Conodont Biostratigraphy and Age of the Early Triassic Fish-Bearing-Nodule Levels from Nanjing and Jurong, Jiangsu Province, South China

Fish-bearing-nodules are found in Early Triassic marine strata in many regions, including East Greenland, East Spitsbergen, Northwest Madagascar, Canada, Angola, and South China. A new Olenekian(Early Triassic) conodont biostratigraphic study for stratum that contains fish-bearing-nodule levels is conducted based on the Longtan(LT) Section of Nanjing City and the Qingshan(QS) Section of Jurong County, Jiangsu Province, South China. A total of 101 samples were collected at the two sections and three conodont zones were recognized: in ascending order, they are Scythogondolella(Sc.) milleri Zone, Novispathodus(Nv.) pingdingshanensis Zone, and Triassospathodus(Tr.) aff. homeri Zone. The Scythogondolella milleri Zone is globally recognized as the uppermost conodont zone of the Smithian and the base of the Novispathodus pingdingshanensis Zone was previously suggested as the marker of the Smithian-Spathian boundary in the Yangtze region. The fish-bearing-nodule levels of Nanjing and Jurong are within the conodont Scythogondolella milleri Zone, laterally correlated well with the upper part of the Novispathodus waageni Zone in Chaohu of Anhui Province that also contains fish-bearing-nodule levels. The conodont biostratigraphic correlation confirms the Early Triassic fish-bearing-nodule levels in the Lower Yangtze region are coeval, with an end-Smithian in age.

Triassic actinopterygian fishes:the recovery after the end-Permian crisis

In the last 15 years,the discovery of several new actinopterygian fish faunas from the Early and Middle Trias­sic of the Tethys,cast new light on the timing,speed and range of their recovery after the end-Permian crisis.In addition to several new taxa having been described,the stratigraphical and geographical record of many others have been greatly extended.In fact,most of the new fossiliferous sites are in southern China,thus at the Eastern end of the Tethys,and furthermore a few are somewhat older(Chaohu,Panxian,Luoping)than the major clas­sical Western Tethys sites(Monte San Giorgio).Following these new finds,it is possible to have a better defi­nition of the Triassic recovery stages.Indeed,after a quite short phase till the end of the Smithian(Olenekian,Early Triassic)in which a rather consistent fauna was present all around the Pangea coasts,a major radiation occurred in the Early-Middle Anisian after the new Middle Triassic fish fauna already appeared in the late Ear­ly Triassic,thus occuring well before what was previously supposed from the Alps localities.Furthermore,the new assemblages from southern China point to an early broader differentiation among the basal neopterygians rather than in the‘subholosteans’,the group that was then dominant in the Western Tethys since the Late Ani­sian.It stands that during the Norian a new basal neopterygian radiation gave rise to several new branches that dominated the remaining part of the Mesozoic.