Sediments and stratigraphy of deep-sea cores from the Tasman Basin

Abstract

Twelve deep-sea cores from the northern Tasman Sea are described and grouped according to sediment characteristics and foraminiferal faunas. Six of the cores from the area between Australia and the Dampier Ridge consist dominantiy of clastics which have been derived from the Australian continental shelf and slope mainly by turbidity currents. Intervening periods when pelagic sedimentation was dominant have occurred. These cores were all taken from depths near the carbonate solution boundary and consequently calcareous foraminiferal tests in the pelagic intervals have been affected by solution. East of Dampier Ridge six cores were taken from the Lord Howe Rise, New Caledonia Basin, and Norfolk Ridge. These consist almost entirely of the calcareous remains of planktonic organisms, mainly foraminifera. Most of the cores are uppermost Pleistocene and Holocene in age, but in one core from the western slope of the Lord Howe Rise Middle to Upper Miocene sediment is unconformably overlain by uppermost Pleistocene and Holocene sediment. Intraformational slumping and/or sediment supply from the top of the Lord Howe Rise through submarine channels produced an unusually thick sediment blanket on the western flank of the Rise in the last 11,000 yr. This thickness suggests that the rate of sedimentation is 35 cm/1,000 yr in contrast to the top of the Rise, in the New Caledonia Basin, and at the base of the Norfolk Ridge, where it is 1-5·5 cm/1,000 yr. On the top of the Lord Howe Rise the rate of sedimentation during the last glaciation was about double that of the last 11,000 yr.