DISTRIBUTION OF BOTTOM SEDIMENTS ON THE CONTINENTAL SHELF, NORTHERN BERING SEA
Distribution of Bottom Sediments on the Continental Shelf, Northern Bering Sea
By DEAN A. McMANUS, VENKATARATHNAM KOLLA DAVID M. HOPKINS, and C. HANS NELSON
STUDIES ON THE MARINE GEOLOGY OF THE BERING SEA
G E 0 L 0 G I C A L S U R V E Y P R 0 F E S S I 0 N A L P A P E R 7 5 9-C
Prepared in cooperation with Department of Oceanography, University of Washington
UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1977 UNITED STATES DEPARTMENT OF THE INTERIOR
CECIL D. ANDRUS, Secretary
GEOLOGICAL SURVEY
V. E. McKelvey, Director
Library of Congress Cataloging in Publication Data
Main entry under title:
Distribution of bottom sediments on the Continental Shelf, Northern Bering Sea.
(Studies on the marine geology of the Bering Sea) (Geological Survey professional paper ; 759-c) Bibliography: p. 1. Marine sediments--Bering Sea. 2. Ocean currents-Bering Sea. I. McManus, Dean A. II. Washington (State). University. Dept. of Oceanography. III. Columbia University. Geological Observatory. IV. Series. V. Series: United States. Geological Survey. Professional paper ; 759-c GC398.5.D57 551.4'65'51 76-608367
For ~ale by the Superintendent of Documents, U.S. Go,·ernment Printing Office Washington, D.C. 20402 Stock Number 024-001-02993-6 CONTENTS
Page Page Abst:r;act ------C1 Distribution of sediments-Continued Introduction ------1 Sand-Continued Previous work ------1 Texture ------· C14 BathymetrY------3 Light minerals______14 Oceanographic setting ------6 Heavy minerals______14 Analyses and within-sample variability ------6 Sediment types ------· 20 Distribution of sediments·------7 Discussion------,------· 22 Gravel______7 Present-day processes of sediment transport------22 Silt ------10 Sediment dispersal______24 Clay------10 Summary and conclusions ------· 27 Sand ------14 References cited·------· 30
ILLUSTRATIONS
Page FIGURE 1. Index map of continental shelf in northern Bering Sea·------C2 2. Bathymetric chart of northern Bering Sea showing station locations ------4 3-15. Maps of northern Bering Sea showing: 3. Current measurements------5 4. Generalized geology ------8 5. Gravel distribution ------9 6. Silt distribution ------11 7. Clay distribution ------12 8. Sand distribution------13 9. Distribution of modal classes of sand ------15 10. Sorting of bottom sediments ------16 11. Ratio of plagioclase to K-feldspar ------17 12. Distribution of factors from Q-mode factor analysis of heavy minerals ______19 13. Heavy-mineral provinces ------21 14. Sediment types------23 15. Distribution of bottom sediment ------28
TABLES
Page TABLE 1. Variance of texture variables------C7 2. Extreme samples in Q-mode analysis of heavy minerals ------· 18 3. R-mode factor analysis of sediment size ------20 4. Extreme samples in Q-mode analysis of sediment size ------22
III
STUDIES ON THE MARINE GEOLOGY OF THE BERING SEA
DISTRIBUTION OF BOTTOM SEDIMENTS ON THE CONTINENTAL SHELF, NORTHERN BERING SEA 1
By DEAN A. McMANus,2 VENKATARATHNAM KoLLA,3 DAVID M. HOPKINS, and C. HANS NELSON4
ABSTRACT INTRODUCTION Most of the sediment contributed to the northern Bering Sea today (modern sediment) is associated with the Yukon River The continental shelf in the Bering Sea is one of runoff and the high-speed currents (30-40 em/sec near the bottom) the largest in the world. Even the shallow, within the Alaskan Coastal Water, which sets northward along northernmost part of the shelf formed by the the coast through Bering Strait into the Chukchi Sea. Most Chirikov Basin and Norton Sound (fig. 1) covers an sediment is silt sized but includes some very fine grained sand and 4 2 clay-sized material. The very fine sand extends northward across area of 11 x 10 km , approximately the area of the the mouth of Norton Sound, where it mixes on the west with relict shelf in the western Gulf of Mexico from the Yukon fine sand to form a palimpsest sand, thence grades Mississippi Delta to the mouth of the Rio Grande. Yet eastward into Yukon silt that covers southern Norton Sound. for the Chirikov Basin and Norton Sound, only a Much of the Yukon silt enters Norton Sound, but there is only a very general picture of the shelf sediments has been thin accumulation there, except near the delta. The silt issues from the sound along the north side, where a silt deposit is in pre available. The purpose of this study is to evaluate the sumed dynamic equilibrium, thereby marking the dispersal role of modern sedimentary processes in the region path through a depression into the coastal current. The modern and to seek a better definition of sediment silt associated with the coastal current is considered a dynamic provenance. A brief summary of part of this work is component of the bottom sediment, which otherwise consists of given in an earlier work (McManus and others, 197 4). relict sand and gravel. The net transport of the silt is through the Bering Strait and into the Chukchi Sea. PREVIOUS WORK Impressed on the steady north ward-setting current are irregular large-velocity fluctuations produced partly by tidal currents and A brief description of the bottom sediments of the partly by the wind regime. For the area as a whole, tidal currents Bering Sea and a summary of cruises to the study and wind drift are believed to be more significant than wave drift area prior to 1965 are presen ted by Creager and or estuarine-type density circulation. Where the coastal current is strongest, the sediment is a relict or McManus (1967), who noted the presence in Norton resid uallag sand and gravel derived from glacial rnaterial or from Sound of modern sediment from the Yukon River but metamorphic bedrock of Seward Peninsula. Under the slower considered the sediment in the Chirikov Basin to be Modified Shelf Water offshore of the coastal water, the bottom relict. A detailed study by McManus, Kelley, and sediment also is relict, in part relict Yukon sand, in part derived Creager (1969) concentrated on the Chukchi Sea from glacial moraines. Modern sediments do not accumulate beneath the Modified Shelf Water, as they do beneath the coastal north of Bering Strait, concluding that the Chirikov water. Basin sediment was not masked by the modern silts Northern Bering Sea was subaerially exposed during the period from the Yukon River, as the Yukon sediment was of eustatically lowered sea level _that coincided with the last being transported across the basin and into the glaciation. However, the surface sediments provide no indication Chukchi Sea as a turbid layer in the lower part of the that the Yukon River has ever drained northward into the Arctic Ocean. Until relatively recent time, the Yukon drained southward water column. Subsequently, the particle size and into southern Bering Sea. The river mouth has been in its present concentration of suspended material in the water northern position for only a geologically brief period. column were measured by McManus and Smyth Seaward size grading in relict sands is ascribed to the present (1970), further substantiating the significance of this day strong current paralleling the isobaths. process in transporting silt and clay across the floor 'Contribution 825 of the Department of Oceanography, University of Washington, of northern Bering Sea. based on work done as part of a joint research program by the U.S. Geological Survey The identification of silt and sand of Yukon origin and the University of Washington and financed by the U.S. Geological Survey. 2Department of Oceanography, University of Washington, Seattle, Wash. 98105. is based, incidentally, upon study of the mineralogy "Lamont-Doherty Geological Observatory, Columbia University, Palisades, N.Y. and texture of a body of sediment clearly of 10964. •U.S. Geological Survey, 345 Middlefield Road, Menlo Park, Calif. 94025. terrigenous origin that thickens toward the present
Cl C2 STUDIES ON THE MARINE GEOLOGY OF THE BERING SEA
100 200 MILES
1 I I I I I 0 100 200 KILOMETERS
ISOBATHS IN METERS
SIBERIA
