A study of organic matter and habitat of gaseous hydrocarbons in the Miocene strata of the Polish part of the Carpathian Foredeep

Abstract

Geochemical studies on the organie matter from the autochthonous Miocene strata of the Carpathian Foredeep demonstrated the presence of gas-prone type 1/1 kerogen in both the Upper Badenian and Lower Sarmatian sediments with rare admixtures of algal type /1 kerogen. The TOC eontents vary from 0.02 to 3.22 wt. %. Down to the depth 3,200 meters the organic matter is immature. Its transformation degree corresponds to the vitrinite refleetance Ro from 0.25 to 0.6% and to the Rock Eval Tmax temperatures from 415 to 438oC. Insignificant variability in spatial and depth distribution of geochemieal parameters and indices (TOC, TE/TOC, Tmax, HI, Ro, CPI, etc.) suggest that deposition conditions of the organic matter were generally homogenous within the full thickness of Miocene sequence down to the recent depth about 3,200 meters. Such conditions resulted in the laek of diversity of the TOC, the genetic type and the transformation degree of the studied kerogen. The Miocene terrestrial OM is immature and generated almost exclusively the microbial methane. The low-temperature thermogenic proeesses have been active beneath the depth about 3,200 meters i.e., mainly under the Carpathian overthrust.