盆山转换与沉积地质记录——以楚雄前陆盆地分析为例

楚雄盆地位于扬子陆块的西南边缘，为一中生代周缘型前陆盆地。根据沉积相特征、层序地层结构和古地理演化的详细研究，结合古哀牢山造山带的构造演化，笔者认为楚雄盆地经历了从古生代被动大陆边缘沉积到中生代前陆盆地沉积的演化。前陆盆地演化的阶段性明显：晚三叠世卡尼期（云南驿组沉积期）和诺利早、中期（罗家大山组沉积期）为前陆复理石沉积；诺利晚期（花果山组沉积期）－古新世（赵家店组沉积期）为前陆磨拉石沉积。磨拉石

Basin-range transition and depositional records:an example from the Chuxiong foreland basin in Yunnan

The Chuxiong Basin located in central Yunnan on the southwestern margin of the Yangtze landmass is a Mesozoic peripheral foreland basin, which is bounded on the southwest by the Honghe fault, on the west by the Chenghai fault and on the east by the Puduhe fault. Tectonically, three units may be distinguished for the basin. They are: (1) western thrusting zone; (2) central depression zone, and (3) 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. Several phases of sediments have been identified in the basin. For example, during the Carnian (Late Triassic) and the early and middle Norian (Late Triassic), the foreland flysch sediments were accentuated. while during the late Norian (Late Triassic) to the Paleocene, the foreland molasse sediments were highlighted. The molasse sediments consist of two categories: marine and continental. The latter are characterized by long time duration, widespread occurrence and greater thickness. On the whole, the basin may have experienced four stages of evolution: basin formation, rapid subsidence, inversion and filling, and final termination. The upward growth and cratonward overburden of the overthrusted orogenic wedges led to the formation of sudden deepening and fining upward sequences during the early stage and shallowing and coarsening upward sequences in the basin during the late stage. In other words, there are gradations from the early flysch sediments to the late molasse sediments, and from deep and narrow basal relief during the early stage to wide and shallow basal relief during the late stage. The centres of subsidence and deposition of the basin once in front of the thrusting orogenic wedges gradually migrated northeastwards (cratonwards). All the data on palaeocurrents, petrography, lithogeochemistry indicate multiple sources of the detritus in the basin, i.e. the detritus were derived dominantly from the ancient Ailaoshan orogenic zone, and subordinately from the eastern uplifted zone.