Reconstruction of the Water Column Structure of Jurassic and Cretaceous Epeiric Seas: Biomarkers and their Carbon Isotopic Composition

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9614769 Kenig The goal of the proposal is to reconstruct the water-column structure of a Jurassic and a Cretaceous epeiric sea using biomarkers and their isotopic composition. More specifically, our efforts will concentrate on the reconstruction of the water-column chemistry, and its evolution during the deposition of two sediment formations, the Oxford Clay (Middle Callovian, UK and the Greenhorn Formation (Western Interior Seaway, Cenomano-Turonian, USA). We will use this information to understand paleo-oceanographic conditions at the onset of water column stratification, biofacies distribution, and organic matter accumulation in epeiric seas. These results will be used to test the relationship between biofacies and benthic oxygen level. These results will be used to further constrain existing paleo-oceanographic circulation models. The first objective is to determine the geographic extent of intermittent anoxic events that characterized the accumulation of the organic mater-rich fossil-laggerstatten of the Lower Oxford Clay. To achieve this, Middle Callovian sediments with well defined biofacies from Scotland, Central and Southern England, France, Germany, Switzerland and Poland will be analyzed for their free, sulphur-bound, and ether-bound hydrocarbon biomarkers. The second objective is to use the molecular fossil record of thermally immature samples from the Greenhorn formation to reconstruct the water-column structure of the Western Interior Seaway during the Cenomanian and Turonian. Three sections will be investigated in detail for their free, sulphur-bound, and ether-bound molecular fossils. This analytical procedure will allow us to target the molecules that are diagnostic for the water-column structure. It will result in the development of an efficient analytical scheme allowing analysis of the vast number of samples necessary for precise constraint of the water-column structure and chemistry of a large geographical area. The third objective will be to geographicall y extend the water-column reconstruction of the Western Interior Seaway during the Cenomanian and Turonian. We will use these results to constrain the computer models of paleo-oceanographic circulation constructed for the Western Interior Seaway. Comparison of the results obtained from the Middle-Callovian of Western Europe will enhance our understanding of paleo-oceanographic circulation in epeiric seas. Based on literature data and our water-column reconstruction, a model of the paleo-oceanographic circulation for the Middle Callovian of Western Europe will be proposed.