Mediterranean Oligo-Miocene stratigraphy and palaeoecology

The global chronostratigraphic subdivision of the Oligocene and Miocene is mostly established in deep-water successions of the Mediterranean region and is based nearly exclusively on biostratigraphic data derived from planktonic fossils (foraminifers, calcareous nannoplankton). More recently the temporal resolution has been considerably enhanced by application of an astrochronological approach. In clear contrast to this are shallow-marine deposits in the Mediterranean: their stratigraphic resolution is rather poor and the correlation with deep-water successions is highly imprecise. Reasons for this are the relative scarceness of planktonic fossils in shallow-water settings and the generally highly incomplete rock record of shallow-water deposits. In addition, research intensity and quality in these areas are to date rather poor although such shallow-marine settings are very widespread all over the Mediterranean. To considerably enhance the stratigraphic resolution of these shallow-water deposits and to facilitate an exact correlation with the reference sections in deep-water successions detailed sedimentological-palaeontological studies will be combined with an integrated stratigraphic approach in selected areas. These areas are on the one hand the Maiella Platform in the Apennine and on the other the Malta-Ragusa Platform between the islands of Malta and Sicily. Both target areas represent carbonate platforms, which have been tectonically stable during the formation of Oligocene - Miocene sediments resulting in widely undisturbed successions. As basic stratigraphic approach, detailed logging of the shallow-marine deposits offers the opportunity of gaining exact biostratigraphic information based on sound taxonomy of larger foraminifers and mollusks. These biostratigraphic data will be integrated into a detailed (third-order) sequence stratigraphic analysis, stable O- and C-isotope studies, geophysical logging (gamma-ray, magnetic succeptibility) and Sr-isotopy. These results will be further supported by an astrochronologic approach which is expected to allow a precise correlation with the Astronomically Tuned Neogene Time Scale (ATNTS). To exclude local palaeoenvironmental interferences a variety of facies types has be studied sedimentologically, (micro)facially and palaeoecologically. A meaningful palaeoecological analysis, however, has to cover a broad spectrum of fossil groups, therefore foraminifers, gastropods, bivalves, echinoderms, coralline red algae and corals will be included. The expected high-resolution stratigraphy in combination with the acquired palaeoecological data will allow reconstructing climate evolution and the palaeoceanographic conditions for the studied time interval (Late Oligocene - late Middle Miocene) in the Mediterranean. This reconstruction will particularly provide deep insight into changes of reef distribution and composition for this time interval and will give a clue for the general controlling factors for carbonate sedimentation, in particular for the spatial-temporal distribution of heterozoan versus photozoan carbonates.

Within this project the study of Circum-Mediterranean rock sections of Oligocene to Miocene age was carried out to refine their age dating and to reconstruct palaeoenvironmental, palaeoclimatic and palaeoceanographic conditions. As stratigraphic tools bio-, sequence- and chemostratigraphy as well as geophysical methods and astrochronology were applied. For palaeoecological and biostratigraphic purposes basic taxonomic studies on several organism groups, such as molluscs, corals, echinoids and calcareous algae had to be performed. The most important section in the Mediterranean from a stratigraphic viewpoint was the Decontra section in the Central Apennine. There, it was possible to refine stratigraphy while integrating all above mentioned methods. This allowed to correlate this shallow water limestone section to the global time scale and to also correlate precisely major global palaeoceanographic events such as oxygen isotope events of global cooling and the Monterey event which is defined by a pronounced change in the stable carbon isotope composition in the oceans. Together with this change phosphates occur in the limestones reflecting environmental perturbations. Within this project these changes are explained by a phosphogenesis model under oxic conditions and this process was clearly influenced by the 400-year-eccentricity changes of the earths orbit. The distribution pattern of rare earth elements allowed a clear assignment of phosphate grains having formed in situ, or being reworked or transported.A carbonate platform in northern Sardinia was studied to elucidate the influence of regional tectonics and global climate on carbonate production. As a major result global climate plays an important role in the production of red algal limestones, but was only effective in the studied carbonate platform when the local/regional tectonic regime switched from a syn-rift into post-rift mode from the early to the middle Miocene.In the North Alpine Foreland Basin it was possible to demonstrate that short cooling phases in the middle Burdigalian (early Miocene; 17.86 Ma and 17.81 Ma) were correlated to climate changes in the Southern Ocean reflecting the complexity and interconnectivity of the global climate system. Modulation of the 400-kyr and 100-ykr eccentricity cycles was the pacemaker of these changes. This interpretation is based on various fossil groups and on biomarkers (alkenone UK37) indicating a temperature drop at the sea surface by 2-3C. Applying a 5 mm continuous sampling strategy to clay- and siltstones of late Burdigalian age we could show that also short term solar cycles (Lower Gleissberg cyle: 65 years, Upper Gleissberg Cycle: 113 years, Suess cycle: 211 years) forced environmental changes and changes in biotic composition on a decadal to centennial scale. This is expressed by the changing composition of calcareous nannoplankton associations and geochemical parameters.