Relationship between chemical composition and magnetic susceptibility in sediment cores from Central Indian Ocean Basin (original) (raw)
Related papers
2010
Three sediment cores in a north-south transect (3 • N to 13 • S) from different sediment types of the Central Indian Ocean Basin (CIOB) are studied to understand the possible relationship between magnetic susceptibility (χ) and Al, Fe, Ti and Mn concentrations. The calcareous ooze core exhibit lowest χ (12.32 × 10 −7 m 3 kg −1 ), Al (2.84%), Fe (1.63%) and Ti (0.14%), terrigenous clay core with moderate χ (29.93 × 10 −7 m 3 kg −1 ) but highest Al (6.84%), Fe (5.20%) and Ti (0.44%), and siliceous ooze core with highest χ (38.06 × 10 −7 m 3 kg −1 ) but moderate Al (4.49%), Fe (2.80%) and Ti (0.19%) contents. The distribution of χ and detrital proxy elements (Al, Fe, and Ti) are identical in both calcareous and siliceous ooze. Interestingly, in terrigenous core, the behaviour of χ is identical to only Ti content but not with Al and Fe suggesting possibility of Al and Fe having a non-detrital source.
Geochemistry of two sediment cores from the west coast of India
International Journal of Environmental Science & Technology, 2005
Copper, Pb, Zn, Ni, Co, Mn, AI, Ca, magnetic susceptibility and loss on ignition of sediments from two cores near Mangalore along the western continental shelf of India have been studied. The sediments have high Al and organic matter contents due to the high sedimentation rate and their proximity to river mouths. Down-core variations of elements indicate a decrease of lithogenous component during probably the past few centuries. While abundance of calcareous shells in some zones has lead to the dilution of most of the metals, it appears that Pb and Mn are associated with this phase. Copper, Zn and Fe are associated with organic matter and detrital particles, whereas Ni and Co are predominantly associated with the insoluble fraction. Oxides/hydroxides of Fe and Mn are absent because of the reducing conditions and the high terrigenous influx. Geochemically, Mn and Fe are present in different phases of sediments (in the insoluble fraction and organic matter respectively). The Fe content of one of the cores is positively correlated with magnetic susceptibility.
Research Article, 2015
The spatial distribution patterns of surficial sediment samples from different sedimentary domains (shallow to deep-sea regions) of the eastern Arabian Sea were studied using sediment proxies viz. environmental magnetism, geochemistry, particle size and clay mineralogy. Higher concentrations of magnetic minerals (high χlf) were recorded in the deep-water sediments when compared with the shallow water sediments. The magnetic mineralogy of one of the shallow water samples is influenced by the presence of bacterial magnetite as evidenced from the χARM/χlfvs. χARM/χfd biplot. However, the other samples are catchment-derived. The high correlation documented for χlf, anhysteretic remanent magnetisation (χARM) and isothermal remanent magnetisation (IRM) with Al indicates that the deep-sea surficial sediments are influenced by terrigenous fluxes which have been probably derived from the southern Indian rivers, the Sindhu (the Indus) and the Narmada-Tapti rivers. A lower Mn concentration is recorded in the upper slope sediments from the oxygen minimum zone (OMZ) but a higher Mn/Al ratio is documented in the lower slope and deep-sea sediments. Clay minerals such as illite (24–48.5%), chlorite (14.1–34.9%), smectite (10.6–28.7%) and kaolinite (11.9–27.5%) dominate the sediments of shallow and deep-sea regions and may have been derived from different sources and transported by fluvial and aeolian agents. Organic carbon (OC) data indicate a low concentration in the shallow/shelf region (well oxygenated water conditions) and deeper basins (increased bottom-water oxygen concentration and low sedimentation rate). High OC concentrations were documented in the OMZ (very low bottom-water oxygen concentration with high sedimentation rate). The calcium carbonate concentration of the surface sediments from the continental shelf and slope regions (<1800 m) up to the Chagos-Laccadive Ridge show higher concentrations (average = 58%) when compared to deep basin sediments (average = 44%). Our study demonstrates that particle size as well as magnetic grain size, magnetic minerals and elemental variations are good indicators to distinguish terrigenous from biogenic sediments and to identify sediment provenance.
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 ).
Variation in the mineralogy and rock magnetic properties of Sites 885 and 886 sediment can be explained by changing environ- mental conditions in the sediment source areas and sediment column. Climatic variations produce changes in the mineralogy and magnetics at these sites consistent with aridification of the Asian source area and cooling forced by tectonic activity. Asian aridifi- cation is noted by gradual reduction of a kaolinite-rich mineral assemblage from the late Miocene to an abrupt mineralogy change at 3.8 Ma to a chlorite- and illite-rich mineral assemblage. At the same time, the eolian mass accumulation rate and ferrimagnetic grain size increases. This event precedes the onset of Asian loess deposition by over 1 m.y., but it is consistent with a coupled envi- ronmental mechanism that explains the rapid onset of loess sedimentation at 2.5 Ma. Both the mineralogy and rock magnetics are overprinted with a diagenetic signal that suggests the sediments proximal to Sites 885 ...