SHPANBERG STRAIT 0 50 MILES I I I I r I 1 I I 0 50 KILOMETERS DISTRIBUTION OF BOTTOM SEDIMENTS ON THE CONTINENTAL SHELF, NORTHERN BERING SEA C3 mouth of the Yukon River (McManus and others, kotka is one of the main bathymetric features, the 1974). No samples were available to us from within Chukotka Trough, a shallow depression extending the river itself, and there are as yet no published northeastward from Anadyr Strait to the Bering descriptions of the bed and suspended load of the Strait. The deepest part of the trough is a closed Yukon River near its mouth. depression that terminates northward against a low In order to provide information on the provenance scarp that lies en echelon with the fault-controlled of the sand-sized sediment, a study was begun of the northern margin of Port Clarence Valley, a heavy minerals; preliminary results and tabulated prominent sea valley extending parallel to the coast data have been presented by Venkatarathnam of Seward Peninsula eastward as far as Port (1971). Detailed studies of the sediment texture and Clarence (fig. 1). gold content in the nearshore area off Nome (Nelson A prominent ridge of diverse surface topography, and others, 1969; Nelson and Hopkins, 1972) the Gambell Shoal, extends northeastward from the produced a better understanding of the complexities western part of St. Lawrence Island. Farther of sediment distribution near the shoreline. Descrip northeast, the Chukotka Trough is adjoined by the tions of sedimentary features recorded by seismic Chirikov Ramp, a gently sloping surface indented by profiling are included in the works of Grim ~nd many shallow branching swales suggestive of a McManus (1970) and Tagg and Greene (1973). north ward draining subaerial stream system. The Detailed bathymetric charts of the Chirikov Basin eastern part of the Chirikov Basin and much of were recently completed (National Ocean Survey Norton Sound is underlain by the Norton Plain, a Maps 1215-10 [1971], 1714-12 [1973], and 1814-10 region of monotonously flat topography that extends [1973]). eastward to the delta of the Yukon River. A broad, low ridge extending parallel to the coast of St. BATHYMETRY Lawrence Island diversifies the southwestern corner The description of the bathymetry that follows is of the Norton Plain. The Savoonga Depression, a based upon and uses the physiographic subdivisions sharply defined depression with maximum water proposed by Hopkins, Nelson, Perry, and Alpha depths exceeding 50 m, lies off the north-central (1976) for the Chirikov Basin area. coast of St. Lawrence Island. Hopkins, Nelson, and The water depth in the Chirikov Basin exceeds 50 Perry (unpub. data, 1973) show that the depression min only a few places; in Norton Sound depths are results from the faulting and folding of underlying generally less than 20m (fig. 2). An average depth for Tertiary sedimentary rocks but that the bottom the entire region might be placed at 30m. Because topography is diversified by intrusive volcanic plugs the depth is shallow and the area large, bottom and by ridges formed by submarine fissure eruptions gradients are very low, even for a continental shelf. of Quaternary age. The gradient down the Chirikov Ramp (fig. 1) is only A south-trending depression, the St. Lawrence 0.1 m/km between the 30-m and 50-m isobaths, the Trough, lies just off the east end of St. Lawrence relatively steep slope off Nome only 3 m/km. None Island. Water depths in this sea valley exceed 40 m. theless, within the broad saucer of the study area, The presence of fault scarps (Grim and McManus, small relief features occur that are significant in 1970) and closure of the bathymetric contours sug interpreting the sediment distribution. gest that tectonic activity may be involved in the The greatest water depths in the study area origin of the sea valley, but scouring by strong north (>150 m) are in the fiords along the Chukotka setting currents and stream erosion during intervals Peninsula; little else is known of the nearshore of low sea level may have played a role. Northward bathymetry along this coast. Offshore from Chu- the St. Lawrence Trough terminates abruptly against a broad constructional ridge, the Northeast Cape FIGURE 1.-Index map of continental shelf in northern Bering Shoal. Other large shoals and depressions trend Sea showing major physiographic units and sources of bathy northward in Shpanberg Strait east of the St. metric data for figure 2. Bathymetry west ofline A is contoured Lawrence Trough. from data on U.S. Defense Mapping Agency Hydrographic The floor of Norton Sound is not marked by a Center charts. Bathymetry between lines A and B is from National Ocean Survey charts cited in text. Bathymetry east of continuous gradient away from the Yukon Delta; line B is from CreagH and McManus (1967). Modified from rather, it contains an east-trending depression sepa McManus, Venkataratham, Hopkins, and Nelson (1974). rated from the Chirikov Basin by a broad ridge 0 *""'
162" ----,--161" -~- • i 1670 ----:~6" ------~165" ------,-164"I - ~~-----I - --.-- -
-- -. ll2",- sTRAtc~ :- ( , 1 I<:y1 /;;:;!tr. . WALES • sTEXPLANATION ,~3" ~50j ~~·~ • -
I '] )' 0 "A, 'C W_NCAI" ' 1 ."'="'"'- "-'->-- "' ..\:,\ I )~\~~ " '""' , " "-<-c::.';,0 ·~-~. • ·~""" )~ . ' I I f '\ \0 00 .<'1: .... r:n : ( /------.-J /J. --3 e.',··"··" 1//~ 40 , ,
I ' I ' ' 30,:'J)/ .. - lJ \ • I -•; _.·.= •. '"r __ UKO·N· ·. ______c______,.,,. SOBATHS0 IO 'N'f >0I MILES ., / r • 7• . • '"' / ;, \.!.. . · . .. . RIV!-R__ --·:-I --- I ----.. _ METeRS -- ~---L_~-----/ ' , _LL__168' l'\.. ()_{__~ '" • -~-~~~·.>. ·_.··.·.·~.-·-•- --- -·,_~ .- '" ' ' -~;. ----~~------~ .J__ - I • '"'~···~w·.· -~~- ."<~ 169 ~. ~- ~ 1
FIGURE 2.-Bathymetric chart of study area showing station locations (McManus and others, 197 4). A more detailed bathymetric chart is given by Hopkins, Nelson, Perry, and Alpha (1976). DISTRIBUTION OF BOTTOM SEDIMENTS ON THE CONTINENTAL SHELF, NORTHERN BERING SEA C5 extending north from the Yukon River delta. Deep The region off the coast of Seward Peninsula passages extend along the coast off Cape Darby and between Sledge Island, Port Clarence, and King Rocky Point. Another long, narrow depression off Island constitutes the Cape Rodney Parallel Valley Nome is separated from the central depression by an Area, a region of low, widely spaced ridges and east-trending shoal. troughs trending northwestward. This province is
170° 168° 166° 164° 162°
CHUKCHI SEA
V\/lV} "
A L A S K A
64° 64° NORTON SOUND
EXPLANATION
0-\0m I0-30m 30mtobottom
Depth and direction of current Current speed shown by length of arrow. See scale below
0 50 I I I I I I CURRENT SPEED, IN BERING SEA CENTIMETERS PER SECOND
FIGURE 3.-Current measurements during early July 1968. Sites of measurement are at bases of arrows. (Mter Coachman and others, 1976, with permission of University of Washington Press). C6 STUDIES ON THE MARINE GEOLOGY OF THE BERING SEA succeeded to the northwest by the Point Spencer westward-extending promontories deflect the flow Shoal Area, which contains a series of large con (Fleming and Heggarty, 1966). The less dense coast structional shoals having crests at approximately al water is piled up against the shore as a thickened 10, 20, and 30 m. Sand waves occur at about 20 m section, and strong currents are produced to move depth on the western flanks of the 10-m shoal (Grim the water, as along south western Seward Peninsula. and McManus, 1970). Under these conditions, relatively warm and dilute, high-velocity water in the area between the shore OCEANOGRAPHIC SETTING and the eastern boundary of the Chirikov Ramp is Hydrographic data are available for only the 4- set north ward. At times when prolonged northerly month open season, when the hydrographic regime winds greatly restrict the flow into the Chukchi Sea, is constituted of warm ( >8°C), less saline (<.31 ° /oo) however, the coastal water spreads out as a surface water along the Alaska coast, and cold, more saline layer on the denser Modified ShelfWaterratherthan water offshore. The Alaskan Coastal Water, formed occupying the entire water column from the shore of largely by river runoff from the coastal lowland the Seward Peninsula to the Chirikov Ramp. between Bristol Bay and the Yukon River, borders A more complete bibliography of the physical that coast, fills Norton Sound, and again borders the oceanography is given in McManus, Kelley, and coast from Nome through the Bering Strait and into Creager (1969). the Chukchi Sea. Steep horizontal gradients in tem perature and salinity mark the boundary with the ANALYSES AND WITHIN-SAMPLE VARIABILITY Modified Shelf Water offshore (see figures in Mc Manus and Creager, 1963, and McManus and others, Samples collected from the stations shown on 1969), which originates in the northern Bering Sea figure 2 were analyzed for sediment texture by during winter ice formation (Sauer and others, 1954). standard sieve and pipette techniques. The approx Although warmed above the< 0°C temperatures of imately 250 samples with complete analysis include the Deep Shelf Water, the Modified Shelf Water is those reported on by Creager and McManus (1967) still cold (0°-4°C) and ranges in salinity from 31.5 to and McManus, Kelley, and Creager (1969). The 33°/oo. graphical estimates of Folk and Ward (1957) were Both the Alaskan Coastal Water and the Modified used to describe the grain-size distribution. Shelf Water have a net movement northward through Of the 204 heavy-mineral separates made by meth Bering Strait (fig. 3) as a result of a sea-surface slope ylene iodide (sp. gr. 3.14-3.17), 120 were examined to (Coachman and Aagaard, 1966). The cause of the identify the minerals in the 1-2.75 and the 2. 75-4.00 difference in sea level between the Bering and Chuk ¢J size fractions. The data on the percent of heavy chi Seas is unknown. At 20-m water depths southeast residue and of individual heavy minerals in each of of Bering Strait, current velocities of 30-50 em/sec the two sizes have been reported elsewhere (Venkata have been measured in the coastal water. In the rathnam, 1971). Only the 2. 75-4.00
