EOCENE AND YOUNGER BIOSTRATIGRAPHY AND LITHOFACIES OF THE CASCADE SEAMOUNT, EAST TASMAN PLATEAU, SOUTHWEST PACIFIC-OCEAN

Six dredgings, five taken during fishing operations, have recovered se dimentary rocks from the volcanic framework of Cascade Seamount, which is built on thinned continental crust on the East Tasman Plateau off eastern Tasmania. The top of the original volcano is now about 600 m b elow sea-level. Planktonic foraminifers and supplementary calcareous n annofossils yielded Late Eocene-Early Oligocene, mid-late Oligocene, E arly/Middle Miocene, approximately Late Miocene and Quaternary ages. T he history of the seamount is more complex than for most seamounts bui lt on oceanic crust and may involve several intervals of volcanism, bu rrowing or dissolution and cavity infilling. Some of the volcanism was subaerial and some submarine. Older rocks include conglomerate, volca niclastic sandstone, and a variety of interstitial sparry calcite, for med under a shallow-water, high-energy regime, whereas later sediments are mainly oozes. The oldest sedimentary rocks are Late Eocene, shall ow water, fully marine with calcareous algae and abundant echinoid deb ris. Two phases, Chiloguembelina-dominated and Globigerinatheka-domina ted, can be differentiated. Warm waters prevailed in the Late Eocene a nd in the Middle Miocene, cooler conditions between and since, consist ent with other indications around the southern Australian margin. Post -depositional alteration consists of phosphatisation and development o f ferromanganese crusts.