Chapter 9 Holocene History of The

Chapter 9 Holocene History of the Laptev Sea Continental Shelf 1 M. L. HOLMES 2 AND J. S. CREAGER 2 Abstract Introduction The 400-km-wide, low gradient Laptev Sea conti The Laptev Sea is one of three epicontinental nental shelf consists of flat terrace-like features at seas lying along the northern coast of central regular depth intervals from 10 to 40 m below present Asiatic Russia (see Fig. 1, Naugler et al., this sea level. The five large submarine valleys traversing the volume). Field work was carried out during July shelf do not continuously grade seaward, but contain and August 1963, aboard the U.S. Coast Guard elongated, closed basins. These terraces and closed ice-breaker Northwind. Ninety-nine stations were basins plus deltaic sediments associated with the sub occupied along approximately 4000 km of track, marine valleys quite possibly mark sea level stillstands, and enable reconstruction of the paleogeography of the and bottom samples collected include 58 gravity Laptev Sea shore line at five periods during post-Wis cores and 62 grab samples (Fig. 1). This paper is consin (Holocene) time. concerned with the analysis of bathymetric data Radiocarbon dates on the silty-clay to clayey-silt and the study of 14 cores from the northeastern sediments from cores of the northeastern Laptev Sea Laptev Sea, and discusses sea-level history and indicate average sedimentation intensity of 2 to 15 paleogeography of coast lines of the Laptev Sea mglcm2/yr. The presence of manganese nodules and during Holocene (post-Wisconsin) time. crusts in surface samples from less than 55 m depths The climatic and physiographic features of and a general decrease in total foraminiferal abun the surrounding area are described by Suslov dances with depth in the cores suggest that the present (1961, p. 125), and Naugler et al. (this volume). deposition rate is less than when sea level was lower. Sverdrup (1927), Suslov (1961, p. 162), and Cod The main components of the shelf deposits are near shore sediments which were spread over the shelf as ispoti (1965) discuss the physical oceanography of Holocene sea level fluctuated and marine currents the Laptev Sea. The extent of various continental distributed modern fine sediment. Rare silty-sand layers glaciations in Siberia are discussed by Flint and and the coarser nuclei of the manganese crusts and Dorsey (1945), Donn et al. (1962), and Flint nodules indicate ice rafting. However, this mechanism is (1971). At various times during the Pleistocene, probably only locally important as a significant tran continental ice sheets covered only the western sporting agent. shores and sea floor of the Laptev Sea, and did not extend east of the present-day Olenek River. A I Contribution no. 734, Department of Oceanography, small thin ice sheet, approximately 250 km in University of Washington. diameter, spread out from the New Siberian 2 Department of Oceanography, University of Washing ton, Seattle, Washington 98105, U.S.A. Islands (Flint, 1971, p. 665). Saks (Samoilov, 1952, 211 Y. Herman (ed.), Marine Geology and Oceanography of the Arctic Seas © Springer-Verlag New York Inc. 1974 I\.) ~ locf 11ct' 12ct' 13ct' 140" 7ft if TAIMYR PENINSULA 144 ~ S· 145 et> G) 146 et> ) o 73"1 -A /~ ~ . ~ 1 147 r ISLAND ,--~ -l7S' 1:tF.J - f'" '. 148 ~t\) ::J 149 Q. ~ m::J c8 "0i:il ~ Q. S- 73° et> 11° ):. ~ g. a?t\) (I) Sounding track, Northwind 1963 _ Bottom sample locations 142- Locations of cores studied o 50 100 , , I 71° Kilometers 12ct' 13ct' 14ct' Fig. 1. Bottom sample locations and track chart, Laptev Sea. Holocene History of the Laptev Sea Continental Shelf 213 p. 307) briefly describes the mouths of the Lena which they seem to be associated. A conspicuous and Yana Rivers (Fig. 1) during the Quaternary. feature of all of these valleys is that they are not He states that during the Karginsky transgression continuously graded seaward, but are marked by a (about 11,500 years B.P.) the Lena formed two series of linear depressions. The depressions in the branches near the area of its present delta. The Yana and eastern Lena valleys occur at depths of mouth of one branch was 300 km northwest of the 25 and 40 m, while those of the Olenek, western present delta, and a separate branch flowed north Yana, and Anabar-Khatanga valleys exhibit clo ward. Saks (Samioilov, 1952, p. 307) also states sures at depths of 30 and 45 m. Similar depres that the mouth of the Yana River during this sions have been found along Hope valley in the period was slightly more than 300 km north of its Chukchi Sea (Creager and McManus, 1965) and present position. Gusev (1959) discusses the evolu in the Kolyma and Indigirka valleys of the