pebbles of selected samples were studied by staining em/sec within 1 m of the bottom in this basin (R. and petrographic techniques, respectively. Sternberg, written commun., 1971). In order to estimate the significance of these data, Two types of major velocity fluctuations oocur in it is necessary to have some measure of the vari the persistent northerly setting current. Regular ability associated with the data points. Although fluctuations of 50-70 percent of the mean velocity such measurements can be based upon replicate grab appear to have a tidal origin (Coachman and Aaga samples at a station and replicate splits of a grab ard, 1966; Coachman and Tripp, 1970). In addition, sample, Kelley and McManus (1969; 1970) report that the general current velocity may fluctuate as much most of the variability for stations on the continental as 100 percent over a period of a day or more, shelf off Washington is associated with between presumably as a result of major changes in atmos splits variation within a grab sample, rather than pheric pressure or the wind regime (Coachman and between-grab sample variation within a station. Tripp, 1970). Winds produce storm surges or setups In the present study, replicate grab samples were raising sea level as much as 4 m along the southern not taken, but replicate splits of 36 grab samples coast of Seward Peninsula (U.S. Coast and Geodetic were analyzed for sediment texture. The number of Survey, 1964). splits was not constant but ranged from 1 to 8 per The generally northward flow of the entire water grab. Replicate analyses of mineral composition column has a direct effect on the coastal water where were too few for a statistical evaluation, as emphasis DISTRIBUTION OF BOTTOM SEDIMENTS ON THE CONTINENTAL SHELF, NORTHERN BERING SEA C7
TABLE I.-Analysis of variance table for texture variables [SS - sum of squares; df- degrees of freedom; MS - mean square] Minimum resolvable Variable df MS F sv ss difference
Percent gravel ·····-··········------·-···· Grabs 58823.55 35 1680.67 28.972 9.9 percent Splits 5569.23 96 58.01 Percent sand ·················· -············· Grabs 88766.50 35 2536.19 28.117 12.4 percent Splits 8659.49 96 90.20 Percent silt ··········· ·· ···------·------Grabs 46185.56 35 1319.59 25.698 9.3 percent Splits 4929.36 96 51.35 Percent clay ------Grabs 1836.20 35 52.46 5.888 3.9 percent Splits 855.45 96 8.91 Median ·-···------·--···-··-··-·············· Grabs 388.14 35 11.09 23.596 .89 ¢'unit Splits 44.83 96 .47 Mean ········------· Grabs 377.98 35 10.79 19.618 .97 ¢J unit Splits 52.98 96 .55 Standard deviation ------Grabs 109.15 35 3.12 13.565 .63 Splits 22.39 96 .23 Skewness ------···· ------·----··- Grabs 8.65 35 .25 3.571 .35 Splits 6.24 96 .07 Kurtosis ··············--·······------·-·-···· Grabs 201.77 35 5.76 3.064 1.79 Splits 180.24 96 1.88 Mode ·······------·--····---· ···-·····-·--- Grabs 789.92 35 22.57 38.254 1.00 ¢J unit Splits 56.20 96 .59 was placed upon a reconnaissance coverage of the minimum significant contour intervals, not to com study area. pare specific values of two adjacent stations for A one-way analysis of variance based upon the significance in relation to a common population. random-effects model was used to provide the results on sediment texture (table 1). There was no data DISTRIBUTION OF SEDIMENTS transformation. The F-ratios compare the variability GRAVEL between grab samples (and since only one grab sample was taken at a station, this variability can be Gravel and gravel-rich sediments occur (1) in thought of as between-station variability) with the Bering, Anadyr, and Shpanberg Straits, (2) in a belt variability between splits of the grab sample. For all approximately 30 km wide along most of the. coast variables, the F-ratio is significant with greater than from east of Nome to the Bering Strait, (3) in the 95 percent confidence; this means that· there is northern part of the Chukotka Trough, (4) in a belt greater variability between grab samples(" stations") about 10 km wide along the north coast of St. than within them. Had this not been the case, further Lawrence Island, and (5) in a· narrow belt that discussion of geographic distribution of the vari extends some 60 km northward from St. Lawrence ables would have been statistically meaningless. Island along the eastern boundary of Gambell Shoal The different values of the F-ratio indicate that (figs. 4 and 5). Although ice-rafting may play a role in some variables are more diagnostic of differences the distribution of pebbly muds, the gravel deposits between grab samples than others (Kelley and Mc observed in detailed studies near Nome are relict or Manus, 1969; 1970). The modal size and percents residual and are derived from glacial drift, outwash, gravel, sand, and silt show the most recognizable alluvium, and bedrock distributed in a complex between-grab differences; percent clay, skewness, pattern in the nearshore area (Nelson and Hopkins, and kurtosis are less efficient. As a measure of the 1972). The coarse deposits near Nome form an degree to which the variables are sensitive to between irregular belt parallel to shore seaward from the grab differences, the minimum resolvable difference modern nearshore sand body; the coarse deposits between means of grab samples can be computed by extend seaward in lobes reflecting offshore distribu using a measure based upon the power of the F-test tion of glacial drift and bedrock outcrops. This same (Mcintyre, 1963; Kelley and McManus, 1969; 1970). model of complex gravel distribution probably ob Because the number of splits was not constant, n 8 tains for all the gravel regions of northern Bering in the equation of Kelley and McManus (1969) has Sea. The lithology of the submerged gravel in the been approximated by n 0 according to the method of central and eastern part of the study area is closely Snedecor (1956, p. 269). The minimum resolvable dif related to the lithology of adjacent coastal areas, ference for each variable, presented in table 1, should whereas the gravel of the western part consists be used only in a broad sense, as representing largely of exotic material. C8 STUDIES ON THE MARINE GEOLOGY OF THE BERING SEA Basaltic volcanic rocks from nearby Quaternary (fig. 4). Gravel off the east coast of St. Lawrence eruptive centers predominate in the nearshore zone Island consists predominantly of granite, limestone, off the mountains of central St. Lawrence Island and sedimentary rocks of local derivation. Along the
174" 172" 170" 168" 166" 164" 162" 160"
C H U K C HI S E A
66'
64"
50 0
50 0 50 KILOMETERS
EXPLANATION . [§]. ' ~ w_Ou Sediments Sedimentary rocks Includes small areas of Triassic ...JQ Alluvium, glacial drift, wind B FIGURE 4.-Generalized geologic map of land areas around northern Bering Sea (Nelson and Hopkins, 1972). 173° 172° 171° 170o 169° 168° 167" 166° 165° 164° 163° 162° 161° tj ~ l 00 1-3 ~ ~ eeo 1-3 0z 0 r:.;f_\/v~:.RL· PEI,J:i,JSUL A ~ 65° eo I 0 ~ 165° 0 I 00== t:r::l tj ;: t:r::l ~ 00 0z 64°"--- 1-3::r: t:r::l C1 0z 1-3 30 20 if z t:r::l ;;z t-t 00::r: tz:j 63°•-- ~~ -~63° z 0 10 20 30 MILES 0 I I I I I I I I I I ~ 0 10 20 30 40 KILOMETERS ::r: ISOBATHS IN METERS t:r::l ~z .. ' I It I I L I ..·_· _L I "O" ''>" .... -~ eo ~~~ t:r::l ,.,. 1620 1610 167• 166° 165° --~ z~ Q FIGURE 5.-Distribution ofweightpercentgravelin bottom sediments. ContourintervallOpercent. "More than" values are shown in nearshore areas where gravel content 00 tz:j is high and increasing shoreward. > 0 ~ C10 STUDIES ON THE MARINE GEOLOGY OF THE BERING SEA Seward Peninsula coast from Solomon to Port sea floor (fig. 6). The area of high silt abundance Clarence, offshore gravel is predominantly quartz extends northward, down current from the delta, ite, quartz-mica schist, garnet-hornblende schist, apparently in fingerlike projections. Although the marble, lime-silicate rocks, and vein quartz derived axial shoal and depression in Norton Sound have a from the local low-grade metamorphic terrane. low silt content, the depression along the northern Between Cape Nome and Cape Wooley, the gravel margin of the shoal contains silt in nearly the same consists of granitic rocks and high-grade meta proportion as found near the Yukon mouth. Silt morphic rocks derived from mountains a few tens of dominates sediments in this depression farther east, miles inland and from two coastal plutons. near Nome, but only on the south side, rather than in A very different suite of rock types is found in the depression proper. A tongue of sediment con gravel along the Seward Peninsula coast westward taining more than 10 percent silt extends north from Port Clarence, near King Island, in Bering westward from Sledge Island toward King Island, Strait, in Anadyr Strait, along the coast of western but little silt is present in the bottom sediments on St. Lawrence Island, and in the finger of gravel either side. This northwest-trending tongue of silty extending north ward from central St. Lawrence sediment is independent of the topography. North Island. Volcanic rocks of acid and intermediate west-trending ridges and troughs are present both in composition (dacite, rhyodacite, quartz latite, and the area of silty sediment and in areas to either side andesite) and plutonic rocks of varied composition where the silt content is less than 10 percent. ranging from granite to gabbro are prominent and In Shpanberg Strait the silt content decreases commonly predominate in gravel samples from these rapidly westward from the Yukon Delta to a point areas. Acid and intermediate volcanic rocks are not about 75 km offshore, where it stabilizes at 10-20 present in the bedrock of western Seward Peninsula percent. Bottom sediments on the shoals have a silt and the smaller islands of Bering