Sedimentary environments of the Middle Permian phosphorite-chert complex from the northeastern Yangtze platform, China; the Gufeng Formation: a continental shelf radiolarian chert

In general, shelf-type radiolarian chert, represented by the Gufeng Chert, usually shows some of the following features: dark color, lack of rhythmical bedding, association with phosphorite, platformal limestone, felsic tuff, abundant organic matter, and sulfides. Shelf-type radiolarian chert is deposited in a poorly aerated restricted basin, or in an oxygen-minimum zone.