Halorina cryptica nov. ichnogen., nov. ichnosp., mass-occurrence of Upper Triassic crustacean microcoprolites from neptunian dikes and sills cutting the Dachstein-type carbonate platform and their paleoenvironmental significance (Northern Apuseni Mountains, Romania)

Abstract

The new crustacean microcoprolite Halorina cryptica nov. ichnogen., nov. ichnosp., is reported from cryptic cavities cutting the Upper Triassic (Carnian to lower Rhaetian) Dachstein-type limestones from the Northern Apuseni Mountains, Romania. The new ichnotaxon is extremely abundant in cavities, neptunian dikes and sills filled with red ferruginous carbonate sediment. The associated microfauna consists of ostracods and rare foraminifera. The microfacies is represented by bioclastic coprolite-bearing wackestone-packstone to grainstone. The red ferruginous carbonate fillings are strongly bioturbated. The neptunian sill located at the top of the studied section contains a rich ichnofauna associated with brachiopod accumulations. It is dominated by the dimerelloid rhynchonellid Halorella, indicating a late Norian-early Rhaetian age. Although neptunian dikes and sills are rather common in the Dachstein-type carbonate platform that extended on the northwestern Tethyan margin, we report here the first record of mass-occurrence of crustacean microcoprolites in neptunian dikes and sills filled with red carbonate sediments of marine origin. They are interpreted here as cryptic cavities with specific palaeoenvironmental features (e.g., lack of light, abundant nutrients, intensive microbial activity) where crustacean arthropods thrived.