East tion of the coastal plain during the Quaternary, Siberian Sea (Naugler et aI., this volume). but gives coast-line positions only for Wisconsin Extensive flat areas occur at remarkably time and for an unspecified period during Neo regular depth intervals on the shelf. The greater gene time. part of Stolbovoy Shoal is between 10 and 15 m in depth, and in the western Laptev Sea between the Anabar River and the Lena Delta the 10- and 15-m isobaths are also very widely spaced. North Results and Discussion east of Kotelny Island, the 20- and 25-m contours may delineate another large flat area, but the bathymetry here is based only on Soviet spot Bathymetry soundings. In the central area of the shelf north of the Lena Delta, two large plains are well devel Sounding data from the Northwind cruise, oped at depths of 30 to 35 m and 40 to 45 m. supplemented by nearly 500 Soviet spot sound The subaerial portions of the Lena Delta do ings, were used to compile the bathymetry of the not extend very far seaward (Fig. 1). The Gulf of Laptev Sea (Fig. 2). The bathymetry of the Bourkhaya and Oleneksky Bay probably represent continental slope is from a chart by Gakkel' delta flank depressions (Bates, 1953) which have (1958). The continental shelf covers approximately been formed by a combination of wave and 460,000 km2, and varies in width from 300 km in current action, local crustal downwarping, and the western part to over 500 km in the east. The compaction of fine-grained sediments with time. shelf break occurs at 50 to 60 m depth, much The larger size of the Gulf of Bourkhaya, the shallower than the 200-m break mentioned by distribution of delta channels, and the lack of Suslov (1961, p. 261) and Eardley (1964) for this barrier islands along the eastern edge of the delta area. The shelf is very flat, with gradients ranging (and their presence to the west) seem to indicate from undetectable, in some areas, to about 5 that most of the Lena River's sediment load is mlkm. The bathymetry is more irregular in the being deposited along the eastern flank of the northwestern area, probably due in part to the delta at present. action of the continental ice sheet which covered The general circulation pattern of surface portions of this region during part of the Pleisto currents in the Laptev Sea is described by Suslov cene. An extensive shoal (called Stolbovoy Shoal (1961, p. 162). A cold current sets southward in this paper), with depths less than 15 m, occupies along the eastern coast of the Taimyr Peninsula the central area of the eastern Laptev Sea. The toward the Khatanga estuary, where it mixes with shoal is probably a primary structural feature the waters of the Khatanga and Anabar Rivers representing the northward extension of the foot and turns eastward. This current, reinforced by hills of the Verkhoyansk Range. Numerous small the outflow from the Lena River, then sets north banks, less than 5 m in depth, occurring on eastward and bifurcates, one branch setting north Stolbovoy Shoal were probably formed as a result ward and the other eastward between Kotelny of the melting of ice cores in small islands. This Island and the mainland (Fig. 2). The northern process has been documented in the case of branch again divides, with the main portion Vasilevsky Bank by Grigorov (1946). proceeding northwestward into the Arctic drift, Five large submarine valleys cross the Laptev while the other branch sets eastward along the Sea shelf and are named after the rivers with northern side of Kotelny Island (U.S. Navy Hy- ~ ..... 100" "'" 75° ~ S'CI) (j) 0'~ ~ II> ::J Q.. ~ m::J <8 "0~ ~ o .... S- CI) 71 ° ~ ~ a- • Core locations (I)m 5 meter contour interval to 100 meters, variable thereafter o 50 100 71° Fig. 2. Bathymetric chart of the Laptev Sea, Holocene History of the Laptev Sea Continental Shelf 215 drographic Office, 1944). Currents generally do The predominant sediment types are silty not exceed 10 cm/sec, although speeds of 25 to 50 clays and clayey-silts, with mean grain sizes from cm/sec have been observed for the northward 7.5 to 8.50. With the exception of cores l36 and flowing curr!!nt in the eastern-central portion of 143 (Fig. I), they are quite uniform with respect to the Laptev Sea. sediment type, mineralogy, and chemistry. Sedi Stolbovoy Shoal would have acted to control ments below sharp unconformities, at 25 cm in the location and magnitude of currents as the sea core l36 and 18 cm in core 143, show many of the level rose and fell over the ridge during late characteristics of deltaic sediments as described Pleistocene and Holocene times. The configura by Shepard (1960) from the Mississippi Delta.

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