European carbonate margins as recorders of past global change: Cretaceous `greenhouse` versus Carboniferous `coldhouse` examples

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Fossil continent - ocean boundaries represent unique archives of regional and global change. Changes in climate, drainage patterns, sediment production and transport, palaeo-sea surface temperatures and seawater geochemistry are recorded in fossil carbonate margins. We propose an in-depth study and comparison of two selected margins (Northern Spain and Greece), which represent significantly different episodes of Earth history in terms of global climate, atmospheric pCO2, seawater composition and carbonate producing biota. The mid-Carboniferous margin (Spain) represents a "coldhouse" example and the Late Cretaceous margin (Greece) provides an example of the "greenhouse" mode of Earth´s system. Firstly, we intend to concentrate on the sedimentologic and sequence stratigraphic framework of both margins. A special focus will be on the quantitative determination of the carbonate production potential, and the role of inorganic versus biologically induced and biologically controlled production. Sedimentological studies will lead to a semi-quantitative reconstruction of middle Carboniferous and Late Cretaceous sea-level changes. Coeval sections across platform-to-basin transects allow for a determination of amplitudes of relative sea-level fluctuations. Compared to the Late Cretaceous these are expected to be different during the middle Carboniferous when glacial eustasy was important. Secondly, we will apply d13C, d18O, Sr-isotopes and trace element ratios to different carbonate materials in order to reveal spatial and temporal variability of sea-surface temperatures and specifically of the palaeo-thermocline recorded in the geochemistry of fossil carbonate margins in Spain. Chemostratigraphy (d13C, 87Sr/86Sr) will be important for the correlation of Upper Cretaceous carbonate margins. A particular novel aspect of this study will be the testing and application of Ca isotopes (d44Ca) to the sedimentary geochemistry of Carboniferous and Cretaceous carbonates from well constrained depositional settings. These results will be compared to core material from modern tropical carbonates with the expectation to gain new insight in the exogenic calcium cycle.