川西北晚三叠世盆-山耦合过程与古地理演化OA

The provenance of the Upper Triassic Xujiahe Formation in the northwestern Sichuan Basin and the temporal evolution of sediment supply of the surrounding orogenic belt are controversial research topics.Moreover,tectonic sedimentary models based on multi-source systems need to be further studied.Based on field outcrops and drilling and logging data,we comprehensively analyzed the Xujiahe Formation's provenance through the characteristics of rock debris,heavy mineral assemblages,paleocurrents,and age characteristics of detrital zircons.By clarifying the filling process of the Xujiahe Formation during the sedimentary period,focusing on the distribution and migration of detrital materials,the basin-mountain coupling relationship and paleogeographic evolution of the orogenic belt around the northwest of Sichuan Basin were revealed.There were three major source areas in northwestern Sichuan Basin during the deposition of the Xujiahe Formation,including the Songpan-Ganzi fold belt,the Longmenshan thrust belt,and the South Qinling Mountains.According to a statistical analysis of the percentage of debris and heavy minerals in sandstone samples from the Xujiahe Formation,the debris and heavy mineral assemblages were classified as follows:the first and second members of the Xujiahe Formation can be divided into two types of combination areas,and the third and fourth members of the Xujiahe Formation can be divided into three types of combination areas.Based on the comprehensive analysis of provenance,combined with the distribution and sedimentary evolution of clastic rocks in the study area,it is considered that during the sedimentary period of the first and second members of Xujiahe Formation,the western Songpan-Ganzi fold belt,and the Longmenshan thrust belt are the main source areas,which supplied a braided river delta that developed in the basin.During the deposition period of the third member of the Xujiahe Formation,a strong uplift occurred in the north-central section of the Longmenshan,which was the source of a fan delta that developed in the northwest of the study area.The low-amplitude uplift of the Micang Mountains began to supply a braided river delta that developed in the eastern part of the study area.During the sedimentary period of the fourth member of the Xujiahe Formation,uplift of the middle and northern sections of the Longmenshan increased,and the Micang-Daba Mountains further overturned and uplifted;meanwhile,the scale of the braided river delta in the eastern part of the study area gradually expanded.The source supply was strong in the west and weak in the north in the early stage,and changed to a northwest joint sand supply in the later stage.The evolution of the Longmenshan thrust belt and Micang-Daba Mountains were dominated by changes in the tectonic sedimentary pattern and material distribution in northwestern Sichuan.By discussing the basin-mountain coupling process in northwestern Sichuan and the sand body distribution law and paleogeographic evolution under various constraints,this study provides a new perspective for the study of the material basis of the Xujiahe Formation.