Stratigraphy of Quaternary deposits of the western Yamal Peninsula and eastern shore of the Yugorski Peninsula has been of interest to many researchers. More then twenty radiocarbon dates of sediments and many isotope characteristic of massive ice beds and ice wedges have been obtained. However, facies composition, structure and interrelation of different formations (e.g., deposits containing massive ice bodies and peat and plant detritus seams) are poorly known. In August 2006 the facies composition was studied in coastal cliffs of the Yamal Peninsula from Lyiakha River mouth to Sabryavpenzi River mouth and on the Yugorski Peninsula from Yary to Levdiev Island. Contacts of main formations and key horizons have been traced in a great number of sections. For the first time lateral boundaries, base and top of massive ice bed were traced on the Yugorski Peninsula. Investigated sediments were divided into several formations.

1. The «Layda» formation is represented by peaty bluish brown loam seen just above sea level and covered by peat to 0.5 m thick. This formation makes up two level (0.5-1.5 and 2-4 m) of flat marshy surface with many lakes. Peat accumulation took place in the interval from 3850 to 980 C¹⁴ years B.P.

2. The «lower» sand formation consists of horizontal, diagonally and cross-bedded sands with loamy seams, practically without plant detritus. The formation composes the First marine terrace (4-8 m high) graded near the shore by aeolian processes.

3. The «upper» sand formation has a complicated structure. It is characterized by cross, diagonal and wavy bedding, abundance of loam and clay interlayers, occurrence of deformed beds and folds. In sediments of the Yamal area, there is a great number of laminae of plant detritus (thickness of about 1-3 cm), driftwood, relict ice wedges up to 3-4 m wide. This formation accumulated for с 30 to 19 ¹⁴C kyr B.P.

A stratigraphically similarly positioned formation of the Yugorski Peninsula contains interlayers of well-rounded pebbles and gravels of up to 0.3-0.5 m thick, with fragments of thick shells and a great number of interbeds consisting of coal pebbles. The specific feature of the Yugorski Peninsula shore is the presence of massive ice beds up to 9 m thick sprouting subhorizontal schlieren ice. These sediments compose the uppermost surface at 27-35 m with massive ice beds lying at the highest localities.

4. The «hasyrei» or «alas» formation is subhorizontally stratified loam and sand with lenses of peat, wood and plant detritus. Its age is about 5,600-8,600 ¹⁴C years B.P. on the Yamal Peninsula and about 4,000-11,000 ¹⁴C years B.P. on the Yugorski Peninsula. Also, there are two peat layers dated to 1-2 and 10-11 ¹⁴C kyr B.P. on the Yamal Peninsula. Therefore, peat accumulation in thermokarst depressions encompasses a considerable part of the Holocene.

5. The diamicton formation is represented by dense fragmented loam with rounded boulders and pebbles in the lowest part of many sections of the Yugorski Peninsula and some sections on the Yamal Peninsula. Pebbles consist of sandstone, siltstone, mudstone and often of granite.

Thus, the massive ice beds conformably lie within the sand formation over the highest surface of the coastal area of the Yugorski Peninsula. The shores of the Baidarata Bay were reworked by active thermokarst process and peat accumulation at least during three periods.

The work was supported by Russian Foundation for Basic Research (Project 05-05-64872).

Reference:

Romanenko F.A., Olyunina O.S. On the structure of Quaternary sediments along the shores of the Baidarata Bay, the Kara Sea. Correlation of Pleistocene Events in the Russian North. International Workshop Abstracts. 4-6 December 2006. Saint-Petersburg, 2006, p. 78.