Sedimentation in the vicinity of Leg 92 Drill Sites: Studies of site survey cores@en

Surveys of the areas surrounding the sites drilled on the Leg 92 19°S transect showed that sedimentation at all except the oldest site is dominated by calcium carbonate deposition. The sediments in the area of the oldest site, west of the Austral Fracture Zone, are being deposited beneath the calcium carbonate compensation depth and are dominated by terrigenous and metal-rich hydrogenous and hydrothermal sediments. The noncarbonate sediments in all of the areas east of the Austral Fracture Zone are dominated by hydrothermal sediment similar in composition to that presently being deposited at the East Pacific Rise. Although no biogenic microfossils were present in smear slides of the sediment, geochemical partitioning suggests that a remnant signal of siliceous biogenic deposition may be preserved, especially in gravity core (GC) 8, which was collected from a high heat flow zone near Site 600. The siliceous sediment may also result from the deposition of amorphous hydrothermal silica from the higher concentrations of pore water SiO2 characteristic of the upwelling waters. Sedimentation on the broad plateaus that characterize each area is quite uniform and suggests that sites on these plateaus will be broadly representative of pelagic sedimentation in the area.

对第92航次（Leg 92）19°S断面钻探点位周边区域的调查显示，除最古老的钻探点位外，其余所有点位的沉积作用均以碳酸钙沉积为主。位于澳大利亚断裂带（Austral Fracture Zone）西侧的最古老钻探点位所在区域的沉积物，沉积于碳酸钙补偿深度（calcium carbonate compensation depth, CCD）之下，以陆源、富金属水成沉积物及热液沉积物为主。澳大利亚断裂带东侧所有区域的非碳酸盐沉积物，均以成分与当前东太平洋海隆（East Pacific Rise）沉积的热液沉积物相似的热液沉积物为主。尽管沉积物涂片未检出生物微化石，但地球化学分配特征表明，可能保存有硅质生物沉积的残留信号，尤其是在采自600号点位附近高热流区的重力岩心（GC）8中。该硅质沉积物也可能源自上升流特征性的高浓度孔隙水二氧化硅所形成的无定形热液二氧化硅沉积。各区域标志性的宽阔海台上的沉积作用均十分均一，表明这些海台上的钻探点位可广泛代表该区域的远洋沉积作用。