Many plate tectonic reconstructions for Southeast Asia are whimsical and place little emphasis on offshore data and in explaining basin evolution. Major issues include determining the palaeolatitude of Borneo, its clockwise or anticlockwise rotation, and understanding the nature of the Proto-South China Sea. Integrating plate tectonic models with patterns of paleoclimate and palaeoenvironment change over time, together with consideration of the geology and individual basin evolution across Sundaland, provides strong constraints in determining which plate tectonic models are realistic. Here we have used palaeoclimate and palaeoenvironment data to make improvements to the GEM plate model, which utilises a rigorously constrained, spherical global reference frame coupled with a spatially consistent interpretation of basement terranes and regional structures to provide an increasingly realistic and predictive plate tectonic model for the region.

Different plate tectonic models show the position of Borneo in the Eocene varying by up to 25° of latitude. Palaeoclimate data based on palynology and climate-sensitive lithologies from the Sunda Shelf provides an independent indication of the degree of Sundaland rotation by locating the position of the southern margin of the northern hemisphere Hadley Cell over time, which global palaeoclimate modelling studies show has been more or less at the same latitude through the Cenozoic. It corresponds to a change from perhumid climates along the equator to seasonal, often monsoonal tropical climates north of about 8° N. Palaeoclimate data favours plate tectonic models that show a more northerly position of Borneo in the Eocene compared to today, with the extrusion of Sundaland then Indochina following collision of India with Asia, and with consequent clockwise rotation of Borneo into its current equatorial position during the Oligocene to early Miocene. Plate tectonic models which propose anticlockwise rotation of Borneo are extremely difficult to accept based on palaeoclimate reconstructions. Also, the nature of paleoenvironments across the Sunda Shelf suggest that this rotation is accompanied by extension, especially during the late Eocene and Oligocene.

In this collaborative, expanded presentation, we show how palaeoclimate and plate positions are intimately related. For example, India’s northward drift into an equatorial position during the Paleocene and its subsequent progressive collision with Asia starting with the Burma Plate explains the dispersal of African and Indian plant lineages into Southeast Asia during the middle Eocene.

This will be followed by discussion of the clockwise rotation of Indochina and Sundaland and the linkage between the development of rifting across the Sunda Shelf with the opening of the South China Sea, emphasising observed late Eocene and Oligocene extension and subsidence rather than complex Sunda Shelf orogenic uplift, as required by other models. Such models imply a wide Proto-South China Sea for which there is no evidence in the Late Miocene to Recent collisional system of NW Borneo. We interpret the Proto-South China Sea as a relatively narrow back arc basin to the West Pacific active margin of SE Asia.

Clockwise rotation came to an end as the Sula Spur (i.e. the northern-most promontory of the Australian Plate) came into contact with Sundaland, from which time Borneo remains in its current equatorial position, with the initiation of uplift of the Central Ranges of Borneo and Meratus Mountains a response to Pacific-derived plate convergence.

Thanks to our SEAPEX-initiated collaboration we are now producing an integrated, high resolution paleogeographic-tectonic model for the evolution of SE Asia that has profound implications for understanding basin evolution across the region. We encourage companies exploring the region to integrate these concepts into their exploration programmes.