Late Triassic (Norian-Rhaetian) brackish to freshwater habitats at a fluvial-dominated delta plain (Seinstedt, Lower Saxony, Germany)

Abstract

The historic Late Triassic outcrops at Fuchsberg and Langenberg near Seinstedt (Lower Saxony, Germany) are constrained to the Norian/Rhaetian boundary interval by means of conchostracan and palynomorph biostratigraphy. A comprehensive revision revealed a fluvial-dominated delta plain that formed in response to the successive transgression of the ‘Rhaetian Sea’ and received siliciclastics from southern source areas. At Fuchsberg and Langenberg, the distal lower delta plain is exposed and brackish subaqueous delta plain wetlands, mouthbar/distributary channel complexes and interdistributary bay subenvironments are reconstructed. Delta formation was controlled by bifurcation of distributary channels and avulsion of delta lobes. A diverse ecosystem is documented: a rich invertebrate fauna of limulids (1 taxon), insects (at least 20 taxa of 9 orders), malacostracans and conchostracans (several taxa) and a vertebrate fauna of amphibians (at least 1 taxon), sharks (9 taxa) and osteichthyan fishes (at least 6 taxa). In particular, fossiliferous interdistributary bay lithologies detail trophic systems of autochthonous subaqueous and parautochthonous riparian habitats. Abundant remnants of cycadophytes, ferns, horsetails and large vertebrates from Fuchsberg and adjacent outcrops of the Seinstedt area enable the reconstruction of vegetated upstream environments at the upper delta plain and floodplain.