Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)

Preliminary study of organic matter in sediments of the Vendryně Formation, Silesian Unit and its potential as a source of hydrocarbons


Eliška Polášková, Petr Skupien

Geoscience Research Reports 50, 2017, pages 293–297
Map sheets: Karviná (15-44)

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Published online: 18 December 2017

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The subject of the present paper is the analysis of source rock potential of the Tithonian Vendryně Formation (formerly referred to as Lower Těšín Beds) in the Outer Western Carpathians. The Formation reaches a thickness extending from about 300 to 400 m, and represents the basal lithostratigraphic unit of the Silesian Nappe.
The study area lies in the town of Třinec and its surroundings. Samples were taken from bedrock outcrops along the banks of the Olše River in the direction from south to north, i.e. downstream, specifically from a railway bridge connecting the towns of Třinec and Vendryně to the last outcrops in Třinec, the Sosna local district/borough (Fig. 1). The outcrops are formed mostly of dark coloured (dark grey, brown-grey) claystones and siltstones, which were deposited under anoxic conditions. In the study area there are deposits rich in organic carbon material (0.5-1.7 % TOC).
The organic material studied in palynological slides was divided into three groups indicating their origin: group of phytoclasts, palynomorphs and amorphous organic matter (AOM). These results were used for determination of the type of kerogen using a model by Tyson (1993). From the analysis of kerogen follows that the amorphous organic matter (AOM) is most abundant, which is favourable for the formation of liquid hydrocarbons occurring in organic-rich shales deposited in shelf seas. The environment believed to have been suboxic. High values of AOM indicate a reducing (dysoxic or anoxic) environment with high potential for preservation of planktonic organic matter. Kerogen of type II > I and II >> I (aquatic type) predominates in the studied samples.
The evaluation of the degree of thermal conversion has shown that the material is largely immature (it did not undergo higher thermal conversion, paleotemperature from 30 °C to 65 °C). Only sporadically, the thermally mature material with thermal conversion at about 80 °C, corresponding to the oil window, was identified.