Tertiary marine rocks occur in small scattered outcrops around Tasmania's north and west coasts, on some islands in Bass Strait, and below sea level in Mussel Roe Bay. All occurrences except those in Mussel Roe Bay and on Preservation Island have been recorded previously. From 64 samples, about 300 categories (form, subspecies, species, genus etc,) of foraminifera have been identified. Planktonic species are generally poorly preserved, but good faunas have been identified from Fossil Bluff, Brittons Swamp and Marrawah, the latter in company with Lepidocyclina howchini Chapman and Crespin and Amphistegina lessonii d'Orbigny. All rocks are of Early and Middle Miocene age (Longfordian Batesfordian, Carter's Faunal Units 6, 8 and 9) with the possible exception of one sample from Mussel Roe Bay which may be Late Oligocene (Janjukian, Faunal Unit 5). All sediments are of shallow water origin, deposited in depths of less than 20, usually less than 10, fathoms. Water temperatures were those of the Warm Temperate to Subtropical Zones in Faunal Unit 6 time, Subtropical during Faunal Unit 8 time and Tropical during Faunal Unit 9 time. Waters may have been slightly warmer in the north-east than in the north-west during Faunal Unit 6 time. Sediments at about 100 feet below sea level in Mussel Roe Bay, and at less than 150 feet above sea level at Wynyard, King Island, Cape Grim, Mt Cameron West, Marrawah, Daisy Creek and Granville Harbour formed during a marine transgression throughout Faunal Units 5 and 6, There seems to be a Faunal Unit 7 hiatus which may represent regression. Higher level sediments (above sea level on Cape Barren and Preservation Islands) and at 170-310 feet above sea level at Brittons Swamp, Redpa, and Marrawah formed during another, more extensive transgression in the time of Faunal Units 8 and 9. Comments are made on the age of some basalts in the north-west of the State; on the relation of these outcropping sediments to those of the Bass Basin; on the common occurrence of large and planktonic foraminifera in a single sample from Marrawah; and a palaeogeographic map is presented.
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Papers & Proceedings of the Royal Society of Tasmania