DEPOSITIONAL ENVIRONMENT AND SOURCE-ROCK CHARACTERISATION OF ORGANIC-MATTER RICH UPPER SANTONIAN – UPPER CAMPANIAN CARBONATES, NORTHERN LEBANON
S. Bou Daher*1, F. H. Nader2, H. Strauss3 and R. Littke1
1 Energy & Mineral Resources Group (EMR), Institute of Geology and Geochemistry of Petroleum and Coal, RWTH Aachen University, Lochnerstrasse 4-20, 52056 Aachen, Germany.
2 Geology Department, Geosciences Division IFP Energies Nouvelles, 1 & 4 Av. de Bois-Préau, 92852 Rueil-Malmaison Cedex, France.
3 Institut für Geologie und Paläontologie, Westfälische Wilhelms-Universität Münster, Corrensstrasse 24, D-48149 Münster, Germany.
*corresponding author, email: Samer.BouDaher@emr.rwth-aachen.de
Samples of Turonian – upper Campanian fine-grained carbonates (marls, mud- to wackestones; n = 212) from four boreholes near Chekka, northern Lebanon, were analysed to assess their organic matter quantity and quality, and to interpret their depositional environment. Total organic carbon (TOC), total inorganic carbon and total sulphur contents were measured in all samples. A selection of samples were then analysed in more detail using Rock-Eval pyrolysis, maceral analyses, gas chromatography – flame ionization detection (GC-FID), and gas chromatography – mass spectrometry (GC-MS) on aliphatic hydrocarbon extracts. TOC measurements and Rock-Eval pyrolysis indicated the very good source rock potential of a ca. 150 m thick interval within the upper Santonian – upper Campanian succession intercepted by the investigated boreholes, in which samples had average TOC values of 2 wt % and Hydrogen Index values of 510 mgHC /gTOC. The dominance of alginite macerals relative to terrestrial macerals, the composition of C27–C29 regular steranes, the elevated C31 22R homohopane / C30 hopane ratio (> 0.25), the low terrigenous / aquatic ratio of n-alkanes, as well as d13Corg values between -29‰ and -27‰ together suggest a marine depositional environment and a mainly algal / phytoplanktonic source of organic matter. Redox sensitive geochemical parameters indicate mainly dysoxic depositional conditions.
The samples have high Hydrogen Index values (413–610 mg/g TOC) which indicate oil-prone Type II kerogen. Tmax values (414 – 432°C) are consistent with other maturity parameters such as vitrinite reflectance (0.25–0.4% VRr) as well as sterane and hopane isomerisation ratios, and indicate that the organic matter is thermally immature and has not reached the oil window. This study contributes to the relatively scarce geochemical information for the eastern margin of the Levant Basin, but extrapolation of the data to offshore areas remains uncertain.
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