Sea-water temperatures of the early Cretaceous derived from stable isotopes of belemnites and TEX86 of organic-rich sediments

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The climatic evolution of the early Cretaceous (Berriasian - Barremian) is currently interpreted in two different ways. The view of a generally warm-equable greenhouse world is contradicted by a rather differentiated picture with cold snaps possibly even causing polar ice caps. Evidence for either one of these views is supplied by a) palaeontological observations, b) stable isotope data, c) sedimentological findings and d) TEX86 data. Stable isotope data of (18O and (13C of both bulk rock and of belemnites have been used for reconstructing climatic variations for the early Cretaceous. Current investigations of stable isotopes of belemnites lack, however, either a high resolution record, a good preservation and taxonomic backgrounds or a well refined stratigraphy so that the records published so far are often characterised by gaps and hiati. This project aims at establishing a stable isotope reference record for the Valanginian - Barremian period in expanded sections of the Boreal Realm. This will be achieved by analysing well preserved and stratigraphically well constrained belemnite guards from NW Germany on a high resolution scale. Comprehensive bed-by-bed collections of belemnites, which have been made accessible only recently, will be investigated in order to understand the climatic variations in the southern part of the Boreal Realm. These results will be compared to organic-geochemical data (TEX86) and published data. This will enable us to decipher the climatic evolution of this period.