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  <item rdf:about="http://drs.nio.org/drs/handle/2264/3660">
    <title>Selective leaching studies of sediments from a seamount flank in the Central Indian Basin: Resolving hydrothermal, volcanogenic and terrigenous sources using major, trace and rare-earth elements</title>
    <link>http://drs.nio.org/drs/handle/2264/3660</link>
    <description>Title: Selective leaching studies of sediments from a seamount flank in the Central Indian Basin: Resolving hydrothermal, volcanogenic and terrigenous sources using major, trace and rare-earth elements
&lt;br/&gt;
&lt;br/&gt;Authors: Mascarenhas-Pereira, M.B.L.; Nath, B.N.
&lt;br/&gt;
&lt;br/&gt;Abstract: Sediments from a site have been investigated where a newly discovered submarine hydrothermal alteration of recent origin is located to identify the source components and estimate their relative contribution. The site is situated on the flank of a seamount in the Central Indian Basin along the 76 degrees 30 minutes E fracture zone which traces the movement of the Rodriguez triple junction. Detailed analyses of major, trace and rare earth elements (REE) on the bulk, leach, residue and clay fraction, and infra red spectroscopy studies of the clay fraction helped characterize the hydrothermal nature of the sediments. Selective dissolution carried out using HCl has allowed the discrimination between a leach phase (leachable Fe-Mn oxide) and a residue phase (refractory). The sediments are iron-rich, majority of Fe, Mn is in leachable fraction and are compositionally comparable to ridge-crest metalliferous sediments. Elemental ratios and geochemical discrimination plots of major element data reveal that the sediments are a mixture of Fe-rich mineral phases on one hand apparently from hydrothermal sources and aluminosilicates such as illite, zeolites, micaceous clays and smectites contributed from the Bengal fan, weathering of basinal basalts and authigenic processes. Ternary mixing calculations of bulk sediment major element data show that 35-45% metalliferous sediments could reproduce Fe and Mn values of our sediments. The shale normalized REE patterns of the bulk sediments are remarkably similar to those of the HCl soluble leach fraction, implying that the REEs in the HCl soluble leach fraction dominate the bulk fraction. HCl leacheates exhibit characteristics of vent fluids as well as seawater with pronounced Eu anomaly with HREE enrichment and negative Ce anomaly. The residue on the other hand has a high concentration of Fe, V, Zn, and Pb indicating a sulfidic input to the sediments. Ternary mixing calculations of REEs carried out on the residual fraction indicate that the sulfide-like material dominates (64-72 %) over terrigenous (10-20 %) and MORB derived (16-18 %) components. This study helped us identify and quantify two types of hydrothermal material in the sediments, dominated by Fe-Mn phases (ferruginous oxides and silicates; Mn-oxides) in leachable fraction and sulfide-like material in residual phases. The clay fraction is mainly composed of dioctahedral smectites and has a composition similar to Alvin nontronite. The geochemical and mineralogical characteristics collectively suggest that these sediment-hosted precipitates formed at relatively low temperatures ranging between 50 and 100 degrees C from a mixture of seawater and hydrothermal fluids. The presence of hydrothermal sediments in the vicinity of a fracture zone suggests the occurrence of localized hydrothermal activity associated with intra plate volcanism. This is probably induced by reactivation of tectonic forces along the fracture zones.</description>
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  <item rdf:about="http://drs.nio.org/drs/handle/2264/3659">
    <title>Occurrence and emplacement of chromite ores in Sindhudurg district, Maharashtra, India</title>
    <link>http://drs.nio.org/drs/handle/2264/3659</link>
    <description>Title: Occurrence and emplacement of chromite ores in Sindhudurg district, Maharashtra, India
&lt;br/&gt;
&lt;br/&gt;Authors: Iyer, S.D.; Babu, E.V.S.S.K.; Mislankar, P.G.; Gujar, A.R.; Ambre, N.V.; Loveson, V.J.
