A Discussion on Sedimentary Environment of the Upper Member of Huaqiao Formation—Chefu Formation of Cambrian in Paibi, Huayuan, Western Hunan

Most of the previous researches showed that, Paibi Section was located in the platform margin slope of southeast margin of the Middle—Upper Yangtze Block, with various types of gravity flow deposits as the significant feature in the third series of the Cambrian, and the main sediments of the Upper Member of the Huaqiao Formation—Chefu Formation were argillaceous limestone and calcirudite. On the basis of the detailed study on the rock constituents and sedimentary structure of the typical sediments, this paper found that the banded limestone with the unstable thickness often appeared lenticular or veined was not the argillaceous limestone but the silty banded limestone, which was composed of the limestone bands- grain limestone, micrite and silty limestone bands- silty limestone, laminated carbonaceous silty limestone. So the banded limestones were the mixed sediments with endogenous carbonate sediments and epicontinental clastic sediments,and showed the typical feature of the shelf sediments formed in the mixed shelf. The sedimentary structures caused by storms, such as hummocky (hollow) cross-stratification, ripple mark, wave-ripple bedding, and underside erosion structure, largely developed in calcirudite and its associated rock association, which composed of the tempestite with different sedimentary sequences. In addition, there were a number of algaes, arthropods, other shallow-dwellers fossils and bony spurs of trilobites in the sediments of the Upper Member of Huaqiao Formation—Chefu Formation. Therefore, the depositional environment of the Upper Member of Huaqiao Formation—Chefu Formation was the mixed shelf environment influenced by periodic strong waves or storms, where were below the normal wave base and above the storm wave base in the Third Series of the Cambrian.