Trace fossils from interdune deposits—an example from the lower triassic aeolian Tumlin Sandstone, central Poland

Abstract

The Tumlin Sandstone, up to 105 m thick, is the deposit of a midcontinent, extensive (at least 1500 km 2) dune field. It consists of dune deposits and of subordinate intercalations of interdune deposits. The latter are represented by horizontally bedded sandstone accumulated in frequently changing conditions: on dry, damp, and wet surface. Dry-surface deposits predominate. Subordinate but relatively common are damp-surface deposits with characteristic adhesion structures, and wet-surface deposits represented by very thin mudstone layers and horizons of wave ripples, which originated in ephemeral ponds. The interdune deposits contain numerous trace fossils whose occurrence is almost entirely connected with wet-surface and damp-surface deposits. The dune deposits are devoid of trace fossils. The following forms have been recognized: ?Arenicolites isp., Cruziana problematica, Diplocraterion isp., Gordia marina, Planolites montanus, Planolites isp., Palaeophycus ?tubularis, tetrapod footprints, radial structures, shallow double furrows, and various oval depressions. In places, intensive but shallow bioturbation of sediment is observable. The trace fossil assemblage is similar to the Scoyenia ichnofacies but lacks Scoyenia and Ancorichnus. The assemblage is more comparable to the mixed Arenicolites-Cruziana ichnofacies sensu Bromley and Asgaard (1979). The invertebrate burrows show an r- selected strategy in sediment colonization. Around the Palaeozoic/Mesozoic transition the highly diversified ichnofauna compared to that of the Permian interdune deposits shows increased colonisation of interdunes by an invertebrate, mainly arthropod, fauna.