Clay mineralogy and geochemistry of surface sediments in the equatorial western Indian Ocean and implications for sediment sources and the Antarctic bottom water inputs

Abstract

Sediments in the equatorial western Indian Ocean are mixed products from biological, terrigenous, autogenic, volcanic, and hydrothermal materials influenced by various circulation and water masses. The sediments record information of sources and sedimentary environments. To identify the different sources of non-carbonate components in the sediments of the equatorial western Indian Ocean and explore the factors influencing their sedimentary characteristics, surface sediments of the equatorial western Indian Ocean were analysed for clay minerals as well as major and rare earth elements following carbonate removal. Palygorskite, as an indicative mineral of aeolian dust from the North Africa-Arabian Peninsula, is ubiquitous in the sediment of the equatorial western Indian Ocean. These non-carbonate materials are mainly derived from the North Africa-Arabian Peninsula as well as the Indus River and Deccan Traps. The study area can be divided into two sedimentary zones according to the water depth, major element content, and related indexes of rare earth elements (δCe, δEu, LREE/HREE). The sediments of Zone II, being influenced by the Antarctic bottom water, are mainly calcareous clay and characterised by a significant positive Ce anomaly and relative MnO enrichment, with relatively high palygorskite, Al2O3 content, and LREE/HREE ratio (mean values of 24%, 13.95% and 14.00). The sediments of Zone I are mainly clayey calcareous ooze, with a relatively weak positive Ce anomaly and a low palygorskite content (20%). Low Al/(Al+Fe+Mn) values in the sediments of Zone I demonstrate slight signs of hydrothermal input. This study revealed that continental weathering debris is an important source of non-carbonate sediments in the equatorial western Indian Ocean and established that the Antarctic bottom water is an integral factor affecting the sedimentary environment in this region. We present a complete regional sedimentological study of the equatorial western Indian Ocean and provide theoretical support for the reconstruction of the paleo-oceanic environment.