMOT OY, “LoTILeg MoT e puTYyog AZenqsy ue uT suTTUNAg smouS ("d"d 000‘0T) TeAe7 229g poteMoT BuTING 3S9M BUTYOOT pueTST uNTgq uZeYyINOS Fo YyDIeyYS “TS eun3tTy d@ O000'b y iM TA { yA 4 UY ZZ, COS Wu gr eae, CR Sa FE WQWOr aa ae EG —— Rr ee te hi CUED ART SW we NW; WM IZ SHS WW b QIN TUT Ter NMRA da ooo‘o! oe TAT PORTAL Ti ©) 7 Oo. te 8, 88 wo Af FE clam flats existed in the vicinity of the drumlins, channel sands were being deposited elsewhere. As sea level rose and the barrier island transgressed, the glaciomarine and glacial deposits were covered with barrier and estuarine sands. However, the accretion was slow enough to allow continuation of the shellfish population on the clam flats. As the waves began to attack the drumlins just seaward of the relict estuary, a sand spit built across the mouth of the channel behind the drumlins and closed off this estuarine circulation. With estuarine cir- culation cut off from the basin, marsh peat began to develop. The fresh- water peat, identified in drill-hole log PIC, occurred during a brief fluctuation in sea level or during the complete closure of the basin away from the estuary. The result is a modern brackish pond which is now maintained by a manmade dike. The logs of PIC and PIG show unusually high elevations for blue clay in a Plum Island drill hole. PIC was drilled 60 feet to refusal, which was determined by seismic profile to be the surface of bedrock. This is an example of the marine clay being draped over a preglacial bedrock high with little later erosion. However, the log of PIG shows silt at 22 feet. On top of the uppermost silt horizon is a gravelly layer with angular rock fragments, typical of the weathered zone over the glacio- marine clay. Glaciomarine clay does not appear until 65 feet. Between these depths is a sequence of alternating clay-silt and sand layers with a semi-indurated layer at 32 feet. The sand and silt are highly quartz- ose. The blue clay, where it grades into silt-sized material, is usually also highly quartzose. Therefore a sharp discrimination between the silt and the clay is often difficult. Drill hole PIH is the most southerly hole on Plum Island. At 25 feet, the drill bit passed into poorly sorted, coarse, angular gravel with a silt cap on the pebbles. However, seismic returns indicate a discontinuous "till" velocity beneath this area. If there is a till sequence here, it is likely a thick one on which the southern end of Plum Island is anchored. In con- trast, the presence of the mouth of a large inlet also suggests that there could be a large accumulation of coarse channel deposits. A compromise between the two ideas might be that the surface till of southern Plum Island extends southward beneath a veneer of sand deposited by spit accre- tion. This glacial material has been greatly reworked by wave and current action, but remains near its source, the southern Plum Island drumlin field. Fitting undated drill-hole logs to sea-level curves can be arbitrary. However, the presence here of such environmental determinants as clam- flat facies, fresh-water peat, weathered gravel zones, and glaciomarine clays permits a more certain three-dimensional space correlation with time. To aid this correlation, the sea-level curves proposed by McIntire and Morgan (1963) and Kaye and Barghoorn (1964), are presented in Figures 32 