Late Katian Paraorthograptus pacificus Graptolite Biozone from Xing'an, northern Guangxi, China

Abstract

Based on the study of recently collected graptolites from the Huang'ai – Shengping – Tianlingkou section of Xing'an, northern Guangxi, China, the Paraorthograptus pacificus Biozone (upper Katian, Upper Ordovician) was first recognized in the upper part of the Tianlingkou Formation in this region. The P. pacificus fauna includes 13 species belonging to 6 genera: P. pacificus (Ruedemann), Dicellograptus ornatus Elles and Wood, Dicellograptus minor Toghill, Anticostia lata (Elles & Wood), Appendispinograptusvenustus (Hsü), Appendispinograptus supernus (Elles & Wood), Appendispinograptus leptothecalis (Mu & Ge), Rectograptus abbreviatus Elles & Wood, Rectograptus socialis (Lapworth), Rectograptus songtaoensis Li, Rectograptus cf. songtaoensis Li, Rectograptus sp. and Yinograptus disjunctus Yin & Mu. This assemblage can be easily correlated with the graptolite fauna of the same biozone in the Wufeng Formation in the Yangtze region. Compared with the P. pacificus fauna in the Yangtze region, the diversity of the present pacificus fauna is rather low. The Tianlingkou Formation in northern Guangxi is a clastic deposit with turbidites and represents rapid deposition. Thus, it is an unsuitable environment for graptolite preservation.