Geochemical characteristics of organic matter in the Lower Palaeozoic rocks of the Peribaltic Syneclise (Poland)

Abstract

Organic matter occurring in Lower Palaeozoic rocks of variable lithology was investigated for its origin, depositional environment and thermal maturity. Samples from nine boreholes located in the Polish part of the Peribaltic Syneclise were collected for performing Rock-Eval Analysis, palynological investigation for Thermal Alteration Index (TAI), solvent extraction, preparative layer chromatography (PLC) and gas chromatography-mass spectrometry (GC-MS) of aliphatic and aromatic compound fractions. It was found that kerogen belongs to either type I or commonly, to type II. It derives from variable, planktonic and planktonic-bacterial primary organic matter deposited in dysoxic environments in the eastern part of the Syneclise and in anoxic/suboxic conditions in the western and central parts. Organic matter is in the thermal evolution stage from late diagenesis to advanced metagenesis. Correlation of biomarker parameters, TAI and Rock-Eval results show that the thermal maturity of organic matter falls into three regional groups, increasing from the north-east to the south-west along the crystalline basement of the Eastern European Platform. The organic matter contained in Ordovician and Cambrian sediments of the western part of the Syneclise is overmature, reaching metagenesis. This is most probably related to the activity of the Teisseyre-Tornquist Zone, where the Baltica and Eastern Avalonia paleocontinents collided during the Late Ordovician. It is also reflected in the profiles by elevated values of aromatic hydrocarbon and sulphur compound parameters, which show the highest levels of thermal maturity for organic matter present in the sediments of the Ordovician and Lower Silurian. Local influence of igneous intrusions on organic matter is also visible in changes in thermal maturity values at the direct contact with diabase dykes.

Phenyl derivatives of polycyclic aromatic compounds as indicators of hydrothermal activity in the Silurian black siliceous shales of the Bardzkie Mountains, Poland

“…Thus, we summarize that under unique conditions connected with migration of hydrothermal fluids, the composition of the extractable OM changes significantly, especially in the case of the aromatic fraction. Extracts from Silurian samples of the Polish lowland are characterized by a significantly different molecular composition, with high amounts of alkylnaphthalenes and alkylphenanthrenes, as well as low or nil abundances of phenyl-derivatives (Marynowski et al, 2011b;Skręt and Fabiańska, 2009). The only cause of such a significant molecular transformation can be a specific diagenetic process.…”

“…Such distributions are typical for Silurian sedimentary OM from the Polish lowland (Skręt and Fabiańska, 2009) and representative for a marine OM type. Regular steranes and hopanes are present in low abundance or are totally absent due to the high maturity range.…”

Reply on RC1

“…to the TTZ (Fig. 4; Kanev et al, 1994;Nehring-Lefeld et al, 1997;Swadowska and Sikorska, 1998;Grotek, 1999Grotek, , 2006Grotek, , 2016Skręt and Fabiańska, 2009;Więcław et al, 2010Więcław et al, , 2012. In all stratigraphic units, thermal maturity increases toward SW correspondingly to the increase of burial depth.…”

“…Chronostratigraphic subdivisions and absolute ages refer to Gradstein et al (2012) throughout the text. (Grotek, 1999(Grotek, , 2006(Grotek, , 2016Skręt and Fabiańska, 2009;Pletsch et al, 2010).…”

Thermal history of the East European Platform margin in Poland based on apatite and zircon low-temperature thermochronology

“…These studies revealed a systematic zonation in the degree of diagenesis of Ediacaran to lower Paleozoic rocks that is oriented NE-SW, parallel to the TTZ (Fig. 4; Kanev et al, 1994;Nehring-Lefeld et al, 1997;Swadowska and Sikorska, 1998;Grotek, 1999Grotek, , 2006Grotek, , 2016Skręt and Fabiańska, 2009;Więcław et al, 2010Więcław et al, , 2012. In all stratigraphic units, thermal maturity increases toward the SW corresponding to the increase of burial depth.…”