Abstract

There has been a number of attempts to reconstruct the geological history of the Southeast Asia/South China Sea region. Most attempts have tried to fit in with the ‘subduction theory’ of plate tectonics and have ignored the alternative theory based on ‘an expanding earth’. From my recent studies, I believe that the geological history of this region can be best explained in terms of an expanding earth.

The area now occupied by Southeast Asia covers part of the Late Proterozoic continent of Pangaea. That continent began to break up in the Cambrian with an incursion of the seas. The extent of the seas increased from the Ordovician to the Permian, as the continent continued to break up and spread apart. There was an orogeny in the Late Permian/Early Triassic time, which brought about a withdrawal of the seas from what is now Borneo and Sumatra.

These areas were then transgressed by the seas of the Late Triassic lo Late Cretaceous. These seas withdrew from the West Malaysia area near the close of the Triassic and from the Indo-China and Hong Kong areas in the latter part of the Early Jurassic. After an orogeny in late Cretaceous, the Sumatra-West Sarawak areas became welded onto the Malayan (Sunda) landmass and the seas became confined to the northern half of what is now the island of Borneo. From the Proterozoic until the Late Oligocene, the general break up was the result of a general north-south spreading.

The landmass covering the present South China Sea-Gulf of Thailand area began to break up in the Late Oligocene, with marine conditions in the east along the coast of what is now northwest Borneo and non-marine conditions along what is now the Gulf of Thailand and offshore West Malaysia. This break up was the result of a general east-west spreading. The area of the present South China Sea continued to open with further transgression of the sea from the northeast during the Early Miocene.

An orogeny within the Middle Miocene brought rifting to the east of Natuna Island and the opening of the Malay Basin to the seas. There was possibly a major tectonic movement in the mid-Pliocene in the Malay Basin which brought about uplift and folding, followed by sub-marine erosion. In the late Pliocene the seas became more transgressive, and in the late Pleistocene they covered all of what is now the Gulf of Thailand and South China Sea.

The orogenies within the South China Sea area, since the Late Oligocene, were connected with the general east-west spreading, which resulted from the expansion of the earth.