Brachiopod biogeochemistry and isotope stratigraphy from the Rhaetian Eiberg section in Austria: potentials and limitations
Korte, Christoph; Thibault, Nicolas; Ullmann, Clemens V.; Clémence, Marie-Emilie; Mette, Wolfgang; Olsen, Troels K.; Rizzi, Małgorzata; Ruhl, Micha
published: May 1, 2017
ArtNo. ESP155028402000, Price: 29.00 €
The end-Triassic is characterized by one of the most severe biotic crises of the entire Phanerozoic, with strong carbon cycle perturbations potentially predating the biotic event. In order to improve and test the chemostratigraphic framework for the Rhaetian Stage, which culminated in the end-Triassic extinction, a total of 675 and 108 carbonate δ13 C and δ18 O values have been measured from bulk rock carbonate and articulate brachiopod samples from the Rhaetian Eiberg quarry succession (Northern Calcareous Alps, Austria) respectively. Both brachiopod and bulk rock oxygen isotope trends are compatible with a sedimentologically-constrained basinal deepening, culminating in unit 3 of the latest Rhaetian Eiberg Member. Brachiopod calcite δ18 O evolving from –1.4‰ to –0.5‰ V-PDB in this interval is offset to heavier values than bulk carbonates by circa 0.5 ‰, compatible with biomineralization in deeper water than the calcite composing the bulk rock micrite. Significant metabolic disequilibrium effects on brachiopod carbon isotope ratios are suggested by a clear negative correlation between δ13 C values and Sr/Ca ratios of the samples. Consequently, chemostratigraphy based on brachiopod δ13 C data, especially with regard to short-term events, is limited. High-resolution bulk rock δ13 C data show a >1 ‰ increasing trend throughout units 3 and 4 of the Hochalm Member, and first two units of the Eiberg Member reaching values of circa +2.5‰. This trend is reversed by a circa 1‰ negative shift across the boundary of units 2 and 3 of the Eiberg Member. This latter negative shift, known as the "Late Rhaetian Event", represents an important chemostratigraphic marker in the Eiberg quarry section, but its superregional significance remains to be confirmed.