渝东南地区下志留统石牛栏组混合沉积作用及对生物礁发育的制约

渝东南地区下志留统石牛栏组广泛发育碳酸盐与陆源碎屑的混合沉积。通过野外观察、薄片鉴定、同位素分析等手段，对研究区石牛栏组混合沉积作用及对生物礁的制约进行了研究。结果表明，渝东南地区石牛栏组主要发育泥质灰岩与砂质泥岩、泥晶灰岩与泥岩、生物灰岩与灰质泥岩3种混积层系和泥质灰岩、砂质/粉砂质灰岩、含粉砂生物礁灰岩（生物灰岩）、灰质粉砂岩、灰质泥岩6种混积岩。沉积环境的演化过程表现为早期浅水混积陆棚—中期生物礁滩—晚期礁前斜坡及浅水混积陆棚；陆源碎屑含量从底部到顶部总体为降低的过程，与海平面的演化规律存在一定的耦合。混合沉积主要发生于浅水混积陆棚及生物礁滩/斜坡2种沉积环境。在石牛栏组生物礁发育过程中，陆源碎屑的注入是制约生物礁及生物群落发育的根本原因。

Mixed sedimentation and constraints on reef of Shiniulan formation in lower Silurian, southeast of Chongqing

Mixed sediments of carbonate and clastic origin are widely developed in Shiniulan formation of lower Silurian, southeast of Chongqing. Taking the typical Shiniulan profile as the study object, through the field observations, thin section analysis, isotope analysis and other means, the mixed sediments and the constraints on the reef of Siniulan formation are studied. The results show that, there mainly developed argillaceous limestone and sandy mudstone, micritic limestone and mudstone, biological limestone and lime mudstone, which have formed three diamictic strata. There develops the argillaceous limestone, sandy limestone, silty clay limestone, silty reef limestone (biogenic limestone), gray siltstone, lime mudstone, that is, six kinds of gray diamictites. In Siniulan formation, the depositional environments are mainly early shallow mixed continental shelf, that is, interim reef deposits-advanced reef slope sedimentary evolution, and the terrigeneous content reduces from bottom to top in the overall process, and the mixed deposition occurs mainly in shallow mixed continental shelf and reef and beach/ramp, two depositional environments. It is confirmed that, in the Shiniulan reef development process, the injected terrigeneous debris is the major cause which has constrained the development of the reef and the biological communities.