International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

STORM-INDUCED EVENT DEPOSITS IN THE TYPE AREA OF THE GRUND FORMATION (MIDDLE MIOCENE, LOWER BADENIAN) IN THE MOLASSE ZONE OF LOWER AUSTRIA

Pages: 87 - 102

Authors: REINHARD ROETZEL, PETER PERVESLER

Abstract: Excavations in the type area of the Grund Formation (Middle Miocene, Lower Badenian) in Lower Austria showed four different lithofacies. Sandy beds with typical vertically arranged sedimentological features like erosive base, basal concentrations of coarse shell debris, mud-clasts and clast-horizons, normal graded beds, horizontal lamination of the upper plane bed, concentrations of plant and wood debris, asymmetrical ripples at the top, and synsedimentary deformation structures point to storm-induced event deposits. The sands were mainly deposited as tabular to slightly wedge-shaped sand-sheets; only extreme events produced channel-shaped sediment bodies. Pelitic layers at the top of such event-strata represent fair-weather conditions. The basal shell debris mainly contains mixed, synchronous-allochthonous, highly fragmented but determinable marine faunas from shallow to moderately deep environments. Together with land snails and bones of terrestrial vertebrates bottom currents transported the shelly fauna from shallow-marine to offshore areas. Paleocurrent data from groove marks, gastropod orientation, asymmetrical ripples and small dunes point to a transport towards ESE–E–NE, from a coastal area at the margin of the Bohemian Massif. The various lithofacies clearly reflect a proximal–distal trend from the shoreface to the offshore area. The development from the Skolithos to the proximal Cruziana ichnofacies to the proximal–archetypical Cruziana ichnofacies indicates an upward deepening from middle shoreface to upper offshore environments. The role of the Early Badenian transgression versus extreme storm events responsible for the proximal–distal trend and the lithological and ichnological development is discussed.

Keywords: Neogene, Miocene, Molasse Zone, Grund Formation, storm deposits, ichnofacies

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Volume 55 no. 2 / April 2004

Volume 55 no. 2