Chronostratigraphy and deposition rates in the Okinawa Trough region

Abstract

Six representative cores from Okinawa Trough have been dated using AMS 4C, Standard C and ESR methods, and comparatively analysed. Systematic measurements of the oriented samples taken from the cores were conducted for obtaining their remnant magnetic polarity. With the aid of the dates obtained, particularly the AMS C ages of planktonic foraminiferal tests, two polarity events and two polar wanderings of the earth magnetic field have been defined . Calculations of the deposition rates for all the six core sites indicate rather high values in the trough plain, at least equivalent to those rates reported for the region of the East China Sea. They commonly range from 10 to 30 cm/ka, and even greater than 40 cm/ka in some localities. The deposition rate varied widely with topography and periods of time. In general, it is greater during the postglacial period than during the last glaciation. The chronostratigraphy in the Okinawa Trough region established through this study argues against the previous dominant consensus of low deposition rate in this region due to lack of sediment resource.