CSDMS 2015 annual meeting poster SalikAndersRosing
Sediment Deposition in the Cretaceous North Sea – a Modelling Approach
Kresten Anderskouv, Centre for Cross-disciplinary Chalk Research and Institute of Geosciences and Natural Resources Management, University of Copenhagen, Denmark.
Christian J. Bjerrum, Centre for Cross-disciplinary Chalk Research and Institute of Geosciences and Natural Resources Management, University of Copenhagen, Denmark.
Courtney K. Harris, Virginia Institute of Marine Science, Virginia, United States.
Abstract:
The Upper Cretaceous (~100-66 Ma) of Northwest Europe is characterized by thick successions of chalk, a biogenic pelagic sediment consisting of shell fragments of coccolithophores, a group of haptophyte primary producers. These deposits serve as important reservoirs for hydrocarbons and ground water. In recent decades, it has become clear that these deposits were shaped by depth contour following currents and gravity flows, and not simply a result of uniformly vertical settling of coccoliths (Surlyk and Lykke-Andersen, 2006), leading to spatial variability in reservoir properties
It has been conjectured, that the warm Cretaceous Greenhouse climate and high sea level resulted in the breakdown of the oceanographic front at the continental shelf edge, as we know it today in mid-latitude areas (Hay, 2008)). Furthermore, the deep shelf conditions and very warm seasons most likely resulted in the continental shelf seas having a stratified structure similar to that of the open oceans, leading to a thinning of the surface Ekman layer. With warmer climate, evaporation on stratified continental shelf seas may have resulted in preconditioning of the waters where winter cooling may have caused cascading of dense, higher-salinity coastal waters. Such cascading may have resulted in significant oxygenation of deeper shelf waters and lead to depth contour following currents in the intermediate waters in and below the pycnocline.
Here we explore a modelling approach to assessing the quantitative physical basis for these conjectures. The 3D Regional Ocean Modeling System (ROMS) is coupled to a sediment transport module permitting assessment of the oceanographic processes influencing the chalk thickness variation as a function of idealized shelf bathymetry configurations. The numerical modeling grid is configured to represent the overall geometry of the paleo-North Sea during the Late Cretaceous. Model forcing for seasonal variations in winds, freshwater fluxes and temperature is informed by results from global climate models of the late Cretaceous, while the critical shear stress and settling velocity of chalk ooze is derived from experimental values.
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