Physiographic Characteristics of the continental Margin, Northeast Taiwan

Abstract

The continental margin off northeastern Taiwan consists of five major physio­ graphic units which are the East China Sea continental shelf, the East China Sea conintinental slope, the Southern Okinawa Trough, the Ilan continental shelf and the Ilan Ridge. This physiographic framework is provisional and may be revised if better physiographic names are proposed.
The East China Sea continental shelf is relatively wide with a smooth surface marked locally by low-relief features resulting from sea-level fluctuation during the late Pleistocene and by volcanic activities of the back-arc rifting.
The East China Sea continental slope varies laterally in slope gradient and topography. The continental slope is marked by a variety of slumping or sliding scars, erosional gullies, and debris ow deposits or turbidites. The submarine canyons are another prominent topographic feature occurring on the slope. The submarine canyons indent the continental shelf and modify the linear shelf-slope transtition region into an irregular shape. The western end of the Southern Okinawa Trough has curvelinear bathymetric contours at the maximum depth of about 2,000m. The trough is mainly con ned by the continental slope to the north and by slopes o the Ryukyu volcanic islands.
The Ilan continental shelf is the seaward continuation of the Ilan Plain along the northeastern coast of Taiwan. The shelf is fan-shaped, and the width varies from about 10 km o the Lan Yan Hsi River to about 2km at the coastal cities of Touchen and Suao. This shelf protrudes onto the slope seaward with the accumulation of the sediments transported by the Lan Yan Hsi River.
The Ilan Ridge is a long and narrow ridge extending seaward from the Ilan shelf. The ridge separates the forearc basin of the Nanao basin to the south from the backarc basin of the Okinawa Trough to the north. The Ilan Ridge is con ne by the Ryukyu volcanic islands to the east and is relatively narrow in areal extent as compared to the Ryukyu island chain.
The shelf-slope transition region where the water mass exchange process takes place between the East China Sea and the Kuroshio Current is characterized by an irregular topography. This topographic effect on the Kuroshio edge exchange process is worthwhile to be investigated in greater detail.

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