PRELIMINARY REPORT OF THE TH95 GEOLOGICAL AND GEOPHYSICAL SURVEY RESULTS IN THE ROSS SEA AND DUMONT D'URVILLE SEA

Geophysical and geological surveys of the TH95 cruise on the R/V HAKUREI-MARU, in the abyssal basin and the continental rise area of Dumont d'Urville Sea (DDS) offshore of Adelie and Wilkes Land, and Victoria Land Basin (VLB) in the western part of the Ross Sea continental shelf, were carried out in the 1995-96 austral summer season. The deformed very thick sedimentary sequences, which are interpreted to have been deposited in the pre-rift and rifting stage, are revealed under thick post-break-up pelagic sedimentary sequences in DDS. There are several basement highs of (1) the igneous basement, including ultra-mafic rocks, which was uplifted in associated with the fracture zone, (2) the uplifted oceanic basement which is deformed by the normal fault, (3) the structural high with anomalous basement, which is interpreted as a piece of micro-continent, in DDS. These phenomena suggest the wide area of DDS is underlain by the characteristic intermediate type of crust between oceanic and continental. Even the deep structure of most of the Ross Sea continental shelf is not clear by the strong sea bottom multiples, more than 7km of thick sedimentary sequences in VLB is confirmed with MCS and OBS survey. The sequences are deformed by the extensional normal faults along the western margin and the Terror Rift. Geological samples which were recovered in the VLB gave important evidence of the late Ross Ice Shelf advance and retreat history.