Sedimentary evolution and sea-level fluctuation of a Paleo-Tethyan Permian carbonate-dominated succession from central China

Abstract

The Paleo-Tethys experienced major geographic, tectonic, climatologic, and environmental changes during the Permian. A newly documented and complete Permian carbonate-dominated succession (>3 km) in the Xikou section, Zhen'an, Shaanxi, central China provides a unique opportunity to record its depositional environment evolution, sea-level fluctuation, and associated paleogeographic and paleoclimatic perturbation of the eastern Paleo-Tethys. Field observation and petrographic analysis document eighteen facies and indicate evolutional facies of a carbonate ramp within the Xikou section. The vertical distribution of those facies in the Xikou section indicates a fluctuated sea-level during the Permian, which reflected the global climatic changes and was associated with eastern Paleo-Tethys evolution. The relatively low sea-level accompanied by high-frequency fluctuations during the Asselian to Artinskian may be related to the expansion of glaciation (P1 and P2), while the followed significant rising at Kungurian may reflect the major deglaciation of the Late Paleozoic Ice Age (LPIA). The abrupt falling of sea-level at the end of the Capitanian was globally synchronous and may be relevant to mid-ocean ridge spreading and superimposed with global cooling (P4), which was in accord with the skeletal grain replacement of the fusulinaceans and dasyclads by small foraminifers and Gymnocodium, and was considered as a major reason for Middle Permian Extinction. The early Wuchiapingian characterized by densely mixed sequences of carbonate and siliciclastic intervals had a highly frequent fluctuating sea-level, which may be influenced by high frequent short-term climatic variations. The sea-level falling after it reached its highest stand during the middle Wuchiapingian, was suggested as a far-field response to the expansion of the Permian glaciation episode P4, or as a result of a regional tectonic transition from extension to compression relevant to the eastern Paleo-Tethys evolution. In addition, the overall rising trend of the sea-level and the thick succession in the Xikou area suggest that the South Qinling belt was primarily under an extensional setting during the Late Carboniferous to Early Triassic, in response to Tethys rifting, which may imply the subduction of Mianlue Ocean was possibly beyond the Permian.