The nature of the Proterozoic-Cambrian transition in the northern Amadeus Basin, central Australia

The nature and completeness of the rock record is vital in determining whether evolution across the Proterozoic-Cambrian boundary was episodic or explosive. This study documents the nature of the Neoproterozoic-Cambrian transition within the Arumbera Sandstone of the northern Amadeus Basin, central Australia and demonstrates an erosional surface close to this major stratigraphic boundary. We are not able to recognise major facies differences between the largely unfossiliferous lower units I and II and the rich trace fossil bearing beds of units III-IV. Horizons above and below the purported Neoproterozoic-Cambrian transition were traced laterally and searched for both trace and body fossils in an attempt to locate a local boundary between the Neoproterozoic and Cambrian. A single nonconformity bound sedimentary cycle above the major erosional surface dividing Arumbera II and III is recognised. The lowest sedimentary cycle of Arumbera III is devoid of trace fossils, but at correlative levels in the Ooraminna Sub-Basin, this horizon bears elements of the Ediacara fauna, reported for the first time herein. We, therefore, suggest that, contrary to previous studies, the Neoproterozoic-Cambrian transition is not coincident with the widespread seismic reflector but, in areas of more complete sedimentation, actually lies above it. This study also presents new stratigraphic, ichnological and palaeontological information from the Neoproterozoic-Cambrian transition in central Australia, identifies areas of potentially continuous sedimentation and provides a basis for correlation of the Arumbera Sandstone with other Neoproterozoic-Cambrian successions within Australia and beyond.