Sedimentary response to the contrasting provenance and oceanographic conditions on the continental shelf of India

Abstract

The present study sets out to elucidate how magnetic minerals derived from wide array of source regions respond to shelfal sedimentary processes in a complex shelf system. Bulk sediment magnetic mineralogy comprised of detrital magnetic (magnetite, titanomagnetite, titanohematite) particles with variable concentrations and grain sizes. A prominent change in magnetic mineral contribution from mafic to felsic dominated sediment province is clearly evident through a trend of decline in magnetite content manifested by fining of magnetic crystal size. Elevated magnetite content followed by the presence of fine and coarse-grained magnetic particles, and mere variations interms of mineralogy can be attributed with the enhanced magnetic contribution from the Deccan basalt (DcB) in the shelf sediments off Narmada, Tapti, Mahi, and Sabarmati (NTMS) River system, Arabian Sea. A distinct shift in magnetite content accompanied by abrupt fluctuations in clastic grain size in the sediment core off Ganga-Brahmaputra (G-B) shelf, Bay of Bengal indicate the major change in detrital sedimentation. A major change in the magnetic mineralogy linked with enhanced supply of titanomagnetite particles marks the onset of mafic sourced material in the sediments off Pennar – Swarnamukhi (P–S) shelf, Bay of Bengal. Magnetogranulometry data revealed that magnetic crystal size is independent of physical grain size above >40 μm in NTMS and G-B, and >20 μm in P–S samples. Decoupling is largely due to polycrystalline nature, where fine-grained magnetic particles occurred as inclusions within silt and sand fractions. We demonstrate that multi-proxy approach presented in this study can be effectively used to assess the influence of the contrasting provenance and oceanographic conditions on the shelfal sediment dynamics.