Biochronostratigraphy of the Reingraben Turnover (Hallstatt Facies Belt): Local black shale events controlled by regional tectonics, climatic change and plate tectonics

For the first time, two outcrops near Bad Durrnberg (2 km SSW Hallein, Austria) allowed for a continuous multistratigraphical investigation of the Reingraben Turnover in the Hallstatt facies belt. After a phase of reefal sedimentation during the Julian 1 (Early Carnian), a sudden increase in terrigenous input (Reingraben Turnover) caused the breakdown of the carbonate factory at the beginning of the Julian 2 (late Early Carnian). In starved basins produced by syndepositional tectonism, black shales locally accumulated. Stable isotopes of oxygen and carbon do not suggest a change in seawater chemistry during the turnover. Shallow-water carbonate production resumed slowly during the Tuvalian (Late Carnian), and complete recovery was finished near the Carnian-Norian transition. Because similar events are recorded globally, climatic changes (monsoonal circulation) controlled by plate tectonics are favoured as triggers of the event. Based on lithology and microfacies, detailed sampling, and analysis of conodont faunas and the resulting detailed conodont zonation enabled us to establish the duration of the Reingraben Turnover (Julian 1/IIc to Julian 2/II).