The goal of this project is to improve our understanding of both the intensity as well as the lateral and temporal persistence of the oceanic anoxic events in the western Tethyan realm, and at the same time to test models of stagnant oceans with photic-zone euxinia versus models of expanded oxygen minimum zones. A further goal is to estimate the importance of hydrothermal and volcanic activity relative to continental biogeochemical weathering as a source of nutrients and trace metals. We propose to investigate trace-metal distributions and phosphorus contents in sediments of the western Tethys, which were deposited during the three major oceanic anoxic events of the Cretaceous – the Valanginian, early Aptian, and Cenomanian-Turonian boundary oceanic anoxic events. We investigate Fe, Zn, U, V, Re, Mo, and Cr contents and enrichments as proxies of changes in redox conditions; P, Ba, Cd, and As as indicators of nutrient contents and changes therein, and Ir, Co, Sc, Cr, V, Ni, Cu, Zn, Mn, W, and Cd as elements which are preferentially issued by hydrothermal activity. These analyses have been and will be performed on sediments along basin-shelf transects, from environments with dysaerobic to anoxic conditions to environments which were well oxygenated. Furthermore, we plan to submit the samples to different types of acid extraction and normalization techniques, in order to standardize analytical procedures.
The importance of this project lies in the observation that Cretaceous oceanic anoxic events are related to phases of rapid environmental change: their study may help us to identify and constrain forcing mechanisms and feedback loops that are implied in periods of global change. This is all the more important since most of the processes to explain the origin of oceanic anoxic events during the Cretaceous - such as increased atmospheric CO2, global warming, sea-level rise, increased continental weathering and phosphorus input, increased oceanic productivity, platform drowning and the disappearance of reef systems, and extinction and major evolutionary overturn are observed today as the consequence of anthropogenic change. To this comes that oxygen depletion within surface and intermediate water bodies of certain regions in the Pacific and western Atlantic has recently been observed.