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Lower Permian organogenic buildups within the Northern part of Timan-Pechora basin are mounds-type structures. They are characterized by an extremely irregular distribution of reservoirs which are linked to facial zones and genetic features of the deposits. Two types of buildups were distinguished qualified as microbial and skeletal mounds formed by different paleo-communities of benthic organisms. The composition and textural-structural features of prevailing limestones within these buildups there is a key to understand the distribution of reservoirs within the area of study.

Based on the results of the core analysis of boundary Lower to Upper Devonian (D 1 l-D 3 tm) interval by X-ray fluorescence analysis supplemented with CO 2 determination and loss on ignition, X-ray diffraction analysis of clay fraction of the rocks and clays, electron microscopy and EDS, analysis of stable isotopes of carbonate carbon and oxygen, etc., we revealed lithological and mineralogical-geochemical features, which testified to the ancient influence of infiltration water systems to the rocks during the ascent of previously submerged strata into the aeration zone. In the sections studied, we showed a definite vertical geochemical zonation, expressed in changing zones from top to bottom: a) zone of marine slightly altered limestones; b) zone of hydrolysis and infiltration in argillaceous dolomites with signs of paleokarst; c) zone of secondary dolomites; d) zone of low-altered limestones. The established sequence is characteristic for the processes of regressive infiltration epigenesis and assumes the existence of a subaerial unconformity between a andb zones.