and 33. Kaye and Barghoorn assume a high stand of the sea before 14,000 B.P.; McIntire and Morgan suggest that the high stand was before S| Before 10,500 BP 4.900 BP *®STACKYARD ROAD “K” Present MHT. Present MHT 3,625 BP SPARKER RIVER “Bb” __Present_MHT * PARKER RIVER “Bc” Eustatic Stability Present MHT Present * PARKER RIVER “L” Present _MHT__ *RADIOCARBON DATES Figure 32. Sea-level Trends as Presented by McIntire and Morgan (1963) for the Plum Island Area. The levels shown here are based on radiocarbon dates. Matching the stratigraphy determined in the above study with that presented by McCormick (1968) suggests an approximate time frame as in Figures 30 and 31. 52 "eole pueTs] wmtq 94? OZ (£96T) ueSLow pue SLTIULOW FO YI YIM [TOM SeoTse SAINI STY], “eeTy UOJSOg 9Y} UT B3eq WOLY SAIN) [TSAST-BaeS SATIETOY eB pouTUII}0q (y961) uxtooysreg pue okey “Cg 9mn3TYy (7961) uLooysreg pue ofey fAaarng [edTZo0TOeD “S*N wor eso COO! COOK! 000'% 0001) C00. 0006 0008 -0004 0009 000% 000” 0006 —0coz = 200! os Eee es pe 3 BoM 808- gee 002- 0006 0008 0004 0009 0006 000% 0006 0002 300) (6) 1926300 3BU0198 SUVIA M DIVIS IVANOZIWOW 53 VIA] VIS 1NISIWS MO1I® ONY JACOBY 13239 MH 9TVIS THdLUBA 10,500 B.P. Both authors admit room for improvement in fixing the curves to dates so far removed from the present. McIntire says (personal commun- ication, 1971) that he might revise his time-level relations, particularly the more distant ones. Kaye and Barghoorn suggest a higher sea stand during deposition of the glaciomarine clay. Clay deposits were lifted above sea level during unloading of the earth's surface with deglaciation. These clays were mantled with a thin layer of coarse-grained weathered material. The maximum relative low stand of the sea at -60 feet does not explain clay induration at this level or below. Therefore, induration may have been due in part to the diagenetic altera- tions suggested by Coleman and Ho (1967). Both sea-level curves agree on the low stand of the sea. Since most of the sediment recorded in the drill logs was deposited after the low stand of the sea, it is therefore significant to make the agreement between these two sea-level curves for the period from 10,000 B.P. to the present. Figures 30 and 31 are dated as about 10,000 B.P. or at the low stand of the sea. The lower part of Figure 31, which shows how the southern Plum Island basin was closed off, could have a date of about 4,000 B. P., due to the relative levels of the marsh sequence and of the sea at this time. In general, the drill-hole data show a rather uniform rise in sea level after a low stand at about -60 feet. This rise allowed the develop- ment of shellfish flats in low-energy fringing environments as well as the more rapid accretion on the dynamic sand flats. 54 VI. DEVELOPMENT OF A BARRIER ISLAND The findings of this study give all major barrier-island theories some support. As early as Dana (1894) and Gilbert (1890) littoral transport was considered a valid barrier-building mechanism. Johnson (1925) suggested that wave-cut drumlins provided sediment for the development of spits and pocket beaches in the Nantasket area near Boston, Massachusetts. Figure 34 is a reproduction of a similar suggestion by Nichols (1941) for the development of Castle Neck. Nichols did not have the benefit of subsur- face data, and was unaware of the