Verdine and glaucony facies from surficial sediments of the eastern continental margin of India

Abstract

The present paper reports the first mineralogical description of green grains (verdine and glaucony) from sediments of the eastern continental margin of India. Only 24 of the 82 sediment samples studied, at depths between 18 and 247 m, contain green grains and their percentages in the coarse fraction (125–250 μm) range from 6 to 40%. Of these, 13 samples from the inner shelf (18–70 m) contain irregular dark green grains, 6 samples from the outer shelf (70–125 m) contain dark green pellets and a few dark green internal moulds of skeletal materials, and 5 samples from the continental slope (160–247 m) contain dark green moulds and infillings of planktonic and benthic foraminifers. The green grains found at depths between 18 and 125 m consist of poorly crystalline phyllite V with very little detrital clay. At 170 m depth, odinite (young phyllite V) occurs and further seaward between 200 and 247 m, glauconitic smectite is present. All verdine and glaucony grains studied show an early stage of evolution and the colour does not reflect their evolution. The verdine and glaucony from the slope sediments may correspond to the Last Glacial Maximum and the outer shelf verdine facies formed during the subsequent transgression. The inner shelf green grains may represent the present day formation of verdine.