The present status of Tasmanian Cambrian biostratigraphy

In Tasmania, no definite fossiliferous lower Cambrian rocks are known, but trilobite faunas are found in middle (Cambrian Series 3) and upper (Furongian) Cambrian sediments in the Dundas, Fossey Mountain, Dial Range, Beaconsfield and Adamsfield Troughs, the Smithton Basin and in the Rocky Boat Inlet-Surprise Bay area. Correlations of these faunas with the northern Australian biostratigraphic scale are possible mostly using assemblages of agnostoid arthropods.

The successions within the Dundas and Fossey Mountain Troughs belong to three main lithological groups. The youngest of these is the Owen Group extending from about the base of the Mindyallan Acmarhachis quasivespa Zone to the top of the Cambrian. In the Adamsfield Trough, the Denison Group is the equivalent of the Owen Group. The Tyndall Group and correlates occurs below the Owen Group in the Dundas and Fossey Mountain troughs, and represent the upper unit of the Mount Read Volcanics. The Tyndall Group ranges in age from about the base of the Boomerangian Lejopyge laevigata Zone to the base of the Acmarhachis quasivespa Zone. The pre-Tyndall Group rocks, representing the earlier parts of the Mount Read Volcanics and the related volcano-sedimentary units, are mainly of Floran to Undillan age. In the Dundas Trough, faunas range in age from possible Late Templetonian to Payntonian. Dial Range Trough faunas range in age from Floran to late Mindyallan. The few faunas from the Fossey Mountain Trough are of Boomerangian to Mindyallan age. The Smithton Basin faunas range in age from early Boomerangian to late Idamean, although a possible early Cambrian fauna is present.

In the Adamsfield Trough faunas range in age from early Boomerangian to possibly Datsonian. The single Cambrian fauna from the Beaconsfield Trough is probably late Undillan to Boomerangian in age and the three faunas from the Rocky Boat Inlet-Surprise Bay on the South Coast range in age from possibly middle Cambrian to Payntonian. The biostratigraphic information herein, in conjunction with recent geochronologic data, suggests that the age of the base of the Guzhangian Stage is better placed at about 498 Ma rather than the presently accepted figure of 500.5 Ma.