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

K. S. N. Reddy ¹, T. Lakshmi Prasad ¹, N. Babu Rao ¹

Affiliations
1 Department of Geology, Andhra University, Visakhapatnam - 530 003, IN

Abstract

Along and across the east coast of India between Yarada and Gangavaram, sediment samples were collected from different microenvironments of the beach representing lower foreshore, middle foreshore, upper foreshore, berm, backshore and dune, at four stations(Yarada, Dibbavanipalem, Valametta and Gangavaram) in different monsoon seasons (NE and SW) for the period of two years (1997 to 1999). All the nucroenvironments except at Dibbavanipalem have not shown cyclic deposition and erosion with monsoons Out of Four-Size ranges +60 (+0 25 mm), +120 (-0 25 to +0 125 mm), +170 (-0 125 to +0 088 mm) and +230 (-0 088 to +0 063 mm), the -0 125 to +0 088 mm and -0 088 to +0 063 mm size range shows rich concentration of heavy minerals The heavy mineral content in the bulk sediment samples ranges from 0 53 - 48 56% in December, 1997 and 0 83 - 53 22% in December, 1998 Opaques, sillimamte, garnets, pyroxenes, amphiboles, zircons, monazite, rutile, biotite, tourmaline and apatite from the beach sands of Yarada-Gangavaram are reported Opaques are concentrated in fine fraction while garnets are concentrated in coarse fraction Scatter plots of heavy mineral assemblages and erosion/accretion indicates as the rate of erosion increases, heavy mineral concentration slightly increases in dune, backshore and foreshore Sub-Environments and the concentration of heavy minerals decreases with increase of erosion in berm sub-environment. The concentration of heavy minerals in nucroenvironments is not only related to erosion/accretion but also related to their densities Khondalite, chamokite and leptynite of the Eastern Ghats appear to be the major source for the above heavy mineral assemblages.

Keywords

Marine Geology, Beach Profile, Heavy Mmerals, Yarada-Gangavaram Bay, Visakhapatnam, Andhra Pradesh.

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D. Rajasekhara Reddy ¹, V. S. S. Prasad ¹, V. Malathi ¹, K. S. N. Reddy ¹, D. D. Varma ¹

Affiliations
1 Department of Geology, Andhra University, Visakhapatnam - 530 003, IN

Abstract

The economic potentiality of the heavy minerals in the beaches between Baruva and Bavanapadu extending for about 45 km was examined. In the sub-surface sediments, the heavy minerals were studied at an interval of 1 m up to a maximum depth of 5.8m. In general the concentration of heavy minerals is high in dunes followed by backshore and foreshore regions. Heavy mineral content increases from surface to sub-surface in dunes, decreases in foreshore and does not vary much in backshore. The heavy minerals include mainly ilmenite, garnet, sillimanite and ortho-pyroxenes with minor amounts of amphiboles, zircon, monazite, rutile etc. Majority of the heavies such as ilmenite, monazite, zircon etc. are concentrated in finer fractions while some of the heavies like garnet and sillimanite are concentrated in coarser fractions. The inferred reserves estimated for the area indicate its economical potential.

Keywords

Heavy Minerals, Dunes, Backshore, Foreshore, Economic Potential.

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C. V. Raman ¹, K. S. N. Reddy ¹

Affiliations
1 Department of Geology, Andhra University, Visakhapatnam - 530 003, IN

Abstract

Textural distribution patterns of seafloor sediments from the Mahanadi-Nagavali shelf, northwest Bay of Bengal, are used to evolve a model for the regional sediment-dispersal system. Mean size trends, standard deviation, skewness and correlation of negative skewness with silt/Clay ratios reveal certain patterns, each being specific to an area(s) of shelf. Sediment distribution patterns show that the near shore environment is occupied by sand and clayey sand, while the inner and middle shelf regions are covered by sandy silt, silty calcareous sand, silty clay, silty sand and sand-Silt-Clay. The outer shelf is largely covered by clayey silt. Relict carbonate deposits are preserved on the outer shelf at ∼100 m off Rushikulya to Baruva. Palimpsest sediments cover the Sonapurapeta-Bavanapadu shelf at depths of 0-60 m.

Mud dispersal in the study area offshore is caused by transport components along and across the shelf. The Mahanadi-Devi River system is the principal source of sediment for the Mahanadi-Nagavali shelf. The Nagavali and Vamsadhara rivers are a minor source of sediment towards the southern part of the shelf, and their detrital inputs are largely deposited on the shelf adjacent to the river mouths. Sediments in the study area are transported and advected southward (bottom nepheloid layers ?). The Mahanadi-Nagavali shelf response to the present hydraulic regime is recorded in the modern sand facies and the offshore mud facies, particularly the silty clays.

Keywords

Continental Shelf, Sediment Dispersal, Grain Size, Relict Sands, Bay of Bengal, India.

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K. S. N. Reddy ¹, D. Deva Varma ¹, E. N. Dhanamjaya Rao ¹, B. Veeranarayana ¹, T. Lakshmi Prasad ²

Affiliations
1 Department of Geology, Andhra University, Visakhapatnam - 530 003, IN
2 Department of Earth Sciences, Yogi Vemana University, Kadapa - 516 001, IN

Abstract

Heavy mineral analysis was carried out for the beach and fore dune sediments along 60 transects of Nizampatnam-Lankavanidibba coastal area. The heavy mineral assemblage in this area with decreasing abundance of opaques (Ilmenite + magnetite, 47.67%), pyriboles (20.35%), garnets (3.66%), epidote (3.23%) and with less than 3.0% concentration of sillimanite, zircon, staurolite, kyanite, apatite, spinel, monazite, biotite, topaz, leucoxene and chlorite. The heavy mineral concentrations are high in the finer fractions i.e., +120 and +230 (ASTM) than the coarse fraction (+60) of sand. In the seven sectors, heavy mineral assemblage is same but their concentrations are different. The sectors nearer to the river mouth contain high concentration of high specific gravity heavy minerals (ilmenite and magnetite) than sectors away from the river mouth. The redistribution of heavy minerals is controlled by creek dynamics, longshore currents, size and specific gravity of the heavy minerals.

Keywords

Heavy Minerals, Coastal Sands, Longshore Currents, Tidal Channels.

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