Cruise Proposal : AGSO Cruise 147 : Stratigraphy, Tectonic History and Palaeoclimate of the Offshore Tasmanian Region

The Tasmanian region's geological history bears on the history of the entire southern margin of Australia. The southern margin is already a major producer of petroleum from the Upper Cretaceous and Paleocene sequences in the Gippsland Basin, and has given encouraging exploration results in several other basins. The Otway Basin, in particular, is the scene of major recent offshore gas discoveries in the Cretaceous sequence. Both the west Tasmanian margin and the South Tasman Rise have petroleum potential.
The targets on the forthcoming Rig Seismic sampling cruise of 31 days (AGSO Cruise 147) are on the
west Tasmanian margin, the South Tasman Rise, the East Tasman Rise, and the adjacent oceanic areas.
The general bathymetry of the region is shown in Figure 1. The targets were defined by the early 1994 Tasmante cruise (Exon et al., 1994), which used the French research vessel l' Atalante on an exchange
basis to swath-map the sea bed. About two-thirds of both the South Tasman Rise (STR) and the west
Tasmanian margin were mapped, an areal coverage exceeding 200 000 km 2. The very accurate 1:250
000 scale bathymetric maps and sonar images arising from the Tasmante survey provide an unequalled
source of structural information. A simplified bathymetric map of the region, based largely on the Tasmante swath-mapping, is shown in Figure 2.
The aim of the present sampling cruise is to ground truth the maps and ideas arising from the Tasmante
cruise. It is designed to sample basement and Phanerozoic sedimentary rocks in all three continental
blocks, Cainozoic volcanics in continental and oceanic terrains, and Cainozoic sediments on the continental blocks, by dredging and coring. This will help elucidate the Phanerozoic history of the area with emphasis on petroleum geology and plate tectonic hisory, and also the Cainozoic and especially Quaternary history with emphasis on plate tectonic history, and changes in climate and sedimentation patterns. Water column sampling is designed to provide more information about oceanographic controls on sedimentation. An additional aim is to sample manganese nodules in deep water to assess them as a potential resource, by the use of free-fall grabs. As a result of interest in the volcanic cones about 100
km of Hobart, mapped during the Tasmante cruise, which define major fishing grounds, two photographic profiles and one dredge are planned for there. The main sampling areas are discussed briefly below.

塔斯马尼亚区域的地质演化史，与澳大利亚整个南部大陆边缘的演化史息息相关。该南部大陆边缘已是吉普斯兰盆地（Gippsland Basin）上白垩统与古新统地层的主要油气产出区，同时在其他多个盆地中也取得了令人振奋的勘探成果。其中奥特韦盆地（Otway Basin）更是在白垩系地层中斩获了近期重要的近海天然气发现。塔斯马尼亚西部大陆边缘与南塔斯马尼亚海台（South Tasman Rise，STR）均具备油气勘探潜力。
即将开展的为期31天的Rig地震采样航次（澳大利亚地质科学局（AGSO）航次147）的勘探目标区涵盖塔斯马尼亚西部大陆边缘、南塔斯马尼亚海台、东塔斯马尼亚海台以及邻近洋域。
该区域的整体水深地形见图1。本次航次的勘探目标由1994年初的Tasmante航次（埃克森等，1994）划定，该航次依托法国研究船“阿塔兰特号”（l' Atalante）以互换作业模式完成了海底条带测图。南塔斯马尼亚海台（STR）与塔斯马尼亚西部大陆边缘约三分之二的区域均完成了测图，覆盖面积超过20万平方千米。Tasmante航次所获取的高精度1:25万比例尺水深地形图与声呐图像，为构造信息研究提供了无与伦比的数据源。本次航次基于Tasmante条带测图成果编制的区域简化水深地形图见图2。
本次采样航次的核心目标是对Tasmante航次所生成的水深图与相关研究构想进行实地验证。本航次将通过拖网取样与岩心钻探的方式，对三个大陆地块的基底岩系与显生宙（Phanerozoic）沉积岩、大陆及洋域的新生代（Cainozoic）火山岩，以及大陆地块上的新生代沉积物开展采样工作。此举将有助于阐明该区域的显生宙演化史，重点聚焦油气地质与板块构造历史；同时也能助力解析新生代（尤其第四纪）的演化历程，重点关注板块构造历史、气候变化与沉积模式变迁。水体柱样采样则旨在获取更多关于海洋学过程对沉积作用控制机制的相关信息。本次航次的另一目标是利用自由下落式采泥器采集深水区域的锰结核，以评估其作为潜在矿产资源的开发价值。鉴于Tasmante航次测图发现距霍巴特（Hobart）约100千米处存在火山锥群，且该区域为重要渔场，本次航次计划在此开展2条摄影剖面测量与1次拖网取样作业。主要采样区域将在下文进行简要介绍。