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Michael Wagreich
Institut für Geologie, Universität Wien, michael.wagreich@univie.ac.at

The main objective of IGCP 463 is to investigate and understand conditions which resulted in the change from anoxic to oxic sediments deposition in the world oceans during the Late Cretaceous. This change, representing a unique event during the last 250 million years of the Earth history, may have been caused by changes in the operating mode of various earth processes such as changes in global ocean chemistry, the opening and closing of seaways, climatic change from greenhouse to icehouse conditions, or it may signal changes in palaeoproductivity.

In the Upper Cretaceous of the Austrian Eastern Alps distinct deep-marine red bed successions (Cretaceous Oceanic Red Beds - CORB) are known from the following palaeogeographic realms:

Helvetic/Ultrahelvetic realm:. In eastern Austria CORBs are known from the "Buntmergelserie", where dark grey limestone-shale rhythmits of Albian to Cenomanian age are overlain by light grey, white or red limestone-marl cycles of Turonian to Campanian/Maastrichtian age. Analysis of foraminiferal assemblages indicates a bathyal environment well above the CCD.

Penninic realm: In the Rhenodanubian Flysch Zone near Salzburg and Vienna distal turbidites are intercalated within intervals of red, mostly carbonate-free shales. Ages of red bed intercalations are Cenomanian?, Coniacian and Late Campanian.

Austroalpine realm: In the Northern Calcareous Alps CORBs are ubiquitous in the Nierental Formation of the Gosau Group (mainly Campanian - Maastrichtian). CORBs comprise red and grey marls and marly limestones with variable amounts of turbidite intercalations and high contents of planktonic foraminifera.

These successions comprise parts of the northern margin of the Tethyan Ocean during the Cretaceous, and define a slope - ocean/deep-water flysch basin - slope transect. The occurrence of CORBs in such an orogenic setting was strongly influenced by synorogenic clastic input, which masked red bed sedimentation. Sedimentation rates were a major parameter controlling red bed deposition especially in Flysch basins and orogenic wedges.