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Leafy marl layer in the Entrischenbrunn gravel pit (Photo. M. Sachse 23.4.2020)

DFG Project 523893203

Structural changes of herbivory during the Middle Miocene time interval in the Upper Freshwater Molasse (OSM)

There are numerous active sand and gravel quarries in the Bavarian part of the North Foreland Basin, in which fossil leaf assemblages repeatedly appear. The special tectonic and sedimentological conditions of the molasse trough can thus enable the spatial and temporal recording of vegetation structures. On the one hand, a decrease in the flow regime and thus the grain size from east to west, and on the other hand, a decrease in age due to the dipping of the deposits to the south can be detected. In conclusion, a temporal change in the flow regime from an intertwined to a meandering river system can be observed.

The six dated alluvial forest patches discussed here, with a total of around 16,000 recorded leaves, cover a time interval from around 16 million years ago (Burtenbach) to 12 million years ago (Aubenham) and thus cover the mid-Miocene climatic optimum together with the subsequent cooling phase. This can be seen in the successive disappearance of evergreen elements. In addition to the temperature changes, differences in groundwater availability – possibly due to climatic conditions – are also reflected in the floral communities. For example, Entrischenbrunn – dominated by Populus mutabilis, a form closely related to today's Euphrates poplar – shows a much drier character than the slightly younger, nearby Unterwohlbach site.

Leaf of Populus mutabilis with feeding traces, galls, egg clutches and traces of fungal infestation. (Ent 891, Collection A. Gröger, Munich). © Sammlung A. Gröger

As such, trace fossils can provide a unique and direct record of the plant-insect interactions of the past and provide information that normally are not available solely from the separate data of insect or of plant fossils. The knowledge acquired in this way could also make a valuable contribution with regard to necessary stabilizing land planning measures in view of the current development towards a "Tertiary climate“.

Over the next 3 years, it is planned to first photograph and taxonomically record the leaves. Subsequently, the feeding traces will be cataloged and statistically analyzed.

The project was initiated by the Hessian State Museum Darmstadt and is funded by the DFG (GZ: WA 1492/17-1). Collections from the Augsburg Natural History Museum, the Bavarian State Collection of Palaeontology in Munich and various private collections will be accessed for this project.

Responsible for the project at the Landesmuseum:

Prof. Dr. Torsten Wappler

Die Haupthalle im Eingangsbereich des Hessischen Landesmuseums

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