Middle Triassic (Anisian) Conodont Biostratigraphy at the Shaiwa Section, Guizhou, South China

The Nanpanjiang Basin is a key area for paleontological and biostratigraphical study of the Middle Triassic. Herein we studied Middle Triassic conodonts from a well-exposed section, the Shaiwa Section, which is located at the northwest end of the Nanpanjiang Basin. A total of six Anisian conodont zones are recognized; in ascending order, they are: the Nicoraella germanica Zone, the Nicoraella kockeli Zone, the Paragondolella bulgarica Zone, the Neogondolella constricta Zone, the Neogondolella cornuta Zone, and the Paragondolella excelsa Zone, respectively. The first occurrence of Nicoraella kockeli defines the Bithynian-Pelsonian boundary. The Pelsonian-Illyrian boundary is defined by the first occurrence of Neogondolella constricta . The Anisian-Ladinian boundary cannot be recognized at the Shaiwa Section due to the absence of conodont indicative of the Ladinian. However, the new conodont data indicate that the uppermost strata could be very close to the boundary. The abrasion of conodont surfaces provides evidence for demonstrating reworking at the Shaiwa Section, which makes some conodonts possess a longer stratigraphic range than previously recorded. The variation in relative abundance between blade-shaped conodonts and platform conodonts indicates that segminiplanate elements probably preferred deeper and oxygenated environments whereas a restricted marine environment is more suitable for segminate elements.