Cambrian and earliest Ordovician fauna and geology of the Song Da and adjacent terranes in Vietnam

• Published in: Geological magazine Vol. 159; no. 1; pp. 55 - 80
• Main Authors: Hughes, Nigel C, Peng Shanchi, Peng Shanchi, Harper, David A. T, Myrow, Paul M, Ngan Kim Pham, Ngan Kim Pham, Wernette, Shelly J, Zhu Xuejian, Zhu Xuejian
• Format: Journal Article
• Language: English
• Published: Cambridge University Press 01.01.2022
• Subjects: Arthropoda; Asia; Brachiopoda; Cambrian; detrital zircon; Dong Son Formation; Far East; faunal provinces; Gondwana; Ham Rong Formation; invertebrate; Kaotaia xuanensis; Lower Ordovician; nesosilicates; new taxa; Ordovician; orthosilicates; paleogeography; Paleontology; Paleozoic; silicates; Song Da Terrane; Song Ma Formation; Stratigraphy; Thanh Hoa Vietnam; Trilobita; Trilobitomorpha; Vietnam; zircon; zircon group
• ISSN: 0016-7568; 1469-5081
• DOI: 10.1017/S0016756821000844

Later Cambrian and earliest Ordovician trilobites and brachiopods spanning eight horizons from five localities within the Song Ma, Ham Rong and Dong Son formations of the Thanh Hoa province of Viet Nam, constrain the age and faunal affinities of rocks within the Song Da terrane, one of several suture/fault-bounded units situated between South China to the north and Indochina to the south. 'Ghost-like' preservation in dolomite coupled with tectonic deformation leaves many of the fossils poorly preserved, and poor exposure precludes collecting within continuously exposed stratigraphic successions. Cambrian carbonate facies pass conformably into Lower Ordovician carbonate-rich strata that also include minor siliciclastic facies, and the recovered fauna spans several uppermost Cambrian and Lower Ordovician biozones. The fauna is of equatorial Gondwanan affinity, and comparable to that from South China, North China, Sibumasu and Australia. A new species of Miaolingian 'ptychopariid' trilobite, Kaotaia xuanensis, is described. Detrital zircon samples from Cambrian-Ordovician rocks of the North Viet Nam and Song Da terranes, and from Palaeozoic samples from the Truong Son sector of Indochina immediately to the south, contain a predominance of ages spanning the Neoproterozoic period and have a typical equatorial Gondwanan signature. We associate the Cambrian and Tremadocian of the Song Da terrane with areas immediately to the north of it, including the North Viet Nam terrane and the southern parts of Yunnan and Guangxi provinces of China.