Pragian (lower Devonian) Conodonts from the Nahkaoling Formation of Central Guangxi, South China

The global or interregional correlation of the Pragian has long been an intractable problem in the Early Devonian stratigraphy. Several Pragian conodont zonal scales have been proposed to improve this situation on the basis of evolutionary lineages of eognathodondtids and early polygnathids, and/or lowest (or highest) occurrence of some distinct species of Pedavis, Latericriodus, Caudicriodus, and Pelekysgnathodus. Although impeded by many objective constraints, the universally applicability of these Pragian conodont zonal scales needs to be tested. The present new investigation of conodont fauna from the Nahkaoling Formation of central Guangxi, South China leads to the recognition of 15 species in 8 genera, with extremely abundant and diverse eognathodontids facilitating reliable interregional correlation. The conodont-based, zonal subdivision of Murphy (2005) for Nevada and western North America can be partially adapted to the South China Pragian. The middle and upper parts of the Gaoling Member of the Nahkaoling Formation mostly refer to the lower Pragian irregularis-profunda Zone, whereas the base of the overlying middle Pragian profunda-brevicauda Zone is positioned close to the upper boundary of the Gaoling Member by the lowest occurrence of Gondwania nevadensis. It is suggested herein that the entry of this species can act as a reliable mark for the base of the profunda-brevicauda Zone when the nominal species G. profunda is absent. The Mahuangling Member of the Nahkaoling Formation is mostly attributed to the middle Pragian because of the occurrence of the sigma morph of Pseudogondwania kindlei in its uppermost part. It is for the first time that the applicability of the Pragian conodont-based zonal scale of Murphy (2005) is successfully corroborated out of western North America.