Abstract:

ccording to the grain sizes,microbiological assemblage,mineral composition and minor elements,the features of siliceous sediments deposited in the glacialmarine environment in the central trough and south lower slope of Bransfield Strait,Antarctica were discussed in the paper.Siliceous sediments,mainly diatom ooze or silty diatom ooze,are dominated by the fine grained clastics with particle diameter less than 0.063 mm.Material components include the microbiological remains,clay minerals,volcanic products and terrigenous clastics.The microbiological assemblage show almost all the siliceous organism,chiefly diatom tests and uncommonly radiolaria and siliceous foraminifera.Among the nonbiogenous components,an important proportion is clay minerals with smectite formed by halmyrolysis of volcanic ash and terrigenous illite as the major species.Kaolinite and chlorite are relatively less in quantity.The terrigenous components include heavy minerals,primarily unsteady association such as olivine,pyroxene and hornblende,light ones dominated by quartze and felspar and debrics mainly basic volcanics.Geochemically,the siliceous sediments is different from the superficial sediments deposited in open ocean in minor elements.The siliceous sedimentation of present area under the glacialmarine environment is mainly controlled by the diversified material supplies,certain leading role of biosedimentation,fine grained terrigenous clastics (including the volcanics) with silty and clay sizes,and relatively high sedimentation rate,and directly influenced by the geological and tectonic background.