Mixed sedimentary characteristics and controlling factors of Upper Paleozoic Group in Northern Qaidam Basin

Various mixed sedimentary rocks and sequences with different formation mechanisms were formed in Late Paleozoic strata of Northern Qaidam Basin. Types of mixed sedimentary rocks can be divided into three categories based on differences in petrology and size:eclipse source conglomerate, mixed sedimentary rock with coarse clastics, marl and lime mud stone, and mudstone with fossils. Mixed sequence formed in every environment, mixed facies can be divided into mixed gritty clastic shore, mixed low-energy clastic shore, mixed carbonate platform, and mixed muddy shelf. Sedimentary models were established based on the analysis. The authors believe that the combined action of tectonic movement, eustatic sea level change, paleoclimate and ancient basin slope angle led to the wide development of mixed sedimentary rocks. The nearby existence of the Caledonian tectonic belt and near-provenance sedimentary rocks are prerequisites for the mixture of coarse-grained clastics and biological detritus. Frequent sea level changes and slow slope toe are the direct causes of highly frequency appearance of mixed rocks and sequences.