Sea, but are widely content of less than 10 percent, but silt constitutes distributed in the Chukotka Peninsula and on west more than 30 percent of the sediment in the eastern ern St. Lawrence Island. There is abundant evidence most depression in Shpanberg Strait. A relatively to indicate that the gravel of the western part of the high silt content characterizes the sediments in the Bering Sea consists largely of relict morainal mate depression along the north coast of eastern St. rial derived from the Chukotka Peninsula (Hopkins Lawrence Island. and others, 1969; Silberman, 1969; Grim and Mc The northern part of the Ch ukotka Trough is Manus, 1970; Hopkins and others, 1972; Nelson and characterized by a slightly higher silt content. This Hopkins, 1972). Our detailed studies, however, in· mainly is the smoother and flatter floored part of the dicate that slate and limestone from the York Moun trough, although the closed depression just south of tains mixed with volcanic rocks from Chukotka are a Bering Strait is also included. A high silt content major constituent in the nearshore gravel between marks the western flank of Prince of Wales Shoal; Port Clarence and Bering Strait. Unpublished studies this silt extends northward from Cape Prince of by Hopkins indicate that clasts eroded from sub Wales into the Chukchi Sea. merged outcrops of serpentinite and gabbro are mixed with the glacially transported relict gravel in CLAY some areas near St. Lawrence Island. The distribution of clay-sized particles (fig. 7) is In the region north and west of western St. Lawrence contoured at the minimum resolvable difference, 4 Island, copper sulfide mineral grains of presumed percent. The low F-ratio indicates that this variable Chukotka origin are present in some pebbles of is not so diagnostic of differences between grab altered andesite and diabase. Native copper has been samples (stations) as the silt, which, however, has a found in the sand-sized component of samples from similar pattern. Presumably, the lesser effectiveness this region. of the clay percent in distinguishing between grab samples is associated with the generally low percent SILT age of this size particle in most of the samples. The distribution of the mud (silt plus clay) com In an analysis of the clay mineralogy of 24 selected ponent leads to insights that help us understand the samples from the study area, Moll (1970) concluded sand distribution. Therefore, we shall discuss the that there were two clay mineral assemblages. The distribution of silt and clay before discussing the western assemblage (west of the dashed line in fig. 7), pattern of sand distribution. considered to be the Chirikov Basin assemblage, The highest silt percentages are associated with contains a larger amount of collapsible components the Yukon River and with some depressions in the and lower values of illite and chlorite. Clay minerals 173" 17ZO 1"71° 170° 169° 168° 16"(0 166° 165° 164° 163° 162° 161° t:1 ~ ~ c:ttl ~ 0 z 0 65°,-- ~ ttl --65° ~0 s;:: 00 tz:j t:1 S2 tz:j ~ 00 0 64° z ~ :I:: tz:j (") 0 ~ z~ tz:j ;;z t"'4 00 :I:: 63°~- tz:j t"'4 ~~ ---"63° 0 10 20 30 MILES z I I I I I 0 I I I I I 0 10 20 30 40 KILOMETERS ~ ISOBATHS IN METERS :I:: tz:j ----L------_L____ I I _j 172° 171• 170° ~ ~ ~------~-----_____._- 161° ttl 167" 166° 165" 164° 163° 162° tz:j z~ FIGURE G.-Distribution of weight percent silt in bottom sediments. Contour interval 10 percent, approximately the minimum resolvable difference (9.3 percent). The 0 00 patchiness is statistically significant. tz:j > 0 ...... 0 ...... ~ 173° 172° 171° 170° 169° 168° 167° 166° 165° 164° 163° 162° 161° :,t WM'IO FT~JiNSUL A ~ c -~ 65° t:l 1-4 t'J!j 00. 0z t-3 ::I: t'J!j ~ ~ zt'J!j 0 t'J!j 64° 0 t"" 0 0 to< 0 ~ t-3 ::I: t'J!j t:O t'J!j ~ 1-4z 0 63° 00. 0 10 20 30 MILES t'J!j I I I I I I I I I I > 0 10 20 30 40 KILOMETERS ISOBATHS IN METERS 171° 170• 161° 167" 166° 165° 164° 163° 162° FIGURE ?.-Distribution of weight percent clay in bottom sediments. Contour interval4 percent. The dashed line separates two clay-mineral assemblages. The western assemblage is consid.ered to be the Chirikov Basin assemblage; the eastern assemblage the Yukon River assemblage. t:1 173" 172" 171" 170" 169° 168° 167° 166" 165" 164° 163° 162" 161" ·----;v---r---r------! ~ ~ ~ c::tt1 t-3 0z 0 1-:rj SPE~JCER ~E_ Vv,.\RO F-'E r,J!r·JSUL.A tt1 65° 0~ .r:n== t_!!j t:1 ~ r:n~ 0z ::r:t-3 t_!!j -~64° 0 0z t-3 1-4z t_!!j r:n~ ~ 63"•- ~~ z --63" 0 0 10 20 30 MILES ~ I I I I I t-3 I I I I I t:r:: 0 10 20 30 40 KILOMETERS t_!!j ISOBATHS IN METERS ~ ---~----_j z tt1 171" t_!!j 170• 161° 167" 162° ~ 166" 165" 164° 163" z C) r:n FIGURE B.-Distribution of weight percent sand in bottom sediments. Contour interval 13 percent. t_!!j > 0 ...... CI.J C14 STUDIES ON THE MARINE GEOLOGY OF THE BERING SEA of the eastern assemblage (east of this line) have an Most of the bottom sediments in the study area are inverse ratio and appear to be associated with the poorly to very poorly sorted (fig. 10). The very poorly present-day Yukon River sediment. sorted sediments are gravels or silts. The best sorting is found in the sands near the Yukon, off some beaches, and at two depths on various shoals, 34m SAND and 20 m, the shallower depth being the crest of TEXTURE some shoals. The distribution pattern of percent sand (fig. 8) is merely the complement of the sum of the other LIGHT MINERALS distributions because of the closed-number system. Thirty-six samples were analyzed for light min The pattern does, however, more clearly indicate the erals in the 2.75-4.00class. Quartzformsmorethan high sand content of the shoals at the western tip of 50 percent of the fraction in samples from the east St. Lawrence Island, in Port Clarence, in Shpanberg west shoal in Norton Sound and in the northern half Strait (particularly the western shoal), and in Norton of the Chirikov Basin. Elsewhere feldspar is the Sound. Variation within the uniformly sandy Chiri major component. A plot of the ratio of plagioclase to kov Basin is not depicted, as the use of a smaller K-feldspar (fig.11) shows a dominance of plagioclase contour interval would produce unreliable results. near the Yukon River, including most of Norton Instead, the distribution of the modal class is used Sound and Shpanberg Strait, and near the basalts of (fig. 9). central St. Lawrence Island. K-feldspar predomi The large F-ratio for the mode indicates that this nates in samples from off the east and west ends of variable is very diagnostic in differentiating be the island and is the dominant feldspar in most of tween grabs (stations), but it should be noted that the the Chirikov Basin. In northeastern Norton Sound, class interval used in figure 9 is one-half the mini the K-feldspar content is high but not dominant. mum resolvable difference (table 1). The pattern shown is therefore statistically questionable, though HEAVY MINERALS geologically reasonable. The heavy-mineral content of the totall-4 sand One of the sedimentary characteristics illustrated class, disregarding beach samples, rarely exceeds 10 by a distribution of modal sizes is grading, com percent, although a maximum of 78 percent was monly presented as a function of water depth or recorded. For the fine sands (2. 75-4.00 if> class), which distance from shore. In the present study area, there include the most common modal sizes, heavy are two prominent examples of size grading. In the mineral contents exceeding 16 percent are observed eastern part of Shpanberg Strait, grading is from 2.5- in brownish sand at depths of 34-36 m west of St. 3.0 if> sand to the finer-than-4 material that covers Lawrence Island, adjacent to the volcanic rocks of most. of Norton Sound. The 3.0-3.5 ¢ and 3.5-4.0 the central part of the island, on the shoal crests (20 sands seem to be closely associated with the silt m) in Shpanberg Strait, along the Nome coast, and in distribution pattern and to form a pattern distinctly the Cape Rodney Parallel Valley Area and the Point different from that of the 2.5-3.0 mode that dom Spencer Shoal Area (Venkatarathnam, 1971). inates Shpanberg Strait. Venkatarathnam (1971) lists the heavy-mineral The second example of size grading begins with assemblages and delimits a number of heavy the medium sand (1.5-2.0 ) in the nearshore part of mineral provinces on the basis of the total sand (1-4 the Cape Rodney Parallel Valley Area. Seaward, the cP) fraction. In an attempt to better define the re mode is 2.0-2.5¢ down the eastern flank of the Chiri lations among provinces, 100 samples of the 2.75- kov Ramp area. It is 2.5-3.0 ¢ throughout the rest of 4.00 fraction were subjected to a Q-mode factor this province and becomes 3.0-3.5 ·r/Jin the Chukotka analysis following the procedure of Imbrie and van Trough to the west and in the southern part of the Andel (1964), with the constraint that the mineral Norton Plain. In the center of the Chukotka Trough data (percentages) were transformed into percent of and near eastern St. Lawrence Island, the mode is range, even though, as Imbrie and van Andel (1964, 3.5-4.0 if>. This size grading extends to the secondary p. 1144) point out, "the proportionally large standard mode in each of these modal zones. The secondary error of small percentages produces very noisy data." mode in the coarser grained zone is the same as the Consequently, our use of the percent range trans primary mode in the adjacent finer grained zone. As formation is open to question; on the other hand, comparison with the bathymetric chart shows (fig. ignoring the minerals present in small percentages 2), however, this size grading cannot be related could mean ignoring some very important minerals directly to either water depth or distance from shore. (Blatt, 1967). I::' ~ ~ to MODAL SIZE c::: Coarser than 1.0-1.5 ~ .....