Lenz, O. K. ; Wilde, V. ; Riegel, W. (2012)
Lake Messel and other isolated Paleogene deposits on the Sprendlinger Horst, Hesse, Germany.
In: Schriftenreihe der Deutschen Gesellschaft für Geowissenschaften, 80
Artikel, Bibliographie

Kurzbeschreibung (Abstract)

The Upper Rhine Graben is the prominent central segment of a major rift zone in Central Europe, the European Cenozoic Rift System (ECRIS). Probably following pre-existing structures, initial weakness along the future Upper Rhine Graben and its shoulders is indicated by Paleogene volcanism. Therefore, a series of about half a dozen isolated occurrences of Paleogene sediments has been found on the Sprendlinger Horst, the northern extension of the Odenwald basement which is flanking the Upper Rhine Graben to the northeast in southwest Germany. Among them, Lake Messel, a maar lake which formed 47.8 +- 0.2 Ma ago, is the best known. Most of the others also represent the filling of volcanic structures, respectively maar lakes. A continuous core from Lake Messel revealed a complete reference section of early Middle Eocene lake deposits (Messel Formation), including 90 m of clastic lake sediments overlain by 140 m of the classical “Messel oil shale”, a continuous succession of finely laminated bituminous claystones. The lamination in the meromictic lake was caused by annual algal blooms forming light layers that were superimposed on the terrigenous background sedimentation as represented by dark layers (Lenz et al., 2010). These oil shales provide a unique high-resolution archive for palaeoenvironment and palaeoclimate of a time interval of ~640 kyr during the Paleogene. The character of the annually laminated sediments allowed studies at an unprecedented resolution with regard to Paleogene times, the most recent greenhouse period on Earth. The highly resolved pollen record from the oil shale now provides insights into the dynamics of a climax vegetation and thus serves as a record for vegetation changes and their potential cyclicity within the last greenhouse system. Our palynological study shows that the Messel oil shale provides an important reference for understanding the effects of orbital forcing on vegetation in an equable warm climate. The observed cycles closely correspond to the short eccentricity, obliquity and precession periods and to some extent to sub-Milankovitch periods (Lenz et al., 2011). Based on these results, the study is now extended to other nearby Paleogene deposits. In three of them (“Offenthal”, Groß-Zimmern” and “Prinz von Hessen”) scientific wells have been drilled. They also revealed undisturbed clastic sediments and finely laminated bituminous oil shales. In total, more than 340 m of lake sediments have been encountered. In both “Offenthal” and “Groß-Zimmern” about 30 m and in “Prinz von Hessen” about 70 m of oil shale is included. Based on preliminary stratigraphical data the lake deposits are probably of Middle Eocene age, although the exact age relationship of these deposits is still unknown. First results of palynological investigations show that they will significantly add to our understanding of vegetation and climate variability during the Eocene “hothouse”.

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