滇西洱源县军马场下三叠统青天堡组冲积扇-三角洲沉积体系研究

The alluvial fan-delta depositional systems in the Lower Triassic Qingtianbao Formation,Junmachang,Eryuan,western Yunnan

滇西洱源县位于扬子地块西南缘丽江拗陷盆地南侧。在详细野外剖面测量和室内分析的基础上,对研究区下三叠统青天堡组地层的宏观特征(颜色、原生沉积构造)、物质组分、岩石结构及古生物特征等进行了系统研究,划分出冲积扇、河流、三角洲3类沉积相,并进一步划分出河道充填、三角洲前缘和前三角洲3个沉积亚相及辨状河道、洪泛平原、水下分流河道、分流河道间、河口砂坝、席状砂6个沉积微相。研究表明,军马场下三叠统青天堡组垂向上表现为冲积扇—河流—三角洲的退积型沉积特征,表明在早三叠世青天堡时期盐源-丽江盆地发生了大规模海侵,盆地水体加深,军马场地区经历了由陆相到海相的沉积演化序列。

The present paper gives a detailed description of macroscopic features,compositions,textures and structures and organic fossils in main rock types from the Lower Triassic Qingtianbao Formation,Junmachang, Eryuan,western Yunnan. The facies classification is involved in three sedimentary facies including alluvial fan, fluvial and delta facies,three sedimentary subfacies including channel filling,delta front and prodelta subfacies, and six sedimentary microfacies including braided channel, flood plain, subaqueous distributary channel, interdistributary bay,channel mouth bar and sheet sand microfacies. The vertical retrogradational sequences of the alluvial fan,fluvial and delta deposits in the Lower Triassic Qingtianbao Formation in the Junmachang region shows that the widespread transgressions once took place in the Yanyuan-Lijiang basin during the Qingtianbaoan of the Early Triassic,resulting in the sedimentary evolution from the continental facies to the marine facies in the Junmachang region.