&lt;br/&gt;
&lt;br/&gt;Abstract: In the present study, the occurrence and emplacement of chromite ore deposits from two abandoned mines (Kankavali (Janoli) and Wagda) in the Sindhudurg district of Maharashtra, India are presented. These ores, that occurred as lenses and are associated with metamorphic and ultrabasic rocks, consist of octahedral grains of chromite, while clinochlore is present between the interstices of these grains. The Kankavali (janoli) and Wagda ores revealed a dominance of Cr sub(2) O sub(3) followed by FeO and variable proportions of Al sub(2) O sub(3), MgO, and SiO sub(2). The former deposits have a slightly higher Cr sub(2) O sub(3) (average 52 wt %) and FeO (approx. 18 wt %) than those from Wagda (Cr sub(2) O sub(3) approx. 50 wt %, FeO approx. 25 wt %). The similar Cr values (0.73) for Kankavali (Janoli), 0.74 for Wagda) correspond to those reported for typical podiform-type chromite deposits. It is suggested that the ores were emplaced as phacoliths in folded outcrops with a steep easterly dip and northwest-southeast trend. It is postulated that the continuation of the fold structure from Janoli to Wagda (approx. 4.5 km apart) and the probable (sporadic) occurrence of chromite along this stretch. The possibility of the contribution of chromite grains from these areas to the coastal placer deposits cannot be ruled out.</description>
  </item>
  <item rdf:about="http://drs.nio.org/drs/handle/2264/3658">
    <title>Denitrification: An important pathway for nitrous oxide production in tropical mangrove sediments (Goa, India)</title>
    <link>http://drs.nio.org/drs/handle/2264/3658</link>
    <description>Title: Denitrification: An important pathway for nitrous oxide production in tropical mangrove sediments (Goa, India)
&lt;br/&gt;
&lt;br/&gt;Authors: Fernandes, S.O.; LokaBharathi, P.A.; Bonin, P.C.; Michotey, V.D.
&lt;br/&gt;
&lt;br/&gt;Abstract: Net nitrous oxide production and denitrification activity were measured in two mangrove ecosystems of Goa, India. The relatively pristine site Tuvem was compared to Divar, which is prone to high nutrient input. Stratified sampling at 2-cm intervals within the 0- to 10-cm depth range showed that N sub(2)O production at both the locations decreased with depth. Elevated denitrification activity at Divar resulted in maximum production of up to 1.95 nmol N sub(2)O-N g sup(-1) h sup(-1) at 2 to 4 cm, which was three times higher than at Tuvem. Detailed investigations to understand the major pathway contributing to N sub(2)O production performed at Tuvem showed that incomplete denitrification was responsible for up to 43 to 93% of N sub(2)O production. Nitrous oxide production rates closely correlated to nitrite concentration (n = 15; r = -0.47; p &lt; 0.05) and denitrifier abundance (r = 0.55; p &lt; 0.05), suggesting that nitrite utilization by microbial activity leads to N sub(2)O production. Nitrous oxide production through nitrification was below detection, affirming that denitrification is the major pathway responsible for production of the greenhouse gas. Net N sub(2)O production in these mangrove systems are comparatively higher than those reported from other natural estuarine sediments and therefore warrant mitigation measures</description>
  </item>
  <item rdf:about="http://drs.nio.org/drs/handle/2264/3657">
    <title>Seabed morphology and gas venting features in the continental slope region of KrishnaeGodavari basin, Bay of Bengal: Implications in gas–hydrate exploration</title>
    <link>http://drs.nio.org/drs/handle/2264/3657</link>
    <description>Title: Seabed morphology and gas venting features in the continental slope region of KrishnaeGodavari basin, Bay of Bengal: Implications in gas–hydrate exploration
&lt;br/&gt;
&lt;br/&gt;Authors: Dewangan, P.; Ramprasad, T.; Ramana, M.V.; Mazumdar, A.; Desa, M.; Badesab, F.K.
&lt;br/&gt;
&lt;br/&gt;Abstract: Increased oil and gas exploration activity has led to a detailed investigation of the continental shelf and adjacent slope regions of Mahanadi, KrishnaeGodavari (KG) and Cauvery basins, which are promising petroliferous basins along the eastern continental margin of India. In this paper, we analyze the high resolution sparker, subbottom profiler and multibeam data in KG offshore basin to understand the shallow structures and shallow deposits for gas hydrate exploration. We identified and mapped prominent positive topographic features in the bathymetry data. These mounds show fluid/gas migration features such as acoustic voids, acoustic chimneys, and acoustic turbid layers. It is interesting to note that drilling/coring onboard JOIDES in the vicinity of the mounds show the presence of thick accumulation of subsurface gas hydrate. Further, geological and geochemical study of long sediment cores collected onboard Marion Dufresne in the vicinity of the mounds and sedimentary ridges shows the imprints of paleo-expulsion of methane and sulfidic fluid from the seafloor. To understand the origin of the mounds and their relationship with gas hydrate/cold seep formation, we analyzed the multi-channel seismic reflection (MCS) data close to the mounds. The MCS data show that the subsurface layers beneath the mounds are folded. Below the folded overburden, we observe zones of no coherent reflections probably originating from Miocene sequence. Since the study area is located in shale tectonics regime where Miocene sequences are known to be overpressured, we interpret the zones of no coherent reflections as Miocene shale diapirs. The upward movement of shale diapirs has folded the overburden layer and resulted in the formation of numerous faults/fractures. These faults act as permeable pathways for fluid/gas movement facilitating the formation of gas hydrate and cold seeps close to shale diapiric mound</description>
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