Depositional environment of the surface sediments in Central Indian Basin (CIB), Indian Ocean, between 8°–18°S latitude and 72°–79°E longitude, based on their geochemical characteristics

Abstract

To establish the depositional environment of the surface sediments in the Central Indian Basin, Indian Ocean, major and trace element compositions of different sediment types were studied. The study area composed of terrigenous–siliceous transition, calcareous, siliceous, and red clay sediments. The sediment type changed due to various physico‐chemical conditions with varying proportions of biogenic, hydrogenetic, early diagenetic, and detrital inputs. An oxidative environment is present throughout the basin with variable intensity. The terrigenous input was variable in all sediment types, while its signature was traceable up to 15.30°S latitude. The variable distribution pattern of Mnexcess and Feexcess indicate that apart from continental source, there were additional sources of supply for both these elements, with which most of the trace metals like nickel, copper, chromium, vanadium, yttrium, rubidium, and thorium were associated. The Al/Ti ratios of the sediments indicate a terrestrial influence of fluvial nature up to as far as 14°S latitude while, in the calcareous zone, the influence of volcanic precursors was observed. The present study envisages that Alexcess in the sediments adjacent to the ridges and fracture zones might indicate that Al in these areas is not entirely derived from the continental source.

The Geochemistry and Bioturbation of Clay Sediments Associated with Amalgamated Crusts at the Gagua Ridge

“…As proposed by Chen et al (2018) [3], when the inner nodules sank into the sediments, the middle Fe-Mn crust of the amalgamated crusts may have grown hydrogenetically under oxic conditions from the surface of the inner nodules into the sediments. Positive Mn* values and V/Cr ratio values (<2) of the Gagua Ridge sediment samples, which are related to the redox conditions [41], indicate an oxic environment. The dissolved oxygen may be supplied from bottom water continuously into the sediment column through void burrows, which may produce the same solution environment as the bottom seawater and obstruct the diagenetic growth of 10-Å manganates.…”

“…Ti is generally considered to be continentally derived, and is the most stable element under varying physicochemical changes. Therefore, assuming that all Ti is mineralogically bound to the terrigenous fraction, Ti was used to calculate the terrigenous percentages in sediments and the excess of multiple elements (e.g., Al, Fe, Mn, and Ba), in order to assess the relative contributions of terrigenous and nonterrigenous components [11,[39][40][41]. However, Ti may be enriched in hydrogenetic crusts and nodules due to effective surface complexation from the water column on oxide surfaces [42], suggesting that this method may not work in the two mixed sediment samples, because the samples contain a remarkable amount of fine Fe-Mn oxides.…”

“…In the eastern flank of the Gagua Ridge, all the samples have positive Mn* values, with an average of 0.84. Alternatively, the V/Cr ratio can also be applied for determining the redox condition of the sediment [41,45], where values of >4.5 indicate an anoxic environment, and <2 indicates an oxic environment. All our sediment samples showed values of <2.…”

Trace Elements and Sr, Nd Isotope Compositions of Surface Sediments in the Indian Ocean: An Evaluation of Sources and Processes for Sediment Transport and Dispersal

“…Based on these geochemical evidences, it was suggested that the Ganga-Brahmaputra (G-B) river system supplied terrigenous flux of sediments reach up to 8°S (Nath et al, 1989). However, in a recent study, it has been reported that traceable terrigenous signature of G-B system is observed up to 15.5°S in the Central Indian Basin (Sensarma et al, 2018).…”

Distribution and Diagenesis of Phosphorus in the Deep‐Sea Sediments of the Central Indian Basin

“…The highest P det content is observed south of 15°S where the sediments are dominated by pelagic red clays. The estimated higher terrigenous sediment content (Sensarma et al, 2017) in the CIB pelagic clays may, in fact, reflect the presence of higher lithogenic material in these sediments and not necessarily from the terrigenous sources (Nath, 2001). The sediments in the south (14°S) has higher 232 Th concentrations (3.88 dpm/g) compared to the northern locations (2.76 dpm/g at 12°S; Borole, 1993).…”