Palaeoenvironmental interpretation of a Triassic-Jurassic boundary section from Western Austria based on palaeoecological and geochemical data

摘要: A section spanning the Triassic-Jurassic boundary is described from near village of Loruns in Vorarlberg region western Austria. At Loruns, uppermost Triassic characterised by bedded carbonates Kossen Formation supporting a stenotopic fauna indicative shallow sub-tidal environment normal marine salinity. The may be represented as sequence developed on top 1.1 m thick red mudstone lower Schattwald Shale, which interpreted to have been deposited marginal environment, possibly mud flat. Above beds, upper Shale thin-bedded marl and dark limestone beds with an earliest Hettangian macrofauna dominated epifaunal filter-feeding bivalves, including ostreids, mytilids oxytomids, suggest shallow, subtidal, salinity-controlled typical interplatform lagoon. Carbonate production rejuvenated later Early development oolite, subtidal oolitic oncolitic unit bearing echinoderms conditions. Low ThU ratios remainder are result reduced thorium carbonate-rich sediments not authigenic uranium anoxic sediments. In evidence for anoxia (or dysoxia) absent where values, determined gamma-ray spectrometry, above 5. negative excursion δ13C positive δ18O due secondary geochemical effects, organic diagenesis or precipitation caliche during paleosol development. Alternatively, excursions reflect primary signal recording short-term decline productivity. Comparison values between Lorfus oolite indicate no significant long-term changes evident that any environmental perturbations were restricted possible boundary.