Preliminary report of geological and geophysical surveys off Amery Ice Shelf, East Antarctica

Geological and geophysical surveys off the Amery Ice Shelf, East Antarctica, were carried out during the 1984-1985 Antarctic summer season. The surveyed area involves the continental shelf, slope, rise, the abyssal plain and part of the Kerguelen Plateau. Thickness of the sedimentary layer beneath the continental shelf is estimated to be more than 3.5km from a sonobuoy result. A series of upper strata progrades seaward and is eroded at the sea bottom. In the continental slope, rise and the abyssal plain, the presence of sediments whose thickness exceeds 6km is confirmed. The sediments seem to become thicker toward the continent, particularly the center of Prydz Bay to which the Lambert graben is thought to extend from the inland of Antarctica. In the southwestern margin of the Kerguelen Plateau, the acoustic basement rises toward the Plateau, and is thinly covered by an acoustic transparent layer whose age is relatively old. Dipping strata suggest that the acoustic basement consists of highly consolidated sedimentary layers which have been subjected to a complex tectonic movement related to the origin of the Plateau

PRELIMINARY REPORT OF GEOPHYSICAL AND GEOLOGICAL SURVEYS IN THE AMUNDSEN SEA, WEST ANTARCTICA

Geophysical and geological surveys in the Amundsen Sea, West Antarctica were conducted during the 1986-1987 Antarctic summer season. The study area covers the continental rise and the abyssal plain. The surveys revealed the existence of the sedimentary basin in the Amundsen Sea as the westward extension of the Bellingshausen Sea Basin. The basement of the basin becomes shallow in depth and rough in topography toward the west in a manner of stepwise change along the continental rise and the abyssal plain, which are clearly observed in seismic sections. In the continental rise, the presence of thick sediments which exceeded about 2.0s in two-way time was recognized. Characteristic sedimentary facies patterns in the continental rise such as dunes, channels, buried channels and migrating waves were observed in the upper parts of the sediment columns. In the abyssal plain, the acoustic basement showed remarkably complex relief and distorted reflections were observed in the sediments deposited on structural lows of the basement. The sediments were generally thin, about 0.5s in two-way time. From the viewpoint of depth, location, configuration, reflection pattern of the acoustic basement and thickness of total sediments, the study area can be divided into three parts, i.e., eastern part, central part and western part. The boundaries between them may be assumed to correspond to fracture zones which extend from the Pacific-Antarctic Ridges

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