Morphological and Seismic Characteristics of the North Mien-Hua Submarine Cany on off Northeastern Taiwan

Abstract

The North Mien-Hua Canyon on the East China Sea Slope off north-eastern Taiwan is a multi-headed canyon. For distinct heads immediately below the shelf edge coalesce to form a single canyon near the 900 m isobath in the lower slope region. Morphologically, the North Mien-Hua Canyon can be divided into two distinct units: the upcanyon segment which is the fan-shaped sloping region extensively cut by these four tributary canyons, and the down canyon section which is short and straight with no tributaries.

These four tributary canyons are characterized by steep-sided V-shaped troughs with high reliefs in excess of 500 m, suggesting intense down-cut· ting of the canyon. The single canyon course on the lower slope still maintains a V-shape in cross-section but with a curved and irregular canyon bottom, implying partial sediment infilling. The seismic profiles show termination of parallel reflectors of slope sediments against the canyon walls and slumping features, providing evidence of downslope submarine exca· vation along the canyon course. Cut-and-fill features are only recognized in the downcanyon section. Morphological and seismic characteristics indi· cate that the upcanyon segment is dominated by erosion and the downcanyon section is represented by multiple episodes of canyon erosion and deposition.

The North Mien-Hua Canyon began as submarine incisions or gullies on the upper part of the East China Sea Slope. Downslope excavation deepened and widened the gullies into tributary canyons which in turn flowed downslope and joined together to form a single canyon. The seismic data provide no evidence of faults along or across the canyon course, suggesting the origin of the canyon might not be fault-related.

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