The Early Cambrian Balang Fauna, Eastern Guizhou, China
Jin Peng1,2, Yuanlong Zhao1, Hongzhen Feng2, Lu Yao1, Qin Qin1 and Xu Yan1
1 College of Resource and Environment Engineering, Guizhou University, Guiyang, China
2 College of Earth Sciences and Engneering, Nanjing University, China
The Early Cambrian Balang Formation (eastern Guizhou, China) is composed of gray to gray-greenish silty shale or muscovite-rich shale and mudrock. It was deposited in a slope facies belt juxtaposed between the Yangtze platform to the west and the Jiangnan basin to the east. Trilobite biostratigraphy places the fauna in Cambrian Series 2 (Dunyunian Stage, equivalent to the late Chanlangpuian and Botomian), between the Early Cambrian Chengjiang Biota and the Middle Cambrian Kaili Biota. The age-equivalent Guanshan Biota was preserved in shallow water settings, whereas the Balang Biota was preserved in deeper water, in shelf margin to slope facies.
The upper part of the formation yields an important Burgess Shale-type biota, including a diverse skeletal fauna, non-mineralized invertebrates, algae, and a rich ichnofauna. The eocrinoid Guizhoueocrinus and the trilobite Redlichia (Pteroredlichia) are the most common and characteristic taxa of the fauna. The fauna also contains trilobites, trilobitomorpha, bradoriids, large bivalved arthropods, coelenterates, brachiopods, priapulid worms, molluscs, stalked eocrinoid echinoderms, hyoliths, chancelloriids, brachiopods, phyllocarids, bradoriids, and palaeoscoleids.
The preservation of an unusually large quantity of high quality articulated eocrinoid specimens, including those preserved attached to skeletal fragments of hyolithids, trilobites and bradoriids, indicates that the fauna was smothered and rapidly buried by obrution events. Only one species of eocrinoid is presnt; it exhibits a complex ontogeny involving changes in ambulacral symmetry, position and number of thecal plates and sutural pores, and number and disposition of brachioles.