黔北桐梓狮溪志留纪埃隆晚期石牛栏段的生物滩相

Bank Facies of the Shihniulan Formation( late Aeronian,Llandovery,Silurian) at the Shixi section,Tongzi,northern Guizhou

志留纪兰多维列世埃隆晚期,滇黔桂古陆以北的陆表海缓坡上沉积了石牛栏组石牛栏段浅水灰岩。珊瑚—层孔虫为主的后生动物格架岩建造的点礁分布北界仅延伸到桐梓水坝塘一带;更远岸的狮溪镇白芷垭剖面虽然远离古陆剥蚀区,层状灰岩中极低的粉砂质、泥质含量指示高清澈度的环境指标,内碎屑和少量生屑混合沉积的滩相灰岩沉积深度在最大浪基面之上,但珊瑚—层孔虫密度偏低,后生动物格架岩的丰度以及个体大小均达不到礁灰岩的标准,也不呈现生物礁特有的正向海底地貌。本文实例诠释了海底深度变化显著制约底栖群落的古生态分异,后生动物点礁栖居的深度范围有限。

Limestones of the Shihniulan Member（ Shihniulan Formation,late Aeronian,Llandovery,Silurian） are typical shallow marine facies covering the ramp setting of the northern Dian-Qian-Gui Land on the Upper Yangtze Epicontinental Sea spatially. Patch reefs comprising rich metazoan contributors of coral-stromatoporoid assemblages are limited palaeogeographically along the Shuibatang of the Tongzi County. Bedded limestone sequences from northward off-shoal setting at Baiziya section,Shixi show less silty and muddy components implying higher clarity of the marine water in palaeoenvironmental parameters. Bank facies composed of intraclastics and less bioclastics at the Baiziya section were formed in a depth above the major wave-base. However,complexity of the ecological niche illustrate as lower abundance and smaller-sized in coral-stromatoporoid frameworks; they aren＇t considered as the reefal limestone types. Furthermore,no positive relief is recognized from the limestone units herein. This palaeoecological pattern suggests that differentiations of the benthic communities were essentially constrained by depth varieties of the marine floor. Depth range idealized for inhabitation of metazoan patch reef was relatively narrow.