中国科学院南京地质古生物研究所机构知识库

Ningqiang Formation (late Telychian, Llandovery, Silurian), characterized by nearly 3000 m of shales intercalated with carbonates, is situated between Ningqiang (S. Shaanxi Province) to Guangyuan (N. Sichuan Province) adjacent to the northwest margin of the Yangtze Platform. The high diversity "Xiushan Fauna", and abundant reef development, illustrate a relatively warm and persistent shallow marine environment in these early Silurian sediments. The sequence shows reef radiation after recovery from the end Ordovician mass extinction events. Multiple horizons of reef-building occurred within a relatively short geological interval and resulted in more than 30 patch reefs up to 200 in in diameter and 1-50 m vertically, composed of abundant fossils. Reef biota include frame-building corals, stromatoporoids, bryozoans, and microbialites, and reef-associated organisms such as crinoids, brachiopods, trilobites, gastropods, nautiloids and ostracods. Three reef-related biotic associations are recognised: a) reefs dominated by framework with crinoids and microbia; b) reefs dominated by only crinoids and microbia; and c) crinoid-dominated facies. Seven representative reef examples illustrate different morphologies and growth styles. A high terrigenous debris input and shallow epicontinental ramp, which lacked obvious topographic variation, were major controls which resulted in rather simple reefs; sedimentation was apparently the main constraint on lateral and vertical extension of reefs, and prevented large-scale reef complexes developing.