Biodiversity and plankton-benthos coupling: an integrated ecosystem analysis from the Late Cretaceous Chalk
Zusammenfassung der Projektergebnisse
The present project was focused on the benthic macrofauna, palaeoecology and the geochemical environment of the uppermost Campanian–Lower Maastrichtian pelagic chalk section at Kronsmoor (ca. 50 km northwest of Hamburg, northern Germany). The study of the benthic macrofauna from the Lower Maastrichtian (upper Kronsmoor and lower Hemmoor formations) shows complex ecosystem dynamics in the aftermath of a latest Campanian cooling event. The benthic macrofossils show a significant increase in abundance from the lower part of the section (B. obtusa Zone) to the upper part (B. sumensis/A. tridens Zone) by 1:2 to 1:3 (in some groups even more) within an interval of ca. 25 m without apparent changes in the monotonous chalk lithofacies. This abundance increase was observed in both, body fossil assemblages and in macrofossil remains from large-scale bulk rock samples systematically collected from the section, in the latter reproduced by means of counting and weighting the washing residues. Furthermore, the diversity is also higher in the upper part in contrast to the lower part. Concomitant to the systematic abundance and diversity studies, a palaeoecological analysis was conducted and the guild structure shows an up-section rising importance of the epifaunal suspension feeder guilds from ca. 50 % up to 85 % in the upper part of the section. These robust results strongly suggest a shift in nutrient supply at the seafloor, i.e. increasing food availability. Other physico-chemical environmental factors such as oxygenation, substrate, water depth and salinity can be excluded as main drivers of the observed biotic changes. The analysis of inorganic geochemical proxies (carbonate content, carbon and oxygen stable isotopes as well as detailed elemental datasets) support a productivity increase by means of different independent proxies (e.g., Sr/Al). The up-section decreasing terrigenous input is accompanied by an increase in CaCO3 content of up to >95 % in the upper part of the target interval, indicating that the enhanced productivity was not related to a general rise in land-derived nutrient input. The cooling event at the end of the Campanian, well reflected in a conspicuous δ18O increase at Kronsmoor, resulted in an intensification of oceanic circulation that caused a spread of intermediate-depth waters from high- to low-latitudes. This latest Campanian to earliest Maastrichtian change in marine circulation thus triggered upwelling of cool and nutrient-rich water masses from the north onto the shelf of the northwest European Chalk Sea. Biotic and geochemical proxies are largely in line with the assumed upwelling scenario. However, in several of the geochemical proxies, a strong variability is visible that starts during the Early Maastrichtian, indicating fluctuation of environmental conditions on short-term timescales. In the case of the terrigenous proxies (e.g., Ti/Al, Zr/Al), this can be best explained by a change in the provenance and/or style of the terrigenous input, i.e., increased importance of dust input during cooler climatic conditions (also inferred by Linnert et al., 2016 based on the calcareous nannofossil data from the Kronsmoor section). As aeolian dust input exerts a major control on marine fertility in open marine/oceanic settings, this process was the other major trigger of the observed productivity changes. The cyclic covariation of certain productivity (among others δ13C values) and terrigenous input proxies indicate that orbital (i.e., obliquity) forcing of dust input applied a significant control on surface water productivity during the Early Maastrichtian. Thus, this covariance influenced both, the organic matter and the CaCO3 fluxes as well as the end-Cretaceous carbon cycle that actually fluctuated on high-frequency Milankovitch timescales. Finally, the new high-resolution carbon stable isotope curve from Kronsmoor allows to calibrate the position of the base of the Maastrichtian from the Tethyan stratotype in Tercis (France) to the Boreal chalk facies with great precision, permits a detailed δ13C correlation to other important Campanian–Maastrichtian boundary (CMB) sections and resulted in a refined age model for important bio- and chemostratigraphic events across the CMB. The now concluded project thus clearly demonstrates the importance of high-resolution, integrated approaches including detailed palaeontological, stratigraphical, sedimentological and geochemical analyses in order to fully understand complex palaeoenvironmental changes and correlation issues.
Projektbezogene Publikationen (Auswahl)
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(2016): The benthic macrofauna from the lower Maastrichtian chalk of Kronsmoor (northern Germany, Saturn quarry): taxonomic outline and palaeoecologic implications. – Acta Geologica Polonica, 66: 671–694; Warszawa
Engelke, J., Esser, K.J.K., Linnert, C., Mutterlose, J. & Wilmsen, M.
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(2016): The impact of the Maastrichtian cooling on the marine nutrient regime – Evidence from mid-latitudinal calcareous nannofossils. – Paleoceanography, 31(6): 694–714; Washington
Linnert, C., Engelke, J., Wilmsen, M. & Mutterlose, J.
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(2017): Early Maastrichtian benthos of the chalk of Kronsmoor (northern Germany): implications for Late Cretaceous environmental change. – Palaeobiodiversity and Palaeoenvironments, 97: 703–722; Frankfurt
Engelke, J., Linnert, C., Mutterlose, J. & Wilmsen, M.
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(2017): High-resolution Campanian–Maastrichtian carbon and oxygen stable isotopes of bulk-rock and skeletal components: palaeoceanographic and - environmental implications for the Boreal shelf sea. – Acta Geologica Polonica, 67: 47–74; Warszawa
Wilmsen, M. & Niebuhr, B.
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(2018): Tracking Late Cretaceous environmental change: geochemical environment of the upper Campanian to lower Maastrichtian chalks at Kronsmoor, northern Germany. – Cretaceous Research, 84: 323–339; Amsterdam
Engelke, J., Linnert, C., Niebuhr, B., Schnetger, B., Brumsack, H.-J., Mutterlose, J. & Wilmsen, M.
