Multistratigraphy of condensed ammonoid beds of the Rappoltstein (Berchtesgaden,southern Germany): unravelling palaeoenvironmental conditions on ‘Hallstatt deep swells’ during the Reingraben Event (Late Lower Carnian)

Two new sites of condensed Hallstatt Red Limestones were found in the Rappoltstein mountain range near Berchtesgaden (SE Bavaria). Conodont and ammonoid assemblages allowed for a concise age-dating of the lower two of seven already described Hallstatt ammonoid horizons as latest Ladinian to Lower Carnian (Upper Triassic). Biostratigraphy, microfacies analysis and stratigraphic cross-correlation of other Hallstatt sites allowed the documentation of the Late Lower Carnian ‘Reingraben Event’ within a mixed allochthonous–autochthonous carbonaceous lithofacies at the Rappoltstein, and gave further insights into the special architecture of the so-called ‘Hallstatt deep swells’ and the Hallstatt Basin. δ¹⁸O_phos of conodont apatite was measured in order to reconstruct marine palaeotemperatures. The reconstructed low seawater temperatures may be at least due to different palaeoclimatic scenarios that could have preceded the ‘Carnian crisis’.     

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 Dürrnberg (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).