Lacustrine Eocene oil-shales as archives for palaeoclimate and palaeoenvironment in Central Europe

Abstract

A series of about half a dozen isolated occurrences of Paleogene sediments can be found on the Sprendlinger Horst (Hesse, Germany), 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 meromictic maar lake formed 47.8 +- 0.2 Ma ago, is the best known of these occurrences, most of them representing the filling of volcanic structures, respectively maar lakes. Another Eocene maar is known from Eckfeld (Eifel Hills, W-Germany). The annually laminated oil shale from the early Middle Eocene maar lake at Messel provide unique palaeoenvironmental and –climatological data from a time interval of ~640 kyr during the Paleogene. The lamination in the lake was caused by annual algal blooms forming light layers that were superimposed on the terrigenous background sedimentation as represented by dark layers. Therefore, the character of these “varved” sediments allowed studies at an unprecedented resolution with regard to Paleogene times, the most recent greenhouse period on Earth. A temporally highly resolved pollen record from the oil shale of Messel now provides insights into the dynamics of a climax vegetation and serves as a record for vegetation changes and their potential cyclicity within the Paleogene greenhouse system. Since annually laminated sediments of Quaternary maar lakes have been widely used as ideal archives of vegetation response to rapid climate change in an icehouse system, the Messel oil shale is now an important reference for understanding the effects of orbital forcing on vegetation under an equable warm climate. Time series analyses of the pollen record clearly show cyclic variation in the quantitative composition of palynomorph assemblages during the 640 kyr interval of the Middle Eocene. The observed cycles closely correspond to the short eccentricity, obliquity and precession periods and to some extent to sub-Milankovitch periods. Periodicities of 82/83yr, 200/210 yr, ~600 yr and 1100 to 1600 yr comparable, for instance, to Gleissberg (~87 yr) De Vriess/Suess (~210 yr) or Dansgaard-Oeschger (1470 yr) events of the Quaternary can be recognized. To support these results, our study is now extended to other nearby Paleogene deposits. In three of these deposits (“Offenthal”, Groß-Zimmern” and “Prinz von Hessen”) scientific wells have been drilled. They revealed also undisturbed clastic sediments and more than 70 m of finely laminated bituminous oil shales. Based on preliminary stratigraphical data the lake deposits are probably also of Middle Eocene age, although an 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”. Further comparisons can be made with results of previous studies of the Eckfeld maar sediments

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This paper was published in TUbiblio.

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