New data on stratigraphy of the surficial sedimentary mantle of the Taz and Gydan peninsulas have been obtained in the course of the Russian-Norwegian project PECHORA (Palaeo Environment and Climate History of the Russian Arctic) which can be used for interregional correlation. These sediments, described within the two terrace levels 25-30 m and 40-55 m, are represented by various marine and fluvial facies. The sedimentological, palaeontological and geochronometrical data allow to distinguish several successive sedimentation stages in the first half of the Late Pleistocene.

The early stage is reflected in a sand formation up to 40 m thick, which is inserted into a plateau built of glacial and glaciolacustrine sediments of the well-known Sanchugovka horizon of the Middle Pleistocene. This sandy formation has an average OSL age 143 kyr (by 7 dates). The character of the basal contact and abundant plant detritus is evidence of rapid increase of erosion rates during the sedimentation. This should relate to final stages of the Middle Pleistocene glaciation and possibly to draining an ice-dammed lake during a transition to the Late Pleistocene.

Sandy and silty clay marine sediments are positioned higher stratigraphically (but not hypsometrically) and have an average OSL age 135 kyr (by 6 dates). The littoral facies contain numerous in situ shells of bivalves and gastropods and their abundant burrows. Typical boreal species Buccinum undatum, Macoma baltica, Modiolus sp. and Mytilus edulis have been identified. Together with the geochronometric data they imply an interglacial transgression and correlation with MIS 5e (Nazarov, 2005). This marine formation can serve as the main stratigraphic marker for correlation between the Ob and Yenissei regions. Its age counterparts are the Shuryshkary peat and alluvium of the high right-bank terrace on the Lower Ob (Astakhov et al. 2005), the Malaya Kheta alluvium (Astakhov, Mangemd, 2005) and the Karginsky marine strata on the Yenissei (Arkhipov, 1990).

South of the Gydan Ridge fluvial sands, silts and clays with rare lenses of peat and ice wedge casts are incised into the described formations. According to OSL dates and non-finite radiocarbon ages they were formed during a relatively long period since 108 to 69 kyr. This time span corresponds to cold events of MIS 5d to MIS 4, but the traces of an ice sheet have not been found south of the Gydan Ridge. The studied sediments by OSL dates can be correlated with the fluvial sands and subaerial deposits underlying and overlying the Upper Pleistocene glaciolacustrine formation on the Lower Ob (Astakhov, 2006).

A totally different situation occurs north of the Gydan Ridge. Buried glacial ice and diamicton with typical for basal till sedimentological features lie at the base of the succession. They are overlain by outwash and sediments of ice-dammed lakes. Most likely they were deposited during the last West Siberian glaciation correlative with the Early Valdai in European Russia, and probably refer to the time span from MIS 5d to MIS 4.

Reference:

Nazarov D. Correlation of principal Late Pleistocene events in the central part of the West Siberian Arctic. Correlation of Pleistocene Events in the Russian North. International Workshop Abstracts. 4-6 December 2006. Saint-Petersburg, 2006, p. 70.