Middle Norian (triassic) Conodonts from Timor, Southeastern Tethys – Taxonomy, Biochronology and Biogeographic Implications

The middle Norian (Alaunian substage, Late Triassic) of the Tethys is characterized by scattered conodont successions with a biozonation of relatively low and inaccurate resolution. Timor Island is one of the most important areas for studying and integrating accurately the conodont record into the ammonoid biochronolgy of Norian, However, it has received rare study. For bridging the gap of correlation between Norian conodonts and ammonoids, three ammonoid-rich Hallstatt-type pelagic blocks, which located in the Kupang area, near the western coast of Timor, were examined, resulting in abundant platform conodont collections. The taxonomy of epigondolellids, which are the dominating forms during the middle Norian, is revised with a thorough redescription of Epigondolella abneptis, which is the name-giving species of the genus Epigondolella and subfamily Epigondolellinae. Based on our material, genus Mockina is revisedas a synonym of Epigondolella. Our data indicate that, Ancyrogondolella disappearsat the end of the Alaunian 1 and is replaced by Epigondolella starting in the latest Lower Norian. The genus Parvigondolella already appears in the Alaunian 3 and thus much earlier than previously recorded. Eight new species are described: Ancyrogondolella spatulatiformis sp. nov., An. praemanueli sp. nov., Epigondolella praeabneptis sp. nov., E.circularis sp. nov., E. finalis sp. nov., E. circumspinatus sp. nov., E. baunensis sp. nov. and Norigondolella timorensis sp. nov. Three conodont biostratigraphic schemes are proposed, including range zones (RZ), interval zones (IZ) and concurrent range zones (CRZ). On the basis of RZs 4 zones can be discriminated whereas the IZ and the CRZ concepts provide a higher resolution of each 6 zones. Out results indicate that the CRZ scheme is better than the other two schemes, because of accuracy and better fit with the ammonoid defined lower and upper boundaries of the Alaunian substage. The occurrences of Ancyrogondolella, Epigondolella and Norigondolella fauna from west Timor, display a high similarity with South Qiangtang block, suggesting a close geographic connection between west Timor and South Qiangtang block during the Norian, which is contrasted to previous studies that they were totally separated with a significant distance. Furthermore, the appearance of Norigondolella steinbergensis in west Timor also demonstrated the connection as this species previously has been regarded as the difference between west Timor and South Qiangtang block. Besides, the absence of Norigondolella in the Lhasa block may indicate that this block was less connected to west Timor than the South Qiangtang block during Norian.