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A. C. Narayana ¹, K. Pandarinath ¹, A. R. Karbasi ¹, B. R. Raghavan ¹

Affiliations
1 Department of Marine Geology, Manga]ore University, Mangalagangotri, Karnataka 574 199, IN

Abstract

Moderately well-sorted silica sands of aeolian origin occur at various locations along the South Kanara coast. They contain a very low percentage of heavy minerals. The silica content is comparatively more in the medium-size fraction than in the finer fraction. Higher concentrations of AI, Fe, and Ti are associated with finer fractions. The average silica content (96.6%) shows that these white sands are of high grade quality. The very low magnetic susceptibility values are indicative of low Fe content.

Keywords

Silica Sand, South Kanara, Karnataka, Sedimentology.

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A. C. Narayana ¹, K. Pandarinath ¹

Affiliations
1 Department of Marine Geology, Mangalore University, Mangalagangotri 574 199, Karnataka, IN

Abstract

Grain-size statistics are employed in sediment transport studies. The alongshore transport of sediment in shallow regions (30-50m depth) and deeper regions (>l50m depth) is in north and south directions, whereas in the depth range of 50-75m, the sediment transport direction is towards the south. The onshore-offshore sediment transport study reveals that the sediment transport direction is towards onshore where fluvial influence is absent and the direction is towards both onshore and offshore where the fluvial influence is prevalent. The studies further reveal the different energy regimes of transportation.

Keywords

Sedimentology, Grain-Size Statistics, West Coast, Mangalore, Continental Shelf, Karnataka.

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K. Pandarinath ¹, Sushma Prasad ¹, S. K. Gupta ¹

Affiliations
1 Physical Research Laboratory, P. O. Box No. 4218; Navrangpura, Ahmedabad - 380 009, IN

Abstract

The crystallinity of the clay mineral illite, which is a climatically sensitive parameter, was studied for palaeoclimatic inferences from a core raised from Nal Sarovar in western India. The changes in crystallinity of illite in the top 3m of the core showed that the climate was wetter than present from ∼6.3-4.6 ka BP and was followed by a relatively dry phase which has continued up to the present. These palaeoclimatic observations are largely similar to those obtained from δ¹³C and C/N ratio variations in the top 3m of the core. From the deeper (>3m) section, a wet spell around 50 ka BP was identified in an otherwise continuous spell of aridity between 7 and 73 ka BP. The presence of a red bed dated to -50 ka BP (depth 1285-1324 cm) also suggested that the climate was wet followed by dry conditions during this period.

This interpretation of palaeoclimatic changes deciphered from the Nal Sarovar core differs in some detail from the Rajasthan palaeoclimatic record and that available from south India.

Keywords

Palaeoclimate, Crystallinity Index, Clay Minerals, Late Quaternary, Rajasthan.

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R. Shankar ¹, K. Pandarinath ²

Affiliations
1 Department of Marine Geology, Mangalore University, Mangalagangotri-574199, IN
2 Ocean Science and Technology Cell, Mangalore University, Mangalagangotri-574199, IN

Abstract

We studied three sediment cores from the southwestern continental margin of India for their mineral magnetic properties like magnetic susceptibility (χ_If), susceptibility of anhysteretic remanent magnetisation (χ_ARM), isothermal remanent magnetisation (IRM), saturation isothermal remanent magnetisation (SIRM) and inter-parametric ratios (χ_ARM/χ_If and χARM/SIRM), besides particle size characteristics. We demonstrate here that magnetic susceptibility and other mineral magnetic parameters can be used to demarcate the Early Holocene intense monsoon conditions. High values of χ_If, χ_ARM IRM_20mT,SIRM and χ_ARM/χIf and χ_ARM/SIRM in the core-bottom indicate the peak wet period -11 to 9 ka B P. The values decrease rapidly at 8 38 ka B P, in concert with a reduction in rainfall. Our interpretation is strengthened by particle size data on a limited number of samples. Silt and sand contents are higher in the pre-8.38 ka B P, high-susceptibility samples than in the post-8.38 ka B P, low-susceptibility samples. The high values of concentration-dependent parameters and χ_ARM/χ_If in the core-tops are probably due to an increase in rainfall during the past 100-400 years. We also used the mineral magnetic parameters to correlate the sedimenct cores.

