Re-evaluation of unconformities separating the "Ediacaran" and Cambrian systems, South Australia

The stratotype for the proposed Ediacaran System is located in the Flinders Ranges of South Australia. The top of the stratotype, which by definition coincides with the base of the Cambrian System, is located at the contact between the Pound Subgroup and the overlying Parachilna Formation. Regional mapping and stratigraphic analyses by earlier workers have suggested that this contact reflects a regional unconformity. Recent detailed mapping and re-evaluation of conflicting stratigraphic relationships has cast doubt upon this conclusion. It appears that the contact is locally a sharp change in facies and not a significant stratigraphic break. The implications of this are twofold. First, it suggests that the presently proposed upper boundary of the Ediacaran System stratotype may actually lie well within the Lower Cambrian. This would require a re-evaluation of the stratotype as well as a downsection shift of the Proterozoic-Cambrian boundary. Second, it may indicate that the Ediacaran fauna of South Australia are much younger than previously supposed, thereby minimizing the perceived gap between this fauna and younger Cambrian faunas.