Determination of rare earth, major and trace elements in authigenic fraction of Andaman Sea (Northeastern Indian Ocean) sediments by Inductively Coupled Plasma-Mass Spectrometry (original) (raw)
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Downcore variation of rare earth elements (REEs) in the authigenic Fe-Mn oxides of a sediment core (covering a record of last ∼ 40 kyr) from the Andaman Sea, a part of the Indian Ocean shows distinctive positive Ce and Eu anomalies. These positive Ce anomalies (Ce* = 1.1 ∼ 1.8) are ascribed to be due to oxidation of deep sea sediments. The large positive Eu anomalies (i.e., Eu* >1.8 to 3.2) occur within a time span near the glacial/interglacial transition (∼ 7000-14,000 yr BP) which could be due to the past hydrothermal activity or to the effects arising from sea level changes. During glacial times, the Andaman Sea was almost completely isolated due to low sea level, leading to a reduction in sediment supply from the Ayeyarwady River. The variations of metal abundances (i.e., Ca, Al, Mn, and Fe) in the authigenic fraction provided independent information to evaluate the water column physicochemical changes during the glacial/interglacial transition period. The studied sediment core records changes in riverine inputs and reflects depositional changes related to sea level fluctuations and climatic events over the past 40 kyr in the Andaman Sea.
Adopting sequential extraction procedures, Ba, Cu, Mn, Ni, V and Zn concentrations were determined in the moderately reducible, organically bound, carbonateassociated and adsorbable fractions within a sediment core collected from the Indian sector of the Southern Ocean. The elemental abundances were studied with reference to the Last Glacial Maximum (LGM), deglaciation and Holocene periods. The study showed, with the exception of Ba, elemental abundances in the following order: moderately reducible > organically bound > carbonate-associated > adsorbable fractions. Ba showed high affinity to organically bound and carbonate-associated fractions. Ba concentration revealed large variability (200-1400 ppm) within the carbonateassociated fraction and is related to the reduced carbonate productivity during LGM and increased carbonate productivity during deglaciation as well as Holocene intervals. The relative increase in the concentration of V, Mn and Ni in the reducible fraction suggests enhanced suboxic conditions during LGM. The decreased concentrations of V, Mn and Ni during the deglaciation and late Holocene indicate oxygenated conditions. The suboxic conditions during LGM could be attributed to reduced ventilation resulting from reduced strength of the global thermohaline circulation at this time interval.
Major and trace elements of sediments from a~13-m long piston core (SK187/PC33) from the western Bay of Bengal have been investigated in this study to infer about the changes in provenances and related controlling factors during the last glacial-interglacial period. Factor analysis of these geochemical dataset ascertains dominant role of riverine supply of sediments in regulating the geochemistry of SK187/PC33 sediments. The Al-normalized major (K and Ti) and trace elemental (Cu and Cr) ratios of these marine sediments fall within the ranges observed for their major provenances, viz. sediments from the Ganga, Brahmaputra and the Godavari-Krishna (GK) rivers and depth profiles of these ratios showed significant variations with synchronous excursion at around the last glacial maxima (LGM), implying a change in their provenances with relatively reduced Himalayan contribution during this climatic event. Inverse model calculation of Al-normalized elemental ratios of the sediments estimated an average sediment contribution of 66 ± 13% and 34 ± 13% from the Himalayan and the peninsular Indian rivers to the core site respectively. Consistent with the depth profiles of elemental ratios, the estimated sediment contributions from the Himalayan rivers are observed to decrease by~30% from the Himalayan rivers, particularly that of the Ganga, to the studied location during the LGM. Lowering of sediment supply from the Himalaya (Ganga) during the LGM is due to weakening of south-west monsoon and reduction in available exposure area for weathering due to extent of glacier cover. Outcomes of this study underscore the strong linkage between erosion and climate.
Indian Journal of Marine Sciences, 1999
The alkali and alkaline earth metals both major (Na, K, Mg, Cal and minor (Li, Rb, Cs, Sr) were analyzed in 75 surface sediment samples from an area covering the continental shelf, slope and the deep sea regions. Lithium, Rb, Cs and Sr averaged 7.2, 42.5, 12 and 27.2 ppm respectively. Rubidium and Sr showed north-south trends. Starting from the northern sector, the former increased and the latter decreased towards the mouth of R. Godavari. This behavior is explained by the dissolved transportation index (DTI) according to which the transport of Rb takes place mainly in the particulate and th at of Sr in the dissolved phases. Lithium and Rb are correlated well to K suggesting a detrital origin for the elements. The alkali and alkaline earth metal distribution of the study area revealed a strong signature of R. Godavari. Strontium showed a good anticorrelation with the biogenic fraction of Mg (Mg B). It attained peak concentrations in the carbonate sands of the northern outer shelf which according to previous reports are of the late Pleistocene age. Sediments although rich equall y in carbonate and from proximate stations, contain variable concentrations of Sr probably due to a differential time-dependent leaching of the metal as these carbonate deposits may have been formed at different stages of the regressive-progressive cycle of the late Quaternary sea level.
