The history of turbidite deposition at Site 1202 can be subdivided into four stages based on the main constituents of the coarse grains in sediment (Figs. F6, F7):
A brief description and interpretation is given below. According to C.-Y. Huang et al. (2005), during MIS 4, the site was already bathed in deep ocean water, as it is today, as shown by the common occurrence of deep-sea benthic foraminifers. Submarine volcanic eruptions related to backarc rifting were frequent and therefore supplied more pumice and volcanic grains to the site during MIS 4 and early MIS 3 (65–52 ka) (Fig. F7D). Distal turbidites in the form of fine sandy layers also occurred and became more frequent during this interval. The next 10 k.y. (52–42 ka) witnessed frequent deposition of turbidites and truncations. The turbidite layers can reach up to 15 cm in thickness and are rich in mica flakes and quartz grains, presumably derived from the terrains of Central Range of Taiwan. Microfossils, if present, are almost all displaced biota from the continental shelf (C.-Y. Huang et al., 2005). Occasionally, bark and crustacean remains are present, implying quick burial and proximity to a terrestrial source region. The thickness and frequency of turbidite deposition decreased from 42 to 36 ka and finally decreased to zero by ~32 ka (Figs. F6, F7A). Notably, slate chips became enriched in the turbidite layers after 42 ka and became predominant until 32 ka (Fig. F7C) (C.-Y. Huang et al., 2005). The reason behind such a major change in the composition of the turbidites is not clear. C.-Y. Huang et al. (2005) suggested implicitly that a major switch of transporting conduit may have occurred from an old submarine canyon (Channel C in Fig. F2) to the present channel (Channel A, which connects directly to the mouth of Lan-Yang River). This might have been related to the jumping of rifting axis to the north, or to northward migration of the Lan-Yang River during deltaic development, or a combination of both.