Vegetation dynamics in a disturbed lacustrine record: The Eocene maar lake of Groß-Zimmern (Hesse, SW Germany)

Abstract

Palynological studies of lacustrine sediments in Eocene maar craters on the Sprendlinger Horst (Hesse, SW Germany) are complemented by 26 core samples from Groß-Zimmern. In addition, diatoms have been studied to assess palaeolimnological conditions. The palynomorph assemblage proves a middle Eocene age more or less coeval to the upper part of the nearby lacustrine succession at Messel. The core includes 33 m of massive to finely laminated bituminous shale abruptly following the underlying breccia of the diatreme filling. The lacustrine deposits are characterised by frequent mass movements and redeposition probably due to tectonic activity in combination with syn- and postsedimentary subsidence in the lake basin. Together with a diatom assemblage characteristic for shallow to moderately deep water, this indicates that the core was drilled in the area of a marginal syncline rather than in the centre of the basin. Freshwater conditions with low nutrient levels were inferred for Lake Groß-Zimmern from diatoms and coccal green algae. Despite the strong disturbance of the sedimentary record, results of cluster analysis and non-metric multidimensional scaling (NMDS) of the palynomorph assemblages can be compared to the undisturbed succession from Messel. This includes successional stages of the azonal vegetation in the crater area during an initial and early recolonisation phase as well as in the zonal vegetation, which are related to the reoccupation of the crater area by a thermophilic forest. Furthermore, slight changes of the climate can be inferred.