Geophysical processes and biosphere: article

Аnnotation: Quaternary lacustrine complexes of two regions were formed in different paleogeographic conditions. On the Baltic Shield, they accumulated during the active admission of glacier water into the depressions, which determined the diversity of the lithological composition and texture of the sediments. They range from varve silts with dropstones (facies of glacial-dammed lakes), to mixed-grained sands with wavy stratification (shallow-lake facies). In Northern Yakutia, the accumulation of lacustrine complexes occurred in closed thermokarst (alas) depressions due to the redeposition of uneven-aged sediments of the ice complex with silted composition. This is associated with a more homogeneous composition of alass deposits and a reduced development of flowing water sediment textures. In the lacustrine complexes of both regions, deformation structures of various types are widely developed, which are sensitive indicators conditions of sedimentation and diagenesis. Similar structures - folded deformations (convolution) of convective and (or) cryogenic mixing of weakly consolidated sediments, having a similar morphology (narrow antiform and wide siniform folds). Although these structures are externally similar to seismites, they are usually associated with interruptions of lacustrine sedimentation, which almost completely excludes the possibility of their formation as a result of seismic liquefaction of sediments. A characteristic feature of the structure of alas sediments is the widespread presence of pseudomorphs in polygonal-veined ice found in the lacustrine complexes of the North-West sporadically. The lacustrine complexes of the North-West occurring under the moraine are also distinguished by the presence of intense glacial dislocations.