The development of river-mouth systems is controlled by tectonics and sea-level and climate change in the long run. Due to obvious difference in tectonic activities between the western Taiwan coast and the eastern Zhe-Min coast, coastal evolution patterns in response to late-Quaternary sea-level and climate change are quite different across the strait, resulting in different depositional systems along their present river deltas. We take Ou and Zhoushui River deltas as their representatives to explore their different coastal behaviors and resultant depositional strata in the late Quaternary.

The Ou River drains an area of ~1.80×10⁴ km2 in the northeastern Zhe-Min Uplift zone with the headwater elevation of 1856.7 m and total river length of 388 km. It carries mean annual water and sediment discharges of 1.67×10¹⁰m3 and 2.22×10⁶ tons, respectively. The Zhuoshui River drains an area of 3157 km2 in central Taiwan with the headwater elevation of ~3400 m and total river length of 187 km. It carries mean annual water and sediment discharges of 0.61×10¹⁰ m3 and 54×10⁶ tons, respectively. In comparison, the Zhuoshui River has an average sediment yield of ~17000 tons/km2, two orders of magnitude higher than that of the Ou River (~120 tons/km2). The former produces a coarse-grained (coarse sand and gravel dominated) fan delta in the river mouth, while the latter creates a tide-dominated delta with silt and fine-sand predominance.

Core strata show MIS 3 deposition in the present Zhoushui River Delta is over 50 m thick, formed in a foreland basin with a rapid subsidence rate of 1.2 mm/yr. They are composed of more than four fluvial channel-floodplain cycles, potentially registering Heinrich cycles and fluvial channel switch events. In contrast, MIS 3 strata are usually less than 20 m thick in a relative stable coast. They consist of a transgressive system tract in the lower, topped by a several meter thick paleosol formed during the MIS 2 lower sea level. An elevated MIS 3 highstand sea level is therefore indicated to reach up to -24 m.

Holocene strata in the Zhoushui River Delta are also thicker and coarser than those in the Ou River Delta. The latter received abundant fine-grained sediments from the Yangtze River by alongshore current. Both river watersheds and deltaic coasts are significantly influenced by typhoon and East Asian monsoon activities. For the Zhoushui River Delta, it is majorly shaped by river flood events induced by typhoons and summer monsoon. However, the Ou River Delta is greatly shaped by coastal erosion induced by typhoons and alongshore sediment replenishment by winter monsoon.