Syed Masood Ahmad

Clay minerals and Sr-Nd isotopes of the sediments along the Western margin of India and their implication for sediment provenance

Mineralogy and Sr–Nd isotopic composition of the <2-μm fraction of the Holocene and late Pleistocene sediments from 12 gravity cores collected along the western margin of India were used to delineate the provenance and understand the response of isotopes with respect to the source rock composition. Holocene sediments show distinct clay mineral associations representing three major sources: illite, chlorite-rich sediments from the Indus, smectite-dominated sediments from the Deccan Traps, and kaolinite and smectite-enriched sediments from gneissic rocks. The mixing of Indus-derived sediment with the Deccan Traps-derived sediment or the Deccan Traps-derived sediment with gneissic rock-derived sediment occurs in the deeper water cores. Sr isotopes are very sensitive to weathering and laterization. Weathering does not influence Nd isotopes. The 87Sr/86Sr ratios of the Holocene sediments in shallow water cores are higher and fluctuated widely than those in deeper water cores. ϵNd correlates well with the clay mineral associations, indicating source rock composition or mixing of source sediments. Kaolinite-enriched sediments coupled with high Sr ratios and low ϵNd on the SW margin of India suggest intense chemical weathering in the hinterland. The influence of the sediment from the Ganges–Brahmaputra, transported by the Bay of Bengal waters during the NE monsoon surface current or SW monsoon underwater current, on the composition of the sediments of the SW Indian margin is insignificant. The late Pleistocene sediments reflect a decrease of hydrolytic processes resulting in decrease of smectite and Sr isotopic ratio. Clay minerals and ϵNd values suggest that the provenance and transport pathways of the late Pleistocene sediments are the same as those of the Holocene for each region.

Glacial to Holoceneδ13C variations in intermediate depth water masses of North Indian Ocean

Theδ18O andδ13C compositions of glacial- to Holocene-aged benthic foraminifera in a core collected from the eastern Arabian sea (water depth 1230 m) were determined to investigate glacial—interglacial variations in the intermediate depth water chemistry of the North Indian Ocean. In addition, we determined theδ13C composition of Holocene benthic foraminifera from seven cores for which theδ18O andδ13C of benthic foraminifera from last glacial maximum (LGM) were reported by Kallel et al. (1988). Theδ13CDIC in the intermediate waters was generally depleted by 0.3–0.4‰ during the last glacial maximum compared to Holocene.

Geochemistry of ferromanganese nodules from the Central Indian Basin

Abstract The major and minor elements and mineralogical composition of a suite of abyssal ferromanganese nodules from the southwestern and south-central portion of the Central Indian Basin suggest two accretionary processes for the formation of these nodules: (a) hydrogenous precipitation of colloidal metal oxides from seawater; and (b) oxic diagenesis, which involves reactions in oxidised sediments. Samples from the south-central part of the basin have high Mn Fe ratios with todorokite as principal Mn phase. These nodules also contain relatively high concentration of elements associated with manganese. Nodules from the southwestern part have less todorokite, low Mn Fe ratios and higher concentrations of minor elements associated with iron. There is a significant correlation between Mn and Cu, Ni, Ba and Zn contents, while Ti, P, Pb, Co, Sr, Y and Zr concentrations are related with total Fe contents. An estimation of the growth rates from the chemical composition indicates that the nodules from the central region have relatively higher values (17.0–37.4 mm Ma−1) than nodules from the western part (4.2–14.7 mm Ma−1).

Stalagmite Inferred High Resolution Climatic Changes throughPleistocene-Holocene Transition in Northwest Indian Himalaya

Investigated for d18O and d13C isotopes, mineralogy and growth rate, a 20 cm long and 230Th-dated calcite stalagmite from Kalakot (Jammu and Kashmir Himalaya), has recorded high resolution precipitation variability during the Pleistocene-Holocene transition. At present, the study area is influenced by both the Indian Summer Monsoon (ISM) and Westerlies. The StalAge model indicates that the stalagmite grew between 16.3 ka to 9.5 ka BP under the ideal isotopic equilibrium conditions as revealed by the Hendy test results. The d18O and d13C values range from -5.41 to -8.82% and -7.09 to -10.84% respectively. Although the U/Th chronology is poor due to low Uranium content in the samples resulting in relatively large errors, the first stalagmite inferred precipitation variability reconstructed from NW Indian Himalaya makes this study significant. The near footprints of three global events, e.g., Older Dryas (OD), Allerod period and Younger Drays (YD) can be noticed at ~14.3-13.9, 13.9-12.7 and 12.7-12.2 ka BP. The precipitation strength was weaker during the OD and YD, but was stronger during the Allerod interstadial. By the termination of YD interval, the climate seems fluctuating in the NW Himalaya. There seems variation in commencement, duration and termination of the above mentioned events in different parts of the globe due to latitude location and response time.