THE MICROVERTEBRATE REMAINS AND ASSEMBLAGE SEQUENCES ACROSS THE SILURIAN/DEVONIAN TRANSITION IN WEST QINLING, CHINA

ZHAO Wen-jin, WANG Nian-zhong, ZHU Min, JIA Lian-tao

Abstract  West Qinling is an important area for the study of the Silurian/Devonian Boundary (SDB) in the South China Block. The SDB sequence in the Putonggou Section includes the upper part of the Yanglugou Formation and the lower part of the Xiaputonggou Formation, in which microvertebrate remains (thelodonts, placoderms, acanthodians and chondrichthyans) in association with conodonts and brachiopods have been collected. Two microvertebrate assemblages are recognized in the Putonggou Section: the Yanglugou Assemblage from the upper part of the Yanglugou Formation, and the Xiaputonggou Assemblage from the lower part of the Xiaputonggou Formation in association with the conodont Icriodus woschmidti woschmidti. The Yanglugou Assemblage yields the acanthodians Gomphonchus sandelensis and Ischnacanthidae gen. indet., and the Xiaputonggou Assemblage includes the thelodonts (Parathelodus scitulus, P. asiaticus and P. cornuformis), the acanthodians (Nostolepis gracilis, N. striata, N. tewonensis, Gansuichthys liui, Poracanthodes zoigenensis, Poracanthodes cf. P. porosus, Ischnacanthys sp.), the chondrichthyan (Arauzia ? sp.), and the placoderm (a pectoral fin fragment of Chuchinolepis ? sp.). Based on the correlation with the microvertebrate biozones in East Baltic, the Yanglugou and Xiaputonggou assemblages are referred to the late Pridoli and the early Lochkovian respectively, thus providing paleoichthyological evidence for the location of the SDB in West Qinling.
Key words  West Qinling, South China; Silurian, Devonian; microvertebrate assemblage