Three hundred and sixty-five surface and near-surface seabed samples provide the basis for an assessment of regional lithofacies variations on the Tasmanian shelf and in eastern and western Bass Strait. Quartz-rich sands with variable amounts of shell debris occur on the innermost shelf and on the rises flanking the central Bass Strait basin. They are essentially modern deposits derived in the main from Pleistocene near shore sand bodies reworked and transported landwards during the Holocene marine transgression. Muddy sediments of the middle shelf off eastern Tasmania and in central Bass Strait are sites of present-day sedimentation, but they are likely to form only a thin veneer, and include coarse material probably reworked from the Pleistocene and early Holocene substrate. Extensive areas of the middle and outer shelf, particularly off southern and western Tasmania, are floored by dominantly relict bryozoan sands and gravels. Fine-grained and shelly, slightly quartzose sands in areas of the middle shelf consist of relict sediment, and sediment from the late Holocene transgressive marine sand sheet, in about equal proportions. Four main suites of heavy minerals are present in the surface sediments. Provenance relationships with sources in the adjacent hinterland suggest that little offshore sediment transport parallel to the coastline has taken place. Rare grains of cassiterite were identified in marine sediments lying off the tin-producing areas of northeastern Tasmania, but 10 ppm Sn was the maximum value recorded in the geochemical analyses. Some phosphatisation of relict limestone gravels on the middle and outer shelf off northwestern Tasmania has taken place, but the highest recorded whole-rock analysis was 3.6 percent Pi>0. Density of sample stations in this part of the shelf is low.

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Exmouth Offshore Resource Map Series 1:1m

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Image showing the gravity station coverage and relative reliability over Australia, Updated to May 2012

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