Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

M. Thamban ¹, K. Reghunadh ¹, K. Sajan ¹

Affiliations
1 Marine Geology Division, School of Marine Sciences, Cochin University of Science and Technology, Cochin - 682 016, IN

Abstract

The surficial mangrove sediments in the estuarine course of Eranholi river were sampled at 21 locations and analysed for the determination of organic matter, iron and manganese in 2 mm size fraction of the sediments. The study indicated that the these constituents are apparently controlled by the spatial variation of the physico - chemical factors of the estuary such as pH and Eh, base exchange and adsorption characteristics and the texture of the sediments, tidal influence and proximity to the mangrove vegetation in the prevailing estuarine environment.

Keywords

Geochemistry, Marine Sediments, Mangrove Environment, Tellicherry, Kerala.

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V. Purnachandra Rao ¹, M. Thamban ¹

Affiliations
1 National Institute of Oceanography, Dona Paula - 403 004, Goa, IN

Abstract

The calcareous deposits on the western continental shelf of India, off Bhatkal (water depths 50 to 58 m) occur as crusts, sheets, cylinders and reddish brown mudstones. The outer layers of the crusts are micrite-dominated and beneath this layer detrital/carbonate sands with thin heavy mineral laminations are found. Textural studies indicate that the detrital sands are derived from dunes. Drusy calcite and neomorphic calcite cements are associated with the sands. Sheet deposits contain coarse calcareous component-dominated layer within micrite layers and abundant micrite cements. These are similar to dune associated calcretes.

Cylinders are rhizoliths and show different stages of ischolar_main calcification. Circular bodies. about 0.15 mm to 0.70 mm diameter, interpreted as vascular cylinders of the ischolar_main tissues are typical. Radial fibrous calcite and spar calcite with inclusions indicate neomorphic cements. Reddish brown mudstones contain calcified ischolar_main-hair sheaths, micrite glaebules and reworked pollen suggesting that these are indurated soils. X-ray diffraction studies indicate the presence of ferroan calcite, quartz, pyrite and dolomite in rhizoliths and ferroan calcite, goethite and quartz in mudstones. Mudstones and some rhizoliths are Fe-rich and some other rhizoliths are Fe-poor but enriched with Mg and Mn. The particulate matter in the calcareous deposits were initially at the proximity of the coast and cemented by metastable calcites during the ultimate Pleistocene interglacial sea-level stands on the shelf. Pedogenic cementation processes overprinted and developed them into eolianites and paleosols during the subsequent Late Pleistocene sea-level regression. The compositional differences of these deposits were apparently controlled by type of sediments and associated sedimentary environments.

Keywords

Sedimentology, Calcretes, Rhizoliths, Paleosols, Continental Shelf.

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S. Diju ¹, M. Thamban ²

Affiliations
1 Department of Geology, Government College Kasaragod, Vidyanagar, Kasaragod - 671 123, IN
2 National Centre for Antarctic and Ocean Research, Department of Ocean Development, Headland Sada, Vasco da Gama 403 804, Goa, IN

Abstract

X-Ray diffraction and textural studies were carried out on 25 surficial sediments collected from Chandragiri River, estuary and shallow marine areas off the river located in Kasaragod district, Kerala for understanding the provenance of the clay minerals. The riverine sediments are dominated by sandy silt to silty sand, whereas the estuarine sediments consist of clayey silt to silty sand and the shallow marine sediments are dominated by clayey silt. Kaolinite and gibbsite dominate the sediments with minor amounts of illite and smectite with the complete absence of chlorite in all depositional environments, supporting the intense chemical weathering occurring in the study area. Illite is relatively higher in the shallow marine sediments compared to the estuarine and riverine sediments, suggesting the influence of morphological characteristics of clay minerals and hydrodynamic conditions in their lateral distribution. Smectite is subtly and systematically higher in shallow marine environment, which is attributed to the fine size nature of this mineral. Although various processes may redistribute clay minerals within the aquatic systems, it is possible to identify the source rocks and weathering characteristics from the detrital clay mineral studies. The major source rocks contributing towards the clay mineral distribution in the study area are the Precambrian crystalline rocks, laterites and the Tertiary sedimentary formations exposed along the coastal belt.

Keywords

Clay mineralogy, Texture, Estuarine sediment, Provenance, Chandragiri River, Kasaragod, Kerala.

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