Basic geochemical characteristics of sediments in the Okinawa trough

A total of 21 elements, Si, Al, K, Na, Ca, Mg, Fe, Mn, Ti, P, Cu, Co, Ni, Zn, Pb, Cr, Rb, Sr Ba, Cd and C_org(organic carbon), was determined in the trough. Average contents of most elements were found to be higher in the trough bottom than in the western and eastern slopes. We call these elements the indicator elements because of their “transition” property. This is in keeping with the “intermediate” geographical position of the trough where the continental crust turns to oceanic crust. Though the authigenic fraction of some elements here increases, the detrital fraction of most elements is still dominant, indicating that the influences of terrigenous and volcanic detrital materials on the trough sediments are still dominant. The abundant biogenous component in the trough is characterized by the increase of Ca, Sr, and C_org contents. Ca existes mainly in the form of CaCo₃ that is mostly found in various shells. Sr often easily replaces Ca within the shells. A belt-shaped distribution pattern of elements was found in the south and a “block” pattern in the north trough. Such distribution patterns are directly controlled by water depth, topography, current sediment type, and mineral, biological, and volcanic processes. This paper was published in Chinese in Oceanologia et Limnologia Sinica15(4): 371–379, 1984.