RIASSUNTO
ABSTRACT
Phosphorites mainly of upper Miocene age were discovered on underwater rises of the Sea of Japan. High-quality phosphorites involve diatom and terrigenous- diatom rocks substituted by phosphate. Rich phosphorites containing up to 30% P 2 0 5 were not known Jon marginal seas before. The paper dwells upon mineral and chemical composition of phosforites. Connection between phosphatogenesis and inflow of cold oceanic waters rich in dissolved inorganic phosphate has been proved.
INTRODUCTION
For the first time phosphorites in the Sea of Japan were discovered in dredged ""matter during the 30 R/V Pervenetz cruise, organized by Pacific Oceanological Institute of the Far Eastern Branch of the USSR Academy of Sciences in 1978. Since that time the problem of the Sea of Japan phosphorites has been paid great attention to. Distribution of phosphorites on seafloor, their composition and mineralogy were studied "" some genetic construction were made. The present paper comments on briefly all the items above.
Phosphorites were sampled by dredges, scoops, bed cores during regional geological investigations carried out by research vessels of the USSR Academy. Four scientific cruises had been dedicated especially to the detailed studying of phosphorites. Two of them were conducted on Yamato Rise, the others - on East-Korean Elevation. In Laboratory the phosphorites were studied by methods of optical microscopy, x-ray, lR-spectroscopy and thermal analysis as well as electronic microscopy.
ACTUAL MATERIAL
Occurrence of phosphorites
Phosphorites usually occur on tops and upper parts of slopes of large underwater rises of the Sea of Japan. Phosphorites were found on North and South Yamato Ridges, Oki-Ridge as well as on Kristofowitch, East-Korean, Ullindo, Hackusan-Se elevations. Low-phosphatic carbonate concretions in negligible quantities were observed on continental slope of Prymorie (Fig.1). Some rare phosphatic fish bones (vertebral bones and otholites) were discovered in ooze at Yamato Rise foot. The most rich and abundant phosphorites distributed on seam01mts will be of supreme concern below.
Phosphorites occur chiefly on depths in the range of 1300-1800 meters, though some samples containing phosphorites were taken from the depth less than 1000 meters and more than 3000 meters.3,4 Best concentrations of phosphorites were found in upper slopes of elevations, there occurred some areas with amount of phosphorite fragments in rough detritial rocks of bottom sediments coming up to 80%.
Kinds of phosphorites
All the high performance phoshporites in the Sea of Japan involve phosphatized diatom and terrigenous-diatom ooze or rocks. According to morthology and inner structure they are divided into phosphatic nodules, massive phosphorites fragments and poorer psefitepsommitic rocks with phosphatic cement. Phosphatized carbonate nodules and phosphatic fish bones mentioned above pertain to the other type, but in our view, it is of low importance.