PRELIMINARY REPORT OF GEOLOGICAL AND GEOPHYSICAL SURVEYS OFF QUEEN MAUD LAND, EAST ANTARCTICA

The geological and geophysical surveys off Queen Maud Land, East Antarctica were carried out during the 1985-1986 season using R/V HAKUREI-MARU. The survey covered areas of Gunnerus Ridge and the upper continental rise to the abyssal plain off Syowa Station. The basement of Gunnerus Ridge is supposed to be continental crust by magnetic data, gravity data, sonobuoy data and dredged rocks. The oceanic basement is confirmed in seismic and gravity data to have a deepening trend and to form a thickening sedimentary basin toward the foot of the continental slope. The maximum depth and thickness exceed 9.0s in two-way time from sea level and 3.0s in two-way time between sea bottom and acoustic basement, respectively on seismic lines. The age difference of the oceanic crust is discussed using seismic character difference of the top of acoustic basement. The sediment section of the basin is divided into three prominent sequences and discussed in terms of seismic stratigraphy. The heat flow data show slightly lower values than a world ocean average value, and this may suggest that the age of the oceanic basement in this area is relatively old

MEASUREMENTS OF REMANENT MAGNETIZATION ON THE SEDIMENT CORES OBTAINED IN TH-85 CRUISE

Paleomagnetic measurements were carried out on five sediment cores collected from the sea bottom off the Queen Maud Land, Antarctica during the TH-85 cruise of R/V HAKUREI-MARU. The specimens for paleomagnetic study were taken out as a vertical series of 2-cm cubes from each core (PC-601,-602,-603,-605 and -606). Remanent magnetization of these specimens after demagnetization at optimum alternating field (10 mT) was measured using an SCT superconducting rock magnetometer. Reliable paleomagnetic results were obtained from these cores. Except PC-601 the remanent magnetization through almost all the length of the cores has deep and negative inclination. Shallow or positive inclinations are found around 2.5m from the top of PC-602,3.6m of PC-605 and 3.9m of PC-606. Providing that the age of the top of the core is the present and that shallow or positive inclinations are correlated with the Blake Event, the sedimentation rate of PC-602,-605 and -606 is 2.3,3.3 and 3.6cm/1000y, respectively. Since PC-603 does not show any positive inclination throughout the core, the age of the core may be assumed younger than that of the Blake Event and the sedimentation rate may be estimated greater than 7.1cm/1000y. Although several reversals are observed in PC-601,it is difficult to estimate the age of these reversals, because of the lack of data for the upper part of the core. It seems, however, to indicate that the sedimentation rate of PC-601 is smaller than the other cores. Although the sedimentation rate of five cores was paleomagnetically estimated as mentioned above, all of the shallow or positive inclinations in the cores may not correspond to some of the geomagnetic reversals or excursions, because many of them were found in sandy parts of the sediment and moreover only the fossils of radiolaria of the middle to late Pleistocene were observed in all the cores