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The Late Oligocene Palaeogeography, Palaeolandscape and Palaeodrainage of Indochina and Southeast China

Wilson, Kerri
Getech Group, Leeds, United Kingdom.

During the Late Oligocene, the South China Sea had begun to open, with major displacement along the Red River and Song Ma Fault zones. This has a number of consequences and related effects, most notably the opening of the Gulf of Thailand rifts and Malay Basin, and in the Cuu Long and Nam Con Son Basins. In the north, the Sichuan-Chuxiong Basin palaeo-drainages now exited into the Song Hong Basin. It is uncertain as to whether the Khorat Basin drainage remained in isolation, or temporarily flowed into the Phu Khan Basin where clastic progrades have been identified at this time. The denudation of the Indosinian Highlands across the Gulf of Thailand-Malaysia-southern Vietnam region, seems to have been quite swift geologically and we postulate that this reflects the underlying tectonic processes, rather than only erosion. Whatever the balance of these processes, by the Late Oligocene, the area was heavily broken by individual rifts, with short-headed drainages bringing coarse clastics into developing lakes. Larger axial drainages had begun to form during this time connecting the Pattani and Malay Basins. However, we do not interpret any connection between these systems and the West Natuna Basin until the Miocene.

The Late Oligocene palaeogeography map of Indochina and southeast China comprise mapping, in ArcGIS, of palaeoenvironments, palaeolithologies and palaeodrainage. The reconstruction of palaeotopography and palaeodrainage comprises a variety of techniques that link an understanding of the underlying tectonics with landscape evolution. All this provides a spatial context for representing and investigating the past distribution of these elements.

The late Oligocene is an important time for both reservoir and source rock development. Therefore the ultimate aim is to achieve a dynamic landscape model that brings together tectonics, surface processes and climate with which explorationists can confidently predict depositional systems: sediment volumes; character; and distribution, and therefore extend interpretations beyond the extent of existing data (e.g. wells, outcrop). Such models implicitly include information on the underlying tectonics that can influence the nature and timing of trap formation, expulsion, burial history and for providing explorationists with a visual link between tectonics and source to sink relationships (the distribution of accommodation space and sediment source areas).

 

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012