Some Geological Results of the Bottom Sampling from the Sea off Kwanto District Western Margin of the Northern Pacific (Report of the Cruise GDP-1, 1972)

Abstract

The first cruise of the Japanese Geodynamics Project (GDP-1), which aimed at a combined geophysical and geological survey, was carried out in August, 1972. There were five corings with heat flow measuring at the position along the line of 33°30′N, across the Izu-Ogasawara Trench. One of the sediment columns was olive-brown clay, and one collected on the east slope of the Izu-Ogasawara Trench was sandy deposit containing many glasses and scoria fragments. Angular sandstone gravels were obtained at a station on the wall of a submarine canyon of the Ogasawara Ridge. The age of the rocks is most probably Middle Pliocene from the evidence of foraminifers and nannofossils. Bottom materials were collected at the top plane of the Takuyo Seamount II. Nannofossils were found from the pieces of phosphate rocks coated with ferro-manganese compounds in the materials, and were correlated to Late Cretaceous (Turonian~Maastrichtian) in age. Many spines and tubercles of sea-urchins, which indicate the Mesozoic age, were collected from the materials. The occurrence of these fossils offers additional data for the study of the history and movement of the seamounts and ocean floor around the seamounts of northwestern Pacific.