Pleistocene topography of the south- eastern end of Castle Neck. Hoyt (1967) proposed relict beach ridges as the origin of barrier islands. Fisher (1968) suggested a mechanism similar to that of Gilbert's (1890) spit-accretion. There are in this study area drowned relict drum- lins linked by deposits caused by littoral drift. However, the erosion of the drumlins was not the only source, because the Merrimack River was contributing large amounts of sediment during the building of the barrier islands and spits. The remainder of Plum Island (north of Camp Sea Haven, Figures 1 and 2) which was not part of this study area, may have a structure similar to the southern end of the island. It is suggested that Pleistocene topography and bedrock highs anchor the island at these locations. Anan (1971) finds evidence in his offshore sediment analysis of a relict delta near the mouth of the modern Merrimack River. The delta was flanked by low barriers which probably moved landward in response to the sea's transgression. A three- dimensional analysis of other barriers on this coast would certainly ex- pand the historical and stratigraphic concepts of the Pleistocene and Holo- cene sediments. 55 WOTTIAL QLAMD STAGE OF THE CASTLE NECK AREA STAGE L FOURTH STAGE 10) THE CEVELOPUENT OF THE CASTLE NECK AREA STAse W SECOND GUAGE mM) THE CEVELOPMENT OF THE CASTLE MECK AREA STAGE IZ (Moss. Dept. of Public Works-U.S. Dept. of the Interlor ; Cooperative Geologic Project, Bulletin 7, 1941.) sine * i TURD STAGE Wd THE CEVELOPMENT OF THE CASTLE NECK AREA STAGE OL Figure 34. Nichols (1941) Suggested that Castle Neck Originated From a Series of Beaches and Spits Building Around Drumlins. His ideas seem quite accurate when com- pared with subsurface data. 56 VII. CONCLUSIONS Concluding remarks deal with two separate phases of the study. The first six items summarized below deal with the development of field tech- niques; the remaining items deal with geologic interpretations resulting from this study. Ih A seismic refraction study should precede the drill-hole study if both are to be done. Drilling equipment that is capable of reaching the deepest bedrock regardless of the nature of the overburden should be selected. A high explosive should be used as the seismic energy source to avoid signal attenuation. Preliminary time-distance plotting should be done in the field using a nomogram solution to gain an accurate judgement about the location of future profile lines. Dunes or large accumulations of dry sand should be avoided when running seismic profiles. Shallow-refraction seismic methods are successful near the shore if attention is given to the following problem areas: a. The "blind zone'' due to a second layer of intermediate velocity. b. The non-zero intercept due to a dry layer between the surface and the water table. c. Apparent sediment velocities due to thickening or thinning of a low-velocity layer. d. Attenuations of seismic energy in a layer underlain by peat. e. Apparent bedrock velocity due to either a highly irregular surface or a steeply dipping surface. Seismic and drill-hole results suggest a well-defined bedrock surface. Bedrock topography is highly irregular and varies from surface outcrop to depths in excess of 150 feet. Mantled on this bedrock surface is till and many Pleistocene topographic highs. This