Gordon Subgroup (Ordovician) carbonates at Precipitous Bluff and Point Cecil, southern Tasmania, Australia

The palaeogeographically and biostratigraphically important Ordovician carbonate sequence at Precipitous Bluff is at least 360m thick. The lowest 130 m, the New River Beds, consist of bryozoan algal biospararenites of Chazyan to Blackriveran age. These beds were probably deposited in a high energy subtidal environment with minor periods of intertidal deposition. The upper 50 m of this lowest unit contains abundant Calathium, bryozoans and corals. The succeeding 230 m of biosparites, biomicrites, argillaceous carbonates and siltstones, the Precipitous Bluff Beds, are dominated by trilobites, brachiopods and bryozoans, range in age from Trentonian to Cincinnatian and were probably deposited in deeper water than the New River Beds. The Prion Beach Beds at Point Cecil, five km south of Precipitous Bluff, are laceous micrites containing a trilobite/brachiopod fauna and include strata of Blackriveran and rentonian age and are thus biostratigraphically correlated with the upper part of the New River Beds and at least part of the Precipitous Bluff Beds. Vertical carbonates along New River Lagoon and sheared carbonates at Point Cecil suggest structural complications perhaps associated;with a continuation of a large, possibly transcurrent fault, trending north along New River.