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| Hauptseite > Publikationsdatenbank > Organisch-geochemische und mikroskopische Charakterisierung diskreter, organisch reicher Lagen des Messeler Ölschiefers |
| Hauptseite > Publikationsdatenbank > Organisch-geochemische und mikroskopische Charakterisierung diskreter, organisch reicher Lagen des Messeler Ölschiefers |
| Poster | PreJuSER-42562 |
; ; ; ;
2004
Please use a persistent id in citations: http://hdl.handle.net/2128/168
Abstract: The Messel Pit fossil site near Darmstadt, Germany, is famous because of its numerous well-preserved mammal and other fossils, and therefore, in 1995 became a UNESCO-World Heritage (www.unesco-welterbe.de/en/). The respective host rock, the Messel oil shale is still a matter of intensive studies. This dark, finely laminated organic rich mudstone, was deposited in a Maar lake in the Lower Middle Eocene about 47Ma ago during a time span of 1 to 1.5 Ma. One subunit, the so-called ’Middle Messel Formation‘ can be subdivided by several specifically named marker beds (M, $\alpha$, $\beta$ and $\gamma$), but also by some further layers with distinct macroscopic characteristics. The two layers investigated here represent green-brown deposits with a maximum thickness of up to one millimetre only. They are encountered at a level of 35 cm (herein after referred to as ’layer 0,35m u$\alpha$‘) and 100 cm (herein after referred to as ’layer 1,00m u$\alpha$‘) below Marker Bed $\alpha$. Typically, both layers are extremely ductile, and thus can easily be manually separated like individual paper-like book-sheets from their adjacent host rock. Because of their leather-like plasticity, they must be considered to be rich in organic material. Accordingly, it was the objective of this study to reveal the type of organic matter they consist of. This approach tested the lateral variation of organic matter of layer 0,35m u$\alpha$ and layer 1,00m u$\alpha$ by comparison of the molecular compositions exhibited by the analytical results of temperature programmed pyrolysis-gas chromatography and thermovaporisation-gas chromatography which need small sample amounts only. In addition, the molecular compositions of the C$_{15+}$-soluble organic matter of the layers were compared to their adjacent host rocks. The bulk parameters like total organic carbon (TOC), total sulphur (TS), and the hydrogen index (HI) confirm higher contents of organic matter for both layers, with stronger enrichments for layer 1,00m u$\alpha$. Layer 1,00m u$\alpha$ exhibits a surprising high sulphur content of 7 %, which can not be explained so far but may represent a high microbial degradation of the organic matter. In respect to the molecular compositions, influences by migrated organic matter can be excluded due to a maturity stage below 0.5% Rr (mean Tmax below 430$\circ$C and a strong predominance of the odd- to-even-numbered n-alkanes). Lipid compositions with predominance of the odd-numbered n-C$_{23}$ to n-C$_{31}$ alkanes pointing to high proportions of terrestrial plant material are in contrast to HI values above 620mgHC/g TOC. Thus, high bacterial/microbial contributions have to be assumed which is confirmed by individual biomarker data. Both layers and the host rock have incorporated similar amounts of bacterial/microbial organic material. In contrast, layers 0,35m u$\alpha$ and 1,00m u$\alpha$ exhibit similar enrichments of algal and terrestrial plant organic matter compared to their host rock. In respect to the deposition of layers 0,35m u$\alpha$ and 1,00m u$\alpha$, it is certain that both do not include any other kind of specific organic matter in comparison to their host rocks. However, identical enrichments of both algal and terrestrial organic matter may be explained by increased bioproductivity, but much more probable seems a nearly to zero diminished sedimentary input. Accordingly, for the time of deposition of layers 0,35m u$\alpha$ and 1,00m u$\alpha$, a short period of a relative arid climate, with extremely small amounts of rain fall and therefore, more or less no erosion can be assumed.
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