~ 0 1.0- 1.5 z 1.5-2.0 0 2.0-2.5 '"%j 2.5-3.0 to 0 3 .0-3.5 ~ 3.5-4.0 0 Finer than 4.0 ~ ~ en tJj I::' ~ tJj z @ 0z ~ :I: tJj (1 0 z~ tJj z ~ t:-< en :I: tJj t:-< _'"':j z 0 0 10 20 30 MILES I I I I I I I I I I ~ 0 10 20 30 40 KILOMETERS :I: tJj ISO BATHS IN METERS :;1:1z J72"' to tJj z~ 0 FIGURE 9.-Distribution of modal classes of sand. The class interval is less than the minimum resolvable difference. en tJj > Cl,_. CJl 0 ...... O'l 173" i65" 16 4 " 163" 162~ (.I" -.-----· ~---- PLANATlON Phi SORTI NG unit We ll sorted 0.63 Moderately sorted 1. 2 6 Poorly sorted 1.89 2 . 52 } Very poorl y sorted 65" 3. 1 5 ~ 3.78 c::: t:l E xtrem ely poorl y sorted i. f 6')" ...... I t':l w 0z >-3 :I: t':l s:: ~ t':lz 0 t':l - · ~ 64" 0 s0 ><: 0 ~ >-3 :I: t':l ttl t':l ::d z0 '63° w 0 10 20 30 MILES t':l I I I I I > I I I I I 0 10 20 30 40 KILOMETERS ISOBAT HS IN METERS f72" 163" FIGURE 10.-Sorting of bottom sediments. Contour interval 0.63¢ unit. tj -en >-3 l:lj -cto EXPLANATION >-3 i FELDSPAR RATIO i 0 i - i z > 4 0 2 - 4 "%j 1-2 to I 0 0 . 5-1 I 0.25-0. 5 I ~ ~65' 0 < 0 .25 ) I ~ en M tj -~ Mz >-3en z0 >-3 ::I: M (") z0 >-3 -z Mz >>-3 t"' en ::I: M t"' _"%j z 0 0 10 20 30 MILES I I I I I ~ I I I I I ::I: 0 10 20 30 40 KILOMETERS M ISOBATHS I N METE AS zl:lj 172" to M l:lj -z 0 en FIGURE 11.- Ratio of plagioclase to K-feldspar in the 2.75-4.00 ¢class. M > 0 1-' -..J C18 STUDIES ON THE MARINE GEOLOGY OF THE BERING SEA TABLE 2. - Values of 13 variables for samples of four highest loadings for each factor in Q·mode analysis of heavy-mineral composition 2 ~ "'~ "'~ "'>< "'>< 1i ., Factor Sample g g 0"' ,. ,."' .D -~ ·s ~ c. ~ .!;; 2' c. ~ ~ ~ 2' " ~ g ·c "'0 "'0 :.a 0 ·;s ·a 'B .D c. ., "' "' 0 .s .D :E E ~ e t: E ·s. "'c. c. 0 s" " :a " "-1 " 0: .5 0 u «: "' 0 0" «: ~ "' :.::"' u I TT018-23 1.000 16 32 5 7 1 1 15 21 1 2 1 TT018-22 .998 18 32 10 6 2 2 9 <0.5 20 <0.5 < 0.5 69ANC- 116 .919 15 32 5 14 1 1 4 1 17 <0.5 0.5 69ANC-111 .910 12 34 16 9 2 2 4 <0.5 20 <0.5 1 II ...... GR493-A 1.000 4 3 9 5 1 60 1 8 4 <0.5 5 VC067-116 .957 <0.5 3 6 13 4 62 1 4 2 4 VC067-99 .947 1 4 5 24 4 51 1 5 1 5 VC067-67 .936 1 4 7 16 6 51 1 8 2 4 III 68ANC- 116 1.000 21 3 1 1 71 1 2 <0.5 69ANC-97 .970 11 1 2 <0.5 82 4 69ANC-88 .959 6 1 <0.5 1 90 <0.5 1 68ANC-102B .642 1 35 4 10 1 36 1 11 <0.5 IV TT018-10 1.000 1 45 29 2 7 <0.5 6 1 4 <0.5 5 TT018-40 .957 7 45 20 6 2 2 4 2 7 <0.5 1 68ANC-84 .875 3 23 32 11 5 <0.5 11 2 11 1 <0.5 1 68ANC-156 .859 9 38 6 15 3 1 8 3 11 <0.5 1 3 A Q-mode analysis was run, using 13 nonopaque time, only of provenance. Whether or not the areas of minerals for each of the 100 samples. Four factors high loadings of this and other factors are now "explained" 90 percent of the variability displayed receiving sediments of the inferred provenance will by the samples (table 2). The fifth eigenvalue con be discussed later. stituted only 2 percent of the trace. These factors are Although Factor II is expressed most strongly by considered to indicate sediment provenance, although garnet, and thus might appear to be monomineralic the mineralogy of the rocks on the adjacent land is (table 2), comparison with the other factors suggests poorly known. The mineral assemblages do not that the epidote, staurolite, chloritoid, and sphene appear to have been altered by selective removal of are significant. Accordingly, the factor appears to be unstable grains due to weathering. In fact, the heavy formed of metamorphic minerals, and the distribu mineral grains show little evidence of weathering; tion (fig. 12B) indicates the source area to be the this holds true even for the most easily weathered metamorphic rocks of southwestern Seward Penin species, such as olivine. Size sorting of minerals may sula. The factor is mainly developed within and have had some effect upon the assemblages. We note, inshore from the depression along the coast near for example, an increase in amphibole and pyroxene Nome and in the Cape Rodney Parallel Valley Area and a decrease in garnet in the 2. 75-4.00 ct> class with just to the west. The role of this and other factors decreasing median size of the total sand fraction. amid the Point Spencer Shoal Area requires detailed However, comparison of abundances in the 1.0-2.75 study. o and 2. 75-4.00 ct> classes suggests that size sorting is Factor III consists of olivine and clinopyroxene not a dominant effect, as the mineral composition of derived from the Quaternary olivine basalts (table 2) the two classes is essentially the same in a given and can easily be correlated with volcanic rocks in sample (Venkatarathnam, 1971). Variations in the the adjoining land area (fig. 12C). mineralogy of the source rocks that supplied detritus As Factor IV is the final factor, its distribution (fig. to the study area appear to control the heavy-mineral 12D) may reflect a complementary element to the variation in the bottom sediments. sum of the other factors. The multimineral composi Factor I is thought to represent Yukon River sand. tion of the factor enhances this possibility. This does Its distribution (fig. 12A) shows high values near the not, however, appear to be the most probable inter Yukon Delta, and there is a similarity between the pretation. distributions of high Factor I loadings in Norton Factor IV consists of clinopyroxene, amphibole, Sound and the 5 A B t:l ...... U1 >-3 ~ 65° 65° c::ttl ...... >-3 0z 0 'Tj 64' 64' 64° ttl 0 ~ 0 ~ U1 ISLAND trl 63' 63° 63° t:l 0 20 40 MILES 0 20 40 MILES E2 WH WH trl 0 20 40 60 KILOMETE RS 0 20 40 60 KILOMETERS ~ U1 172° 170° 168° 166° 164° 162° 172° 170° 168° 166° 164° 162° z0 >-3 :I: trl 0 0z >-3 65° 65° z ztrl ;; t""' U1 :I: 64' 64' trl t""' _'Tl z 0 :::0 >-3 63° 63° :I: trl :::0z ttl trl 172° 170° 166° 164° 162° z~ 0 U1 FIGURE 12.-Distribution (percent) of factors from Q-mode factor analysis of heavy minerals in the 2.75-4.00 cfJ class. A, Factor I. B, Factor II. C, Factor III. D, Factor IV. trl > ...... 0 ~ C20 STUDIES ON THE MARINE GEOLOGY OF THE BERING SEA sula and areas farther west in Siberia (Tilman and Norton Sound. Factor IV sediment can be divided others, 1969), extends southeastward beneath Ana into southeastern Seward Peninsula and Chukotka dyr Strait and across southwestern St. Lawrence h-m provinces on the basis of the plagioclase/K Island, thence eastward south of the central and feldspar ratio (fig. 11), which is greater than 1 in the eastern part of the island (Patton and Csejtey, 1971; southeastern Seward Peninsula province. The south Scholl and Marlow, 1970; Nelson and others, 1974). eastern Seward Peninsula sediment occupies the Patton (1971) suggests that east of St. Lawrence shoal in Norton Sound, and very similar sediment Island, the Okhotsk volcanic belt swings north occurs in patches in the eastern part of Shpanberg eastward, passing beneath Norton Sound to connect Strait. with a north-trending volcanic complex of similar The southwestern Seward metamorphic h-m prov lithology and age in the hills of southeastern Seward ince is confined to the area of parallel-relief topog Peninsula. raphy between N orne and Bering Strait. The remain Bottom sediments with high values for Factor IV der of the Chirikov Basin is dominated by the cover the bottom in the western part of Bering Strait Chukotka h-m province. Several small Quaternary and extend from there southward through western olivine basalt provinces are shown in figure 13. Chirikov Basin and the Anadyr Strait. The principal Scrutiny of the detailed data indicates that several minerals of Factor IV dominate heavy-mineral as other small provinces can be distinguished off each semblages in bottom samples collected south of end of St. Lawrence Island and near Cape Prince of Anadyr Strait and along the southern Chukotka Wales (Venkatarathnam, 1971), butnoneoftheseare coast, where the order of abundance is: rock frag recorded by the factor analysis, and they are not ments, amphibole, clinopyroxene, and epidote (Lisit distinguished in figure 13. Venkatarathnam (1971) syn, 1966). The Factor IV sediments are thus dis notes that the sediment in an area north of eastern tributed across the sea bottom in areas adjoining most St. Lawrence Island has a somewhat mixed coasts where the Okhotsk volcanic belt is exposed. assemblage not recorded by the factor analysis. These sediments are derived in part from submarine More obvious mixtures of provinces can be noted in outcrops, but much of the area in which they occur is figure 12, where samples have loadings > 0.5 for underlain by the drift of glaciers that originated on more than one factor. Chukotka (Nelson and Hopkins, 1972; D. M. Hop kins, C. H. Nelson, and R. B. Perry, unpub. data, SEDIMENT TYPES 1973). Factor IV is also strongly developed in bottom The data on the mineralogy of the fine sand, sediments in northeastern