Structural and Lithological Comparison of Convolutions in Lacustrine Complexes (Q3-4) of the Baltic Shield, Northern Yakutia, Tien Shan

In order to clarify the genesis of liquefaction folds (convolutions) developed at lithological boundaries in lacustrine sediments, such structures in three regions were compared. Folds in each region differ in morphology, composition of sediments, and the vertical gradient of their density and viscosity upon deformation. It is proposed to use the ratio of the widths of syn- and anticlinal folds in the convolution horizon (K_s) to analyze the latter, in which K_s > 1 corresponds to the normal viscosity gradient, and K_s < 1, to its inversion. Convolutions of the Baltic Shield and Yakutia from K_s ≥ 1 are noted in the most liquefied sediments with unstable density stratification (sands-on-silts), which indicates the possibility of their spontaneous formation during lithogenesis. Folds with K_s ≈ 1 are widespread in Yakutia, which indicates their cryogenic genesis. Convolutions in the Tien Shan were formed with stable sediment stratification in terms of density (silts-on-sands); low-fluidized coarse-grained sediments with viscosity inversion were also involved in deformation. These features indicate the seismic initiation of liquefaction processes. The results substantiate the lithogenic genesis of convolutions in lacustrine complexes of the Baltic Shield, cryogenic and lithogenic in Yakutia, and seismogenic in the Tien Shan. It is proposed to determine the scatter of the K_s value in the diagrams for diagnosing the genesis of convolutions. For lithogenic structures, this parameter is shifted to the region with K_s > 1, and for seismites, it is relatively symmetric with respect to K_s = 1.