From Jurassic through Early Miocene there was active rifting of the south China and north Australian continental margins. Magnetic anomolies of the marginal seas indicate that microcontinents were drifted as far as Borneo. Together with island arcs, these microcontinents formed the nuclei against which distal turbidites accumulated, with their source perhaps as for away as the Mekong Delta.

The post Oligocene convergence of Australia and the Philippines against Indonesia, effected by subduction of extinct marginal sea lithosphere, resulted in uplift of the ancient microcontinents and their turbidite drapes to form new provenance landmasses for shallow water sedimentation in adjacent basins.

Plate tectonic basin classification cannot be successful unless the Plate tectonic basin classification cannot be successful unless the important role of the microcontinents is recognised. Their presence in the Southeast Asian developing orogen hinders the formulation of an elegant classification.

Introduction

The need for classification is basic to all human fields of endeavor. The complexities of Nature prevent the formulation of a perfect classification and commonly the allocation of a classification name or symbol camouflages our ignorance. Just as no two orogenic belts are identical, so no two basins are identical. The dangers of worldwide classifications are well illustrated by attempts to force the Alpine orogenic ‘norm’ or the Appalachian geosynclinal ‘norm’ on the rest of the world. We now know enough to reelize that these attempts were misguided. Basic classification should not fall into this some trap. In applying a model which has been successful elsewhere, the local idiosyncrasies of Nature must first be fully evaluated.

EXISTING S E ASIAN CLASSIFICATIONS

Two brave attempts at classification appeared independently in 1975. The more detailed one by Murphy (1) subdivided the basins into "shelfal", "continental margin", "archipelagic" and "marginal seas". As broad general categories, they are satisfactory, but "shelfal" and "continental margin" categories are so broad as to fall short of usefulness. Soeparjadi et al used categories such as "outer arc", "foreland", "interior cratonic" and "open shelf on continental margin". Some of these terms are open to misinterpretation when compared with the rest of world. "Interioratonic" conjures up a vision of a stable craton of ancient ancestry and implies that the basin is unrelated to plate margin tectonics.

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