Norton Sound, near the particularly as summarized by figure 13, and the late Mesozoic volcanic and plutonic rocks exposed on pebble lithology provide a basis for interpreting the southeastern Seward Peninsula. provenance of the sediments studied. To interpret the One method of better evaluating the relations sediment processes, however, requires knowledge of among the factors is to consider only that part of the sediment texture. Although the texture has been each factor distribution having loading values great discussed in terms of gravel, silt, clay, and sand, no er than 0.5. By this criterion five main heavy-mineral summary of the textural data has been presented. To provinces can be identified (fig. 13). To prevent provide this information, an R-mode factor analysis confusion with physiographic provinces, the heavy (Dixon, 1970) was run, using as variables the percent mineral provinces will be referred to as h-m sediment in each 1/2-¢ or 1-<1> class. The two class provinces. intervals were used to emphasize the sand sizes The Yukon h-m province extends from the delta dominating the sediment in the Chirikov Basin. The across Shpanberg Strait to the depression along the five factors are considered to be driven by those end of the St. Lawrence Island. Along the northern variables having a loading greater than about 0.4 margin of the province, the Yukon sediment is mixed (table 3). Two of the factors are simple, representing with that of the adjacent provinces, particularly in silt-clay (Factor I) and fine gravel (Factor III). The TABLE 3.- R-mode factor analysis of sediment size. Factor loadings> +0.4 [Five factors "explained" 74 percent of the variability] Phi sizes Factor -5 -4 -3 -2 -1.5 -1.0 -0.5 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 5 6 7 8 9 10 11 12 I . 0.43 0.86 0.96 0.94 0.93 0.89 0.80 0.85 II 0.71 0.85 0.90 0.87 0.75 -0.50 III . -0.77 -0.91 -0.83 -0.81 IV . 0.68 0.75 -0.51 -0.67 -0.47 v ...... 0.70 0.73 ·0.49 I::) 17 3" 167" 166" 165" 640 163" 162" 61° rn ->-3 l :::0 -c::to EXPLANATION >-3 0 Yuko n p rovince z Southwestern .S~w ar d metamo.rphic prov ince 0 >-.j Quaternary ohvme basalt provm ces to 65° Chuko tka province 0 Southeastern Seward Peni nsula prov in ce ~ Affinities uncertain 0 I 65" s:: rn trl I::) ~ trl rn~ 0z :r:>-3 trl n 0z z>-3 ztrl >-3 > t"' rn :r: trl t"' 63 _>-.j z 0 0 10 20 30 MILES ;:§ I I I I I 'I I I I :r: 0 10 20 30 40 KILOMETERS trl ISOBATHS I N METERS :::0z 1720 to trl ~ 166" 163" z 0 rn FIGURE 13.-Heavy-mineral provinces determined on the basis of loading values >0.5 for Q-mode factor analysis. Severa l local provinces not detected by factor analysis trl and not shown are defined by Venkatarathnam (1971). Note mixtures of provinces in areas where loading of> 0.5 occurs for more than one factor. > n 1:\:)...... C22 STUDIES ON THE MARINE GEOLOGY OF THE BERING SEA TABLE 4.-Values of the 24 variables for extremal samples of each factor in Q-mode factor analysis of sediment size Phi size Factor Sample li:o. -5 -4 -3 -2 -1.5 -1.0 -0.5 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 5 6 7 8 9 10 11 12 I .. 68 ANC 152 0 0 0 0 0 0 0.03 0.02 0.02 0.04 0.06 0.17 0.51 2.95 50.49 29.34 10.49 0.68 0.74 1.02 0.23 1.16 0.45 1.60 NW 261-42 0 0 0 0 0 0 .04 .13 .31 .42 .45 .42 .82 24.40 44.68 12.74 6.96 2.88 1.92 .72 1.44 .72 .48 .48 II. AWF365 0 0 0 0 .20 0 .03 .09 .09 .17 .37 .61 1.12 1.33 1.70 4.19 49.38 17.20 6.45 3.88 3.48 3.30 2.43 3.98 68 ANC 231 0 0 0 0 .81 .35 .11 .35 .27 .43 .36 .25 .13 .68 4.54 6.37 35.40 19.83 9.23 4.23 3.48 3.93 3.19 6.06 NW 261-9 0 0 0 0 0 0 0 .04 .04 .04 .04 .67 .75 1.02 2.04 7.47 35.11 19.63 12.47 6.10 3.18 3.98 3.45 3.98 III . 68 ANC 112 0 0 0 0 .67 .81 1.63 2.31 4.67 11.46 26.61 32.37 15.52 2.54 .30 .06 .27 .80 0 0 0 0 0 0 TT019-31 0 0 0 0 0 .37 8.06 10.15 12.26 18.78 15.18 16.04 9.14 5.91 2.11 1.56 .37 .06 0 0 0 0 0 0 IV 68 ANC 94 0 35.91 41.30 9.85 2.90 1.47 .59 .40 .25 .64 1.17 .36 .32 .39 .70 .88 .76 .15 .08 .18 .20 .06 .18 1.46 68 ANC 243 14.91 7.92 20.43 18.74 8.07 3.72 3.16 2.23 2.18 1.92 2.46 2.20 2.34 2.21 .63 .35 1.22 .82 .90 .89 .81 .65 .53 .69 TT019-29 0 .95 36.50 27.14 8.08 4.90 4.79 3.55 3.37 2.56 1.70 .94 .41 .96 .56 .36 .86 .60 .48 .32 .21 .22 .07 .46 v 69 ANC 112 0 0 0 0 0 .16 .16 .01 .04 .12 .23 4.92 23.98 55.21 8.40 1.75 2.24 .51 0 .49 .19 .21 .07 1.30 TT018-26 0 0 0 0 0 0 0 0 0 0 .92 4.32 41.08 38.11 5.79 1.27 1.51 .39 .43 .40 .55 .46 .82 3.95 other three factors are bipolar; that is, they consist of coast, 5-15 em/sec representative of the Chirikov high loadings that are positive and negative. This Basin, and 2 em/sec representative of the Chukotka complementary arrangement of high positive and Trough. negative loadings might be produced by geologic Assuming that 1 m from the bottom the Alaskan processes, closure of the closed-number system, or Coastal Water moves at a velocity of 30-40 em/sec other causes. The effect of closure was evaluated, and the Modified Shelf Water at a velocity of 5-15 using the technique of Kelley (1971); at the 95 percent em/sec, then comparison can be made with one of confidence level, it can be shown that the bipolarity various "competency curves" for sediment transport, is not due solely to closure. Consequently, it is that of Sundborg (1956). Sternberg (1971) concluded assumed that this bipolarity is geologically signifi from in situ measurements that these curves ade cant-for example, that in Factor IV the 2.0 and 2.5 'i 30 MILES z 20 0 o tO I 1 - 'I I I Jo Jo KILOMETERs 0I ' 10 20 ~ 0::: tr:l ISOBATHS '"METERS ' I I l -----1______1_ ____---l___ I I I i I ~ z 172• 171° 169• ·--- ljj 167° 166° 165° 164° 163° tr:l z~ FIGURE 14.-Sediment types determined on the basis of loading values> 0.5 for Q-mode factor analysis. Data for "extreme" samples for each type are presented in table 5. 0 00 Note mixtures of sediment types. tr:l > C"::l ~ CJJ C24 STUDIES ON THE MARINE GEOLOGY OF THE BERING SEA than, under standard conditions and, other things Another type of meteorological current is the wind being constant, may be more easily transported. setup. In the study area, this effect is most evident The current measurements near the bottom and in along the southern coast of Seward Peninsula, where the water column represent many types of motion. sea level may rise as much as 4 m and remain at that Swift, Stanley, and Curray (1971) classify the water level for a short period (U.S. Coast and Geodetic motions on a continental shelf as (1) intruding Survey, 1964). This rise or setup results from strong oceanic currents, (2) tidal currents, (3) meteorological southerly winds and is particularly effective here, currents, and (4) density currents. The most pro because it is not only proportional to the shear stress nounced current in the study area is the northward on the water but is inversely proportional to water flow resulting from the slope of the sea surface, depth (Wiegel, 1964). Consequently, over the very which presumably falls into the class of intruding shallow shelf of northern Bering Sea, the importance oceanic current. Its dominance is manifest in the of decreasing water depth to the wind setup is greater lack of a net reversal lasting more than a few days. than usual. The water with its contained sediment The role of tidal currents in the study area is un piled up against the Seward Peninsula coast must certain. At least two waves of semidiurnal period are later be removed to the north, as part of the net flow known, and the number may exceed five (K. Aaga of water toward Bering Strait. ard, written commun., 1970). Two of the several Of the meteorological currents, the most critical in sources of complexities in interpreting these long the study area is probably the wind-driven current, period waves are the similarity in period of certain as wind-driven currents, or wind drift, can be effec tidal species and inertial waves at this latitude and tive in transporting sediment if the water depth is the considerable wave reflection that occurs. From less than the depth of frictional resistance. If 10 the current m~asurements, it appears that the veloc knots is a reasonable estimate of a common wind ity of the long-period waves is o£ the same order of velocity here (U.S. Coast and Geodetic Survey, 1964), magnitude as that of the average current through the the depth of frictional resistance can be computed as region, tens of centimeters per second (K. Aagaard, 80 m (Sverdrup and others, 1942, p. 494), meaning written commun., 1970). Under certain conditions, that wind-generated currents probably produce a then, the tidal currents might double the speed of the frictional effect on the bottom throughout the study water movement, thereby significantly increasing area. The extent to which this effect would be sediment transport, and possibly initiating erosion. recorded by the current measurements is unknown, Such transport would be in a generally "northward" however. Locally, the wind can reverse the north direction. Under opposite conditions, in opposition to ward-setting current and produce southerly water the average northward-setting current, the water transport for a short time (Husby, 1971). movement may be almost stopped, and sediment The density currents in the classification of Swift, transport may be greatly reduced. Stanley, and