The island of Taiwan was formed as a result of collision of continental and oceanic plates, which may have occurred as recently as post-Miocene time. The epicontinental sea on the autochthonous block includes three sedimentary basins, the Southern basin, south of the Peikang-P'enghu basement high, the Northern basin, between the basement high and the Kuanyin swell, and the Taiwan basin on the shelf of the East China Sea north of the Kuanyin swell. North and west of the island, offshore seismic profiles show that there is acoustic basement above which predeformation and postdeformation sedimentary layers are separated by a widespread unconformity. This unconformity developed after the Miocene. Therefore, we conclude that the predeformation layer was folded under the influe ce of the Miocene tectonic movement on the margin of the China mainland.

Although the sediments of western Taiwan and those offshore to the north and west were deposited in the same sedimentary basin, the tectonic events on land differed from those offshore. On land the orogeny was intense and late, and its influence was limited to development of structures in western Taiwan. Therefore, the youngest structures on land may be the sites for the accumulation of oil. The offshore part of the basin was not influenced by this late tectonic movement. Thus, the sedimentary deposits and the structures resulting from the Miocene tectonic movement on the margin of the continent should be considered as the possible sites for the generation and accumulation of hydrocarbons offshore.