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 delta(13)C excursion began with
a 1.8parts per thousand positive shift in Plenus Marls Beds 1-3 (R.
cushmani Zone), a trough in Bed 4, a second delta(13)C shift of 0.8parts
per thousand 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 delta(13)C 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 delta(13)C 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. (C)
2001 Academic Press.