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TENTH INTERNATIONAL CONFERENCE ON PERMAFROST

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Massive Ground Ice on the South-Western Coast of the Kara Sea
N.G. Belova Faculty of Geography, Lomonosov Moscow State University, Moscow, Russia

Introduction
Massive ground ice (MI) is widespread on the continental coast of the Kara Sea. The discussion about the MI genesis has been going on since when it first became the object of study. Some researchers believe that MI is of intrasedimental origin, wh ile the others assume that it is of buried origin. Even now, after 50 years of studying the issue, there is no agreement of opinion. Researchers are still debating even over such well -known and well-studied areas of MI occurrence as the territories of the Marresale Polar Station, Bovanenkovo gas condensate field located in the valley of the Seyakha River on the Yamal Peninsula, or Shpindler stow located on the coast of the Yugorskiy Peninsula. In 2005-2008 MI collected in two key areas ­ the western coast of Baydaratskaya Bay in the area of the Oyuyakha River mouth [Belova et al. 2008] and in the area of Kharasavey village located on the Yamal Peninsula ­ were studied [Belova et al. 2010]. It was found out that the MI of the southwestern coast of the Kara Sea occurs in sediments of various age and genesis and that it varies in the formation time and mechanisms.

MI was formed as a result of liquid water freezing. The lower layer MI with the thickness of up to 3 m occurs conformably to the enclosing sediments and has a lighter isotopic composition, as compared to the upper layer MI (lighter by 3.2 based on the 18 value). The chemical composition of the MI in both layers is ultra-nonsaline.

Massive ground ice on the western coast of Baydaratskaya Bay
A 25-45 m high steeply-sloping plain is adjacent to the shore in the area of the Oyuyakha River mouth. Along the shoreline it is lowered down to 15-20 m by numerous thermokarst basins (hasyreys). A number of sections are underlain by a clayey stratum with fragmentary material. The stratum is compared by F.A. Romanenko and his co-authors [2007] with Kara diamicton described by V.N. Gataullin [Forman et al. 2002]. Its uneven table which often retreats under the sea waterline is unconformably overlain by a sandy stratum having a complex structure, the thickness of up to 28 m and enclosing MI. Mos t of the stratum is composed of fine sand and silty sand that are enriched with plant detritus or are peaty. The sands bedding is cross, oblique and convolute, often interlaid with sandy silts, clayey silts and rolled pebble size coal. The stratum contains fragments and scallop shells of marine mollusks, bones and tusks of mammoths. The sandy stratum is characterized by a continental type of salinity and is dated using the radiocarbon method from 22.5 (1 date) to 44.9 -49.6 (3 dates) thousand 14 years ago, i.e. at the limit of the method operation [Romanenko et al. 2007]. This lets us assume that the stratum began to form earlier, as early as 60-50 thousand years ago (MIS 4-3) during the phase of the retreat of the Kara Sea shelf ice sheet. MI occurs in the sandy stratum in two layers. The ice of the upper (habs.= 9-15 m) and lower layers (habs. = 0-9 m) differ in thickness, structure and composition. The upper layer MI with the thickness of 3-6 m has an erosional upper contact, the isotopic composition of 18 = ­21.8... ­15.0 (Table 1), and its structure is similar to that of basal glacier ice. The 18 (D) and deuterium excess (d) values do not have a visible connection, which is the evidence against the assumption that The composition of pollen and spores in the upper layer MI was determined by A.K. Vasilchuk at the end of 2011. Exotic far transported pollen of thermophilic grounds that is characteristic of the polar glaciers ice is not present. The ice contains spores of green mosses which are not present in atmospheric glacial ice. According to A.K. Vasilchuk, such composition of palynospectra indicates the intrasedimental mechanism of ice formation (Vasil'chuk & Vasil'chuk 2010). However, we believe that the upper layer MI is basal glacial ice which is very different from atmospheric glacier ice in the mechanisms of formation and in composition. Such palynospectra components as spores of green mosses could be included into the basal glacier ice together with bed sediments. In this case ice would be highly contaminated and dislocated [Vasil'chuk & Vasil'chuk 2010], which corresponds to the characteristic of the upper layer MI. The primary indicator of the fact that MI is of buried origin is the erosional upper contact of MI that shears the stratification in ice with angular unconformity (there is no sign of secondary thawing in the overlaying sediments). The upper layer MI can be classified as glacier ice due to: 1) complex MI structure with lying folds and shear deformations; 2) similarities between MI facies and basal glacier ice facies in modern glaciers; 3) absence of the connection between 18 (D) and d, absence of significant fluctuations in the isotopic composition (5 -6 based on the 18 value). We can assume that the MI was formed 60-50 thousand years ago during the Yermak (Early Weichselian) period (Q III2, MIS 4-3) at the stage of degradation of the Kara Sea shelf ice


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EXTENDED ABSTRACTS 3) the inverse relationship between the changes in the 18 (D) and d values; the values of the isotopic composition that becomes lighter gradually in the direction from ice lenses above the MI towards the upper part of the deposit; and 4) the composition of palynospectra in ice is similar to the spectra in the enclosing sediments.

sheet. The lower layer MI was formed in the sandy stratum of fluvioglacial, coastal-marine and lacustrine-alluvial sediments. Apart from the buried perennial snow patches and lacustrine ice, there were also formed small ice and ice-ground strata as well as lenses and veins in the sediments. The upper layer MI was formed later, after a brief process of the ice sheet regeneration as a result of burying basal ice and its selvages.

