Pyrolysis-GC characterization of whole rock and kerogen-concentrate samples of immature Jurassic source rocks from NW-Germany |
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| Authors: | Carol Arnosti Peter J Müller |
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| Institution: | 1. EREX, Egypt;2. Department of Geology, Ain Shams University, Cairo 11566, Egypt;3. Petro Amir, Cairo, Egypt;1. CONICET, Museo Argentino de Ciencias Naturales “B. Rivadavia”, Av. Angel Gallardo 470, C1405DJR, Buenos Aires, Argentina;2. Sinopec Argentina Exploration and Production Inc., Manuela Saenz 323, Puerto Madero, Ciudad Autonoma de, Buenos Aires, Argentina;1. Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, Universitätsstr. 150, 44801, Bochum, Germany;2. Institut für Geologie, Leibniz Universität Hannover, Callinstraße 30, 30167, Hannover, Germany;3. LBEG, Stilleweg 2, 30655, Hannover, Germany;1. Département de Géologie, Laboratoire LGRN, Université Mohamed Ben Abdellah, Faculté des Sciences Dhar El Mahraz, B.P. 1796, Fès-Atlas, Fès, Morocco;2. Laboratoire GET, Université Paul Sabatier, Toulouse, CNRS, IRD, OMP, 14 Avenue Edouard Belin, 31400, Toulouse, France;3. Naturalis Biodiversity Center, Leiden, Netherlands;4. Utrecht University, Faculty of Geosciences, Department of Earth Sciences, Netherlands |
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| Abstract: | Nine rock samples from three Jurassic stratigraphic units of a shallow core from NW Germany were analyzed by pyrolysis-gas chromatography. The units contain a mixed Type-II/III kerogen (Dogger-α), a hydrogen-rich Type-II kerogen (Lias-), and a hydrogen-poor Type-III kerogen (Lias-δ). All of the kerogen was immature (Ro = 0.5%). Two sets of kerogen concentrates (“AD”: HCl/HF followed by a density separation, and “A”: only acid treatment) prepared from the rock samples were also analyzed to make a detailed comparison of the pyrolysates of rock and corresponding kerogen-concentrates.Hydrogen-index (HI) values of the kerogen concentrates prepared from organic-carbon poor rock were nearly 200% higher than HI values of the rock samples. Changes in HI were minimal for the samples containing Type-II kerogen. The A and AD samples from the Corg-poor rock yielded pyrolysates with n-alkane series of very different molecular lengths. Pyrograms of the rock samples had n-alkane series extending to n-C14; the chromatograms of the A samples reached the n-C14-nC20 range. The AD samples from Corg-poor rock and all three sample types from the Corg-rich rock had n-alkane series up to n-C29. The benzene/hexane and toluene/heptane ratios for the Corg-poor rock and A samples were far higher than for the AD samples, which had ratios similar to those of all three sample types from the Corg-rich rocks. These results indicate that choice of kerogen preparation method is critical when Corg-poor samples are analyzed. |
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| Keywords: | kerogen source rock pyrolysis-gas chromatography hydrogen index n-alkanes |
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