Distribution and Composition of Verdine and Glaucony Facies from the Sediments of the Western Continental Margin of India
Published:January 01, 2000
M. Thamban, V. Purnachandra Rao, 2000. "Distribution and Composition of Verdine and Glaucony Facies from the Sediments of the Western Continental Margin of India", Marine Authigenesis: From Global to Microbial, Craig R. Glenn, Liliane Prévôt-Lucas, Jacques Lucas
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Investigations 011 green grains from sediments of the western continental margin of India, between Ratnagiri and Cape Comorin, (water depth 37-330 111) indicate the presence of verdine and glaucony facies. Verdine facies occurs over an area of about 100,000 km2, representing the largest sedimentary basin in the world associated with low fluvial input. Green grains occur as irregular grains, fecal pellets, and infillings/internal molds of microfossils. They are abundant on the shelf off river mouths and their distribution varies with sediment type. Grains vary from dark green to pale green or brownish green. Green grains studied here are a mixture of predominant authigenic green clay and detrital clay minerals and are altered. Both phyllite C and suspected phyllite V- (verdine minerals) associated green grains occur on the continental shelf (between 37 m and 100 111), the former being associated with the transition zone between inner and outer shelf and the latter with relict sands and reefs on the outer shelf. On the continental slope, suspected phyllite V occurs at depths between 100 111 and 235 111, followed by phyllite C at 280 m depth and glauconitic smectite of the glaucony facies at 330 m. As these grains are composed of a mixture of predominant authigenic clay, detrital clay, and some altered products, their major element composition differs from those of the green grains (reported elsewhere) that contain pure authigenic clay. The low REE contents and flat shale-normalized REE patterns suggest that the REEs were inherited from the substrate.
We suggest that the size of the verdine deposit is related to the influx of iron rather than the amount of fluvial discharge. The color and morphology of the grains do not reflect the authigenic mineral or its evolution. Green grains 011 this margin formed at different times when the sea level was at different depths during the Late Quaternary. The distribution of verdine and glaucony facies on the southwestern margin of India is different from those of the distribution along the east coast of India, Senegal, and French Guiana margins, suggesting different paleogeography and subsidence history of the western Indian margin during the Late Quaternary.
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Marine Authigenesis: From Global to Microbial
This volume is a collection of 33 state-of-the-art papers focusing on various aspects of authigenic and diagenetic marine minerals and related global elemental cycling. The commingling of the various studies of authigenic minerals in this volume, including the most recent advances in knowledge concerning the occurrence and origins of phosphorites, glauconites, dolomites, siderites, manganese-iron associations, barites, ironstones, and other marine chemical sediments/sedimentary rocks of early authigenic/diagenetic origin, is partly the result of the increasing awareness that there are many overlaps, even direct co-associations, between different authigenic minerals, both in time, space, and genesis. Taken together, this compilation represents a holistic approach towards marine authigenesis that considers the integrated whole more than the simple sum of its parts.