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

P. S. N. Murty ¹

Affiliations
1 N.M.D.C. Limited, Meghahatuburu Project, IN

Abstract

Three drainage sub-basins in Chikmagalur dristict of Karnataka State have been selected for quantitative study of groundwater recharge. Computations show that out of the total quantity of water received by the three drainage sub-basins from rainfall, 8-13% is contributed to groundwater recharge.

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A. L. Paropkari ¹, Ch. M. Rao ¹, P. S. N. Murty ¹

Affiliations
1 National Institute of Oceanography, Dona Paula 403004, Goa, IN

Abstract

Total phosphate in the sediments ranges from 0.15 to 0.29% in the bulk samples and from 0.09 to 0.23% in the acid soluble fractions of the samples. There was no appreciable variation in the phosphate within the Gulf and no significant relation was observed between phosphate content and texture of the sediments. Invariably higher concentrations of phosphate were associated with the acid soluble fractions as compared to the acid insoluble fractions. The contributions made by the acid insoluble fractions to the phosphate concentration in the bulk samples was probably through the detrital minerals with which it might be associated, while the contributions made by the acid soluble fraction was probably in the form of adsorbed phosphate than in association with the carbonate phase.

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P. S. N. Murty

Abstract

No Abstract.

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Ch M. Rao ¹, A. L. Paropkari ¹, A. Mascarenhas ¹, P. S. N. Murty ¹

Affiliations
1 National Institute of Oceanography, Dona Paula, Goa 40300, IN

Abstract

Phosphate content in the bulk sediments range from 0.02 to 2.17% and on carbonate free basis it varies from 0.03 to 6.57%. The partition studies indicate that contribution from the acid resistant detrital minerals (HCl insolubles) is negligible. In the inner shelf, the phosphorus is mainly associated with iron (as ferric-phosphate?) and organic carbon. In the outer shelf/slope its association with carbonate suggests its authigenic/diagenetic origin. This is also supported by X-ray diffraction studies wherein the apatite peak is revealed in some samples. In general, sympathetic relationship of phosphorus with organic carbon in the study region indicates genetic relationship between these two elements, which is an important condition for phosphatogenesis. Further, these studies suggest that the outershelf/slope region between Bombay and Quilon is the promising area for detailed exploration for phosphorite deposits.

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CH. M. Rao ¹, P. S. N. Murty ¹

Affiliations
1 National Institute of Oceanography, Dona Paula 403004, IN

Abstract

The modern sediments accumulating on the western continental margin of India between 17° and 13° latitude are composed predominantly of terrigenous material in the inner shelf with moderate organic carbon content (< 3%), carbonate sediments in the outer shelf with low organic carbon content (< 1%) and organic carbon rich (upto 12%) carbonate sediments in the slope region. The bulk and partition geochemistry of the surface sediments reflect the complex intermixture of several sedimentary components (lithogenic, authigenic and biogenic) and enable the identification of geochemical processes that are responsible for the incorporation of elements into the sediments. The elemental concentrations are found to be related to the distribution of three major components i.e, terrigenous debris (Si, Al,Ti, Fe, Mn, Cu), authigenic Calcium Carbonate (Sr, P) and organic carbon (P, Ni, Zn).

Keywords

Geochemistry, Marine Geology, West Coast of India, Continental Margin Sediments.

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P. S. N. Murty ¹, G. P. Mohapatra ¹, D. R. S. Reddy ¹, M. Hariprasad ¹

Affiliations
1 Geological Survey of India, Marine Wing, East Coast Division-II, Visakhapatnam-530 023, IN

Abstract

The bathymetry contours show that the morphological features of shelf and slope off Visakhapatnam coast are mainly due to erosion and local deposition, while those of Godavari delta are due to high rate of deposition. Features such as terraces, pinnacles and ridges on the continental shelf at different depths are inferred to be vestiges of palaeostrand lines caused by sea level changes during the Pleistocene/Holocene period. The mass wasting near the shelf break off Godavari River could have led to the levelling up of the rise area with the slope giving rise to a smooth and cancave surface. The dissected topography of the northeastern part of the continental slope is inferred to be the effect of erosion and mass movement due to turbidity currents. The abyssal plain is influenced both by the peninsular rivers draining into the area as also by the Bengal Fan. The bathymetric surveys in abyssal plain delineated the boundary between western sedimentary basin influenced by peninsular river sediment and the eastern sedimentary basin having Bengal Fan sediment. The channels and valleys observed on the eastern side of this boundary are the continuation of Bengal Fan channels.

Keywords

Bathymetry, Morphological Features, Bengal Fan Channels.

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P. S. N. Murty ¹

Affiliations
1 Geological Survey of India, Marine Wing, East Coast Projects - II, 41, Kirlampudi Layout, Visakhapatnam - 530023, IN

Abstract

The distribution of calcium carbonate in Visakhapatnam shelf sediments is controlled by the mollusca shells and shell fragments and foraminifera. The high concentrations near the river mouths are indicative of the detrital contribution also. The concentrations decrease from top to sub-bottom levels due to more dilution by the detritus from the adjoining area and less deposition of non-detrital calcium carbonate in the geological past.

Keywords

Visakhapatnam Shelf, Calcium Carbonate, East Coast.

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P. S. N. Murty ¹, M. Rama Murty ¹, G. P. Mohapatra ¹

Affiliations
1 Geological Survey of India, Marine Wing, Op East Coast-II, Marripalem, Visakhapatnam - 530 018, IN

Abstract

Lime mud occurs within 100-225 in isobath in the outer shelf along the East Coast of India, Bay of Bengal off Kakinada-Bheemunipatnam coast. A thin capping of Non-Carbonate clay/mud varying from 10-200 cm overlies the lime mud. The capping is thicker in the peripheral zone Lime mud is greyish white to creamy white resembling plaster of Pans and comprises minor ooids, pelloids, mud aggregates, foraminiferal tests and few terrigenous detrials. The maximum thickness of lime mud probed is 2 89 m.

Texturally, lime mud is sandy silt within top one meter subsurface level followed by silt up to 2 83 m subsurface depth. Chemical data show a maximum concentration of CaO -52 08% (CaCO₃ - 92 95%), Sr 0 66% and Li- 500 ppm. The XRD data show that the major constituent mineral is aragonite (85-90%) followed by Mg - calcite/calcite together with or without halite. The aragonite crystals are typically stubby and bladed with irregular outline and pointed terminations under SEM Textural, mineralogical and chemical parameters and coarse fraction studies suggest that lime mud might have been formed in shallow water environment as chemical precipitate during late Pleistocene/early Holocene and subsequently transported to deeper parts of the shelf.

Keywords

Lime Mud, Calcium Carbonate, Outer Shelf, Aragonite, Strontium, Chemical Precipitate, Visakhapatnam Coast, Andhra Pradesh.

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