TASMANTID AND HOWE,LORD SEAMOUNTS - BIOSTRATIGRAPHY AND PALAEOCEANOGRAPHIC SIGNIFICANCE

Dredged calcareous sediments associated with the volcanic edifices of Gascoyne, Taupo, Derwent Hunter, Stradbroke, Britannia, Moreton and Re corder Seamounts (Tasmantid Seamount chain) and Nova Bank, Argo Bank, Capel Bank and Gifford Guyot (Lord Howe Seamount chain) have yielded a diverse biota including abundant foraminiferids and calcareous algae. These fossils constrain hypotheses on the age and environment of form ation of the seamounts and also give data on oceanographic conditions existing at the time of accumulation of the sediments. All sediments a ccumulated in normal marine salinities. Gascoyne Seamount sedimentatio n originated in tropical to subtropical water 15-20 m deep but age-dia gnostic fossils have not been recovered. Taupo Seamount includes sedim ents with a Late Miocene foraminiferid fauna with abundant calcareous algae but lacking Lepidocyclina. Water temperature was tropical to sub tropical. Derwent Hunter Seamount has a similar biota but includes Lep idocyclina. The age is earliest Middle Miocene. Stradbroke Seamount yi elded Middle Miocene ooze but this probably represents part of its his tory significantly after the initial volcanic phase of its buildup. Br itannia Seamount contains earliest Middle Miocene (N9) L. howchini, pl anktonic and encrusting foraminiferids and calcareous algae suggesting accumulation in shallow water. Conditions were tropical to subtropica l. Moreton Seamount yielded a latest Miocene tropical ooze and Recorde r Seamount produced no identifiable biota. The Lord Howe chain seamoun ts yield ages consistent with the hypothesis that they formed as the I ndo-Australian plate moved north at a steady rate (6 cm/yr) over a sta tionary hotspot. Nova Bank samples are both latest Oligocene and earli est Miocene in age and accumulated in outer continental shelf depths. Argo Bank consists in part of lepidocyclinid limestone of Middle Mioce ne age. Gifford Guyot has calcarenite of latest Early Miocene age with volcanic debris suggesting that this is the age of part of the buildi ng phase of that seamount. Capel Bank samples yielded only Quaternary ooze. Several younger samples were recovered and these yield data on t he interval after the initial phase of seamount formation. Many such d ata are from cavity and burrow infill in the primary (or oldest) sedim ent. Others are nonlithified ooze samples.