Pleistocene topography can be inferred largely from the modern drumlin configurations, although some glacial topography has been reworked by the sea or buried by coastal deposits. Deposited on this glacial drift is a thick layer of glaciomarine clay. The clay, of nonuniform thickness, appears to cover most o7 10. glacial topography that was submerged during the time of clay deposition. The clay is not encountered at one particular eleva- tion, but rather resembles a cloth draped over an uneven surface. Clay horizons in the local area vary from 40 feet above sea level to 60 feet below sea level. During the subsequent low stand of the sea, this glaciomarine clay was exposed to subaerial conditions and a weathered horizon con- sisting of weathered clay and coarse clastic material eroded from nearby Pleistocene topography. In addition, fresh-water vegetation in areas beyond tidal waters developed a fresh-water peat. An approximate time frame for this low stand of the sea is about 10,000 B.P. (Kaye and Barghoorn, 1964). As sea level rose relative to the land, estuarine and marsh sedi- ments accumulated behind a landward migrating barrier. Drumlins were eroded, some so much that they are barely distinguishable today. Finally the sea-level rise leveled off to its current rate of 0.3 feet per century (McIntire and Morgan, 1963), and the barriers became anchored against both buried and exposed Pleistocene deposits. 58 LITERATURE CITED ANAN, F.S., "Provenance and Statistical Parameters of Sediments of the Merrimack Embayment, Gulf of Maine,'' Unpublished Ph.D. Thesis, Univer- sity of Massachusetts, Boston, Mass., 1971. BLOOM, A.L., ''Postglacial Stratigraphy and Morphology of Central Connecticut ,"' Guidebook for Field Trips tn Connecttcut, New England Intercollegiate Conference, New Haven, Conn., 1968, 305 pp. BOOTHROYD, J.C., Personal Communication, 1971. CHUTE, N.E., and NICHOLS, R.L., "Geology of Northeastern Massachusetts," Bulletin No. 7, Cooperative Geology Project, Massachusetts Department of Public Works and U.S. Geological Survey, 1941. CLAPP, C.H., "Geology of the Igneous Rocks of Essex County, Massachusetts," Bulletin 704, U.S. Geological Survey, Washington, D.C., 1921. COASTAL RESEARCH GROUP, Coastal Envtronments, N.E. Massachusetts and New Hampshire Field Trip Guidebook for the Society of Economic Paleontolo- gists and Mineralogists, University of Massachusetts, Boston, Mass., 1969, 462 pp. COLEMAN, J.M., and HO, C., “Early Diagenesis and Compaction in Clays," Proceedings of First Sunpostumn on Abnormal Subsurface Pressure, School of Geology and Department of Petroleum Engineering, Louisiana State University, 1967, pp. 23-50. CURRIER, L.W., "The Seismic Method in Subsurface Exploration of Highway and Foundation Sites in Massachusetts," Circular 426, U.S. Geological Survey, Washington, D.C., 1960. DANA, J.D., Manual of Geology, American Book Co., 1894, 1,087 pp. DAVIS, C.A., "Salt Marsh Formation Near Boston and Its Geological Signifi- cance,'' Economie Geology, Vol. 5, 1910, pp. 623-639. DOBRIN, M.B., Introduction to Geophysical Prospecting, 2nd ed., McGraw- Hill, New York, 1960, 446 pp. DUANE, D.B., "A Study of New Jersey and Northern New England Coastal Waters,'' Shore and Beach, Oct. 1969. FISHER, J.J., "Barrier Island Formation Discussion, Geological Soctety of America Bulletin, Vol. 79, 1968, pp. 1,421-1,426. FOLK, R.L., Petrology of Sedimentary Rocks, 2nd ed., University of Texas, 1968, 190 pp. GILBERT, G.K., "Lake Bonneville,'' Monograph 1, U.S. Geological Survey, Washington, D.C., 1890. 