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Structure, Composition, and Origin of the Yedoma Suite around the Laptev Sea

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Schirrmeister, L. , Wetterich, S. , Grosse, G. , Siegert, C. and Kunitsky, V. (2007): Structure, Composition, and Origin of the Yedoma Suite around the Laptev Sea , INTERNATIONAL CONFERENCE «CRYOGENIC RESOURCES OF POLAR REGIONS» Salekhard, Russia.06-20.06.2007. .
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Abstract:

Yedoma, consisting of so-called Late Pleistocene Ice Complex deposits, is a special type of permafrost formation widely distributed in Northeast Siberia, especially in the coastal lowlands of the Laptev and the East Siberian Sea as well as on the New Siberian Archipelago. Its most impressive characteristics is the supersaturation with segregated ground ice in the deposits (gravimetric ice content 40 to 250 wt %), the occurrence of huge ice wedges, and its total deposit thickness of 10 to 60 m. A wide variety of hypotheses for the genesis of these deposits were developed in the past decades. Our study, based on eight years of intensive investigations of Yedoma exposures within joint German-Russian expeditions along the Laptev Sea coast, in the Lena River Delta, and on the New Siberian Archipelago, provides the first integrated study of a wide variety of Ice Complex sequences in this region and new insights into their genesis. Yedoma sequences consist of several buried palaeo-soils of different maturity formed within a polygonal landscape. Variations in organic carbon contents (1 to 25 wt %) as well as numerous datasets of palaeo-environmental proxies reflect changing environmental conditions during the period of Yedoma formation. Based on heavy mineral analyses, the clastic sediment material mainly originated from nearby located mountain ridges or rocky hills. Accumulation of the Yedoma Suite occurred as the result of a complete transformation of the hydrological regime proved by the consistent occurrence of fluvial sand deposits below Yedoma horizons, dated between 50 to 100 ky by Optical Stimulated Luminescence and U/Th methods. The fluvial dominated hydrological regime shifted to an irregular runoff from the mountain and hill areas fed by highly a seasonal runoff from perennial snowfields. This runoff occurred over less-inclined, poorly drained plains in the Laptev Sea shelf lowland in front of the mountains. The highly seasonal runoff from these snowfields delivered clastic material from nival-eolian and proluvial processes in the mountain ridges into the alluvial plains and were a main sediment source for the Ice Complex accumulation. Additional eolian transport and reworking of the same clastic material has contributed to Yedoma formation. In these plains, the long-term formation of ice wedge polygons took place, resulting in the presence of very large ice wedges, netlike and horizontally banded cryostructures, as well as the alternating accumulation of sandy to silty runoff material, and of peaty soils in polygon depressions. The period of Yedoma formation covers the glacial, interstadial and glacial MIS 4 to MIS 2 stages of the Late Pleistocene. Numerous palaeo-ecological datasets and abiotic proxies confirm this stratigraphical order. The dated onset of Yedoma accumulation varies between the regions (ca 80 to 28 ky). The ending time of the accumulation is also different (ca. 28 to 10 ky) depending on regional conditions. The uppermost part of Yedoma is mostly covered by Holocene deposits. Parts of it, however, have been strongly degraded by extensive thermokarst during the Holocene warming.

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