Sedimentary erosive processes and sediment dispersal in the Gaoping Submarine Canyon in the southwestern Taiwan margin

The Gaoping submarine canyon, connected to the Gaoping River in the coastal plain in SW Taiwan, continues the dispersal path of Gaoping River sediments from an active, small mountainous drainage basin to the receiving South China Sea basin. Using seismic reflection sections, Chirp sonar profiles and bathymetric mapping, this study reveals the characteristic erosive processes responsible for multiple cut-and- fill features, deeply entrenched thalweg and sediment dispersal in the canyon, closely related to turbidity currents in the canyon. The river-canyon connection setting of the Gaoping Canyon with its extreme climatic conditions and active tectonic activity is favorable for the generation of turbidity currents at the canyon head. The upper reach of the Gaoping Canyon is distinguished by three distinct morpho/sedimentary features. The canyon head is characterized by V-shaped axial thalweg erosion. The proximal segment of the upper reach is dominated by a deeply incised canyon pathway with trough-like morphology. Cut-and-fill features are common along the canyon floor, resulting in a flat-floored pathway. Sliding and slumping are dominant features on the steep canyon walls, producing and transporting sediments to the canyon floor and partially filling up the canyon thalweg. The distal segment is characterized by erosive features where deeply down- cutting erosion occurs mainly in the outer bend of the major sea valley, forming the V-shaped entrenched thalweg. The recurrences of turbidity currents have caused continuous incision of the canyon head and have kept the connection between the canyon head and the river mouth during the Holocene highstand of sea level. The upper reach of the Gaoping Canyon is linked to the drainage area, and remains active as a conduit and/or sink for terrigenous and shallow marine material. Oceanic flood sedimentation operates in the Gaoping River- Canyon system; inferred turbidity currents flush river sediments into the canyon head where the canyon thalweg is the most erosive. Presently, the upper reach of the Gaoping Canyon can be considered as a temporal sediment sink rather than a major sink.