Discovery of Early Triassic conodonts in western Gangdisê and the establishment of the Tangnale Formation

Abstract

Most geologists believe that there are no Early and Middle Triassic strata in the W. Gandisê stratigraphic subregion, but the present authors have found Early Triassic conodonts for the first time in the Shiquanhe area, including five conodonts genera (Form genera): Pachycladina, Neohindeodella, Cornudina, Hadrodontina and Hibbardella sp. etc. Then we affirm that Early Triassic deposits exist in the Gandisê stratigraphic subregion, and establish the Tangnale Formation. The conclusion is new important complementary basal data for Triassic stratigraphy division of Gangdisê, reconstructing palaogeography and studying Gangdisê from Paleozoic to Mesozoic island-arc evolution and transition.

New biostratigraphic evidence of Late Permian to Late Triassic deposits from Central Tibet and their paleogeographic implications

“…A complete conodont succession ranging from the Late Permian to the Triassic has thus been established, based on the limestonedominated Dibuco section (Ji et al, 2006;Wu et al, 2007) and the Wenbudangsang section (Wu et al, 2014). The dolomite-type succession has also been recognized in the Zozo section (Ji et al, 2007a;Zheng et al, 2007) and the Namutso section (Wu et al, 2017) (Fig. 7).…”

“…Pachycladina, a shallow water facies index fossil of the Late Induan to the Early Olenekian, is frequently found in dolomitic rocks. Specimens of this genus have been widely reported in the western Tethyan area (Perri and Andraghetti,1987;Aljinovic et al, 2006;Kolar-Jurkovsek et al, 2017), the USA (Solien, 1979), South China (Wang and Cao, 1981;Jiang et al, 2000), and Tibet (Xia and Zhang, 2005;Zheng et al, 2007).…”

“…Studies investigating Triassic conodont biostratigraphy in Tibet were initially performed in southern Tibet in the mid-1970s (Wang and Wang, 1976). To date, marine Triassic sections have been shown to cover the Lhasa terrane (Ji et al, 2006(Ji et al, , 2007a(Ji et al, , 2010Wu et al, 2007Wu et al, , 2014Wu et al, , 2017Wu et al, , 2018Zheng et al, 2007) and the Qiangtang terrane (Xia and Zhang, 2005;Guizhou Institute of Geological Survey, 2005;Zhang et al, 2005;Li et al, 2018). The recognized conodont biozones from different parts of Tibet could be well correlated with the international zones established by Sweet et al (1970) (Fig.…”

“…Triassic conodont studies in the Lhasa terrane began in the 1980s, focusing on regions near Lhasa City, where only the Early Triassic Triasspathodus homeri zone and Norian Epigon dolella fauna of the Late Triassic were reported (Sun et al, 1981;Ji et al, 2003). Dramatic progress was achieved in the 21 st century, with successive discoveries of more marine Triassic sections (Ji et al, 2006(Ji et al, , 2007a(Ji et al, , 2007b(Ji et al, , 2007c(Ji et al, , 2010Zheng et al, 2007;Wu et al, 2007Wu et al, , 2014Wu et al, , 2017Wu et al, , 2018. A complete conodont succession ranging from the Late Permian to the Triassic has thus been established, based on the limestonedominated Dibuco section (Ji et al, 2006;Wu et al, 2007) and the Wenbudangsang section (Wu et al, 2014).…”

“…However, Triassic sedimentary data remain rare at present, especially in the BNSZ, where a Lower Triassic deposit has never been reported and is thus believed to be missing, which contrasts greatly with adjacent areas where Triassic marine sediments were disclosed to be well developed. For example, in the Lhasa terrane to the south, Lower Triassic deposits are widespread in the western portion (Ji et al, 2006(Ji et al, , 2007a(Ji et al, , 2007b(Ji et al, , 2007cWu et al, 2007Wu et al, , 2014Wu et al, , 2017Wu et al, , 2018Zheng et al, 2007), and a complete Triassic succession has been established in accordance with the sections found in the Coqen and Wenbudangsang areas (Ji et al, 2007b;Wu et al, 2007Wu et al, , 2014, implying that the west Lhasa terrane was in a carbonate platform setting during the Triassic (Ji et al, 2018a;. Similar deposits were found in South Qiangtang as well (Guizhou Institute of Geological Survey, 2005;Zhang et al, 2005;Li et al, 2018).…”