Western Tasman Sea Floor

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Abstract
The western Tasman Sea floor is characterised by physiographic units that tend to parallel the coastline of south-eastern Australia. The margin has a narrow continental shelf and a steep continental slope. Sediment derived mainly from northern New South Wales and Queensland in the north, and from Tasmania and Victoria in the south, has built a system of fans forming the lower continental slope, continental rise, and Tasman Abyssal Plain. Areas of swale topography occurring along the distal margin of the 1,200-mile-long and 60—120-mile-wide Tasman Abyssal Plain represent regions where density-current-transported muds have overflowed on to abyssal hill topography and around the bases of seamounts. One to 2 km of flat-lying sediments form the abyssal plain and consist of graded beds of calcareous and terrigenous sand, silt, and clay in the uppermost 2–4 m. Calcareous ooze covers the Lord Howe Rise, the tops of seamounts, the continental slope of eastern Australia, and the abyssal hills at depths less than about 4,500 m, while brown pelagic clays occur at greater depths. The upper continental slope ranges from smooth sedimented slopes consisting of 500–3,000 ft of prograded Tertiary to Quaternary sediments off Sydney, to filled canyon systems with up to 20,000 ft of Cretaceous to Recent sediments in the Bass Strait, to steep slopes with eroded Tertiary slope sediments off Tasmania. The Tasmantid seamount chain consists of 11 major seamounts aligned north-south in an intermediate position between the north-east - south-west trends of the ridge-basin province of the deep Tasman Basin and the north-west - south-east trending Lord Howe Rise; it may be part of an incipient rise formed during the early to mid Tertiary between the diverging Australian and New Zealand continents.