Trace fossils versus pseudofossils in Lower Triassic playa deposits, Germany

Trace fossils and various sedimentary markings are preserved in positive epirelief on rippled sandstone beds in Lower Triassic (Lower Buntsandstein) playa deposits of Germany. They are commonly linked to sand-filled shrinkage cracks (pseudofossil Manchuriophycus) and originated within the sediment along a sandstone–claystone interface. Both the trace fossils and the markings are similar in appearance. A remarkable complex trace fossil consists of a backfilled main burrow with bulbous extensions and a terminal brush-like cluster of radiating rays. The responsible tracemaker seems to have been a highly specialized arthropod with segmented antennae to produce such a compound locomotion, resting and feeding trace. It has explored the sand–clay interface by moving through a sand-filled crack and has probed the sediment with a very efficient technique. All parts of the compound trace fossil are regarded as incertae sedis. During diagenesis, burrow portions, shrinkage cracks and micro-morphological features were locally affected by delicate dendroid sedimentary markings previously considered organic in origin. More likely, the presented material can be assigned to the pseudofossil Aristophycus, which originated diagenetically by sediment fluidization along the sand–clay interface. It can be regarded as an internal dewatering structure with horizontally oriented sand stringers, which seems to require physical properties typical of shallow marine environments and epicontinental basins with alternations of claystone and siltstone/fine-grained sandstone.