Micropalaeontology of the Late Proterozoic Arcoona Quartzite Member of the Tent Hill Formation, Stuart Shelf, South Australia

Abstract

Shales of the Late Proterozoic Arcoona Quartzite Member of the Tent Hill Formation, Stuart Shelf, South Australia, contain a well-preserved microfossil assemblage consisting of leiosphaerid acritarchs, cyanobacterial filaments and relatively large organic sheets interpreted as probable fragments of vendotaenid algae. Stratigraphically, the Arcoona Quartzite Member is thought to be the equivalent of the ABC Range Quartzite of the Flinders Ranges, which underlies metazoan-bearing sandstones of the Pound Subgroup but overlies recently discovered animal fossils of the basal Wilpena Group. The ABC Quartzite is included in the stratotype of the Ediacarian System proposed by Cloud & Glaessner (1982). The Arcoona assemblage thus provides an excellent opportunity for microfossil-based biostratigraphic characterization of sequences containing the earliest invertebrate biotas. Arcoona microfossils illustrate well both the problems and potential of Precambrian micropalaeontology. The morphologic complexity and diversity of the leiosphaerids is limited; however, the assemblage as a whole compares closely with microbiotas of late Vendian age from the Georgina Basin in northern Australia and the Nama Group in Namibia, as well as with several localities in the Northern Hemisphere. The assemblage described here differs from phytoplankton assemblages of both late Riphean and Cambrian age found in many other parts of the world.