INFILLING SEQUENCES AND OROGENESIS IN THE CHUXIONG FORELAND BASIN,YUNNAN

The Chuxiong Foreland Basin,a Mesozoic foreland basin installed on the southwestern margin of the Yangtze plate has seen two stages of development;the foreland flysch infilling stage from the Carnian to Norian (Late Triassic),and the foreland molasse infilling stage from the late Norian to Rhaetian (Late Triassic),during which two second-order sequences and four third-order sequences were correspondingly generated.The progradation velocities of the Ailaoshan frontal thrust zone got control of the upwarping amplitudes of the basement and the subsidence rates of the Chuxiong Foreland Basin,and the uplifting amplitudes of the thrust zone commanded the supply rates of the terrigenous clasts.Seeing that the accommodation spaces and supply rates are considered to be two fundamental factors for controlling sequence stratigraphic framework of the basin,the migration of the foreland thrust load is interpreted as the key factor for controlling the sequence stratigraphy of the basin.The research results in the present paper have disclosed the characteristics and processes of orogenesis with the aid of the infilling sequences in the basin.The early and middle deepening-upward second-order sedimentary sequences in the basin indicate that the thrust load was prograded onto the cratonic basement.The upwarping rates of the crust decreased,and the supply rates of sediments increased.The mutual superimposition of the third-order sedimentary sequences has revealed the multiphase and multistage orogenesis in the orogenic zone.