Preliminary results of the TH99 geological and geophysical survey in the Cooperation Sea and Prydz Bay area

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Geophysical and geological surveys were carried out in the 1999-2000 austral summer season for the TH99 cruise aboard the R/V Hakurei-maru. The survey includes the abyssal basin and the continental rise area of the Cooperation Sea (CS) and Prydz Bay (PB), offshore of Mac Robertson Land and Princess Elizabeth Land, Antarctica. In the northern abyssal plain of the CS, a mantle-like sequence (G) appears at a depth of 10 s two-way travel time (TWT), or approximately 13 km. The sequence disappears south of 64°S, in the southern part of the CS. These observations suggest that the southern part of the CS and PB is underlain by intermediate type crust that is characteristic of oceanic and continental material. The deep structure of most of the PB continental shelf is not clear due to strong seafloor multiples. More than 7 km of thick sedimentary sequences in the northwest area of PB are confirmed by the MCS survey. Very thick sedimentary sequences, interpreted as prerift, rift and drift sediment can be observed under thick pelagic sediment. Geological samples, which were recovered in the CS and PB, offer important evidence on the recent history of drift sediments caused by iceberg floes. Two cores reached 0.78 Ma (Bruhnes-Matsuyama (B-M) boundary) in magneto-stratigraphic measurements, and they gave distinct age determinations for recent sediments.
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