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The mid‐Cretaceous North Atlantic nutrient trap: Black shales and OAEs
by J. Trabucho Alexandre (Utrecht University), E. Tuenter (KNMI), G.A. Henstra (University Utrecht), K.J. van der Zwan (Shell Technology India Private Limited), R.S.W. van de Wal (Institute f or Marine and Atmospheric Research Utrecht)H.A. Dijkstra (Institute f or Marine and Atmospheric Research Utrecht)P.L. de Boer (Utrecht University)
Organic‐rich sediments are the salient marine sedimentation product in the mid‐Cretaceous of the ocean basins formed in the Mesozoic. Oceanic anoxic events (OAEs) are discrete and particularly organic‐rich intervals within these mid‐Cretaceous organic‐rich sequences and are defined by pronounced carbon isotope excursions. Marine productivity during OAEs appears to have been enhanced by the increased availability of biolimiting nutrients in seawater due to hydrothermal alteration of submarine basalts in the Pacific and proto‐Indian oceans. The exact mechanisms behind the deposition of organic‐rich sediments in the mid‐Cretaceous are still a matter of discussion, but a hypothesis which is often put forward is that their deposition was a consequence of the coupling of a particular paleogeography with changes in ocean circulation and nutrient supply. In this study, we used a global coupled climate model to investigate oceanic processes that affect the interbasinal exchange of nutrients as well as their spatial distribution and bioavailability. We conclude that the mid‐Cretaceous North Atlantic was a nutrient trap as a consequence of an estuarine circulation with respect to the Pacific. Organic‐rich sediments in the North Atlantic were deposited below regions of intense upwelling. We suggest that enhanced productivity during OAEs was a consequence of upwelling of Pacific‐derived nutrient‐rich seawater associated with submarine igneous events.
|Trabucho Alexandre, J., E. Tuenter, G.A. Henstra, K.J. van der Zwan, R.S.W. van de Wal, H.A. Dijkstra and P.L. de Boer, The mid‐Cretaceous North Atlantic nutrient trap: Black shales and OAEs Abstract (html) Complete text (pdf: 2 MB)|