The texture of sedimentary basin-orogenic belt system and its influence on oil/gas distribution: A case study from Sichuan basin

Based on geomorphology, structure, texture and evolution, the texture of sedimentary basin-orogenic belt system in Sichuan basin and its peripheral orogenic zones could be classified into two types, which are linearly abrupt margin-plate systems and diffusely gradual interior-plate systems. The linearly abrupt margin-plate systems include Sichuan basin and its surrounding Mount Longmen, Mount Micang and Mount Daba, which are not only the western and northern marginal areas of Sichuan basin, but also the western margin of Yangtze plate in south China. The systems possess clearly different lithospheric textures, abrupt boundaries and great contrast in today’s geomorphology between the basin and mountains with typical fold-thrust belts and foreland basins. The formation and evolution of the margin-plate systems is controlled by the differences of lithospheric textures between the basin and the mountains and evolutionary process of the surrounding mountains. The diffusely gradual interior-plate systems are composed of Sichuan basin and its adjacent Mount Qiyue, Mount Dalou and Mount Daliang, which are the eastern and southern marginal areas of Sichuan basin, and located within the Yangtze plate. There are the similar lithospheric texture and gradual boundaries between the basin and the adjacent mountains without foreland basins and large-scale fold-thrust belts. The formation and evolution of the interior-plate system is made by the tectonic deformation outside the basin and multi-layer detachment within the sedimentary cover of the basin. The evolutionary process of the basin and orogen systems has a great control on today’s oil/gas distribution chiefly through the effect on petroleum preserving conditions in Sichuan basin. Today’s medium-large scale gas accumulations and most of the natural gas proved reserves in Sichuan basin were mainly distributed in the areas influenced by the linearly abrupt margin-plate systems, especially those under the control of Qinling Orogenic zone.