Disturbed Stratification in Late Pleistocene Sediments of the Khibiny Pluton (Kola Peninsula)статья
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Дата последнего поиска статьи во внешних источниках: 26 июня 2019 г.
Аннотация:The paper presents a description of three Late Pleistocene sections within the Khibiny pluton, cropping out on the proximal slope of the Kukisvum morainic ridge, a fluvioglacial terrain in the valley of the Kukisyok River and a glacial complex in the valley of the Vuonnemyok River. Various small disturbances of the primary stratification were found in the first two sections. These structures do not form horizons that are sustained along the strike and are associated with the top of sandsilt sediments with horizontal or wavy bedding of shallow-lacustrine genesis. They form small wavy bends, «tongues», ovoids and flexural shales that could not be preserved at the bottom of the basin, and, consequently, formed after overlapping deposits accumulation. Analysis of the cross-bedding character 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 Kukisyok River. In the glaciolacustrine varve clays of the third section (the Koashva open pit), extended horizons of plicative disturbances of 0.5–2 m in thickness and of 300 m in length were studied.The soft-sediment deformations covering the unstructured horizon consisted of coarse grains dispersed in sand-silt matrix, which means the deformation was caused by either a glacial flood or a mudflow. The study revealed no signs of seismic liquefaction during formation of the folded structures. The relevance of the performed study is determined by the fact that it has become an opportunity not only to clarify the formation conditions of Quaternary Khibiny deposits but also to develop the objective criteria for determination in the mentioned section of the softsediment
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 region’s seismic hazard level.