End-Triassic crisis and “unreefing” led to the demise of the Dachstein carbonate platform: A revised model and evidence from the Transdanubian Range, Hungary

The Dachstein platform was an extensive carbonate developed on the westernmost shelf of Neotethys during Late Triassic, now preserved in various tectonic units disrupted Alpine orogeny. Despite being focus a multitude sedimentological, paleontological and other studies, demise this remains controversial, with contrasting views timing causes cessation its growth, duration gap above, which at many places includes Triassic-Jurassic boundary (TJB), depositional environment overlying strata. Here we present new stable isotope cyclostratigraphic data from sections Transdanubian Range (Hungary) capture termination uppermost Triassic Limestone onset Hettangian (Early Jurassic) sedimentation following hiatus. Previously, TJB regarded as textbook case tectonically-driven drowning event or, alternatively, production due to emergence caused by significant sea level fall TJB. However, recognition global biotic change environmental perturbations calls for assessment their possible role platform. Oxygen carbon isotopic composition bulk carbonates were measured Kőris-hegy (Bakony Mts.), Tata (Tata Horst), Vöröshíd (Gerecse Mts.) Paleogeographically, these three represent proximal distal transect. Other Pisznice Tölgyhát yielded additional sedimentological data. sharp surface separating Jurassic formations carries no or only minimal relief outcrop scale. Thin section studies reveal small-scale irregularities, stylolites, microborings ferruginous filling, thin clay-rich layer TJB, indicative submarine, perhaps polygenetic, hardground. In first meters lowermost beds abundant ooids occur, crinoids become common. each studied sections, abrupt negative shift is recorded gradual rebound more positive values characterizes Chemostratigraphy allows correlation elsewhere. Range, initial excursion least part purported main are not Combined bio- cyclostratigraphy strata permits astrochronologic estimate early hiatus that longer than few hundreds thousand years. Our results highlight submarine erosion, partly related acidification, point end-Triassic extinction several groups system. “Unreefing”, ecological collapse reefs, led regime shift, transformation rimmed ramp, preservation sediment. This model uniformly applicable platforms them, unlike platform, survived unrimmed architecture Early elsewhere Neotethyan shelf. may explain features sedimentary record across events reef collapse.