Plancton foraminifera, biostratigraphy and palaeoclimatology across the Eocene/Oligocene boundary in Loburg 1/90 borehole (Sachsen-Anhalt)

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Borehole Loburg 1/90 (Sachsen-Anhalt, Germany) records the Eocene/Oligocene transition beds of the southeastern part of the ancient North Sea quite completely. The worldwide temperature drop of that interval of time is currently under multidisciplinary investigation by several groups of scientists. Our own stable isotope research has already shown that such a considerable temperature drop has alreay existed in the North Sea Basin of that time, but its exact stratigraphic position has been under intensive discussion (and with conflicting opinions). Using benthic foraminifera for biostratigraphy in a former project, we have already been able to contradict previous opinions and date the time of the temperature drop into a stratigraphical interval somewhat above the Eocene/Oligocene boundary, which would coincide with the interruption of the palaeogeographic connection between the Tethys and the North Sea and thus the inflow (via Poland) of warm Tethyan watermasses.During this project´s research, we have been able to support these views by our new biostratigraphy using plancton foraminifera. Moreover, we have been able to date the Eocene/Oligocene boundary into the uppermost part of the Upper Schönwalde Formation. Additional information about the separation of ocean current vs. antarctic glaciation influences onto the dO18 curve (leading vs. heavier values) has been derived from Mg/Ca analysis of calcite shells (pointing to the same explication as described above). In the final phase of our research on the Loburg foraminifera, we intend to carry out more Mg/Ca measurements (again in order to decipher the two possible influences onto the dO18 trend from each other) and also use strontium isotope stratigraphy in order to confirm (if possible) our stratigraphical conclusions derived from the foraminifera (both benthic and planctic). Final goal of the project is a summarizing interpretation, based on a set of interdisciplinary and solid data, of the palaeoclimatic and palaeooceanographic evolution of the ancient North Sea across the Eocene/Oligocene transition.