Middle-Upper Ordovician Shallow Platform to Deep Basin Transect, Southern Tasmania.

There is a profound change in sedimentary environment and in fauna going from the Middle-Upper Ordovician of Ida Bay to Surprise Bay over a present distance of only 25 km. The transition is from peritidal carbonates at Ida Bay, to subtidal carbonates at Precipitous Bluff to deep subtidal calcareous shales at Pt. Cecil to deep water micrites, graptolitic shales and carbonate turbidites at Surprise Bay. The blind (Nanshanaspis, Bulbaspis) or large eyed (Telephina) trilobites at Surprise Bay suggest sub-photic or twilight depositional conditions and a phosphatic, ironstone hardground enriched in metals and with imploded nautiloids suggests a zone of nutrient-rich upwelling currents at about 300 ± 50 m water depth. Macrofauna from Ida Bay is mainly endemic and is associated with Midcontinent province type or endemic conodonts. The shelf edge sections at Precipitous Bluff and Pt. Cecil contain more widespread macrofossils and Midcontinent conodonts whereas the macrofauna from the deep-water deposits is widespread or cosmopolitan and is associated with North Atlantic province conodonts.