59 HAWKINS, L.V., and MAGGS, D.,"Nomograms for Determining Maximum Errors and Limiting Conditions in a Seismic Refraction Survey With a Blind- Zone Problem, Geophystcal Prospecting, Vol. 9, 1966, pp. 526-532. HOYT, J.H., "Barrier Island Formation," Geologtcal Soctety of America Bulletin, Vole. 78) LOG7 sa Ppem Le liZo— ees O's HOYT, J.H., "Barrier Island Formation: Reply," Geological Soctety of America Bulletin, Vol. 79, 1968, pp. 1,427-1,432. JOHNSON, D.W., Shore Processes and Shoreline Development, Wiley, New York, 1919, 584 pp. JOHNSON, D.W., New England-Acadtan Shoreline, Wiley, New York, 1925, 608 pp. KAYE, C.A., and BARGHOORN, E.S., "Late Quaternary Sea-Level Change and Crustal Rise at Boston, Massachusetts, With Notes on the Autocompac- tion of Peat," Geological Soctety of America Bulletin, Vol. 75, 1964, pp. 63-80. LEET, L.D., Earth Waves, Monographs in Applied Science, No. 2, Harvard University Press, 1950, 122 pp. LINEHAN, D., "Seismic Prospecting in New England," Transactions, 23rd Annual Meeting of the American Geophystcal Unton, Pt. 2, 1942, pp. 227-228. LINEHAN, D., "Seismology as a Geologic Technique," Application of Geology and Setsmology to Highway Location and Design in Massachu- setts, Highway Research Board Bulletin 13, National Research Council, 1948, pp. 77-85. McCORMICK, C.L., "Holocene Stratigraphy of the Marshes at Plum Island, Massachusetts,'' Unpublished Ph.D. Thesis, University of Massachusetts, Boston, Mass., 1968. McINTIRE, W.G., and MORGAN, J.P., ''Recent Geomorphic History of Plum Island, Massachusetts, and Adjacent Coasts," Coastal Studies Series No. 8, Louisana State University, New Orleans, La., 1963. MEIDEV, T., "Nomograms to Speed Up Seismic Refraction Computations," Geophystes, Vol. 25, 1960, pp. 1,035-1,053. POWERS, M.C., "A New Roundness Scale for Sedimentary Particles," Journal of Sedimentary Petrology, Vol. 23, 1953, pp. 117-119. SAMMEL, E.A., 'Surficial Geology of the Ipswich Quadrangle, Massachu- setts,"' Geological Quadrangle Map GQ-189, U.S. Geological Survey, 1963. 60 SEARS, J.H., ''The Physical Geography, Geology, Mineralogy, and Paleon- tology of Essex County, Massachusetts," Essex Institute, Salem, Mass., 1905. SJOGREN, B., and WAGER, O., "On a Soil and Ground Water Investigation With the Shallow Refraction Method," Engineering Geology, Vol. 3, 1969, p. 61. 6 | iy ay ; + Dray vey APPENDIX DRILL-LOG SUMMARIES The logs of 17 drill holes follow. The information is only a summary of each log. Preliminary field data and the detailed descriptions from a binocular microscope in the laboratory are included at the right of the column; the tick mark indicates the center location of the sample taken. Grain size was estimated visually by comparison with sieved sediments of known size. Sorting was estimated from the sorting chart of Folk (1968) and the roundness chart of Powers (1953). Depth in feet is logged to the left of the colum. 63 SAND, QUARTZ AND FELDSPAR, 1.5 PHI, MODERATELY SORTED, SUBROUNDED J] = SAND, QUARTZ, 1.0 PHI, MODERATELY SORTED, SUBANGULAR =| — WOOD FRAGMENTS — SAND, GREY QUARTZ, 2.5 PHI, MODERATELY SORTED, SUBANGULAR ©..