Characteristics and environmental significance of late carboniferous brachiopods within the Qijiagou Area, Southern Margin of the Junggar Basin

Abstract

ABSTRACT The Qijiagou section on the southern margin of the Junggar Basin preserves thick and extensive Carboniferous carbonate rocks, and is the type section of the Upper Carboniferous in the Junggar Basin. Here, we studied the lithological assemblages and brachiopod fossils of the Upper Carboniferous Qijiagou Formation on the southern margin of the Junggar Basin. Outcrop observations indicate laterally variable thicknesses of this unit, comprising thick-bedded, fossiliferous, channelised, sandy, and calcareous limestone. Petrographic observations revealed four microfacies, indicating deposition of the formation in diverse depositional environments, including lagoonal to delta-dominated middle shelf settings. In addition, we identified 15 species of brachiopod fossils in 11 genera which belong to Spiriferida Waagen, Productida Sarycheva et Sokolskaya, and Strophomenida Öpik. Thus, based on the characteristics of the lithological assemblage and brachiopod fossils, we infer that the Qijiagou area had a relatively warm environment in the middle and late Late Carboniferous. This included a turbulent and shallow water body with two regressions which occurred in a carbonate platform sedimentary environment.