Lithological-geochemical types of deposits of Cretaceous-Paleogene flysch of the Ukrainian Carpathians and conditions of their formaition

Abstract

The results of lithological, mineralogical and geochemical investigation of Cretaceous-Paleogene flysch deposits of the Ukrainian Carpathians are cited here. There are three main lithological-geochemical types of these deposits which differ in the composition of rock-forming ingredients of biogenic origin (SiO2 biog, CaCO3, Corg): grey limestone-clayey-terrigenous (type-I), non-carbonate or low-carbonate-clayey-terrigenous (type-II), and black carbonate-silica-terrigenous-clayey (type-III). The deposits of the first type are attributed to alkaline-oxic (oxic-calcitic), the second – to acid and low-alcaline oxic (oxic with redeposited glauconite), the third – to reducing (siderite, dolomite or ferrodolomite and low-reducing calcitic) and strong by reducing (primary-sulfidic or hydrogen sulfidic) mineralogical-geochemical facies. The forming of the Barremian-Albian (Shypot suite; Spas suite) and Oligocene (Menilite suite; Dusynska suite) organic-rich sediments in the Ukrainian Carpathians we associate with the phase of oceanic anoxic events OAE-1 and OAE-4 in the Carpathian segment of the Tethys, where anoxic reducing environments favoured to fossilization of huge amount of the dispersed organic matter. The structural-fabric features and composition of separate lithological types of silicites and diagenetic concretions of the Lower Cretaceous and Oligocene of the Ukrainian Carpathians show that their sedimentogenesis and diagenesis took place in conditions of strong oxygen deficit. The studied siliceous rocks can be considered as indicators of the anoxic events in the Carpathian segment of Tethys ocean. It is shown, that alcaline-reducting environments which was the most favourable for the diagenetic transformation of sedimentary organic matter in to petroleum hydrocarbons, prevailed in the organic-rich deposits of Oligocene age.