Thomas Rainer

The Donets Basin (Ukraine/Russia): coalification and thermal history.

The Donets Basin (Donbas) is one of the major late Paleozoic coal basins in the world. The Donbas Foldbelt is an inverted part of the Donets Basin characterized by WNW–ESE-trending folds and faults. The age of basin inversion is under discussion. Large parts of the Donets Basin host anthracite and meta-anthracite. Low-rank coals are restricted to the western and northern basin margins. Vitrinite reflectance patterns along the Gorlovka Anticline indicate syn-deformational coalification. Vitrinite reflectance isolines are displaced along thrusts, clear evidence that main coalification predates late faulting. 1-D and 2-D numerical models were applied to elucidate the factors that control coalification in the western Donets Basin (Krasnoarmeisk Monocline, Kalmius–Torets Depression, South Syncline). The models indicate that the depth of the seams and the heat flow during maximum (Permian) burial are the most important parameters. The thickness of late Carboniferous and Permian rocks increased from the southwestern basin margin towards the basin center. Permian erosion along the Krasnoarmeisk Monocline and in the Kalmius–Torets Depression was on the order of 2–3 km. More rocks were eroded southeast of the Donetsk–Kadievka Fault Zone (4–5 km). Heat flow during maximum burial was in the range of 40–75 mW/m2. Heat flow in the Krasnoarmeisk Monocline and the Kalmius–Torets Depression increased in a northeastward direction from 40 to 55 mW/m2. Heat flow at the eastern edge of the Kalmius–Torets Depression and in the South Syncline was in the range of 60–75 mW/m2 and increased towards the southeast. The resulting coalification pattern in this area was overprinted by thermal events in the northern Krasnoarmeisk Monocline and the South Syncline. These are probably related to (Permian?) magmatic intrusions. Coked coal occurs at the contact to presumed Permian sills and dikes southwest of Donetsk.

Depositional environment and source potential of Jurassic coal-bearing sediments (Gresten Formation, Höflein gas/condensate field, Austria)

Coal-bearing Jurassic sediments (Gresten Formation; Lower Quartzarenite Member) are discussed as source rocks for gas and minor oil in the basement of the Alpine–Carpathian frontal zone (e.g. Höflein gas/condensate field). Core material has therefore been analysed to characterize depositional environment and source potential of the Lower Quartzarenite Member (LQM). Geochemical data from the Höflein condensate are used to establish a source–condensate correlation. The LQM was deposited in a flood basin with transitions to a delta-plain environment. Coal originated in frequently flooded mires and evolved within an oxygenated and acidic environment. It is inferred from geochemical data that organic matter from aquatic macrophytes and gymnosperms contributed to coal formation. Wildfires were abundant and oxidation of plant remains occurred frequently. This resulted in the formation of dull coal with very high inertinite contents. Bituminous shales were formed in deeper waters under dysoxic conditions. Apart from abundant algae and micro-organisms, it is concluded that there was an increased contribution of higher land plants relative to macrophytes to the biomass of the shales. Despite high inertinite contents, coal within the LQM has a significant oil potential. Bituminous shales contain a Type III–II kerogen. According to pyrolysis–gas chromatography data, coal and shale generate a high wax paraffinic oil. The organic matter is immature to marginal mature (0.55% Rr). Bituminous shales are considered a potential source for the Höflein condensate. Coal may be the source for gas and minor oil in the Klement Field, but is not the source for the condensate. The equivalent vitrinite reflectance of the condensate is 0.8%, suggesting condensate generation at 4–4.5 km depth. The Gresten Formation reaches this depth near its depocentres, implying southward-directed migration of the Höflein condensate.