Curray (1971) probably are not effective Few measurements have been made that pertain to in the study area because the shallow depth permits meteorological currents. Even the wind measure mixing throughout much of the water column, there ments are from land stations whose records may be by breaking down stratification, and because of the biased by local topography. Assuming that these intensity of the other processes. wind speeds are representative and that over 60-90 A range of conditions is apparent from this dis percent of the year the winds are 1-16 knots (U.S. cussion, but the greater intensity of processes in the Coast and Geodetic Survey, 1964), and assuming coastal water, particularly along the Seward Penin reasonable fetch lengths and wind durations, then sula coast, is clear. The northward transport of water the deepwater wave characteristics can be calcu everywhere except in Norton Sound should be re lated, using the method of the U.S. [Army] Beach flected in the present-day distribution of sediment. Erosion Board (1961, p. 16a). From the equation of SEDIMENT DISPERSAL the maximum horizontal orbital velocity of water particles at the bottom (Shepard, 1963, p. 61), it Bottom sediments may be classified as modern, appears that waves are effective in initiating sedi relict, or palimpsest (Emery, 1952; Swift and others, ment motion to an average depth of about 20m, and 1971). In the Bering Sea, modern sediments are those to greater depths during storms. A residual current that consist of material recently introduced into the or wave drift might thus play a critiGal role in water marine environment and dispersed by present-day less than 20 m depth, but probably not in the deeper currents. Relict sediments consist entirely of mate water. rial introduced into the sea at some time in the past. DISTRIBUTION OF BOTTOM SEDIMENTS ON THE CONTINENTAL SHELF, NORTHERN BERING SEA C25 Palimpsest sediments are a mixture of modern and farther south. In the process, a smooth topography is relict sediments. Recognition of these different types being formed. of sediment is commonly facilitated by a study of The sands underlying the Shpanberg Strait have their biogenic components, as the relict sediment the same mineral assemblage as these very fine may contain a relict fa una or other evidence of age. sands (fig. 13). The fine sands in the strait (Factor V, R. E. Echols (written commun., 1971) examined fig. 14) ·are coarser, however, and are formed into Foraminifera in the surface layers of many samples ridges and depressions. As the low current velocities of sediment that we believe on the basis of sedi (10 em/sec) of the Modified Coastal Water in the mentological inference to be relict. The fauna con strait (McManus and Smyth, 1970) are incapable of sists chiefly of benthic arenaceous forms and seems transporting this fine sand, presumably it is relict to be entirely derived from the thriving living pop from a time of lowered sea level when the Yukon ulation. Relict tests, if present, are completely mask River extended farther southwest. ed by modern ones. As a result of the relict arena The ridges and depressions in Shpanberg Strait ceous tests being destroyed, removed, or reworked are probably relict. The modern current regime there downward into the sediment, the benthic Foraminif does not appear capable of constructing topography era cannot be used to differentiate relict from of this sort, although it may be adequate to preserve modern sediment. it. The westernmost depression may be a graben The modern sediments most easily identified in the (Grim and McManus, 1970) or a drowned stream study area are the silts of southern Norton Sound. valley (D. M. Hopkins, C. H. Nelson, and R. B. Perry, Their location near the Yukon Delta, the dominance unpub. data, 1970). The other ridges probably were of silt in the rivers in this climate (Taber, 1943; built in shallow water early in the Holocene trans Lamar, 1966), and the mineralogy of the associated gression. A sampling transect across a ridge that sand suggest a Yukon origin. Moreover, the dis crests at about 20 m shows that sand on the summit tribution pattern of the deposit to the north and is finer than sand on the flanks; if the sediments in northwest of the delta can be related to the north the ridge were affected by some present-day process west-setting coastal water, part of which must enter such as wave-stirring, one would expect to find the Norton Sound. Although part of the silt may be coarsest sediment on the ridge crest. 'J'he summit derived from south of the study area and may be sand is brown and richer in heavy minerals than the carried into the area in the coastal water (McManus sand on the flanks, suggesting that it has been and Smyth, 1970), the Factor Ilsedimentofsouthern affected by shoreline processes, probably during the and central Norton Sound is thought to consist 20m stillstand that produced shoreline deposits off mostly of modern Yukon silt (fig. 14). Nome (Nelson and Hopkins, 1972)andPointSpencer The R-mode factor analysis of phi sizes suggests (Hopkins, 1967). that the 3.5, 4.0, and 5 classes might be geologically The main effect of the topography upon modern related to one another. Accordingly, if the 5 Yukon River lay 80 to 160 km south of its present s It should be noted that an alternative explanation for the origin oft~~ very fine sa?d position during early Holocene time. Displacem~nt is that at the present time it is being formed into a deposit by the un~nnng of the rehct sand. The relict sand, instead of the Yukon River, would be the proXImate source of the of the outlet to its present position occurred no earher very fine sand. This is thought to be an unlikely explanation, however, ~a use the ~ery than 6,200 years ago (Nelson and Creager, 1977) and fine sand appears to be associated with the coastal water that has velocities appropnate for it.s transport. An extended series of measurements on transport of the very fine sand possibly as recently as 1,200 years ago (Dupre, 1977). is needed. 0 t-.:) 00 173" 1-!2.., 171' 170' 169" 168° 162' 161° BERING STRAI:;:-~---.''Ioo 50[ -4o~-;y-~·· ----·· 167" .-- 166' . lf 50 .· .IO. · ... ·· . . ------·--·- 1_ c . 1!11.I. . . ..· .... ··.. I --· " .·.d.. 't;;r) / YUKON SILT --T--·--'14'- - 163' S'-.. ,_._ ... C . f RN IF""li EXPLANATI \>· ·. · · MODE ...... A PALIMPSEST lb...d! Modern Yukon very fineON sand and relict Yukon fine sand ~ Modern Yukon silt and relict southeastern -;-.. ·..,.-...... · 60 Seward Peninsula and Yukon sands Modern Yukon silt and relict southwestern Seward Peninsula metamorphic sand i Modern and relict St. Lawrence Island sands 65' ,. __ Quaternary olivine basalt sand and gravel I 00 ~ Chukotka - St. Lawrence Island glacial gravels J65' c::: t::l Bering Strait gravel I ...... Southwestern Seward Peninsula metamorphic I t_:l:j sand and gravel ! 00 0 NORT I 8 z •• ' 0 • • ~ A·" ·.A·.·. :I: ~-~;· t_:l:j ~ :<·_... · s:: >::0 64" z t_:l:j 0 t_:l:j 0 ~ 0 0 >< 0 "%j ~ :I: t_:l:j to t_:l:j ::0z ·• 63' 0 0 10 20 30 MILES 00 t_:l:j I I I I I I I I I I 0 10 20 30 40 KILOMETERS > ISOBATHS IN METERS 169' 168' 167" 166' 165' 164° !63' 162' FIGURE 15.-Bottom-sediment distribution from McManus, Venkatarathnam, Hopkins, and Nelson (1974). Relict sediments may include residual material. DISTRIBUTION OF BOTTOM SEDIMENTS ON THE CONTINENTAL SHELF, NORTHERN BERING SEA C29 On a secular scale, the silt in this depression may shoreline. Along the margins of this area, the sand represent a steady-state condition between deposi has been mixed with other relict sands at the time of tion and erosion. Yukon silt is a component of the deposition or later. The results of a single series of bottom sediment as far north as the dashed line in near-bottom current measurements indicate that the figure 15, but we do not consider the small percent of mixing may not be occurring today. These measure silt in this relict sand sufficient to classify the sedi ments also indicate that the current speeds over the ment as palimpsest. The minor silt component here relict sand in Shpanberg Strait are sufficient to underlies high-speed currents that are probably prevent an accumulation on the bottom of the silt capable of moving most of the modal sands. The silt particles that are passing in suspension. Presum fraction must be a very dynamic part of the bottom ably this condition obtains for the other areas of sediment and certainly does not represent the lead relict sands, but measurements have not been made. ing edge of an area of net silt accumulation. Farther The relict southwest Seward Peninsula meta north, the silt is kept in suspension and forms a high morphic sand and gravel (Unit D, fig. 15) lies in a concentration where the coastal water is constricted region in which currents are probably adequate to by Bering Strait. Silt again becomes the dominant resuspend the modal-sized sands. The extremely sediment size along the western margin of Prince of poor sorting is produced largely by an admixture of Wales Shoal, which extends into the Chukchi Sea. Yukon silt. The boundary between the southwest The Yukon silt is clearly the most dynamic sedi Seward Peninsula sand and the Chukotka sand to ment in the study area. Yet no measurements of its the west is exceptionally