Geochemical preconditions for detecting of pre-Frasnian unconformity in the Devonian succession of the Timan-Pechora sedimentary basin

Abstract

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.

Lithological characteristics of the pre-Greben' regional unconformity of the Sizimcelebeyshor Creek of the Chernov Uplift

“…Исследование карбонатных отложений в природных обнажениях является важным при реконструкции условий их образования, выявления в них перерывов и поверхностей несогласий, являющихся границами разноранговых секвенций [9]. В разрезах несогласия могут быть проявлены одной-двумя (или более) эрозионными поверхностями, а в карбонатных разрезах могут сопровождаться развитием карста [7,8].…”