PARATETHYAN PETROLEUM SOURCE ROCKS: AN OVERVIEW

R. F. Sachsenhofer^1*, S.V. Popov², S. Coric³ J. Mayer⁴, D. Misch¹, M.T. Morton⁵, M. Pupp¹, J. Rauball¹ and G. Tari⁴

¹ Chair of Petroleum Geology, Montanuniversitaet Leoben, Peter-Tunner-Str. 5, 8700 Leoben, Austria.

² Paleontological Institute, Russian Academy of Sciences, ul. Profsoyuznaya 123, Moscow 117997, Russia.

³ Geological Survey of Austria, Neulinggasse 38, 1030 Vienna, Austria.

⁴ OMV Exploration and Production GmbH, Trabrennstraße 6-8, 1020 Vienna, Austria.

⁵ Department of Geology, University of Leicester, University Road, Leicester, LE1 7RH.

^* Corresponding author: reinhard.sachsenhofer@unileoben.ac.at

Key words: Source rock, Paratethys, source potential index, organic matter, Eocene, Oligocene, Maikop Group, Menilite Formation, Kuma Formation, Solenovian Event

The Paratethys area extends from Central Europe to the borders of the Caspian Sea in Central Asia and hosts a significant number of petroleum provinces, many of which have been charged by Eocene to Miocene source rocks of supra-regional significance. These include highly oil-prone Middle Eocene marls and limestones in the Eastern Paratethys (Kuma Formation and equivalents) which are several tens of metres thick. Estimates of the source potential index (SPI) indicate that the Kuma Formation in the northern Caucasus and the Rioni Basin (Georgia) may generate 1 to 2 tons of hydrocarbons per square metre (tHC/m²). This implies that the Kuma Formation may also be an important and additional source rock in the eastern Black Sea.

Oligocene and Lower Miocene pelitic rocks (Maikop Group and equivalents) are considered to be the most important source rocks in the Paratethys. Vertical variations in source potential record different stages of basin isolation that reached a maximum during the Early Oligocene (NP23) Solenovian Event. However major variations exist between different sub-basins in the Central and the Eastern Paratethys. In the Central Paratethys, the highest quality source rocks occur in the Carpathian Basin where the Menilite Formation, several hundreds of metres thick, can generate up to 10 tHC/m². Locally the Menilite Formation is about 1500 m thick and continues into the Lower Miocene. In these settings, the Menilite Formation can generate approximately 70 tHC/m². In the Alpine Foreland Basin (Schöneck and Eggerding Formations) and the Pannonian Basin (Tard Clay Formation), oil-prone source rocks are restricted to the Lower Oligocene. In the Eastern Paratethys, the best source rock intervals of the Maikop Group are typically associated with the Early Oligocene Solenovian Event. By contrast, with the exception of the Kura Basin in Azerbaijan, the potential of Upper Oligocene and Lower Miocene rocks is often limited. In total, the Maikop Group may generate up to 2 tHC/m² in the North Caucasus area and 4 tHC/m² in the Rioni Basin.

Middle and Upper Miocene rocks are the main source for oil and thermogenic gas in the Pannonian Basin System, and also contributed to thermogenic hydrocarbons in the Moesian Platform and the South Caspian Basin. In addition, Upper Oligocene and Miocene rocks are the source for microbial gas in several basins including the Alpine and Carpathian foredeeps.

A particular source rock facies is found in the Western Black Sea where diatomaceous rocks with good oil potential accumulated in the Kaliakra Canyon during Early Miocene time. This facies may generate up to 8 tHC/m², but is probably limited to shelf-break canyons.

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