Sedimentology, carbon isotope stratigraphy and micropalaeontology of the Rhaetian Zlambach Formation– Implications for the Dachstein carbonate platform development (Northern Calcareous Alps, Austria)

Wolfgang Mette,Marie-Emilie Clemence,Nicolas Thibault,Christoph Korte,Bernadette Konrad,Clemens Vinzenz Ullmann

doi:10.1016/j.sedgeo.2018.12.009

Wolfgang Mette, Marie-Emilie Clemence + Show 4 more

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https://doi.org/10.1016/j.sedgeo.2018.12.009

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Abstract

Middle to late Rhaetian toe–of–slope to basin deposits (Zlambach Formation) of the Northern Calcareous Alps in the Tethyan realm have been studied with respect to depositional palaeoenvironments and chemo- and sequence stratigraphy, using high-resolution stable isotope and X-ray fluorescence measurements, microfacies and microfossil analysis. Our results show that the Zlambach Formation represents a regressive-transgressive succession which includes one 3rd order and two 4th order depositional sequences as well as several subordinate sedimentary cycles reflecting variations of calciturbidite input from the Dachstein platform due to minor sea-level fluctuations. We present the first high-resolution δ13Ccarb record for the Middle and Upper Rhaetian interval of the west Tethyan open marine realm. The data show, in contrast to earlier suggestions, that growth and progradation of the Dachstein carbonate platform margin was continuous until the early Choristoceras marshi ammonoid zone (upper Rhaetian). In the late C. marshi zone the Hallstatt basin was affected by significant environmental perturbations as recorded by a 1.0‰ Ccarb negative excursion followed by a 1.3‰ positive excursion and contemporaneous fluctuations in benthic microfossil abundance and diversity. The occurrence of comparable carbon isotope excursions in the late C. marshi zone of intraplatform basinal deposits of the Northern Calcareous Alps suggests that these perturbations were of a higher significance than previously thought. These isotope excursions could be related to regional ecologic changes such as the late Rhaetian termination of the Dachstein platform margin growth.

Highlights

The Late Triassic has been intensively studied in recent years with respect to carbon isotope stratigraphy
Our results show a stratigraphic coincidence of significant carbon isotope excursions, rapid depletion of ostracod and foraminifera abundance and diversity and the disappearance of calciturbidites
The Zlambach Formation exposed at Rossmoosgraben section is an open marine regressive-transgressive succession of marl-limestone alternations which was deposited in a toe−of−slope to basin environment and ranges in age from Middle to Late Rhaetian

Summary

Introduction

The Late Triassic has been intensively studied in recent years with respect to carbon isotope stratigraphy. Korte et al, 2005; Richoz et al, 2012; Whiteside and Ward, 2011; Mette et al, 2012; Korte et al, 2017; Zaffani et al, 2018) in general and the late Rhaetian pre-extinction interval in particular still lacks sufficient resolution. This is largely due to the fact that there are few continuous. In the Northern Calcareous Alps, the Rhaetian is represented in continuous successions of intraplatform basinal environments

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