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

P. Divakar Naidu ¹, P. S. Rao ¹, J. N. Pattan ¹

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

Abstract

An investigation on planktonic foraminifera and calcium carbonate content of a box core collected at a depth of 2556 m from the southern part of the Arabian sea indicates faunal changes depicting Quaternary climatic fluctuations. Based on the study the Last Glacial Maxima (LGM) boundary is placed at 65 cm and below LGM. Three warm and two cold episodes are identified.

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J. N. Pattan ¹, G. Parthiban ¹

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

Abstract

Five buried ferromanganese nodules were recovered at different depths of 167-169 cm (A), 172- 174 cm (B), 228-230 cm (C), 328-330 cm (D) and 418-420 cm (E) in a 5 m sediment core from the siticeous sediment of Central Indian Basin (Lat 9°00' S , Long 76°00' E) at a water depth of 5260 m. These nodules were analysed for major, trace and rare earth element(REE) concentrations to understand their genesis and compare with the surface and burled nodules in the top 1 in of the sediment column from the same basin. Nodules A, B, C are of an early diagenetic(Mn/Fe ratio between 9 3 and 15 I), nodule D IS of hydrogenetic(Mn/Fe ratio 1 6) and nodule E is of diagenetic(Mn/Fe ratio 3 0) origin. Total REE concentration ranges between 164 and 497 ppm (av-348 ppm) and is nearly 2 to 3 fold lower than the surface and burled nodules REE are conveyed from the seawater to the nodules In association with a combined phase consistnig of Fe - Ti - P. The shale (NASC) - Normalized REE pattern displays a small convex pattern with a positive Ce-anomaly indicating an oxidized environment while, the presence of positive E u-anomaly in nodules A, B and C probably suggest an aeolian dust. These burled nodules show a moderate middle and heavy REE enrichment (strong in nodules B and C) compared to light REE, but fractionation between middle and heavy REE is not very clear It appears that not much significant Post -Depositional changes have occurred in these buried nodules.

Keywords

Buned Fe-Mn Nodules, Chemical Composlition, Genesis, REE Patterns, Central Indian Ocean Basin.

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J. N. Pattan ¹, G. Pratibhan ², C. Prakesh Babu ², N. H. Khadge ¹, A. L. Paropkari ², V. N. Kodagali ¹

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

Abstract

A closely spaced 75 surface sediments drawn from "Gas Hydrate" Project taken up by National Institute of Oceanography on a regional scale from the Krishna- Godavari Basin (Latitude 15°35' to 16°20' N; Longitude 81° 40' to 82°30E) are analysed for texture, major, and some trace and rare earth elements to understand their source and provenance. Water depth in the study area varies between 300 to 2000 m and there is a WNW-ESE trending sedimentary ridge in the southwestern part of basin. Sediments are mosdy silty clay in nature. Ti - bearing minerals such as titanite and pyrophanite are evident by the strong positive correlation between Ti and Ca (r = 0.89) and Ti and Mn (r =0.67) respectively. An independent behaviour of Zr suggests occurrence of zircon mineral. The strong positive correlation among Al, Fe, Mg and K (r = 0.68 to 0.90) suggests their association with clay. The average total REE (Σ2REE 176±13 ppm) abundance is similar to that of average shale with a flat shale- normalized REE pattern suggest a terrigenous source. High concentration of Fe (6.45±0.43% ), Ti (0.82+0.07%), V (192±23 ppm), Cr (128±13 ppm) and Zr (159±19 ppm) and presence of smectite as a major clay mineral suggest that Peninsular Godavari River has sediment influx from source rocks of Eastern India mainly Deccan Trap, Precambrian and Dharwar formation. Further, it confirms that the role of Ganges-Brahmaputra River sediments to the basin appears to be small compared to the Peninsular rivers.

Keywords

Surface sediments, Geochemistry, Silty clay, Smectite, Titanite, Pyrophanite, Zircon, Bathymetry, Krishna-Godavari Basin, East Coast of India.

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J. N. Pattan ¹

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

Abstract

An ash layer occurs between 10-35 cm depth in sediment cores from the Central Indian Ocean basin. Morphology, major, trace and rare earth element composition of glass shards from the ash layer suggest that the Youngest Toba Tuff of ∼74 ka from Northern Sumatra may be its source. To understand the implication of ash on the elemental distribution, a sediment core (NR-54) where abundant Youngest Toba glass shards occur at 30-35 cm depth interval, was studied. The presence of ash layer resulted in the enrichment of coarse fraction (260%), Al_excess (104%), K (43%) and Al/AI+Fe+Mn (28%), and depletion of Mg (58%), Fe (55Oh) , Mn (50%) , Ti (44%) and biogenic opal (37%). compared to their average concentrations in the core. Therefore, precaution should be taken while studying the parameters indicative of productivity (biogenic opal, coarse fraction and Al_excess), detrital terrigenous influx (AI/AI+Fe+Mn,T i, K and Mg) and redox sensitive metal (Mn), whose concentration is affected by the presence of glass shards from the ash layer in the sediment cores from Bay of Bengal, Central Indian Ocean basin, South China Sea basin arid Western continental margin of India where the widespread Youngest Toba ash is reported.

Keywords

Ash Layer, Glass Shards, Youngest Toba Tuff, Terrigenous Influx, Indian Ocean.

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