In the western Pacific, the Ryukyu fold belt extends southward, parallel with the Taiwan Sinzi fold zone, across the downwarped Okinawa trough, and, at the north end of Taiwan, they merge into the Taiwan Central Range complex. From the Miocene to the late Pleistocene, orogeny in Taiwan was increasingly more intense, pushing westward and northward to fold and thrust the sediments in the Neogene basin toward the west. However, the tectonic influence was limited only to the onshore sediments of the island.

Within the Taiwan Sinzi fold zone along the edge of the continental shelf of the East China Sea, the Taiwan basin covers the Taiwan Strait, the western coastal

End_Page 1449------------------------------

plain, and the foothills as far as the Penghu-Peikang swell, North and west of the island, offshore seismic profiles show an acoustic basement above which are the predeformation and the postdeformation sedimentary layers separated by a widespread unconformity. The unconformity above the acoustic basement developed after the Mesozoic but before the Miocene, whereas the unconformity between the pre- and postdeformation layers developed after the Miocene. Therefore, we conclude that the predeformation layer was folded under the influence of the Miocene tectonic movement on the margin of the China mainland, which had ceased by the Pliocene-Pleistocene so that the young sediments are flat-lying above the unconformity.

Although the sediments of western Taiwan and offshore on the north and west were deposited in the same sedimentary basin, the tectonic movements on land were from a different source from those offshore. The orogeny on land was strong and late with its influence limited to the development of the structures in western Taiwan. The youngest structures may be sites for the accumulation of oil. The offshore part of the basin was not influenced by this late tectonic movement so that the sedimentary environment and the structure resulting from the Miocene tectonic movement on the margin of the continent should be considered as a possibility on the generation and accumulation of hydrocarbons.

End_of_Article - Last_Page 1450------------