In a recent synthesis, it was convincingly shown that the impact of a large asteroid in the Gulf of Mexico coincided with the Cretaceous/Tertiary (K/T) boundary, 65 million years ago, and with the sudden biodiversity decline known as the K/T mass extinction when numerous organisms became extinct. This mass extinction set the stage for the development of modern ecosystems and biota on land and in the sea. Yet, extinction patterns of various fossil groups (especially multicellular animals) are considered incompatible with an instantaneous cataclysm decimating life and suggest environmental deterioration prior to the K/T boundary. Accordingly, various studies suggest that gradual but distinct climatic and/or sea-level changes lead to an accumulation of environmental stress perturbing latest Cretaceous ecosystems prior to the K/T boundary and triggering a longer term onset of extinctions. In this project, we study several K/T boundary successions and especially focus on assessing the extent and effects of gradual environmental and biotic changes in shallow marine ecosystems by evaluating quantitative microfossil records in three separated study areas, the US Gulf Coast, Tunisia and Turkey. These studies are complemented by geochemical analyses to identify climatic and paleoceanographic instabilities that are unrelated to the impact at the K/T boundary.

The main hypotheses to be evaluated in the scope of the project are:

• Is there any evidence of significant sea-level change during the last ~600 kyr of the Maastrichtian and if so, is it synchronous between different basins and therefore likely to be eustatically controlled? In case this is confirmed, the question to be addressed is whether this is also reflected in impoverishment of the faunas or whether there is just evidence of biofacial shifts that are expected in response to changing water depths.
• Is there consistent evidence of climate change as reflected in micropaleontologic and geochemical proxies (e.g., tropical microfossil taxa, δ18O in benthic and planktic foraminifera, TEX86, Mg/Ca)? If so, does the amplitude of these changes exceed background variability and is there any directional change towards the K/T boundary and can it be demonstrated that these gradual changes indeed exert progressive environmental stress as suggested (e.g. Abramovich et al., 2010; 2011)?