The Characteristics of Hybrid Facies and Hybrid Sequence of Xiejiawan Member of Ganxi Formation in the Longmenshan Area

Key words: 
• Longmenshan Mountain

Abstract: Based on the data of cross sections and observation of thin sections,the Xiejiawan Member of Ganxi Formation ,Lower Devonian in the Longmenshan is considered to be generated from hybrid type Ⅰsediments dominative of shelf shales. Its genetic mechanisms include the major intermittent mixing mode, which is resulted from the storm flow, and the autochthonous mixing mode. The sedimentary facies of the Xiejiawan Member can be divided into following microfacies, hybrid shore,hybrid clastic shelf, hybrid carbonate shelf,shore peritidal residual + hybrid tidal flat,hybrid shelf shale + distal storm flow,hybrid continental shelf shale intercalated with proximal sandy storm flow,hybrid shelf shale intercalated with proximal sandy hybrid storm flow,and hybrid shelf shale intercalated with organic bank and point reef. Meanwhile, the Xiejiawan Member is characteristic of type Ⅱhybrid sequence and can be classified into 4 depositional system tracts of SMST,TST,EHST and LHST. Each system tract is superimposed by subsequences of different sedimentary sequences,textural styles and hybrid intensity. Among the all above mentioned sedimentary tracts,the SMST and LHST are of the most intensive intermittent mixing and autochthonous mixing,the intermittent mixing of TST is the weakest one,and the EHST is of weak intermittent mixing and autochthonous mixing.