Radiolarian zonation and volcanic ash layers in two Quaternary sediment cores from the Central Indian Ocean Basin

Abstract

Radiolarian abundance in two Quaternary sediment cores, collected from the Central Indian Basin, was studied and Nigrini's (1971) and Goll's (1980) zones are recognised. New radiolarian zones Collosphaera orthoconus, Lamprocyrtis nigriniae, Lamprocyrtis neopheteroporos and Lamprocyrtis heteroporos are proposed and described to modify Nigrini's and Goll's zonations. A hiatus of 0.2-0.3 M.Y., correspondings to Pseudocubus warrenin zone (Goll, 1980) in core F-88 B, suggest the erosion and redistribution of Pliocene taxa by a bottom water current (probably Antarctic Bottom Water Current). Volcanic ash layers of apparently about 20,000; 30,000 - 40,000; 80,000; 340,000 and younger than 4000,000 years are also recognised, which suggest suboceanic explosive volcanic eruptions during late Quaternary in the area