Tectonic and climatic signals in the Oligocene sediments of the Southern North-Sea Basin (Ernest Van den Broeck medallist lecture 2016)

Abstract

The Oligocene sediments formed between the Pyrenean and Savian tectonic pulses. The earliest Oligocene was characterized by a widespread shallow water transgression. Global cooling coincided with the subsequent retreat of the sea which is also the time of the Grande Coupure faunal turnover. Renewed stepwise transgression resulted in the deposition of the Boom Clay during the Rupelian. High-frequency cyclic changes in water depth of the Boom Clay are driven by waxing and waning of ice masses while lower-frequency cycles can be tectonic signals. By the end of the Rupelian, differential vertical tectonics resulted in considerable erosion west of the Campine subsidence area and in shallower water depth in the eastern part of the southern coastal area. Subsidence of the Lower-Rhine graben resumed at the start of the Chattian. The sea could only briefly transgress over the area outside the graben but in the graben thick Chattian sediments are preserved. Outside the graben, erosion continued to dominate during the Chattian and the Aquitanian. This long period above sea level is due to a combination of the Savian tectonic uplift pulse and a global low sea level.