Taphonomy and palaeoecology of Late Triassic (Carnian) ammonoid concentrations from the Taurus Mountains, Turkey

The deposits of the Carnian Kasımlar Formation within the Taurus Platform Units of south-western Turkey represent an important archive of a Late Triassic ecosystem. New palaeontological information was obtained by analysing the Kasimlarceltites mass occurrence, located within the Kasımlar Formation and named after the Lower Carnian (Julian) ammonoid genus Kasimlarceltites. This is the dominant taxon (> 94%) within the mass occurrence: nearly 775 million ammonoids and 50 million gastropods were extrapolated for the whole extension (at least 5 km2) of the Kasimlarceltites beds. This calculation is one of the main findings within this study, as it is the first time that such a fossil mass occurrence was quantified. Additionally, orientation measurements of the planispiral ammonoids and the helical gastropods enabled reconstructing the history of the mass occurrence and interpreting the underlying transport mechanisms. Further taphonomic aspects (e.g. biofabric, preservation, bioerosion or genetic classification) as well as comparisons with samples of the same acme zone from different localities near Aşağiyaylabel (AS IV, KA I-II) point to a two-phased genetic history. Accordingly, local mass mortality within the Kasimlarceltites fauna due to oxygen fluctuations or methane degassing may have initially led to a primary accumulation. These deposits were then reworked and redeposited basinward by gravity flows to create the present-day secondary allochthonous concentrations.