Rifting of the Okinawa Trough reactivated at ~100 ka, causing the trough to propagate southwest and the Lan-Yang Plain of northern Taiwan (an extension of the Okinawa Trough) to subside. During MIS 4, tentatively dated as 68–52 ka, rifting-related volcanic activity was common in the vicinity of Site 1202, contributing volcanic grains and causing small-scale turbidity currents (Fig. F7D). Several large-scale turbidity currents occurred and laid down thick turbidites between ~52 and 44 ka in response to major seismic activity or slope failure. It is possible that slope failure occurred in Channel C (Fig. F2), which was likely filled in part with metamorphic fragments transported from East Taiwan before the current Lan-Yang River drainage was formed. This explains why the coarse grains in the turbidites consist predominantly of metamorphic fragments (Fig. F7B). The source then switched to the newly developed Lan-Yang River and its extended canyon (Channel A in Fig. F2), causing the coarse grains of the turbidites to become dominated by slate chips derived from the Lan-Yang drainage (Fig. F7C). After 32 ka, the turbidity currents decreased and the site received mainly fine-grained sediments from the sea surface as well as nepholoid layers.
Between 30 and 19.5 ka, the site received sediments mainly from East China and, to a lesser extent, Taiwan. Sea level was at low stand, and the shore line of East China was near the continental break, feeding sediments from the Yangtze and other rivers directly into Okinawa Trough. Fluctuation of sea level caused reworking and sorting of coastal sediments, leading to the deposition of fine particles at Site 1202. After the LGM, sea level began to rise at ~19 ka (Fig. F9B). Initially, the sea level rise may have caused some sediments to become trapped on the continental shelf and the sedimentation rates to decrease slightly (Fig. F10C), but the major contributor of sediments was still river runoff from East China, as reflected by the low chlorite/kaolinite ratio (Fig. F10A). Sea level rose rapidly from 15 to 11 ka and caused stronger flushing and mobilization of sorted, reworked fine particles from the East China Sea continental shelf, resulting in the deposition of thick layers of clay-rich sediments at rates as high as 9 m/k.y. Once sea level rose to –50 m relative to the current stand, the Kuroshio Current entered the Okinawa Trough and dramatically changed the circulation pattern of surface and undercurrents so that sediments derived from Taiwan have mostly been transported to Site 1202 by surface currents and subsurface nepholoid layers. The strength of the Kuroshio Current fluctuated slightly during the Holocene, and the supply of sediments from Taiwan increased at ~1.5 ka (Fig. F10A) in response to increased precipitation in northern Taiwan (Liew and Tseng, 1999; Liew and Hsieh, 2000). The entrance of the Kuroshio Current caused Florisphaera profunda, a deep-dwelling coccolithophorid, to increase in the Okinawa Trough (Fig. F9A); meanwhile, SST rose continuously during 13 to 8 ka from 23° to 26.5°C (Fig. F9E).