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Veronica Alekseeva, Moscow State University (Russian Federation)
Pavel Kabanov, Palaeontological Institute RAS (Russian Federation)
Tatiana Alekseeva, Institute of Physicochemical and Biological Problems of Soil Science RAS (Russian Federation)
Andrey Alekseev, Institute of Physicochemical and Biological Problems of Soil Science RAS (Russian Federation)
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The regional unconformities in tops of the Upper Carboniferous (Late Moscovian) cyclothems on the territory of Russian Plane are marked by paleokarst and the relatively immature paleosols which retain information about the landscapes of sea level lowstand phases. The study of eustatic variations of Palaeozoic sea levels is of great interest for palaeogeographic reconstructions.
The detail study of mineralogical composition of deposit's outcrop of the Late Moscovian stage of Carboniferous in Moscow region has been done. The aim of the investigation was to obtain the micromorphological, mineralogical and geochemical characteristics, which can be used to confirm the subaerial exposure stage in the sedimentary history development and, probably, the pedogenesis connected with this stage. The layers of unconformities are marked out as two-layer profiles, including the calcrete-capped limestone covered by the clay epipedon ("topclay"). Mineralogical composition (bulk and < 2 m) has been done by XRD and FTIR-spectroscopy, the micromorphology of quartz grain surface of the fine sand (0.1-0.25 mm) with SEM, chemical weathering as the ratios of selected chemical elements by X-ray fluorescent method, iron compounds by the complex of paleomagnetic measurements.
According to data obtained the profile under study can be divided into two parts with distinct histories. Low part is present by carbonate paleosol contained palygorskite/sepiolite minerals and developed under oxidizing conditions. The development of karst, presence of micritic calcite, gypsum, iron oxides (including magnetite), preservation of palygorskite indicate the long duration of the soil weathering under seasonal subarid climate. "Topclay" layer is consisted of palygorskite clays which contain a visible amount of terrigenous minerals. This part of the profile was developed under the increasing humidity of climate and visibly less influenced by pedogenesis. Terrigenous component is represented by the quartz grains of 4 major types which confirm their primary water and aeolian transport. The presence of quartz grains with heavy corrosion is the other important characteristic of both parts of paleosol although the dissolution can take place as a result of either soil weathering or diagenetic transformations of sediments.
The landscape reconstructions allow concluding that "Great Carbonate Plains" of the central part of Russian Plane during Upper Carboniferous featured moisture-deficient climate, lack of fluvial runoff, specific soil development, loose and low vascular vegetation.
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