Campanian Orbital Cyclostratigraphy

The knowledge of the durations and the absolute timing of climatic and geological events recorded in the earth history, is a major issue in Earth science. A well calibrated and stable time scale is needed to allow for more precise dating of sedimentary archives of environmental and climate change. The Cretaceous is known as the last long-term extreme greenhouse period of the earth history. The Campanian (83.5 - 70.6 Ma) is the longest Late Cretaceous stage. This interval constitutes a time of increasing climatic detoriation from mid-Cretaceous super- greenhouse to moderate greenhouse climate. So far, a complete record of climate-induced cyclicity and an astronomical time scale for the Campanian is lacking. The proposed project addresses cyclostratigraphy and a floating astronomical time scale for the Campanian stage, based on four continuous cyclic limestone-marl records in the Tethys, i.e. two sections in Austria and two sections in Turkey. Methods used include plankton (foraminifera and calcareous nannofossil) biostratigraphy, carbon and strontium isotope stratigraphy and magnetostratigraphy for a high-resolution chronostratigraphic framework, the identification of cyclic sedimentation by rhythmic variations in parameters like carbonate contents, magnetic susceptibility, gamma ray log, and statistical analysis like data standardization, time series and power spectra analysis, wavelet transformation, and cross correlation between standardized measured parameters and solar insolation. The sedimentology and geochemistry of the sections in overview and of individual precessional cycles in the Campanian will be evaluated by clay mineralogy and XRF element scans. Based on this new time calibration, short-term climate and environmental changes in the late greenhouse world will be investigated, especially causes for changes from anoxic to oxic sedimentation manifested in ubiquitous Cretaceous oceanic red beds.

The knowledge of durations as well as the absolute timing of events and developments recorded in Earth history has always been a major issue in Earth science and is vital for the sound assessment of recent changes in the Earth System. The Austrian Science Fund research project FWF 24044-N24 was addressing prospects to reconstruct a timescale for the Campanian (the longest stage of the Late Cretaceous system; 83.5 70.6 Ma) based on the rhythmic variations of insolation preserved in the climate record. The Campanian is characterised by a transition from the Late Cretaceous hothouse to a more moderate Greenhouse climate and can thus be regarded as a model or template for recent and future climate change and evolution. A great number of signals preserved in geological archives, i.e. variations in the lithological, fossil or geochemical record, indicate palaeoclimatic changes. These rhythmic climate cycles known as Eccentricity (with a mean duration of 405 000 and 100 000 years), Obliquity (approximately 39 000 to 45 000 years) as well as Orbital Precession (17 000 to 23 000 years), also known as Milankovitch cycles, were recorded in sedimentary successions from the Austrian Alps, western Anatolia as well as from the southern Black Sea coast of Turkey. Upon a statistical analysis of orbitally driven sedimentary signals it was possible to establish a time model for parts of the Santonian and the Campanian. The thorough investigation of the Santonian-Campanian boundary in various localities (the Postalm and Schattau sections from the Northern Calcareous Alps, as well as from the Göynük section from northwestern Anatolia) contributed to the establishment of an accurate time model. This research project furthermore involved the construction of a high resolution stratigraphic framework based on plankton biostratigraphy (by use of foraminifera and calcareous nannoplankton), carbon- and oxygen isotope stratigraphy as well as magnetostratigraphy as a robust base for an astronomic timescale for the time interval under investigation. Variations in carbonate content (limestone-marl cycles) and magnetic susceptibility as well as Manganese and Aluminium content were used to identify climate cycles. A time framework for the Santonian Campanian boundary was established and sub-Milankovitch cycles (15000, 10000 and 7500 years) were identified upon a detailed examination of geochemical properties. Volcanic ash layers from Turkish localities were classified and used for correlation purposes. The impact of these climate variations on the Earths system can be observed in sea-level changes, and, more importantly, the Biosphere, especially marine production and plankton evolution.