Physiographic and geological characteristics of shelves in north and west of Taiwan

Abstract

In north of Taiwan the East China Sea Shelf extends from the coastline of mainland China to the southern Okinawa Trough, showing a shelf-slope-basin bathymetric profile. Sea floor of the East China Sea Shelf is generally smooth and flat. It is wide (230 km) and relatively shallow with an average shelf-break depth of 120 m, reflecting the effect of Quaternary glaciation about 15000 years ago. The Pliocene-Quaternary East China Sea Shelf is underlain by thin sequences of about 1000 m thick shallow marine sediments mainly derived from China, forming an eastward dipping sedimentary wedge due to regional tilting and subsidence and representing the youngest part of the Cenozoic rift margin in southeastern China. The Taiwan Strait Shelf has two phases in development: one is the early phase of the Paleocene-Miocene rift margin and the other is the late stage of the Pliocene-Quaternary foreland sedimentation. It is a foreland shelf and its present morphology results from the combined effects of tectonic subsidence and sedimentation overprinting that of the Late Pleistocene glaciation about 15000 years ago. Southeast of the Taiwan Strait Shelf lies the very narrow Kaoping Shelf along the southwestern Taiwan coast. The island shelf is a short, narrow and shallow shelf (100 km long, 20 km wide and 80 m deep). Progradation of Quaternary orogenic sediments from the Taiwan orogen forms the present island shelf off southwest Taiwan. The shelf represents the early stage of foreland basin sedimentation. The transition from a passive margin shelf (East China Sea Shelf), a foreland shelf (Taiwan Strait Shelf) to an island shelf (Kaoping Shelf) along the strike of the fold-and-thrust belt of Taiwan mainly reflects the oblique collision between the Luzon Arc and the Chinese margin from Pliocene to the present. The accompanying uplift of Taiwan orogen, foreland-basin sedimentation, and sea level changes contribute to the formation of these three different shelves adjacent to Taiwan.