sharp; the textural and transport are available. What portion is transported mineralogical boundary coincides with a topo across the mouth of Norton Sound and what portion graphic boundary that probably represents the mean enters the sound? What is the effectiveness ofresus position of the western edge of the strong coastal pension of silt in southern Norton Sound? What is current. It seems tha.t the coastal current has left a the distribution of suspended silt over relict sand relict·or residual lag deposit in a streamlined topog areas within the sound? What proportion of the silt raphy developed on glacial material or on bedrock. issuing from the sound accumulates in the northern Measurements of sediment transport are needed in depression and what is the residence time of a silt the Cape Rodney Parallel Valley Area to verify this particle if the deposit in the depression is in steady hypothesis. state? What is the nature of the movement of the silt Relict or residual gravel appears to be derived from by the high-speed coastal current in the Cape Rodney bedrock, glacial till, or moraines. Most of the gravel Parallel Valley Area? With answers to these ques in the Chirikov Basin is a lag deposit on glacial drift tions, more knowledge of the sedimentary environ derived from Chukotka. Modern ice-rafted pebbles ments would be available for at least the 3-month ice form a significant component of the sediment only free season. The nature ofsedimenttransportduring near the shore (Nelson and Hopkins, 1972). the ice-covered season is unknown. The relict sediments of the Chirikov Basin contain Most of the palimpsest sediment consists of mod no evidence that Yukon sediment has ever accumu ern Yukon detritus mixed with older sediment, but lated there nor that the river formerly drained there are two types of palimpsest sediment that through the basin into the Chukchi Sea. The relict appear to be unrelated to Yukon sediment. Modern· Yukon sands are found only east of a line from and relict sands near western St. Lawrence Island eastern St. Lawrence Island to Nome, and the mod appear to be mixed by some undefined process. The ern Yukon sands are even more restricted in area. modern and relict Quaternary basalt s~nd and Either the characteristics of the Yukon sands are gravel are indistinguishable and hence are classified soon lost during transport on the shelf, or, the mouth as palimpsest. Relative to the modern Yukon sedi of the Yukon River has lain in its present northern ment supply, the modern components of other position for only a brief period. Migration of the river palimpsest sediments is insignificant. mouth seems likelier (Knebel and Creager, 1973; Relict sediments cover the Chirikov Basin, and McManus and others, 1974). indeed most of the study area. As neither their A seaward decrease in grain size is commonly relative nor their absolute age is known, however, we accepted as a criterion for recognizing a deposit of can draw only tenuous inferences about the sedi modern, as distinguished from relict, sand-that is, mentologic history. of sand being derived from the adjacent shore. The In Shpanberg Strait there is a relict fine-grained westward fining of sediment from the shallow water Yukon sand that has been formed into depressions near Seward Peninsula to the relatively deep water and ridges whose crests lie at the level of the 20-m in the Chukotka Deranged Area might be so inter- C30 STUDIES 0N THE MARINE GEOLOGY OF THE BERING SEA preted, but the sediment is too coarse to be supplied J. M., eds., Environment of the Cape Thompson region, from the shore at this time; it is therefore relict rather Alaska: U.S. Atomic Energy Comm., Washington, D.C., than modern sand. Moreover, the heavy minerals in p. 697-754. Folk, R. L., and Ward, W. C., 1957, Brazos River Bar-a study in this relict sand are from source rocks in two areas: the significance of grain-size parameters: Jour. Sed. Petrol the relict sand in the deeper water was derived from ogy, v. 27, p. 3-26. Chukotka, that in the shallow water from Seward Grim, M. S., and McManus, D. A., 1970, A shallow seismic Peninsula. Although the grading in the relict sand profiling survey of the northern Bering Sea: Marine Geology, might have been produced by nearshore processes v. 8, p. 293-320. Hooper, C. L., 1884, Report of the cruise of the U.S. Revenue migrating across the area with changes in sea level, Steamer Thomas Corwin in the Arctic Ocean, 1881: Wash this does not seem likely because similar size grading ington, D.C., U.S. Govt. Printing Office. is not present elsewhere-for example, off St. Law Hopkins, D. M., 1967, Quaternary marine transgressions in rence Island. Rather the size grading seems to have Alaska, in Hopkins, D. M., ed., The Bering land bridge: been produced by the presence, now, of the strong Stanford, Calif., Stanford Univ. Press, p. 47-90. Hopkins, D. M., Nelson, C. H., and Grim, M. S., 1969, Extent 'northward -setting current along south western of glaciation on the floor of northern Bering Sea [abs.]: Inter Seward Peninsula. This current would have a bottom nat. Quaternary Assoc. (INQUA) Cong., 8th, Paris 1969, Ekman effect such as that measured in the Bering Resumees des Communications, p. 209. Strait by Coachman and Aagaard (1966) that would Hopkins, D. M., Nelson, C. H., Perry, R. B., and Alpha, T. R., 1976, Physiographic subdivisions of the Chirikov Basin, northern result in northward transport along the bottom at a Bering Sea: U.S. Geol. Survey Prof. Paper 759-B, 7 p. small angle to the isobaths and left or seaward Hopkins, D. M., Rowland, R. W., and Patton, W. W., Jr., 1972, rather than paralleling the isobaths. By this current, Middle Pleistocene mollusks from St. Lawrence Island and the sediment could be transported seaward. Such a their significance for the paleo-oceanography of the Bering condition for the con tinental shelf off Washington is Sea: Quaternary Research, v. 2, p. 119-134. Husby, D. M., 1971, Oceanographic investigations in the northern described by Smith and Hopkins (1972). The seaward Bering Sea and Bering Strait, June-July 1968: U.S. Coast decrease in current velocity off Seward Peninsula Guard Oceanog. Rept. 40, Washington, D.C., 50 p. would produce a gradient in transport competency, Imbrie, John, and van Andel, Tj. H., 1964, Vector analysis of and probably a similar gradient in grain size. Mea heavy-mineral data: Geol. Soc. America Bull., v. 75, p. 1131- surements of sediment transport are needed to test 1156. the hypothesis of producing seaward fining of relict Kelley, J. C., 1971, Mathematical analysis of point count data, in Carver, R. E., ed., Procedures in sedimentary petrology: sand by present-day processes. New York, John Wiley, p. 407-425. Kelley, J. C., and McManus, D. A., 1969, Optimizing sediment sample plans: Marine Geology, v. 7, p. 465-471. REFERENCES CITED --1970, Hierarchical analysis of variance of shelf sediment texture: Jour. Sed. Petrology, v. 40, p. 1335-1339. Blatt, Harvey, 1967, Provenance determinations and recycling of Knebel, H. J., and Creager, J. S., 1973, Yukon River; evidence for sediments: Jour. Sed. Petrology, v. 37, p. 1031-1044. extensive migration during the Holocene transgression: Sci Coachman, L. K., and Aagaard, K., 1966, On the water exchange ence,v. 179,p. 1230-1232. through Bering Strait: Limnology and Oceanography, v. 11, Krumbein, W. C., and Pettijohn F. J., 1938, Manual of sedimentary p. 44-59. petrography: New York, Appleton-Century-Crofts, 549 p. Coachman, L. K., Aagaard, K., and Tripp, R. B., 1975, Bering Lamar, W. 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Dixon, W. J., 1970, Biomedical computer programs: California McManus, D. A., and Creager, J. S., 1963, Physical and sedi Univ. Pubs. Automatic Computation 2, 600 p. mentary environments on a large spit-like shoal: Jour. Geol Dupre, W. R., 1977, Yukon Delta coastal processes study, in ogy,v. 71,p.498-512. Assessment of the Alaskan Continental Shelf: U.S. Natl. McManus, D. A., Kelley, J. C., and Creager, J. S., 1969, Continen Oceanog. Atmospheric Admin. and U.S. Bur. Land Manage tal shelf sedimentation in an Arctic environment: Geol. Soc. ment Principal Investigators Rept. Year ending March America Bull., v. 80, p. 1961-1983. 1977 (in press). McManus, D. A., and Smyth, C. S., 1970, Turbid bottom water on Emery, K. 0., 1952, Continental shelf sediments of southern the continental shelf of the northern Bering Sea: Jour. Sed. California: Geol. Soc. America Bull., v. 63, p. 1105-1108. Petrology, v. 40, p. 869-873. Fleming, R. H., and Heggarty, D., 1966, Oceanography of the McManus, D. 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Printing 1974, Sea surface circulation, sediment transport, and marine Office, 330 p. mammal distribution, Alaska continental shelf; ERTS Final Report: Natl. Tech. Inf. Service Rept. E74-10711, 77 p. Venkatarathnam, Kolla, 1971, Heavy minerals on the continental Shepard, F. P., 1963, Submarine geology, 2d ed.: New York, shelf of the northern Bering Sea: U.S. Geol. Survey open Harper & Row, 557 p. file report, 92 p. Silberman, M. L., 1969, Preliminary report on electron micro Wiegel, R. L., 1964, Oceanographic engineering: Englewood scopic examination of surface textures of quartz sand grains Cliffs, N.J., Prentice-Hall, 532 p.