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Abstract
Dredged calcareous sediments associated with the volcanic edifices of Gascoyne, Taupo, Derwent Hunter, Stradbroke, Britannia, Moreton and Recorder 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 formation of the seamounts and also give data on oceanographic conditions existing at the time of accumulation of the sediments. All sediments accumulated in normal marine salinities.
Gascoyne Seamount sedimentation originated in tropical to subtropical water 15–20 m deep but age-diagnostic fossils have not been recovered.
Taupo Seamount includes sediments with a Late Miocene foraminiferid fauna with abundant calcareous algae but lacking Lepidocyclina. Water temperature was tropical to subtropical. Derwent Hunter Seamount has a similar biota but includes Lepidocyclina. The age is earliest Middle Miocene. Stradbroke Seamount yielded Middle Miocene ooze but this probably represents part of its history significantly after the initial volcanic phase of its buildup.
Britannia Seamount contains earliest Middle Miocene (N9) L. howchini, planktonic and encrusting foraminiferids and calcareous algae suggesting accumulation in shallow water. Conditions were tropical to subtropical.
Moreton Seamount yielded a latest Miocene tropical ooze and Recorder Seamount produced no identifiable biota.
The Lord Howe chain seamounts yield ages consistent with the hypothesis that they formed as the Indo-Australian plate moved north at a steady rate (6 cm/yr) over a stationary hotspot.
Nova Bank samples are both latest Oligocene and earliest Miocene in age and accumulated in outer continental shelf depths.
Argo Bank consists in part of lepidocyclinid limestone of Middle Miocene age.
Gifford Guyot has calcarenite of latest Early Miocene age with volcanic debris suggesting that this is the age of part of the building phase of that seamount.
Capel Bank samples yielded only Quaternary ooze. Several younger samples were recovered and these yield data on the interval after the initial phase of seamount formation. Many such data are from cavity and burrow infill in the primary (or oldest) sediment. Others are nonlithified ooze samples.
