Palaeoenvironment of the Cenomanian-Turonian transition at Eastbourne, England

Lithology, stable isotopes and planktic foraminiferal analyses of the Eastbourne section at Gun Gardens (southeast England) reflect sea-level fluctuations and changing climatic and oceanographic conditions across the Cenomanian-Turonian transition. The δ¹³C excursion began with a 1.8‰ positive shift in Plenus Marls Beds 1-3 (R. cushmani Zone), a trough in Bed 4, a second δ¹³C shift of 0.8‰ in Bed 7 and a gradually decreasing plateau during deposition of the Ballard Cliff Member. Lithological variations, sharp erosion surfaces, bioturbation and increased detrital influx indicate that sea-level fluctuations, cooling and a marine regression accompanied the δ¹³C excursion within the Plenus Marls, followed by warming and a major marine transgression in the upper part of the Plenus Marls and Ballard Cliff Member. Two faunal turnover phases coincided with the two-phased δ¹³C excursion. Phase I in Bed 3 is marked by the extinction of the deeper dwelling planktic foraminifer Rotalipora, the origination of the thermocline dweller Dicarinella, dominance of the low oxygen tolerant Heterohelix species, and common surface dwellers Guembelitria and Whiteinella. This faunal turnover reflects a lower sea level, enhanced productivity and temporary expansion of the oxygen minimum zone associated with climate cooling and increased upwelling. Phase II near the top of the Plenus Marls (Beds 7-8) is marked by the temporary disappearance of about 50% of the species, increased abundance of surface dwellers and a shift to dominance of low-oxygen tolerant Heterohelix species globally. This faunal turnover may reflect increased primary productivity and a long-term expansion of the oxygen minimum zone associated with climate warming and a marine transgression. Faunal turnover phase II stratigraphically correlates with the global oceanic anoxic event in Italy (Bonarelli Level) and Tunisia (Bahloul Formation), whereas phase I correlates with the onset of organic-rich facies in the upper R. cushmani Zone of these regions. High resolution biostratigraphic correlation is based on planktic foraminifera and the subdivision of Whiteinella archeocretacea Zone into three subzones.