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The Quaternary lacustrine complexes of two regions considered in this work formed in different paleogeographical conditions. In the Baltic crystalline shield, they accumulated as a result of the admission of thawing glacial waters in depressions, and this was favorable for the formation of a diverse lithological composition and sedimentary structures: from varve silts with dropstones (facies of deepwater glacier dam lakes) to equigranular sands with wavy stratification (shallow lacustrine facies). In northern Yakutia, the lacustrine complexes accumulated in closed thermokarst (alas) depressions at the expense of the redeposition of ice silty sediments of various ages. This is responsible for more a homogeneous composition and minor flowing water structures. The lacustrine complexes of both regions exhibit abundant deformation structures of various types, which are sensitive indicators of sedimentary and diagenetic conditions. Similar structures include the fold deformations of convective and/or cryogenic mixing of poorly consolidated sediments (convolutions) with similar morphology (narrow antiform and wide synform folds). Although these structures are morphologically similar to seismites, they, as a rule, are confined to hiatuses in lacustrine sedimentation, minimizing their possible formation as a result of the seismic dilution of sediments. The presence of ubiquitous pseudomorphoses after wedge polygonal ice is a typical feature of the structure of alas sediments, in contrast to rare pseudomorphoses in lacustrine complexes of the Northwest region. On the other hand, under-moraine lacustrine complexes of the latter exhibit intense glaciodislocations, which are absent in northern Yakutia. [ABSTRACT FROM AUTHOR]

The paper presents a description of three Late Pleistocene sections within the Khibiny pluton, outcropping on the proximal slope of the Kukisvum morainic ridge, a fluvioglacial terrain in the valley of the Kukisiok River, and a glacial complex in the valley of the Vuonnemiok River. Various small disturbances of the primary stratification were found in the first two sections. These structures do not form horizons sustained along the strike and are associated with the top of sand-silt sediments with horizontal or wavy bedding of shallow lacustrine genesis. They form small wavy bends, 'tongues", ovoids, and flexural microfolds that could not be preserved at the bottom of the basin and, consequently, formed after overlapping deposits accumulation. Analysis of the cross bedding of the coarse clastic deposits of the fluvioglacial terrace has allowed us to relate its formation to north-to-south glacial water discharge along the trough valley of the Kukisiok River. In the glaciolacustrine varve clays of the third section (the Koashva open pit), extended horizons of plicative disturbances 0.5-2 m in thickness and 300 m in length were studied. The soft-sediment deformations are covered with an unstructured horizon composed of coarse grains dispersed in sand-silt matrix, which means that the deformation was caused by either a glacial flood or a mudflow. The study has revealed no signs of seismic liquefaction during the formation of the folded structures. The relevance of the performed study is determined by the fact that it has become possible not only to clarify the formation conditions of the Quaternary Khibiny deposits but also to develop the objective criteria for determination of the soft-sediment deformation structures associated with thixotropic effects in weakly consolidated sediments. Similar structures are sometimes regarded as seismic convolutions, which can lead to unjustified overestimation of the regional seismic hazard level. [ABSTRACT FROM AUTHOR]