1 Department of Geoscience, Science and Technology, Aarhus University2 Department of Geoscience, Science and Technology, Aarhus University
The objective of this study is to investigate varying sediment fluxes from the Scandinavian landmass during Cenozoic times and to calculate a mass balance from the observed accumulation rates. As the onshore area provides little data to quantify erosion rates and vertical movements of rock mass, we use offshore data from adjacent sedimentary basins (the North Sea and the Norwegian shelf) to calculate the amount of erosion. We have used a broad dataset of seismic 2D lines to map depositional units and a well dataset for the stratigraphic control and the velocity distribution in the sediments. We have therefore obtained accumulation rates in meters per million years for 5 depositional units in three areas - Southern North Sea, Central and Northern North Sea and the Norwegian shelf. Furthermore, taking into account the decay of porosity in sediments with burial depth, we have estimated the sediment volumes at the time of their deposition. Such calculation gives minimum values of erosion rates onshore and a mass balance can be approximated, when considering uncertainties like deposition of sediments outside study area, post-depositional sediment removal and loss of mass due to chemical dissolution. These parameters have been estimated and included in our calculations. Considering that the paleo-landscape of Norway in Paleocene-Eocene times was of fluvial type, we have restored smoothed hypsometry of the Scandinavian mountains after accounting for flexural isostasy. Such approach is in agreement with the so-called ICE hypothesis (Nielsen et al., 2009) which suggests the longevity of the Scandinavian mountains and do not impose tectonic rejuvenation of topography in Cenozoic times. Such episodes of tectonic uplift have been previously suggested as the controlling factors of erosion rates and sediment input in Scandinavia and surrounding basins. The ICE hypothesis suggests a much more profound influence of climate, climate change and related erosional processes (e.g. Alpine-type glacial erosion, periglacial processes) in controlling the erosion rates. We propose that the tectonic activity related to the final stage of opening of the North Atlantic was controlling the high sediment input during Paleocene to Early Eocene times, without invoking the surface uplift. Subsequent Cenozoic epochs were tectonically quiet in the Scandinavian realm. However, the climate has changed quite dramatically. The cooling of climate at the greenhouse-icehouse transition (Eocene-Oligocene boundary) could be a trigger for development of Alpine-type glaciers at high elevation which are efficient erosive agents. This could explain an increase in sediment production observed after a warm and tectonically stable Eocene epoch. Furthermore, histograms of depositional rates in the study area show a common feature with global patterns, that is a few-fold increase in sediment production during last 3-4 million years. This correlates well with the climate cooling, increased frequency of climate change and intense glacial erosion in Scandinavia during Pliocene and Holocene times. Therefore, climate is regarded as the only agent controlling erosion rates during this period.
Geophysical Research Abstracts, 2011, Vol 13, Issue EGU2011-368