ChaSE-ing the chalk: the Chalk Sea Ecosystems project and Late Cretaceous

talk given by Dr James Witts, NERC Postdoctoral Fellow in Palaeoecology, Natural History Museum, London

Abstract:
The onshore Chalk Group of the United Kingdom provides a continuous and well-exposed rock and fossil record spanning the Late Cretaceous (Cenomanian –Maastrichtian stages, ~100 – 72 Ma). As an economically important resource, the chalk has been quarried and studied for >200 years and a detailed stratigraphic framework is available. The sequence is abundantly fossiliferous, recording every marine trophic level from nanno- and phytoplankton to benthic and nektonic molluscs and apex predators. Key events recorded in the Chalk include carbon cycle perturbations during the middle Cenomanian and across the Cenomanian – Turonian boundary (Oceanic Anoxic Event 2 – also associated with peak Cretaceous climate warming and a biodiversity crisis), the highest global sea-levels of the last 250 myrs during the Turonian, and a long-term climate cooling which culminates with the coldest temperatures of the Late Cretaceous during the Maastrichtian.

The Natural History Museum, London (NHMUK) alone contains >55,000 UK Chalk Group macrofossil specimens, including rare taxa and material from now inaccessible localities. Only a fraction of these have been published or are available in public datasets. Many specimens contain limited metadata, and ages or stratigraphic position are poorly constrained. To unlock these ‘dark data‘ we are re-dating >1,500 macrofossil specimens using calcareous nannofossil biostratigraphy. Combining these with data from new fieldwork, we are conducting the first ‘whole-ecosystem‘ study of the functional diversity and ecology of the Chalk Sea, providing an unprecedented record of the effects of global Cretaceous climate change on marine ecosystems at a variety of temporal and spatial scales, all within the same depositional system.

Biography:
I trained as a geologist with an MEarthSci degree from the University of Manchester (2009), completing a PhD on the Cretaceous-Paleogene (K-Pg) mass extinction event in Antarctica with the University of Leeds and British Antarctic Survey in 2016. I then hopped ‘across the pond’ for a Lerner-Gray Postdoctoral Research Fellowship at the American Museum of Natural History in New York (2016-2018) and a postdoctoral position at the University of New Mexico in Albuquerque (2018-2020), studying Cretaceous and Paleogene macrofossils and ecosystems in the US Gulf Coast and Western Interior. After a stint as Lecturer in Palaeontology at the University of Bristol (2021-2023), I moved to the NHM as a NERC Postdoctoral Fellow in Palaeoecology in September 2023.