The significance and provenance of stromatolitic clasts in a probable Late Precambrian diamictite in north-western Tasmania

Abstract

Two types of stromatolitic dolomite boulders occur in a diamictite of possibly late Precambrian age in northwestern Tasmania; they are the oldest Tasmanian fossils so far recorded. The first type comprises dark grey dolomites containing the stromatolite Baicalia cf. B. burra, generally well preserved. The remainder are pale grey rather recrystallised dolomites containing stratiform and columnar-layered stromatolites. Their diagenesis and intrusion by dolomite veins preceded the erosion and redeposition of the clasts into the diamictite. The diamictite contains no diagnostic evidence of glaciation though a glacial origin cannot be definitely excluded. A debris flow mechanism of deposition is favoured. There is no proof in the material examined that either the well preserved Baicalia specimens or the recrystallised stromatolitic dolomites, occurring in clasts in the diamictite, were derived from the Smithton Dolomite. The occurrence of Baicalia cf. B. burra is consistent with a late Precambrian age of the source rocks, and close comparisons can be made with the Skillogalee Dolomite of South Australia.