| _ SAND WITH WOOD BARK, QUARTZ, 1.5 PHI, | MODERATELY SORTED, SUBANGULAR ‘.:.’| _ SILT AND SAND, PREDOMINANTLY QUARTZ, POORLY | SORTED, ANGULAR SAND, GREY QUARTZ, NO SILT, SOME ANGULAR GRAVEL, VERY POORLY SORTED CBE 64 SAND, FELDSPAR AND QUARTZ, 1.0 PHI, MODERATELY SORTED, SUBROUNDED SAND, PREDOMINANTLY FELDSPAR, 2.0 PHI, POORLY SORTED SAND, QUARTZ AND FELDSPAR, -1.0 PHI, POORLY SORTED, ANGULAR SAND, QUARTZ, FELDSPAR, METAMORPHIC ROCK FRAGMENTS , POORLY SORTED, ANGULAR COMPACT SAND SANDY TILL, SILT CAP ON LARGE PEBBLES DECK OF BARGE MODERN MARSH SURFACE MODERN CLAM FLAT SAND AND SILT, CLAM FLAT, 2.0 PHI, POORLY SORTED SAND, COARSE GREY QUARTZ, SHELL FRAGMENT, POORLY SORTED MUDDY LAYERS SAND, FINE GREY QUARTZ COARSE SAND MUDDY GRAVEL ROCK 65 RT DECK OF BARGE MODERN PEAT SAND, GREY QUARTZ, 1.5 PHI, POORLY SORTED, ANGULAR SAND, IRON-STAINED QUARTZ, COMPACT, 2.5 PHI, POORLY SORTED SAND, GRAY QUARTZ, 2.0 PHI, MODERATELY SORTED, ANGULAR, ORGANIC LAYERS SAND, QUARTZ, POORLY SORTED, ANGULAR SAND, QUARTZ, 2.5 PHI, POORLY SORTED GRAVEL, FELDSPAR, METAMORPHIC ROCK FRAGMENTS, 0.0318 MM PEBBLES SAND, QUARTZ, FINE, POORLY SORTED, SUBANGULAR SAND, QUARTZ, 1.0-2.0 PHI, POORLY SORTED, SUBANGULAR SILT, CLAM SHELLS, POORLY SORTED, ANGULAR APPROXIMATE CLAY HORIZON BLUE/GREEN CLAY BLUE/GREEN CLAY MGA BLUE/GREEN CLAY 66 GaLYOS ATIOOd * SATddad AUVT HLIM AV Sa1dddd HLIM AWD Ss )0) SH1sdad NV SNOISNIONI AGNVS Gqu *AWID JOVIUAINI ONVS/AVIO SINIWOVYA GdOOM GaLdOS ATALVYAGON *IHd 0°Z *ZLYVNO “ANS SLNANSVUA AOU DIHYONVLAW *ZLUVNO “GNVS GaluOS ATHOOd ‘IHd 0°Z-S*T “LANUVD ‘ZLuvAdD ‘aNvS IHd O°T “ZiuvNO ATUO “GNVS VOIW HLIM 3AOdY SV ONVS daLYOS ATUOOd AWAA “IHd O°Z-O°T “ZLUVNO *ANVS AAVAH UIAVT LOVANOD GaLYOS ATHOOd *IHd 0°72 *STVHANIW ‘avdsalad ‘Zluvnd “TaNLXIN Lydd GNV GNYS = O'S AGO AVD aNd OL AVIO NHOUd HOUA ADNVHD — Sa1dadad GNY STTZHS WV1D HLIM AVID — OL ONIGVYS - LVL WWID - AVID OL ITIS ONISVD dO GNF UVINONVENS “IHd S$°2 “ZIMVNO ATAD “GNVS — UVINONVENS ‘IHd O°2 ‘Zlavnd AGGOW ‘aNVS — UVINONV ‘UFIIVWS GNV IHd 0°Z ‘zluvnd Amu ‘GNVS — SLNIKOVaI doo — aNvS LlOvdwoD — SINIKOVad dooN — 31NOS ATHOOd ‘IHd S‘T ‘UvdSGTIA HLIM zluvnd amUD ‘aNvS — UVINONY ‘GaLTHOS __ AIAIVASGOW ‘IHd O°7-S*T ‘G@ANIVIS NOYI ‘zZLuvnd ‘aNvS UVINONY ‘AQUOS ATHOOd ‘IFA O'Z __ *SINTWOVUI YINVOYO HLIM UVdSd1ga4a GNV zLlavnd ‘aNnvs (aLYOS ATALVYAGOW ‘IHd S*T ‘ZLuvNd AUD Wuva *‘aNvs — . LV3d AGNVS” — agqNnoaaNs ‘daLuOS ATALVAIGOW ‘Ind ¢*z ‘zluvad ‘anys — 67 SAND, FELDSPATHIC, 1.0 PHI, MODERATELY SORTED. ANGULAR SAND. QUARTZ, HIGHLY ORGANIC SAND. MUDDY. GREY SAND, MUDDY. 2.5 PHI. MODERATELY SORTED, ANGULAR AS ABOVE SAND. OUARTZ WITH SOME GARNET. HEAVY MINERALS, BIMODAL, ANGULAR SAND, QUARTZ, ROCK FRAGMENTS, CLAM FLAT. 2.5 PHI SUBROUNDED MUD, FINE QUARTZ, CLAM FLAT, 3.0 PHI, ANGULAR ALTERNATING CLAY AND SAND LAYERS SLIGHT INDURATION ON CLAY SURFACE BLUE CLAY Pie BLUE CLAY 68 SAND. FELDSPAR. QUARTZ, 2.0 PHI, MODERATELY ‘SORTED, SUBANGULAR SAND, FELDSPAR, 1.5 PHI, MODERATELY SORTED, SUBROUNDED SAND, GREY QUARTZ, 2.5 PHI. POORLY SORTED. SUBROUNDED GRAVEL, METAMORPHIC ROCK FRAGMENTS, FELDSPAR, QUARTZ, POORLY SORTED. ANGUT.AR CLAY AND SILT, QUARTZ SAND, 2.5 PHI, MUDDY, MODERATELY SORTED, VERY ANGULAR SEMI-INDURATED CLAY HORIZON SILT, HIGHLY QUARTZOSE SAND, QUARTZ, 4.0 PHI, MODERATELY SORTED, SUBANGULAR SAND. QUARTZ. 