Aluminum-poor ferromanganoan sediments on active oceanic ridges
Journal of Geophysical Research, 1969
The results of 399 new analyses and 144 analyses from the literature indicate that the carbonate-free fraction of sediments from active oceanic ridges is characterized by very low aluminum and titanium content and high iron and manganese content compared with sediments from other volcanic regions and from inactive ridges. These active ridge sediments appear to originate by volcanic processes associated with ocean-floor spreading and high heat flow. The total mass of these sediments is probably only a few per cent of all deep-sea sediments.
2015
Mineral magnetic and geochemical analyses were carried out on surface sediments from the continental shelf of India. The purpose of this study is to examine the environmental assessment of heavy metal concentrations and its impact in the coastal environment using magnetic techniques and to gain an understanding on the factors controlling metal concentrations and distributions in the east and west coast of India. The strong relationships between Anhysteretic Remanent Magnetization (χARM) and heavy metals can be explained by the role of iron oxides controlling metal concentrations, though the link is also reinforced by the strong tendency of χARM to be associated with the finer particle sizes. Higher values of magnetic susceptibility, IRM20 mT and SIRM are associated with the east coast shelf sediments suggest the presence of high ferrimagnetic content, which can be derived from the weathering products of the Deccan Basalts. χARM can be used as a normalizer for particle size effects i...
Estuarine, Coastal and Shelf Science, 2002
A study of an anoxic sediment core from Authie Bay in northern France has been undertaken; porewaters and sedimentary solid phases have been analysed by several techniques (inductively coupled plasma atomic emission spectroscopy; graphite-furnace atomic absorption spectroscopy; X-ray diffraction; and electron spin resonance spectroscopy). The chemical speciation versus depth of the major elements (Ca, Fe, Mg, Mn, P and Sr), some trace elements (Cd and Zn) and especially sulfur [i.e., dissolved sulfur as Acid Volatile Sulfide (AVS) and Chromium Reducible Sulfur (CRS)] have also been performed using sequential extraction procedures. Together with these analytical data, thermodynamic calculations have been used in order to gain information about the effects of microbial degradation of organic matter in these recent sediments on these elements during early diagenesis and/or the possible generation of new characteristic assemblages of authigenic mineral precipitates of carbonates, phosphates and/or sulfides. Thus, these calculations have shown that iron sulfide precipitates in interstitial waters to give the crystalline form greigite and, to a lesser extent, mackinawite, whereas different divalent metals (noted Me) as Mg, Mn, Sr, Cd, Zn and even Fe interact favourably with Ca 2+ and CO 2 3 [through a removal of these elements from anoxic porewaters by (co)precipitation and/or adsorption on to the sedimentary carbonate phase (calcite)] to give (1) a solid mineral: dolomite [CaMg(CO 3 ) 2 ]; and (2) solid solutions as Me x Ca 1 x CO 3 . The distribution coefficients for these metals in calcite have been calculated and compared to those reported in the literature.
Diagenetic modulation of the magnetic properties in sediments from the Northern Indian Ocean
Geochemistry, Geophysics, Geosystems, 2013
1] Large changes in magnetic mineral concentration dependent parameters by more than 1 order of magnitude occur over 50-150 cm intervals in two marine sediment cores from the oxygen minimum zone in the Gulf of Aden. High-resolution sedimentological and chemical analyses indicate that these intervals are not associated with turbiditic events or sediment reworking, they do not result from changes in carbonate dilution or differences in sediment properties, and they do not correspond to volcanic layers. Magnetic mineralogical analyses reveal a change in magnetic mineral concentration from a magnetite-goethite assemblage to pure magnetite within the peak. The peaks almost disappear when the abundance of magnetic minerals is calculated after correcting for the magnetic moments of each magnetic mineral. Therefore, under the assumption that the variability of the magnetic parameters results from postdepositional mineralogical transformations, a relatively constant amount of magnetite was present at the surface of the sediment. Changes in redox conditions and nonsteady state diagenesis transformations have effectively been observed along both cores. Large values of total organic carbon coincide with poor preservation of biogenic and detrital magnetite, which reflects reductive dissolution of the finer magnetite grains. At the same levels, Fe 2þ release from reductively dissolved magnetite favored precipitation of goethite. The susceptibility peaks coincide with episodes of magnetite preservation caused by reduced surface
Clay Minerals and Oceanic Evolution
Clays and Clay Minerals, 1967
A REVIEW Of mineralogical aI~.d geochemical studies on Recent sediments indicates that the clay fraction of marine sediments is not in isotopic or chemical equilibrium with the oceanic reservoir and will not reflect the chemical environment of deposition. Consideration of the sedimentary geochemistry of the alkali metals suggests that frautionation of these elements, which may be one of the major features of the chemical evolution of ocean water, occurs in the terrestrial weathering environment during the formation of clay minerals and in the subsurface environment during clay mineral diagenesis. It is proposed that during the initial stages of oceanic development the NarK ratio of ocean water was adjusted to a value of forty to fifty by the extensive diagenesis of the existing natural water. With an increase in oceanic volume and a major change in the hydrologic cycling of natural waters the chemical evolution of alkali metals in ocean water has now become primarily controlled by mixing with continental drainage water.