Abstract
This study investigates the Paleogene deep-water depositional system of the Gosau Group at Gams, Styria (Austria). The examined sections of the Danian to the Ypresian age (NP1–NP12) comprise sediments of the Nierental and Zwieselalm Formations. Four deep-water clastic facies assemblages were encountered: (1) pelagic marls with thin turbidites, (2) carbonate-rich turbidites, (3) carbonate-poor turbidites, and (4) marl-bearing turbidites; slump beds and mass flow deposits are common features in all facies assemblages. Based on heavy mineral, thin section, microprobe, and paleoflow analyses, provenance was from the surrounding Northern Calcareous Alps (NCA) rocks and exhuming metamorphic Upper Austroalpine units to the south. In addition, biogenic calcareous material was delivered by adjacent contemporaneous shelf zones. The sedimentary depocenter was situated at the slope of the incipient Alpine orogenic wedge, in frontal parts of the NCA, facing the subducting Penninic Ocean/Alpine Tethys. The evolution of the Gams Basin was connected to the eoalpine and mesoalpine orogeny and the adjunctive transpressional setting. The Gams deep-water depositional system is interpreted as an aggrading or prograding submarine fan, deposited into a small confined slope basin, positioned along an active continental margin, bound and influenced by (strike-slip) faults, related to crustal shortening. The development of the Gams slope basin and its infilling sequences was mainly dominated by tectonism and sediment supply, rather than by eustatic sea-level fluctuations. The basin was cut off during the Eocene due to renewed orogeny. A Quaternary analogue for the Upper Cretaceous to Paleogene basin setting of the Gams area is represented by the Santa Monica Basin in the California Continental Borderland.
Highlights
Since the 1960s, various depositional models of turbidite and other deep-water massflow systems have been proposed [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]
Late early to Late Cretaceous eoalpine thrusting within the incipient Alpine orogenic wedge is linked to the development of several Gosau basins due to subduction tectonic erosion and subsidence at the front of development of several Gosau basins due to subduction tectonic erosion and subsidence at the front of the Austroalpine microplate [20,21,22]
The nannofossil smear slides were studied with a Leica DM 2700P light microscope with ×1000 magnification in bright field (BF), phase contrast (PC), and cross polarized light (XPL)
Summary
Since the 1960s, various depositional models of turbidite and other deep-water massflow systems have been proposed [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]. Fossil clastic deep-water systems are often only partly preserved and exposed, and provide significant research challenges, such as questions on the original depositional settings and the types of basin and basin fills. The siliciclastic and mixed siliciclastic–carbonate deep-water succession of the Upper Gosau Subgroup of Gams (Styria, Austria, Upper Cretaceous–Eocene) represents deepwater, mainly turbiditic deposition [19] within a formerly tectonically active part of the Northern Calcareous Alps (NCA), Eastern Alps (Figure 1). The Gosau Group records a widespread former sedimentary cover on top of the NCA, deposited in the northwestern
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