Conodonts and Carbon Isotopes during the Permian-Triassic Transition on the Napo Platform, South China

Two Permian-Triassic boundary(PTB) sections(Pojue and Dala) are well exposed in an isolated carbonate platform(Napo Platform) on the southwestern margin of the Nanpanjiang Basin, South China. These sections provide an insight into the transition across the PTB and a detailed investigation of the conodont biostratigraphy and inorganic carbon isotopes is presented. The PTB at the Pojue Section is placed at the base of Bed 10 B(a dolomitized mudstone found below a microbialite horizon), defined by the first occurrence of Hindeodus parvus. At the Dala Section, four conodont zones occur. They are, in ascending order, the Hindeodus parvus Zone, Isarcicella staeschei Zone, Isarcicella isarcica Zone and Clarkina planata Zone. Comparison with the Pojue Section suggests the PTB at Dala also occurs at the base of dolomitized mudstone below a microbialite horizon, although the first occurrence of Hindeodus parvus is near the top of a microbialite bed: an occurrence that is also seen in other platform sections. The succeeding microbialite beds developed during the ongoing PTB mass extinction phase. This time was characterized by low carbon isotope values, and a microbialite ecosystem that provided a refuge for selected groups(bivalves, ostracods and microgastropods) that were likely tolerant of extremely high temperatures.

Roadian-Wordian(Middle Permian)Conodont Biostratigraphy,Sedimentary Facies and Paleotemperature Evolution at the Shuixiakou Section,Xikou Area,Southeastern Qinling Region,China

Focusing on the Shuixiakou Section(Xikou area,Zhen’an County,Shaanxi Province,southeastern Qinling region,China),the Roadian-Wordian conodonts are investigated.More than 2000 conodont elements including 6 genera and 14 species have been obtained.Based on these materials,the Guadalupian Jinogondolella nankingensis and J.aserrata zones have been recognized.The Roadian-Wordian boundary is tentatively defined by the first occurrence of J.aserrata in the lower part of UnitⅢin the Shuixiakou Formation.The sedimentary succession of Xikou area records similar sea-level changes to those observed in Laibin area(South China).The 40 m-thick bioclastic limestone of UnitⅣin this section can be correlated with the reefs of Bed 114 in Laibin area.A temperature drop indicated byδ18Oapatite values suggests this Wordian interval coincides with a period of glaciation and global regression.

First Records of Late Triassic Conodont Fauna andδ13Ccarb from the Dengdengqiao Section,Dangchang County,Gansu Province,Northwestern China

Based on a study of 49 conodont and 57 geochemical samples from the Upper Triassic,carbonate-dominated Dengdengqiao Formation,Qinling Basin,China,the Carnian conodonts and carbon isotope records are first reported.Two genera and four species have been identified amongst 87 conodont elements:Mosherella praebudaensis,Mo.longnanensis sp.nov.,Mo.sp.,and"Misikella"longidentata.The presence of Mo.praebudaensis indicates that the lower part(bed 2)of the formation is attributable to the Julian(lower Carnian)substage.A radiolarian fauna identified in a previous study belongs to the upper Carnian,but the sampling horizon is unclear.Theδ13Ccarb curve shows a~1.8‰negative excursion beginning from upper part of bed 3,but its stratigraphic location is uncertain.The Dengdengqiao Formation is clearly at least partly of Carnian age but could include younger strata.The abundant calcareous algae at the section is probably due to some transport rather than preserved in site.The unusual ecosystem with rare marine organisms may reflect long-term stressful and unfavorable conditions at Dengdengqiao.