4.0 PHI, POORLY SORTED, SUBANGULAR SAND, FINE QUARTZ CLAY, TYPICAL PLASTIC BLUE CLAY PIG BLUE CLAY CLAY WITH SILT 69 gg) SH1addd NO dyO LIS ‘1114 aNvsS AV1O NMOUG AVI9 ~NAqWUD AVIO NMOUG ivdd YalVM HSI AVID GNV ITIS NOZIUOH AVID NO NOILVUNGNI ON GaINOS ATALVYACOW ‘IHd O°€ “SINFWOVUI WOU DIHMUONVLAW ‘ZLYVND GANIVIS-NOUI ‘ANVS @aRi0S T1aM ATZLVUAGON “Id S°E *ZIdvN0 ATLNVNINOGAUd SI GNWS ‘THAVaD aNId GNV GNVS UVINONVENS ‘GaALYOS ATHOOd ‘ZLuvNd ‘TaAVUD GNV ANVS TVIMALVN OINVOUO ‘GALYOS 114M ATALVUAGOW ‘IHd $°Z “SINSHOVUA AION DIHAMOWVLAW ‘UvasSaTad ‘zLuvad ‘aNvS UV INONVENS ‘CALMOS ATALVUAGON ‘IHd O°Z ‘UvdSGTad GNV ZJuvAd ‘aNVS 1! Wt i! i! Vo Sq14a3d NO dV) ITIS V BLIN TIIL ACNVS ONTATHAAO TSAVAD ANV ANYS ASYVOD IVIGSIVW DINVDOYO HLIM GaTHOS ATHOOd “LTIS GNV GNVS zruvnd aNIa NvaT) ‘aNvS By INNVENs ‘dalYOS AIALVAGGNW ‘IN O°Z *ZIUWNd ATID “ANVS wWvdsaiags anv 71WwAdD ‘ANVS UVINONVENS ‘GITNOS ATALVUAGON ‘1Hd O'% ‘ZINWNd “aNVS UVINONVANS ‘GILNOS ATYOOd “IHd S°T ‘UVaSTad “AKVS ‘UVINONVGIIS “AFLYOS “ATIOOd “Hd O°@ ‘STVYSNIN AAVSH SUvdSCTad ‘z1yvnd ‘aNvS 70 dg) ziuynd ANIA SI L1IS ‘Sa1##ad NO dVO LIIS HLIM TIIL AGNVS — }'o9* agqnnowsns ‘aayos xTW00d ‘ina o't _ [°°] — OCS “SINANOVUA MOU OIHAYONVLAN GNV UvdSC1ad ‘ZLuvnd ‘aNVS GaLYOS TIAN ATALVUAGOW ‘IHd O°Z ‘Zluvnd ‘aNvS — UVINONVENS ‘GaLuOS 1144 P UVINONY ‘daLuos 14M KIGLVYAGON ‘IHd $*Z ‘SINAWDVYd Goon ‘ziuvnAd ‘aNvs — IHa $°Z ‘ziuvnd ‘aNnvs — qaluos TSM KIGLVYIGON ‘IHd $*Z ‘UvdSC1a4d ANOS HLIM ZLavAd ‘aNVS — waain08 Sd1ddad KO dvd DTIS HLIM TIL Jg9 UVINONVENS “CALUOS KIGLVAAGON “GANIVLS NOU *asuvoo *zravod ‘aXvs Z1awN0 FSUVOD “ANS SUUAW1 ONVS GNV LTIS ONTLVNYALTY UvdSd1ad TION HLIM UISUVOD Ind FAOV SV “UNYS UTINONVSNS “qaluoS ATHOOd ‘IHd O°Z “UvVaSGISd anv ziuvNd ‘aXvs UIAVI LOVaWOD ‘IHd $*Z “zLywNd “aXVS aaogy SV ‘VDIA GNV UvdSaTsa ‘ZTEYNO *ONVS GgaNnougns ‘aa1yos ATHOOd ‘THA S*O “Z1uvnd ‘aNvs aVINONVANS *qgJNoS ATHOOd ‘IHd O°T ‘Zluvnd NV Yvdsalad ‘GN*s = 10) 71 ZIUWNO G4ZIS LI1S dO XIMIVW HLIM TIIL AGNYS — E 11% Ue liaks reel ' | 0-020 ih Tt yy itl AVTD ania — tri! nano ' un a 09 wou aUNIXIN GNVS/AVD — dd ' hy it ' ity tty! What Sid wy tl STISSOd HLIM AVID GaIVUNGNI — ziuvnd LovdWOd aNId ‘GNVS — Theta om aeateo! ty daluos ATHOOd SLNAWDVUA GOOM ‘STVUANIW AAVAH GNV ZIuvNd ‘aNVS il i vt AVI) ania — ity! ' Huy SINANDVUA TIGHS WV10 GaLAOS ATUOOd ‘S119HS WV19 “SLNZWOVUI CQOM ‘YATTWNS CNV IHd S*T ‘zLuvnd ‘aNvs a nh ’ un "i | ©) ™m Vy ' 1! AWIO ania — STIZHS WVID ‘zluvnd “LIIS — WAIAVI GaLvundNI — STIAHS NVID ‘zZLuvno “LTIs — = SLOO’ HLIM AGGNW ‘GNVS — 3 ‘amu ‘ivdd — |i SLNAWDVUA DOU DIHAUONVLIN LUALVM HSM) NMOUG anv vol ‘ ‘Iv WVID ‘111s — |., W ANOS ‘SLNAROWA WV19 SHVID ‘IHd O°€ ‘ZluvNd ‘aNvS — FUNIXIN IIIS aNV Ivad — f GALUOS AIALVYACOW ‘IHa O°Z ‘ANVS ZLuvNd AUD ‘aNvS — | UVINONVGNS “GAIOS ATALVUAGOW *THd S*T “AGGNW “NWS Ur UNCOMPACTED PEAT, SOME SAND SAND, QUARTZ, FELDSPAR, 2.0 PHI, MODERATELY SORTED, SUBROUNDED SAND, QUARTZ, METAMORPHIC ROCK FRAGMENTS, 2.0-0.5 PHI, POORLY SORTED, ANGULAR SAND, QUARTZ WITH SOME ROCK FRAGMENTS, 2.5 PHI, MODERATELY SORTED, SUBROUNDED PEAT SAND, QUARTZ, 3.0-1.0 PHI, POORLY SORTED SAND, 1.5 PHI, MODERATELY SORTED, ANGULAR COMPACT LAYERS- DIFFICULT PENETRATION SAND, MUDDY WITH CLAY AND SILT BALLS, 3.0 PHI, WELL SORTED SAND WITH WOOD FRAGMENTS, QUARTZ, 1.0 PHI, MODERATELY SORTED SAND, QUARTZ WITH MICA, 2.5 PHI, MODERATELY SORTED, ANGULAR SAND, QUARTZ WITH MICA, ORGANIC FRAGMENTS, 2.5 PHI, MODERATELY