It is generally accepted that the eastern limit of the LGM Eurasian ice sheet is to be sought in the Kara Sea, but data on the structure and stratigraphy of the Quaternary deposits are scarce. Based on a large number of seismic records and sediment cores obtained from the southwestern Kara Sea by the former Soviet Union programs and our two expeditions in 2000 and 2001, we present data on the geometry and stratigraphy of Quaternary deposits together with improved sea floor morphology in this area. The overall Quaternary sedimentary cover is subdivided into six major seismo-lithostratigraphic units, SSU VI to I (upwards).

SSU-VI: intercalating sands, silts, and clays, which form up to 200 m thick progradational (prodeltaic) sequence extending northwestwards from the Yamal Peninsula. We infer that this is a composite unit formed by repeated progradations of the Ob River delta at low sea level stands, possibly with the onset of Middle Weichselian glaciation (MIS 4).

SSU-V: stiff diamicton with a chaotic seismic signature, with mostly even bottom surface and rough, hummocky top surface. We correlate this unit, which is mostly confined to the southernmost area, to the Kara Till of the Yamal Peninsula interpreted to have been laid down during the Middle Weichselian glaciation (prior to 30-40 kyr).

SSU-IV: intercalating marine silts and clays in the Yugorskaya Depression east of the Vaigach Island and along the coast of Yamal Peninsula, grading into shallow-marine, prodeltaic, and alluvial sands at water depths <50 m north of the Ob Estuary. This unit was presumably deposited during the interstadial environments (MIS 3) and subsequent sea level fall.

SSU-III: stiff diamicton (subglacial till) with three subunits identified within it. The oldest subunit, correlated to the Kolguev Till of the southeastern Barents Sea, occurs along the eastern flank of the Novaya Zemlya Trough. This till forms a series of morainic constructions up to 100 m thick and presumably marks the maximal ice-sheet extension into the Kara Sea during the LGM. The middle subunit, correlated to the Kurentsovo Till, occupies the bottom of the Novaya Zemlya Trough with several smaller moraines further west. The younger subunit, correlated to the Admiralty Bank Till, is proximal to the coast of Novaya Zemlya and forms distinct high-relief, narrow morainic ridges up to 75 m high. Based on the geometry of these subunits, we infer that the Kolguev and Kurentsovo moraines were formed by ice streams moving from the north along the Novaya Zemlya Trough, whereas the Admiralty Banks moraines were deposited by readvances of an ice cap over Novaya Zemlya during the final stages of deglaciation.

SSU-II: laminated silt and clay, mostly developed in the Novaya Zemlya Trough and adjacent depressions. The largest thickness of 75-100 m occurs in the southern part of the trough, proximal to the LGM end-moraine constructions. We interpret this unit as a time-transgressive lens of glaciomarine sediments formed during the retreat of the ice margin.

SSU-I: bioturbated Holocene marine mud with an average thickness of 2-3 m.

Despite the remaining uncertainties with chronostratigraphy and distribution of some portions of the identified units, the overall picture allows us to characterize the major features of glacial history of the southwestern Kara Sea. Our data also elucidate patterns of riverine drainage within this part of the Eurasian margin. Notably, we found the extension of the Ob river into the southwestern Kara Sea prior to the Middle Weichselian glaciation, but cannot identify traces of a similar extension in this area during the last sea level fall.

Reference:

Gataullin V., Polyak L., Belyaev V., Gainanov V. Late Pleistocene glaciation history of the southern Kara Sea. Correlation of Pleistocene Events in the Russian North. International Workshop Abstracts. 4-6 December 2006. Saint-Petersburg, 2006, p. 26.