Biological markers in bitumens and pyrolyzates of Upper Cretaceous bituminous chalks from the Ghareb Formation (Israel) |
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| Authors: | Jürgen Rullkötter Zeev Aizenshtat Baruch Spiro |
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| Institution: | 1. Institute of Petroleum and Organic Geochemistry (ICH-5), Kernforschungsanlage Jülich GmbH, P.O. Box 1913, D-5170 Jülich 1, Federal Republic of Germany;2. Institute of Chemistry and Energy Research Centre, The Hebrew University, Jerusalem, Israel |
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| Abstract: | The sterane and triterpane distributions of three bituminous chalks from the Upper Cretaceous Ghareb Formation (Israel) were investigated both in the original extractable bitumens and in extracts obtained after pyrolysis of whole rock and isolated kerogen samples at 450°C. Pyrolysis was performed in a closed system under hydrous (whole rock) and anhydrous conditions (isolated kerogens). The carbon number distributions of steranes and triterpanes differ significantly between original bitumen and pyrolyzates. Unlike the bitumens in which diasteranes were not detected, the anhydrous pyrolyzates contain small amounts of diasteranes. The presence of water during pyrolysis leads to an increase of sterane isomerization, the abundant formation of diasteranes and an increase of the ratio. Sterane isomerization maturation parameters show a closer match between original bitumen and pyrolyzates after pyrolysis in a closed system when compared with an open system. |
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