SORTED, ANGULAR PROBE TO 65" INDICATES SANDY MATERIAL TO THIS DEPTH PIF “e) __SAND, FELDSPATHIC, 3.0 PHI, MODERATELY SORTED, SUBROUNDED —SAND, BIMODAL, SILT-SIZED QUARTZ, 1.5 PHI, FELDSPAR, SUBANGULAR __ SAND, FELDSPATHIC, SILT-SIZED QUARTZ, POORLY SORTED — SAND, FELDSPAR AND QUARTZ AS ABOVE — SAND, AS ABOVE BUT INCREASED FINE FRACTION — SAND, GRAY QUARTZ WITH PEBBLES, NO FELDSPAR — SAND, COARSE QUARTZ - UP TO - 1.0 PHI — SAND, FINE QUARTZ — SAND TO SILT, QUARTZ, POORLY SORTED — WOOD FRAGMENTS — INDURATED CLAY — SANDY CLAY, ROCK FRAGMENTS UP TO -1.0 PHI PIA — BLUE CLAY — BLUE CLAY 74 SAND, FELDSPAR, QUARTZ, METAMORPHIC ROCK FRAGMENTS, 1.5 PHI, POORLY SORTED, ANGULAR SAND, GRAY QUARTZ SANDY PEAT SAND, GREY QUARTZ, 3.0 PHI, MODERATELY SORTED, ANGULAR SAND, GREY QUARTZ SAND, QUARTZ AND METAMORPHIC ROCK FRAGMENTS, 2.5 PHI, MODERATELY SORTED, SUBANGULAR ALTERNATING SAND AND CLAY LAYERS GRAVEL, POORLY SORTED - SIZE FROM SILT TO 0.0635 MM PEBBLES, IRON STAINED GRAVEL WITH METAMORPHIC ROCK FRAGMENTS SIZE DISTRIBUTION AS ABOVE, IRON STAINED SAND, QUARTZ, 1.5 PHI INDURATED CLAY BLUE CLAY PIB BLUE CLAY 75 UNCLASSIFIED Security Classification DOCUMENT CONTROL DATA- R&D (Security classification of title, body of abstract and indexing annotation must be entered when the overall report is classified. : BRICINATING Acai vues (onmarate author) ; a 2a. REPORT SECURITY CLASSIFICATION epartment o e Army Coastal Engineering Research Center UNCLASSIFIED Kingman Building Fort Belvoir, Virginia 22060 - REPORT TITLE PLEISTOCENE-HOLOCENE SEDIMENTS INTERPRETED BY SEISMIC REFRACTION AND WASH-BORE SAMPLING, PLUM ISLAND-CASTLE NECK, MASSACHUSETTS. 4. DESCRIPTIVE NOTES (Type of report and inclusive dates) 5. AUTHOR(S) (First name, middle initial, last name) Eugene G. Rhodes “fe 1 July 1973 75 Sul | 8a. CONTRACT OR GRANT NO. 9a. ORIGINATOR’S REPORT NUMBER(S) b. PROJECT NO. Technical Memorandum No. 40 9b. OTHER REPORT NO(S) (Any other numbers that may be assigned this report) 10. DISTRIBUTION STATEMENT Approved for public release; distribution unlimited. 11- SUPPLEMENTARY NOTES 12. SPONSORING MILITARY ACTIVITY Department of the Army Coastal Engineering Research Center Kingman Building Fort Belvoir, Virginia 22060 13. ABSTRACT The wash-bore method of soil sampling was found to be an excellent technique for subsurface study in coastal areas. Phenomena to be considered when interpreting seismic refraction records include a) the "blind zone," b) the non-zero time inter- cept, c), time gaps in the time-distance photo over buried peat, and d) variable thicknesses of dry sand layers. The seismic method successfully located Pleistocene and bedrock topography. However, glaciomarine clay did not show a seismic contrast with respect to sandy, water-soaked sediments. Topography exposed during lower sea level has a dominant influence on modern coastal geology. Barrier islands became anchored on Pleistocene features as the sea level rose and deposition occurred in the estuaries behind the barrier beaches. Major channels of the estuaries migrated landward with the sea- level rise. No radiometric dates were determined from study samples but the sedimentary stratigraphy fits the time frame of other investigators. FORM REPLACES DO FORM 1473, 1 JAN 64, WHICH IS 1 mov 66 4 OBSOLETE FOR ARMY USE. 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