Shifting submarine canyons and development of a foreland basin in SW Taiwan: controls of foreland sedimentation and longitudinal sediment transport

The modem Penghu Submarine Canyon is a sea floor expression of the convergent boundary between the frontal Taiwan orogenic wedge and the Chinese cratonic margin. The canyon is about 180 km long and trends N-S, parallel to the strike of the Taiwan mountain belt. It is similar to 240 m deep at the head increasing to similar to 3200 m deep at its mouth before merging gradually into the Manila Trench. The Penghu Canyon is considered a tectonically controlled canyon rather than a slope canyon dominated by down-slope processes. Tectonic controls prevail over sedimentary processes. Tectonics controls the orientation and location of the Penghu Canyon while sedimentary processes contribute to its excavation and enlargement. The axis of the deep-water, underfilled basin off SW Taiwan dips southward and parallels the strike of the Taiwan orogen with a characteristic longitudinal sediment transport route. Hence, the Penghu Canyon developed under the gravitational mass movement with its main course along the N-S basin axis, not in a SW or SE downslope direction of both margins. The initial Penghu Canyon began at the intersection of the upper slopes of the South China Sea and Kaoping Slopes. Sediment flows cut into the slope sediments following regional dip toward the south, and excavated along the deepest part of the sea floor, forming the present Penghu Canyon. Shifting of axes of Late Pliocene-Pleistocene canyons from onshore SW Taiwan to the present-day position of the Penghu Canyon reflects the evolving foreland basins with a longitudinal canyon transport system progressively migrating southwestward. The linkage of canyon migration and evolution of the foreland basin may have significant implications for the overall sedimentation and tectonics of the SW Taiwan region. (c) 2005 Elsevier Ltd. All rights reserved.