Unlocking UK Chalk macrofossil collections using calcareous nannofossil biostratigraphy: Insights into Late Cretaceous ecosystem change, resilience, and extinction

The Upper Cretaceous Chalk Group of the United Kingdom (UK) preserves one of the most complete and fossiliferous records of greenhouse marine conditions, spanning the Cenomanian–Maastrichtian (~100–72 million years ago). While the Chalk has been intensively studied, a large proportion of its macrofossil record remains under-utilised because specimens collected over the past two centuries commonly lack precise stratigraphic or chronological attribution. Previous studies have demonstrated that nannofossil biostratigraphy of the chalk matrix attached to such specimens provides an effective means of unlocking the ‘dark data’ preserved in historic museum collections. Here we update and expand on those pilot studies by applying the biostratigraphic framework developed within the Chalk Sea Ecosystems (ChaSE) project to a wide range of macrofossil groups to investigate temporal and regional patterns in ecosystem change.  

We apply calcareous nannofossil biostratigraphy to re-date >1,500 macrofossil specimens housed at the Natural History Museum, London (NHMUK), many of which are from now-inaccessible localities and are labelled only with broad lithostratigraphic or geographic information. Small, non-destructive samples taken from the chalk matrix associated with individual macrofossils yield diverse nannofossil assemblages, with preservation ranging from poor to moderate. Despite the variability in preservation, key marker species and bioevents were identified, allowing for confident placement within UK Chalk litho- and biostratigraphic schemes. The reliability matrix being developed will strengthen these results by evaluating a range of criteria (e.g. taxonomic clarity, morphological specificity, geographical and temporal distribution, rarity, preservation quality; Tangunan et al., 2024). This approach aims to provide robust age constraints at sub-stage to zonal resolution, substantially improving the stratigraphic utility of specimens previously unsuitable for quantitative analysis.

To complement the museum-based work, targeted field sampling was conducted at key Chalk localities across England, including Yorkshire, Devon, Dorset, Folkestone, and Eastbourne. These sites span northern, central, and southern Chalk provinces and capture spatial variability across the Cretaceous Chalk Sea. Field-derived calcareous nannofossil datasets will be integrated with the re-dated museum material to refine correlations and to investigate temporal and regional patterns in extinction timing and ecosystem change.

The resulting framework will enable both nannofossil and macrofossil occurrences to be analysed within a consistent temporal context across major Cretaceous climatic and oceanographic perturbations, including the Mid-Cenomanian Event and Oceanic Anoxic Event 2, as well as the transition from peak Turonian warmth into Late Cretaceous cooling. By transforming historic museum collections into stratigraphically resolved datasets, the ChaSE project demonstrates the critical role of calcareous nannofossil biostratigraphy in maximising the scientific value of museum archives and provides a foundation for whole-ecosystem reconstructions of Chalk Sea resilience under extreme greenhouse climates.

 

Reference

Tangunan, D., Bown, P., Hampton, M., Fogerty, T., Gale, A., Twitchett, R., Underwood, C., Witts, J. and Gallagher, L., 2024. Multivariate evaluation rubric for assessing the reliability of Cretaceous nannofossil index taxa and bioevents. Journal of Nannoplankton Research, 42(S), pp.119-119.