Redox Conditions and Paleoenvironment of an Austrian Upper Triassic Konservat-Lagerstätte with the Marine Polzberg Paleobiota as Evidence for the Carnian Pluvial Episode

Abstract Multi-proxyinvestigationswereconductedonclay minerals and redox-sensitive trace elements of the lower Carnian basinal succession from the Polzberg Konservat-Lagerstätte in the Northern Calcareous Alps (Austria). The marine Polzberg succession including the Konservat-Lagerstätte was studied using whole rock geochemistry and mineralogy, which enabled detailed and robust calibration of the Polzberg succession. The Polzberg section revealed the paleoceanographic and paleoclimatological history of the CarnianReifling Basin and traces the global climatic Carnian Pluvial Episode during that period. The age of the Upper Triassic Reingraben Shales at the Polzberg section is refined as early Carnian (Julian 2) within the Austrotrachyceras austriacum Zone. Ammonoids and conodonts provide a detailed biostratigraphic subdivision that forms the basis for analyses of the clay minerals and major, trace, and rare earth elements mirroring the paleoenvironmental and paleoclimate evolution of the Reifling Basin. The Polzberg succession includes lithological and facies changes, from carbonate-dominated to argillaceous deposits, similar to those of coeval units in the Mediterranean Tethys. The Carnian was characterized by a weak (~1‰) positive δ 13 C trend. This was punctuated by a positive shift in the lower Carnian corresponding to the initiation of the Carnian Pluvial Episode, a period representing the onset of early/late Carnian transitional global greenhouse conditions. The type and composition of clay minerals and distribution of trace elements highlight a shift from carbonate-dominated and oxic (water column and sea floor) conditions in the Reifling Formation to argillaceous and anoxic/euxinic bottom water and pore water conditions in the Reingraben Shales with increasing terrestrial influx in the upper part of the Polzberg section.