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ABSTRACT

Although tectonically dislocated at present, the paleogeographic zones of the northern Eastern Alps formed an interconnected paleobathymetric setting during the Upper Cretaceous (Coniacian to Maastrichtian). By comparing the paleoenvironments of the five sedimentary regions, paleo-oceanographic and paleobathymetric models are presented for the northern part of the Alps. These results are in agreement with recent oceanographic findings.

The sediments of the Helvetikum Zone represent continental shelf facies in the north, whereas the Ultrahelvetikum and Marginal Flysch Zone facies indicate upper to lower areas of the continental slope in the northern Tethys. The Flysch Zone exhibits a large scale subduction of the Penninic oceanic-basin. Litho- and biofacies data suggest that the Flysch basin corresponds to an abyssal-trench environment, while wildflysch and conglomeratic turbidite sediments of the Marginal Flysch Zone indicate tectonic fragmentation of the northern slope areas of the Flysch-trench. The Gosau Zone, on the other hand, represents an arctrench gap environment in the south. The Gosau basins were developed on a tectonically mobile Triassic to Jurassic calcareous platform that advanced to the north since the Lower Cretaceous and evolved into a submarine plateau with trench-like basins during the Upper Cretaceous. These basins then received turbidite sediments during the Campanian and Maastrichtian. The record of the Gosau sediments reveals an intra-Gosau synsedimentary tectogenesis of the Austro-Alpine units.

Compared to recent bathymetric data (DSDP), it is suggested the Flysch basin was located below the calcite compensation depth (CCD) in a depth range of about 3,000–5,000 m. The neighboring basins, i.e., the depositional sites of the Ultrahelvetikum and Marginal Flysch in the north, were situated above the CCD, although the mid-slope basin (Marginal Flysch) studied was located below the foraminiferal lysocline. The three Gosau basins studied represent various depth levels, relative to the calcite compensation zone, suggesting a differential subsidence of the calcareous platform during the Coniacian to Maastrichtian tectogenesis. The Reichenhall and Gosau Basins subsided to middle and upper bathyal depths and were above the CCD, the Kössen Basin subsided below a local CCD indicating a strong vertical motion related to isostatic adjustment of the basement rock.

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