Chuaria Walcott, 1899 in the lower Wessel Group, Arafura Basin, northern Australia

Abstract

The carbonaceous fossil Chuaria circularis Walcott (1899) is reported from the Raiwalla Shale of the Wessel Group (onshore Arafura Basin), Northern Territory. As most occurrences of Chuaria are Proterozoic and the majority of these are Neoproterozoic, the Early to Middle Cambrian age previously assigned to the Wessel Group is no longer well supported, especially since the main fossil evidence on which this was based is no longer applicable. A carbonate unit containing a Middle Cambrian trilobite fauna, previously considered part of the Wessel Group, is now interpreted to lie unconformably above this group. The discovery has regional stratigraphic significance in northern Australia and the ages of other poorly dated successions, commonly assumed to be of Early Cambrian age, requires reassessment.