The Characteristics Of Core Sediment In The Middle Okinawa Trough And Analysis On The Sediment Environment

The Okinawa Trough is an expanding back-arc basin between the East China Sea shelf and Ryukyu Island.The region has its unique location and tectonic characteristic.Therefore discriminating the provenances of the sediments and acknowledging the variation of the current are critical for studying on sedimentary environment evolution.Based on the data of grain size,trace elements,rare earth elements and major elements coupled with high-precise AMS14 C dating,this paper dealed with the provenance and sediment environment evolution of the middle Okinawa Trough for the last 5300 a with the sample from the Core HOBAB2–S2.The analysis ongeochemical characteristics showed their affinities to the terrigenous sediments in the study area.In combination with elements features of potential sediment sources,the sediments were mainly originated from Taiwan.Besides,they were also mixed with other materials from the eastern Chinese mainland.The grain size and major elemental depositional fluxes were used to be the indicators of sediment environment,especially the vigor of local current(the current was mainly referred to Kuroshio Current in this paper).Since 5300 a BP,the major elemental depositional fluxes can be divided into four stages as well as the grain-size.As a consequence,according to the curves of grain-size and major elemental depositional fluxes,the conclusions were summarized as follows.Stage I(between 5300–3813 a BP),the strength of the Kuroshio Current(KC)weakened gradually and the input of sediment materials was relatively at a low level.Stage II(from 3813 to 2699 a BP),the strength of KC was weak and in a state of fluctuation.However,the depositional rate was in a high level,which indicated that the input of sediment matters increased.Stage III(from 2699 to 970 a BP),during which the sediment environment was in a stable station and featured with a slow sediment rate,indicating a decreased material input.Since about 970 a BP,the strength of KC strengthened and had a tendency of weakening.The high sediment rate showed the increase of the sediment.