DEVELOPMENT OF THE SHALE DIAPIR-CONTROLLED FANGLIAO CANYON ON THE CONTINENTAL-SLOPE OFF SOUTHWESTERN TAIWAN

Fangliao Canyon is one of several major canyons on the continental slo pe off southwestern Taiwan. This paper evaluates the canyon morphology and its formative processes and origin using multichannel seismic ref lection profiles and bathymetric data. Fangliao Canyon is a small cany on around 10 km wide and 60 km long, an order of magnitude smaller tha n the large canyons of the world. This canyon can be divided into two morphologically contrasting parts: the upper canyon, a relatively stra ight part beginning at the shelf edge and ending approximately at the 600 m isobath, and the lower canyon, consisting of two segments separa ted by a rising linear ridge (shale diapir) and extending downslope to about the 1000 m isobath where its mouths lack submarine fans. Seismi c profiles and bathymetric data provide evidence of submarine erosion forming the upper canyon and the uplift of a shale diapir controlling the formation of the lower canyon. In the upper canyon, truncation of parallel flat-lying strata and sliding/slumping features on the canyon walls are indicative of downcutting and lateral widening of the canyo n. In the lower canyon, the shale diapir uplifted the slope strata and protruded through the overlying slope sediments, producing a ridge ri sing from the sea floor. Here the steep flanks of the shale diapir bec ome the walls of the steep-sided canyons. The interaction of these sed imentary and tectonic processes on the continental slope off southwest ern Taiwan forms the present Fangliao Canyon.