Mineralogy of Quaternary Sediments from the Vema Fracture Zone Valley (Central Atlantic)

Abstract

The content of sediment-forming minerals in two cores from the eastern (ANS45-37) and western (ANS45-48) parts of the valley of the Vema Fracture Zone is studied using semiquantitative XRD analysis of bulk powder sediment samples. The mineral composition of deep-sea sediments from the Amazone Cone is also analyzed for comparison. It appeared that the average composition of the terrigenous component of both cores (according to prevailing quartz, secondary mica, plagioclase and potassium feldspar, as well as smectite, chlorite, kaolinite, illite) is quite similar and approximately corresponds to the composition of sediments from the Amazon Cone. The ratio of four clay minerals suggests supply of terrigenous material to the Amazon and Orinoco due to erosion of the Andes and humid tropical weathering in the lower courses of the rivers with further transport of the suspended load to the ocean. This material was transported to the valley of the Vema Fracture Zone due to interplay between gravitational flows from the South American continental slope and current of Antarctic Bottom Water. In addition, data on biogenic calcite (planktic foraminiferal tests, nannofossils) and opal A (radiolarians, sponge spicules) have been obtained. In the study area, several authigenic (diagenetic) minerals are identified. In particular, siderite and greigite are first found in the sediments from the Vema valley and Amazon Cone, respectively.