Massive ground ice in the area of Kharasavey village
MI in the sediments of the northwestern coast of the Yamal Peninsula in the area of Kharasavey village is confined to the elevations of the table of sandy coastal-marine sediments conformably with the marine sediments overlaid by the clayey silty stratum. The marine sediments compose a 10 m high terrace. All the transitions between the benches of the sediments enclosing MI are gradual. The MI occurs conformably with the stratification of the enclosing sediments and follows the sharp bends of the enclosing sands table. A series of lenses (with the thickness of 2 20 cm) that follow the contours of the deposit table was recorded in overlaid sediments at the distance of up to 2 m above the upper MI boundary. The thickness of the ice body under study is 1 m. The MI is represented by separate ice interlayers with the thickness of 5-35 cm that are separated by ground horizons (1-10 cm). The sands under the MI have a high ice content. They also contain tilted ice schlieren that form a reticulate-lenticular cryogenic structure. MI has an ultra-nonsaline mineralization and mostly sodium chloride salinity type. The isotopic composition (Table 1) gradually becomes lighter in the direction from the ice lenses above the MI towards the upper part of the deposit, and the d values increase proportionally to the decrease in the content of isotopes 18 and D, which indicates that the freezing goes from the top downwards. There is no uniform trend of changes in the content of 18 and D in MI. However, the inverse relationship between the 18 (D) and d values is preserved. It is probable that some interlayers of MI were formed in several stages of freezing. The first data on the composition of pollen and spores in the deposit described were obtained in January 2012 by A.K. Vasilchuk. Ice contains a large amount of palynomorphs. The palynospectra are similar to the spectra in the sediments of the Kharasavey village area that were studied by A.K. Vasilchuk [Vasil'chuk 2006]. No signs of atmospheric origin of MI [Vasil'chuk & Vasil'chuk 2010] were found in the deposit. The reasons in support of the assumption that the formation mechanism of the MI in the Kharasavey village area is intrasedimental mechanism are: 1) occurrence in conformity with the enclosing sediments; lensoid structure of the MI whose table follows the bends of the enclosing sediments stratification; 2) the chemical composition of the MI that coincides with that of schlieren ice and is similar to the chemical composition of water extracted from the enclosing sediments;

Conclusions
1. MI of the western coast of Baydaratskaya Bay forms two layers which differ in the thickness of strata as well as in ice structure and composition. The upper layer was formed in the process of burying the glacier ice by the sediments of the lacustrine-alluvial periglacial plain. The lower layer MI partly represents various primary surface buried ice bodies, partly ­ intrasedimental. 2. MI of the northwestern coast of the Yamal Peninsula in the Kharasavey village area is confined to the elevations of the table of sandy coastal-marine sediments in conformity with the marine sediments overlaid by a clayey silt stratum. MI occurs in conformity with the enclosing sediments. The composition is similar to that of structure-forming ices. It was formed during the epigenetic freezing of the enclosing sediments.

Acknowledgments
The author thanks Dr. H. Meyer, Dr. V.I. Nikolaev and Dr. B.G. Pokrovskiy for conducting the isotopic analysis of the MI samples; Dr. A.K. Vasilchuk for providing the first results of the palynological analysis; Prof. V.I. Solomatin and Dr. F.A. Romanenko for their help in obtaining and interpreting the work materials.

References
Belova, N.G., Solomatin, V.I., Meyer, H. 2010. Isotopic composition of massive ground ice exposure at the Kharasavey coast, West Yamal. Abstracts of the Third Europ. Conf. on Permafrost, Univ. Centre in Svalbard, p. 284. Belova, N.G., Solomatin, V.I. & Romanenko, F.A. 2008. Massive ground ice on the Ural coast of the Baydaratskaya Bay, Kara Sea, Russia. Proceedings of the NICOP, Fairbanks, Alaska, US, vol.1, 107-112. Forman, S.L., Ingolfsson, O., Gataullin, V., Manley, W.F., Lokrantz, H. 2002. Late Quaternary stratigraphy, glacial limits, and paleoenvironments of the Marresale Area, Western Yamal Peninsula, Russia. Quaternary Research 57: 355-370. Romanenko, F.A., Belova, N.G., Nikolaev, V.I., Olunina, O.S. 2007. Particularities of the structure of loose sediments on the Yugorsky coast of Baydaratskaya Bay in the Kara Sea. Mater. V Vseross. soveshchaniya po izucheniyu chetvertichnogo perioda. Moscow: GEOS: 348-351 (in Russian).