Organisch-geochemische und mikroskopische Charakterisierung diskreter, organisch reicher Lagen des Messeler Ölschiefers
Organisch-geochemische und mikroskopische Charakterisierung diskreter, organisch reicher Lagen des Messeler Ölschiefers
The Messel Pit fossil site near Darmstadt, Germany, is famous because ofits numerous well-preserved mammal and other fossils, and therefore, in 1995became a UNESCO-World Heritage (www.unesco-welterbe.de/en/).The respective host rock, the Messel oil shale is still a matter of intensivestudies. This d...
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Personal Name(s): | Gerisch, Stephan (Corresponding author) |
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Contributing Institute: |
Publikationen vor 2000; PRE-2000; Retrocat |
Imprint: |
Jülich
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
2005
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Physical Description: |
XVI, 234 S. |
Document Type: |
Report Book |
Research Program: |
Addenda |
Series Title: |
Berichte des Forschungszentrums Jülich
4172 |
Link: |
OpenAccess OpenAccess |
Publikationsportal JuSER |
The Messel Pit fossil site near Darmstadt, Germany, is famous because ofits numerous well-preserved mammal and other fossils, and therefore, in 1995became a UNESCO-World Heritage (www.unesco-welterbe.de/en/).The respective host rock, the Messel oil shale is still a matter of intensivestudies. This dark, finely laminated organic rich mudstone, was deposited in aMaar lake in the Lower Middle Eocene about 47Ma ago during a time spanof 1 to 1.5 Ma. One subunit, the so-called’Middle Messel Formation‘ can besubdivided by several specifically named marker beds (M, $\alpha$, $\beta$ and $\gamma$), but alsoby some further layers with distinct macroscopic characteristics.The two layers investigated here represent green-brown deposits with amaximum thickness of up to one millimetre only. They are encountered at alevel of 35 cm (herein after referred to as’layer 0,35m u$\alpha$‘) and 100 cm (hereinafter referred to as ’layer 1,00m u$\alpha$‘) below Marker Bed $\alpha$. Typically, both layersare extremely ductile, and thus can easily be manually separated like individualpaper-like book-sheets from their adjacent host rock. Because of their leather-likeplasticity, they must be considered to be rich in organic material. Accordingly, itwas the objective of this study to reveal the type of organic matter they consistof.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 bythe analytical results of temperature programmed pyrolysis-gas chromatographyand thermovaporisation-gas chromatography which need small sample amountsonly. In addition, the molecular compositions of the C$_{15+}$-soluble organic matterof 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 bothlayers, with stronger enrichments for layer 1,00m u$\alpha$. Layer 1,00m u$\alpha$ exhibits asurprising high sulphur content of 7 %, which can not be explained so far but mayrepresent a high microbial degradation of the organic matter. In respect to themolecular compositions, influences by migrated organic matter can be excludeddue to a maturity stage below 0.5% Rr (mean T$_{max}$ below 430 $^{\circ}$C and a strongpredominance 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 toHI values above 620mg HC/g TOC. Thus, high bacterial/microbial contributionshave to be assumed which is confirmed by individual biomarker data. Both layersand the host rock have incorporated similar amounts of bacterial/microbial organicmaterial. In contrast, layers 0,35m u$\alpha$ and 1,00m u$\alpha$ exhibit similar enrichments ofalgal and terrestrial plant organic matter compared to their host rock. In respectto the deposition of layers 0,35m u$\alpha$ and 1,00m u$\alpha$, it is certain that both do notinclude any other kind of specific organic matter in comparison to their host rocks.However, identical enrichments of both algal and terrestrial organic matter maybe explained by increased bioproductivity, but much more probable seems a nearlyto zero diminished sedimentary input. Accordingly, for the time of deposition oflayers 0,35m u$\alpha$ and 1,00m u$\alpha$, a short period of a relative arid climate, withextremely small amounts of rain fall and therefore, more or less no erosion can beassumed. |