A palaeoenvironmental and palaeoecological analysis of fine-grained Paleogene estuarine deposits of North Germany

The lower Tertiary successions of the North German Basin predominantly consist of shallow marine, fine-grained siliciclastic rocks which grade towards the SE and S into continental deposits infilling bays and estuaries. In the study area around the Gorleben salt dome, glauconitic sandstones, siltstones and mudstones were laid down together with tuffs in a depositional environment that is interpreted as a shelf-estuary transition. Syngenetic salt tectonics strongly affected the basin architecture and the composition of the sediments under study. Analysis of the depositional environment is based on sedimentological, mineralogical and chemical data. Although bathymetry and salinity may be often calibrated by means of microfossils by analogy with present-day species, there is much debate as to their validity for palaeodepth reconstructions in the North Sea. Interdisciplinary interpretation of data from biological and sedimentological studies on the same material may improve the quality of the palaeoenvironmental reconstruction. Core examination and the investigation of wireline logs form the basis of the palaeogeographical model of the North German Basin. This model shows a deepening of the basin from the Paleocene through the late Eocene, leading eventually to the transgression of the Rupelian sea into the estuary. The history of the palaeo-shelf and estuary area during the Tertiary is described in analogy with modern depositional environments, such as the present-day Celtic Sea, the western end of the English Channel, the German Bight and the Isle of Helgoland, which is situated above a salt diapir off the North German coast. The climate in this area, however, was much warmer during the Paleogene than today.