Origin of Quaternary sediments of northern West Siberia on the whole and of western Yamal (Marre-Sale) in particular has been under discussion for many years. Many geocryologists believe that the sediments are marine or littoral, and stratiform massive ice was formed underground. The majority of geologists maintain their glacial origin. In this study we investigated two sections of Cenozoic sediments near the Marre-Sale Polar Station, the Yamal Peninsula. The first section is represented by a coastal exposure with stratiform ground ice in it. The second one is derived from a borehole 126 m deep. The same set of methods has been used for analysis of the sediments.

Perennially frozen Cenozoic sediments with massive ground ice are exposed in a coastal cliff 20-25 m high. Two sedimentary units have been distinguished. The upper unit 1-2 m to 20-25 m thick consists of terrestrial non-saline medium and fine-grained sand with interlayers of gray loam of Late Weichselian and Holocene age (Forman et al, 2002). The unit includes a network of ice-wedges up to 2-3 m thick, which penetrate with their ends into underlying marine loamy sediments. Changes of sedimentary environments are emphasized by changes in water-soluble ion composition. The lower unit consists of folded saline marine or littoral clay and loam with rare silt and sand bands. The sediments according to the same group of authors are dated to the Early Weichselian (60-80 kyr BP). The sediments of the lower unit contain stratiform massive ground ice. Geochemical analysis of this unit has shown that all sediments are saline down to sea level.

A borehole 126 m deep was drilled at the same topographic level as the coastal exposure (20 m a.s.l.). The structure of sediments is identical to the coastal sequence (Kritzuk, Dubrovin, 2006). Down to 8.2 m the sediments are non-saline, and deeper they are saline to various degrees. Microstructural studies using granular-mineralogical analysis support marine genesis for the lower unit (Surkov, 2000) and terrestrial origin for the upper unit. The upper unit was formed on a wide floodplain with small lakes. Sand and clay sediments of the lower unit were formed on a shallow marine shelf with constantly changing depths. Distribution curves of the heavy mineral fraction and quartz are similar to sand histograms of modern beaches of the Kara Sea.

Based on the results of our analysis we have been able to reconstruct the sequence of environmental changes and sedimentation conditions in western Yamal. Formation of the clayey part of the sequence occurred during a sea transgression. The saline clayey sediments with lenses of sand and plant detritus weakly transformed by wave action were formed in the coastal zone of the shelf. The upper part of the sequence was deposited in terrestrial environments during the Late Pleistocene and Holocene.

Reference:

Streletskaya I.D., Shpolanskaya N.A., Vasiliev A.A. Structure of Cenozoic sediments in the western Yamal Peninsula and their genesis. Correlation of Pleistocene Events in the Russian North. International Workshop Abstracts. 4-6 December 2006. Saint-Petersburg, 2006, p. 96.