Mesozoic tectonic subsidence in the Chuxiong foreland basin, Yunnan

The Chuxiong Basin in Yunnan on the southwestern margin of the Yangtze landmass is a Mesozoic peripheral foreland basin. Tectonically, three units may be distinguished for the basin:western thrust zone, central depression zone and eastern uplifted zone. In terms of sedimentary facies, sequence stratigraphy and palaeogeographic evolution in combination with tectonic evolution of the Ailaoshan orogenic zone, the basin shows a depositional evolution from the Palaeozoic passive continental margin to the Mesozoic foreland basin. Two phases of the sedimentation have been identified in the Chuxiong foreland basin:the foreland flysch sedimentation during the Late Triassic and the foreland molasse sedimentation during the Jurassic. The following conclusions are generalized on the basis of the tectonic history of the basin. (1) The Late Triassic flysch basin is characterized by high amplitudes of tectonic subsidence. The centres of subsidence and deposition lay in the westernmost part of the basin close to the Ailaoshan orogenic belt. The sedimentary bodies there display the wedge-shaped distribution. (2) The forebulges and centresof subsidence and deposition in the molasse basin migrated landwards during the Jurassic. (3)The Mesozoic rapid tectonic subsidence and wedge-shaped sedimentary bodies indicate the origin of lithospheric flexure in the Chuxiong Basin. (4) The higher sedimentation rates are controlled by both the tectonic and overcompensational sedimentation.