Keywords

Rock Magnetism, Magnetic Susceptibility, Palaeomonsoon, Palaeoclimate, Holocene, Western Continental Margin of India.

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K. Pandarinath ¹, K. R. Subrahmanya ², M. G. Yadava ³, Surendra P. Verma ¹

Affiliations
1 Centro de Investigacion en Energia, UNAM, Priv. Xochicalco s/no., Col Centro, Apartado Postal 34, Temixco, Mor. 62580, MX
2 0cean Science and Technology Cell, Mangalore University, Mangalagangotri 574199, IN
3 Earth Science Division, Physical Research Laboratory, Navrangpura, Ahmedabad 380 009, IN

Abstract

Organic matter in sediment layers of two sediment cores from the continental slope off southwest coast of India was dated by radiocarbon method and sedimentation rates were estimated. The age data show lateral and temporal variations in sediment accumulation rates. Sedimentation rates decrease gradually from the inner shelf to the deep-sea in the study area, with an exception at 332 m water depth. The sediment accumulation rates on the shallower continental slope (332 m water depth; 0.003-0.013 mm/yr) are lower than on the deeper slope (776 m water depth; 0.071-0.190 mm/ yr) during the entire period of core deposition (32.8 ka BP to present). The unusually lower sedimentation rates on the shallower slope region may be the result of prevailing adverse depositional conditions. The sedimentation rates were lower during 32.80-18.98 ka BP and 16.04-8.69 ka BP and higher during 18.98- 16.04 ka BP and 8.69 ka BP to present day. The temporal variations in sedimentation rates reflect the changes in detrital input to the sea as a result of variations in intensity of paleomonsoonal conditions.

Keywords

Sedimentation record, Paleomonsoon, Continental slope, Southwest coast.

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K. Pandarinath ¹, A. C. Narayana ²

Affiliations
1 Oceanography & Climate Studies Group, Physical Research Laboratory, Navrangpura, Ahmedabad- 380009, IN
2 Department of Marine Geology and Geophysics, Cochin University of Science & Technology, Fine Arts Avenue, Cochin - 682016

Abstract

The innershelf sediments of Coondapur were studied for Cu, Pb, Zn, Ni, Co, V, Mn, Cr, Fe, Ti, Al, Ca, organic matter composition and magnetic susceptibility to understand their distribution, enrichment and element burial phases in the sediments. Along most of the transects, the sediments of 30m depth have shown more concentrations of Cu, Zn, Ni, Co, Mn, Fe, Ca and organic matter than those of 20 and 10m depth. The comparisons with sediments of uncontaminated natural formations, innershelf sediments of other unpolluted regions and world averages in different geological formations shows that the study area is unpolluted and the data can be used as a base line for future pollution studies. The sequential leaching of elements shows that they are mainly (∼60-80% of the total content) associated in detrital clay and heavy minerals followed by (∼20-30% of the total) in sulphide phase. The concentrations of all the element (except Mn) in other phases (exchangeable ions, loosely sorbed ions, carbonate constituents and interstitial water) were negligible. Nearly 40% of the total Mn is present in the leachates of EDT A and acetic acid soluble fractions. Mn concentration is almost negligible (6-11 % of the total) in acetic acid-hydroxylamine hydrochloride leachate (oxide phase) and its concentration is considerable (10-30% of the total) in H₂O₂-ammonium acetate leachate (sulphide phase). These observations suggest that reducing conditions may be prevailing in the innershelf off Coondapur.

Keywords

Geochemistry, Pollution, Environment, West Coast of India, Karnataka.

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