UPPERMOST PERMIAN TO LOWER TRIASSIC CONODONT ZONATION FROM THREE GORGES AREA, SOUTH CHINA

摘要

A complete marine uppermost Permian to Lower Triassic succession is well exposed at the Daxiakou section of the Three Gorges area, western Hubei Province, South China. A total of 12 conodont zones are recognized from the uppermost Changhsingian (upper Permian) to Olenekian (Lower Triassic). Of these, the Clarkina yini, Clarkina meishanensis, and Clarkina taylorae Zones characterize the uppermost Changhsingian, whereas the Hindeodus parvus, Isarcicella staeschei, Isarcicella isarcica, Neoclarkina krystyni, Neoclarkina discreta, Sweetospathodus kummeli, and Neospathodus dieneri Zones define the Induan. Early Olenekian conodonts are assignable to the Novispathodus waageni and Nv. pingdingshanensis Zones. Conodont zones across the Permian- Triassic boundary (PTB) beds at Daxiakou correlate well with those established from the Meishan section, the Global Stratotype Section and Point (GSSP) for the PTB. The PTB is placed at the base of Bed 11c at Daxiakou. The Ns. dieneri M1, Ns. dieneri M2, and Ns. dieneri M3 subzones are distinguished from the Ns. dieneri Zone. Both Nv. waageni eowaageni and Nv. waageni waageni subzones are also recognized within the Nv. waageni Zone. The first occurrence of Nv. waageni eowaageni is an ideal marker defining the Induan-Olenekian boundary (IOB), which is calibrated to the base of Bed 86a at Daxiakou and is clearly beneath the ammonoid Flemingites-Euflemingites Zone.