Geochemical characterisation of major and trace elements in the coastal sediments of India
Environmental Monitoring and Assessment, 2010
Thirty-five surface sediment samples from the Indian continental shelf were recovered offshore from the mouths of the major rivers (Brahmaputra, Ganges, Narmada, Tapti, Godavari, Krishna and Cauvery) discharging into the coastal region of both east and west coasts were analysed using inductively coupled plasma atomic emission spectroscopy for selected major (i.e. Al, Ca, Fe, K, Ti, Mg and Na) and trace elements (e.g. Ba, Co, Cr, Cu, Ga, Ni, P and V), after total dissolution. The main objectives are to understand the processes controlling major and trace elements in the surface sediments and to identify natural and anthropogenic sources in the coastal environment using statistically regressed elemental concentrations to establish regional baseline levels. Metal enrichments observed close to the major urban areas in the east and west coasts are associated with the industrialised activities areas rich in Cu and Co in both the east and west coast sediments. Normalisation of metals to Al indicated that high enrichment factors are in the order of Ca>Ti≥Fe>Na>Mg>Co>Cu>Ga>V>Ba except K and P depletion. This indicated that the characteristic of estuarine sediment showed higher level along the west coast of India, which was reflected in the coastal sediments as similar to the source of its origin from the riverine composition and its abundances.
Palaeogeography, …, 2008
Rock magnetic concentration, grain size and mineralogy parameters together with organic carbon, calcium carbonate, redox-sensitive elements, δ 18 O of 'Globigerinoides ruber' and radiocarbon dating were carried out on a 445 cm long sediment core collected at 1380 m depth off Mangalore, southwestern margin of India. The top 290 cm sediments of the core correspond to the last 18 kaBP. The δ 18 O and magnetic records exhibit major events at ∼16 kaBP, 14.5 kaBP, 11.5 kaBP and 9.8/8.6 kaBP related to start and intensity of the summer monsoon and climate change, and are synchronous with that of the western Arabian Sea and North Atlantic. The sediments with high magnetic susceptibility correlate with high sedimentation rates. The sediments are dominated by fine-grained magnetite, but those at intervals of 1.2 -3.8 kaBP and 10 -13.5 kaBP were subjected to diagenetic changes and resulted in the dissolution of fine-grained magnetites and enrichment of redox-sensitive trace elements (Cu, Ni, Zn, V, Mo and U). The sediments between 290 cm and 445 cm correspond to 18-27 kaBP and are characterized by distinct decrease in magnetic concentration, grain size and mineralogy parameters, high organic carbon, low concentrations of redox-sensitive trace elements and abundant pyritized tubules. In other words, the greater reductive diagenetic conditions indicated by rock-magnetic properties are in contrast with the weak sub-oxic conditions revealed by low concentrations of trace elements in the sediments. The seasonal organic matter flux produced during the winter monsoon and moderate sedimentation rates favoured reductive diagenesis in the late glacial sediments. Intermittent bioturbation, however, allowed oxidants to penetrate into the sediments, remobilized redox-sensitive trace elements to the water column and modified the primary geochemical signal of the sedimentary environment. Keywords: Rock magnetic properties, trace metals, reductive diagenesis, sedimentary environment, late Quaternary, SW margin of India enrichment factors (ANEFs) of trace elements with respect to the composition of PAAS (Taylor and McLannan, 1985) are calculated (see ).
Journal of Asian Earth Sciences, 2017
The Paleoproterozoic era is marked by significant changes in the level of oxygen in the atmosphere and chemistry of the ocean, and the presence of world-wide glaciation. Geochemistry of chemogenic sediments provide clues to these changes. The Sausar Group (2478-2250 Ma) of Central India is one of the few places in the world where Paleoproterozoic glacial unit overlained by a cap carbonate horizon has been identified. Major, trace and rare earth element (REE) contents of Paleoproterozoic cap carbonates of the Sausar Group, have been analysed for their implications for ocean redox conditions during interglacial periods of the Huronian glaciation. The La/La*, Gd/Gd*, Lusn/Lasn and Y/Ho ratios of the cap carbonate reflect their pristine marine nature. Conspicuous Ce anomaly (Ce/Ce* up to 1.75), accompanied by the enrichment of Fe, Mn, Zn and U, provides insight into the redox state of the ocean at the time of deposition of the cap carbonate succession. Based on these observations, we infer anoxic depositional conditions in the basin during the interglacial period of the Paleoproterozoic glaciation before the Great Oxidation Event (GOE), and the level of oxygen in the atmosphere fluctuating between 10-5 and 10-2 of the present atmospheric level (PAL).
Rare Earth element patterns of the Central Indian Basin sediments related to their lithology
Geophysical Research Letters, 1992
Rare earth element (REE) concentrations have been determined in terrigenous, siliceous (nodule barren and nodule bearing), calcareous, and red clay from the Central Indian Basin. The bulk distribution of REE, and in particular the relative cerium fractionation, in these surface sediments has been studied in relation to bottom water conditions. REE fractionations within a single depositional environment are found to be characteristic for each sediment type, with flat shale-normalized patterns associated with terrigenous sediments, positive Ce anomalies with siliceous sediments, negative Ce and positive Eu anomalies with calcareous sediments, and LREE-depleted patterns with pelagic red clays. There is no relation of any REE fractionation to bottom water redox conditions. Our results indicate that the REE signatures in marine sediments are not only related to depositional setting, but also to the lithologica! variations, and surficial diagenetic processes. Therefore, these further constraints on understanding REE behaviour indicate that REE fractionations for paleotectonic and paleoredox reconstructions should be used with caution.