High-Fe Layer Silicates of the Sado Ridge, Japan Sea

Abstract

Detailed mineralogical investigations of high-Fe layer silicates from loose sediments (“glauconite” sands) of the Sado Ridge revealed that green aggregates found on submarine rises of the Japan Sea floor have a different genesis. It was demonstrated that round dark green grains approximate micas in composition. Primary volcanic rocks presumably experienced extensive secondary alterations and then were disintegrated. Their disintegration products (protoceladonite) filling the pores were redeposited and buried in the sediment for a long time. Angular green grains, mainly represented by smectite, were also formed at lower temperatures during the disintegration of altered volcanosedimentary rocks. These younger grains did not experience prolonged exposure. Pseudomorphs of siliceous microplankton consist of both hydromica and smectites. They are presumably authigenic products formed with the participation of microorganisms or electrostatic processes (spherical shape), or their combination. The formation mechanism of minerals filling the cavities in pyroclastics is not entirely clear.