Goal: Integrating palaeoenvironmental and climate cyclicities – An optimized stratigraphic framework in the non-marine Lower Cretaceous
Abstract: Studies on climate cycles and changing paleoenvironments in non-marine (continental) archives of the Mesozoic greenhouse earth are hitherto rare, primarily a result of the lack of high-resolution stratigraphy and correlations to the marine record. This project uses the Lower Cretaceous European record as a test site for the integration of ostracod biostratigraphy and assemblage changes, and cyclostratigraphy (orbitally/climate driven cycles). Uppermost Jurassic−Lower Cretaceous non-marine ostracod biostratigraphy has a long tradition, particularly concerning the ‘Purbeck-Wealden interval’ (latest Tithonian to earliest Aptian) in Europe and contemporaneous deposits worldwide, but has, at the same time, always been affiliated with considerable problems and limitations. Notably with regard to supraregional (i.e., inter-basinal) to global scales, serious attempts at correlating the respective deposits, as well as dating and chronological linking of events documented by these, remain problematic – let alone correlation to the marine standard sections. Nevertheless, ostracods are definitely the most useful biostratigraphical and palaeoenvironmental tool in Purbeck-Wealden sequences. The apparent cyclic changes in non-marine ostracod assemblages of the Wealden of southern England (the ‘faunicycles’ of F.W. Anderson) will be revised and analysed for orbitally(?) driven cyclicities based on a multi-proxy study and multivariate statistical analyses. The approach is multiple: Biostratigraphy in the supraregional to global context, cyclostratigraphy using ostracods, lithologic parameters and sediment geochemistry, stable isotope geochemistry, and magnetostratigraphy for chronological control. A selected interval of the Lower Weald Clay of the Weald Sub-basin will be resampled at high resolution and the samples analysed for ostracod assemblage composition and changes, stable oxygen and carbon isotopes of ostracod valves, as well as TOC and XRF, magnetic susceptibility, gamma log, and lithology of the sedimentary rock. These data will be integrated and statistically tested for cyclicities (and the results compared with an accordant statistical analysis of F.W. Anderson‘s ‘faunicycles’). The proposed integrative methodology targets the correlation of the faunal composition change with the variation of geochemical and sedimentological parameters through time and inferences on controlling (palaeoenvironmental) factors and their regulating mechanisms (‘climate changes’, orbital cycles?). The central approach is to ‘turn the tables’ in that the strong facies control – thus far widely considered a substantial drawback as to supraregional biostratigraphical utility of non-marine ostracods – shall be (re )analysed and tested for cyclostratigraphic use. The combination of different methods and data allows the evaluation of their utility on different chronological and geographical scales. These methods can then be efficiently applied on larger scopes and to larger datasets. The proposed integrated project represents a pioneering study in this area of research, and will also be an important contribution towards progress in chemo- and magnetostratigraphy of the English Wealden and the nature of its cycles, as well as Early Cretaceous climate change.