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Ghosh, Swapan K.
- Significance and Genesis of Early Diagenetic Glauconite-Pyrite Assemblage in the Quilon Limestone, Kerala
Authors
1 Centre for Earth Science Studies, Trivandrum, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 24, No 6 (1983), Pagination: 303-310Abstract
Pyrite and glauconite are the only lauthigenic iron minerals present in Quilon Limestone. Pyrite occurs as fossil infiIlings and as disseminated grains having shapes like cubes and framboids. Four morphologically distinct types of glauconite have been identified, viz., capsulated pellets, globular pellets, microfossil casts and moulds. Glauconite occurs as fine sand sized aggregate of clay particles. The colour varies between different shades of green to greyish green.
The XRD pattern of glauconite pellets shows the presence of a mixed layer clay mineral assemblage of chlorite and montrnorillonite. The pyrite-, glauconite- and micrite-fabrics of the limestone show evidence of their formation in early diagenetic stages. Pyrite has formed in a neutral to alkaline pH condition in a localised reducing condition; glauconite also formed in a similar environment. However, overall environment was oxidising in a shallow and quiet inner shelf area.
- Opaline Silica in Tertiary Sediments of Kerala
Authors
1 Centre for Earth Science Studies, Trivandrum 695 010, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 24, No 12 (1983), Pagination: 655-659Abstract
Smooth and well rounded grains of opal are recorded in the Tertiary sediments exposed in Trivandrum and Quilon districts and from deeper levels in the subsurface sediments near Ambalapuzha, in Alleppey district of Kerala. The clear to translucent opal grains vary in size from 0.05mm to about 3mm. Opaline casts of fossil tests with characteristic shapes and organic structures on their surfaces suggest organic activity in selective precipitation of opal inside fossil tests. Silica infillings in partly broken shells of gastropods were also observed. Difference of pH level in porewaters and inside the fossil tests favoured by organic decay in them is considered to be the main controlling factor for their formation.- Geology and Geochemistry of Tertiary Clay Deposits in South Kerala
Authors
1 Centre for Earth Science Studies, Trivandrum 695 010, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 27, No 4 (1986), Pagination: 338-351Abstract
The sedimentary clay deposits in south Kerala are the source of excellent quality kaolinite, formed due to weathering of arkosic sediments of Tertiary and crystalline Precambrian rocks. It has been possible to differentiate two such kaolinite beds in south Kerala based on mineralogy, chemistry and field relationship. At places, the two kaolinite beds are separated by sandstone-clay intercalations. The upper clay bed contains higher amount of impurities of quartz, goethite, hematite and gibbsite. The concentration of these impurities decrease at depth and vary horizontally having no consistent pattern. Study of sedimentary structures within the kaolinite beds, presence of kaolinite pseudomorph of feldspar still maintaining crystal faces, and lignite bed, support the hypothesis that the beds were deposited after a short and rapid transportation in a fluctuating flow regime. The lower elay bed, underlying the sandstone, is impoverished in both quartz and iron minerals. The source material for this clay deposit is the pre-Miocene weathered regolith extensively developed on Precambrian chalnockite- khondalite suites of rocks. After burial, ferric iron oxide from these beds was leached away in a reducing environment. The variation of mineral content and its chemistry in the kaolinite beds, have been related to spatial difference in micro-environment in the stratigraphic horizons in the geologic past and at present.- Trace Metals in Ferromanganese Nodules and Host Sediments of the Indian Ocean
Authors
1 Centre for Earth Science Studies, Trivandrum 695 010, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 32, No 1 (1988), Pagination: 40-47Abstract
Ferromanganese nodules and host sediments collected from Indian ocean were successively treated with distilled water, acetic-acid buffer, acidic solution of H2O2, Oxalic acid buffer and citrate-bicarbonate-dithionile solutions, to relate the partitioning of trace elements, and their chemical association with iron and manganese oxide phases.
Based on the selective dissolution analysis of samples, it is suggested that host sediments contain higher abundance of crystalline oxides of iron and manganese than that in ferromanganese nodules. It was, however, observed that most of trace metals in sediments are concentrated in non-crystalline ferric hydroxide, although its concentration is less than crystalline ferric oxide. Nodules contained much higher abundance of trace metals, both in their crystalline and in non-crystalline phases.
In addition to the crystalline and non-crystalline iron and manganese oxides, a significant amount of trace metals occurs as substitutions of Ca and Mg in carbonates, and also as absorbed ions and as loosely bonded ions. Presence of carbonates and status of crystallinity of oxides of iron and manganese are identifiable by selective-dissolution analysis as proposed in this work.