Subtidal scour troughs and channels of a tempestite in the compressus Zone and stratigraphy/palaeoenvironment in the Upper Muschelkalk (Anisian/Ladinian) of Bissendorf (NW Germany)

Abstract

An excavated surface of a marine subtidal seafloor is described from Bissendorf in the Osnabrucker Bergland of northwestern Germany. This surface is located above a newly discovered bonebed in the compressus Zone of the Ceratitenschichten (MeiBner Fm, moMI) below the Terebratelkalk (Middle Triassic, Anisian/Ladinian boundary, Upper Muschelkalk). This dating was possible by stratigraphically collected ceratites. Sedimentologically it is a bioclastic rudstone, at the base of which very well-preserved horse iron scour marks and gutter casts Occur. The narrow parallel channels and one scour trough were documented on a 105 m(2) large Surface. These are eroded in the underlying marls of the compressus bonebed. The scour trough and the flat subtidal channels are oriented parallel to the coast and to the East and indicate a storm event. In this tempestite all large biogene shells of brachiopods, bivalves, ceratites, but also some bone and teeth remains are enriched in an up to 30 cm thick heterotopic taphocoenosis. Finally the most important and completely exposed Upper Muschelkalk section of Northwestern Germany is presented with a new palaeobathymetrical and -ecological interpretation with the German and international subdivisions.