Late Cretaceous climatic change in a mid latitude setting (Mississippi, USA): a multiproxy palaeoenvironmental study
Zusammenfassung der Projektergebnisse
In my original DFG application I proposed to do an integrated study about the latest Cretaceous climate change. I intended to study sample material from a single cored drill section from Mississippi State USA (Evans Shuqualak Core), which covered a nearly complete lower Campanian through upper Maastrichtian interval. The proposed study involved measurements of TEX86 (palaeo sea-surface temperatures), bulk rock stable isotopes (d13C, d18O), Total Organic Carbon and Total Carbon measurements, calcareous nannofossil abundance counts, morphometry and geochemistry on single coccolith-calcite (Sr/Ca-ratio). With this integrated study I therefore aimed to understand the impact of the late Cretaceous climate change on a lower mid-latitudinal environment (~35°N). Further on I aimed at reconstructing the calcareous nannofossil response to these environmental changes (surface-temperatures, nutrient content). The detailed study of TEX86 revealed a significant cooling throughout the Campanian interval as estimated sea surface-temperatures decreased from 35°C in the earliest Campanian to 28°C during the earliest Maastrichtian. Such amplitude of cooling (~7°C) in such low latitudinal settings (~35°N) highlights the global nature of that cooling, which was likely caused by decreasing pCO2-levels. The climate change started with a continuous gradual cooling trend throughout the early Campanian to early late Campanian but peaked in a steep cooling across the Campanian – Maastrichtian boundary. The general Campanian cooling trend may have supported changes of deep-water formation from low to high latitudes leading to an increased oxygenation of North Atlantic bottom waters. The late Campanian steepening of that cooling may have also triggered the Campanian – Maastrichtian Boundary Event (CMBE), a globally known negative carbon isotope excursion. Most of the common calcareous nannofossil taxa (e.g. Biscutum spp., Prediscospheara spp., Zeugrhabdotus spp.) did not respond to the climate changes during the Campanian. But the gradual cooling likely caused the gradual decrease and extinction of the common Cretaceous species Tranolithus orionatus. A reaction of nannofossils to climate change is seen across the Campanian – Maastrichtian boundary cooling. This boundary cooling may have triggered a possibly world wide retreat of the warm water species Watznaueria barnesiae and an advance of the cool water species Arkhangelskiella cymbiformis towards lower latitudes. The boundary cooling may have also influenced the evolution within the Broinsonia/Arkhangelskiella group as the largest morphotypes disappeared whereas small specimens of A. cymbiformis (~8µm) dominated the event. The influence of the cooling on the palaeoproductivity is unclear. Our low-resolution results of coccolith-calcite Sr/Ca do not indicate any significant changes of productivity throughout the Campanian – Maastrichtian interval. Measurements of coccolith-calcite Sr/Ca did not cover the critical CMBE interval, an interval when climate may have affected the palaeoproductivity.
Projektbezogene Publikationen (Auswahl)
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2013. Calcareous nannofossils and late Cretaceous climate cooling: Campanian through Maastrichtian assemblages from the Evans-Shuqualak borehole (Mississippi). 14th International Nannoplankton Association Conference, Reston, Virginia, USA, 2013
Linnert, C., Lees, J.A., Bown, P.R., Robinson, S.A.
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2014. Evidence for global cooling in the Late Cretaceous. Nature Communications 5:4194
Linnert, C., Robinson, S.A., Lees, J.A., Bown, P.R., Pérez-Rodríguez, I., Petrizzo, M.R., Falzoni, F., Littler, K., Arz, J.A. and Russell, E.E.
