KASIMOVIAN-EARLY GZHELIAN (LATE PENNSYLVANIAN) CONODONTS FROM THE NAQING (NASHUI) SECTION, GUIZHOU PROVINCE, SOUTH CHINA

The Naqing section in Guizhou Province, South China (formerly the Nashui section) comprises over 400 meters of continuously deposited carbonates that range in age from the late Mississippian into the early Permian. The Naqing carbonates are a complexly interbedded series of fine-grained sediments and allochthonous coarse-grained beds that were deposited in a submarine fan in a slope to basinal setting. Conodonts occur in all facies, but are more common, larger in size, and more readily obtained from coarse-grained beds than from fine-grained facies. Middle Kasimovian through early Gzhelian conodont faunas are a combination of North American Midcontinent and Eurasian species and new species apparently endemic to South China. Members of the Idiognathodus magnificus group and a few Streptognathodus are present in middle Kasimovian carbonates. Later Kasimovian beds yielded a complex assemblage of Idiognathodus P₁ elements with restricted lobes and a tendency toward slightly eccentric grooves, the latter forms possibly precursors to I. simulator. Only a few specimens of the S. firmus-S. pawhuskaensis-S. zethus group, which dominates faunas elsewhere, were recovered. An endemic lineage with narrow platforms appears in the middle Kasimovian as I. guizhouensis, which passes through transitional forms before ending with the Gzhelian species I. nashuiensis, which has an Idiognathoides-like P₁ element. The appearance of abundant I. simulator, the biostratigraphic index for the base of the Gzhelian, is accompanied by a new, possibly endemic group of Streptognathodus species in which strongly curved, broad to narrow P₁ elements possess long carinas that merge with the outer transverse ridges. Deposition appears to have been continuous through the Kasimovian-Gzhelian boundary interval, but few conodonts were obtained from the beds immediately below the first appearance of I. simulator. Gzhelian conodonts are also uncommon in succeeding beds, where rare S. vitali and Solkognathus? occur. Although the Naqing carbonates are clearly deep-water deposits, few elements of Idioprionodus and Gondolella, which characterize deeper water, offshore environments in other regions, were recovered.