MIDCRETACEOUS CALCAREOUS AND SILICEOUS MICROFOSSILS FROM THE BASAL GEARLE-SILTSTONE, GIRALIA-ANTICLINE, SOUTHERN CARNARVON BASIN

A diverse assemblage of foraminifera, radiolaria, and calcareous nanno plankton is recorded from basal beds of the Gearle Silstone in its typ e area The calcareous nannofossils place the strata within the tempera te-latitude CC8a Subzone and the Southern Ocean Sollasites falklandens is Subzone; the planktonic foraminifera indicate that the beds belong to the Hedbergella planispira Zone of the Australian region. The biozo nes suggest an early Albian age (later than the earliest Albian). Abun dant calcareous and siliceous plankton and the Marssonella Association of benthonic foraminifera indicate normal-marine depositional conditi ons in a water depth of about 100 m. The transition from Windalia Radi olarite to Gearle Siltstone may reflect a marine transgressive pulse t hat reactivated bottom-water circulation and facilitated a significant increase in the calcareous biogenic component of the sediment. Deposi tion of the basal Gearle Siltstone was coincident with a major increas e in bathymetry in the Papuan, Laura, Carpentaria, Eromanga and Surat Basins in eastern Australia.