Major, Trace, and Rare Earth Elements in the Sediments of the Central Indian Ocean Basin: Their Source and Distribution

Abstract

A large number of surface sediments as well as short sediment cores collected in the Central Indian Ocean Basin have been subjected to various geochemical investigations during the last one and half decade. The studies varied, covering diVerent aspects of sediments and resulting in a number of publications. In the present article, we have put together the data from 82 surface sediments and 14 short sediment cores, including 25 new analyses, to study the trend of their distribution and source at large. The distribution maps of elements show that highest concentrations of Mn, Cu, Ni, Zn, Co, and biogenic opal in the surface sediment occurs between 10¯S and 16¯S latitude, where diagenetic ferromanganese nodules rich in Mn, Cu, Ni, and Zn are present. The studies highlight that the excess element concentration (detrital unsupported) such as Mn, Cu, Ba, Ni, Co, Pb, and Zn have contributed . 80% of their respective bulk composition. These excess elements exhibit strong positive correlation with each other suggesting their association with a single authigenic phase such as Mn oxide. Biogenic opal contributes 30± 50% of the total silica in the siliceous sediment. Aluminum, Fe, and K have contributed . 60% from terrigenous detrital source compared to their bulk composition. In calcareous ooze, Ca, and Sr excess contribute . 95% while, in siliceous ooze it is only 50% of their bulk composition. Nearly 35% of structurally unsupported Al in the sediment raises doubt of using Al as a terrigenous index element to normalize the trace and minor elements. Biogenic apatite is evident by the positive correlation between Ca ( , 1% ) and P. Calcium, Sr, and P depict a common source such as biogenic. Bulk element concentration such as Li, V, Cr, Sc, and Zr are positively correlated with Ti indicating their terrigenous detrital source. Rare earth element (REE) concentration increases from calcareous ooze to siliceous ooze and reaches a maximum in the red clay. Presence of positive Eu-anomal y in these sediments has been attributed to aeolian input. REE in these sediments are mostly carried by authigenic phases such as manganese oxide and biogenic apatite. Based on the distribution of transition elements in the sediment cores, three distinct zonesÐ oxic at top, suboxic at intermediate depth, and a subsurface maximaÐ have been identiWed. Oxic and suboxic zones are incidentally associated with high and low micronodule abundance in the coarse fraction ( . 63 m m) respectively. Ash layers encountered at intermediate depth between 10 to 35 cm are correlative with the Youngest Toba eruption of ¹74 ka 85 from Northern Sumatra. This ash is mainly responsible for the high bulk Al/Ti ratio up to 48.5 (three times higher than Post Archean Australian Shale), other than scavenging of dissolved Al by biogenic components.

Alterations in Geochemical Associations in Artificially Disturbed Deep-Sea Sediments

“…The Al excess values thus obtained should be considered as a minimum estimate, because this estimate assumes that most of Ti is mineralogically bound (Murray and Leinen 1996) and only minor contribution from scavenging or biological incorporation. Maximum Al excess noticed here is about $ 25% and thus much lower than those observed in biogenic sediments from the central equatorial Pacific (50-60%; Murray and Leinen 1996), but closer to 30-35% of excess noticed by other workers in the Central Indian Basin sediments (Banakar et al 1998;Pattan and Jauhari 2001). Lower Al excess values can be explained by higher terrigenous component in these sediments.…”

“…They used the model in areas having higher sedimentation rates than Central Indian Basin. In absence of a suitable model for this area, and to have the comparability with the calculations made for other cores from the Central Indian Basin (Pattan and Jauhari 2001), we have employed the model here and determined the remobilization rates for two cores. The model assumes that the Mn gradient in the sediments reflects the loss of Mn in lower reducing zone and subsequent migration to the oxidizing zone and is represented as U ¼ SqdMn, where U is the flux of remobilized Mn in gcm À2 kyr À1 , S is sedimentation rate (cm kyr À1 ), dMn is the difference between top and bottom of Mn (%) in the sediment core, and q is the in situ dry bulk density of the sediment (g cm À1 ).…”

Ordinary chondritic micrometeorites from the Indian Ocean

“…Pattan et al. () and Pattan and Jauhari () measured trace elements from the sediments in this part of the Indian Ocean. The sediments here contain Th = 11–12 ppm, U = 1–1.5 ppm, and Ba = 3000–4000 ppm.…”

Major and trace element geochemistry of S‐type cosmic spherules

“…It is discernible from Fig. that in contrast to the chondrites, the deep‐sea sediments here are enriched by orders of magnitude in Th (~12 ppm), U (~1.5 ppm), and Ba (3000–4000 ppm) (Pattan and Jauhari ; Pattan et al. ).…”