Problematic fossils in the late Neoproterozoic Wonoka Formation, South Australia

Abstract

Complex biogenic structures are described from the upper Wonoka Formation (late Neoproterozoic) of the Adelaide ‘Geosyncline’, South Australia. The structures are preserved within silty limestones and calcareous siltstones as dark bedding plane markings defining branching arrays of parallel, elongate, curved elements. The fossils bear at least a superficial resemblance to the putative trace fossil Palaeopascichnus, normally preserved in siliciclastic sediments, and reported from a number of late Neoproterozoic sections worldwide. The material from the Wonoka Formation is not a trace fossil, and seems most likely to represent a surface encrusting alga. The nature of Palaeopascichnus needs to be carefully reassessed in the light of the possibility that the Wonoka fossils represent a different preservational window into the same phenomenon. The thin (ca. 2 m) but widespread nature of the fossil horizon makes it a useful stratigraphic marker within the Wonoka Formation, with the potential to aid in regional correlation within the Adelaide ‘Geosyncline’.