Pennsylvanian–Early Permian cyclothemic succession on the Yangtze Carbonate Platform, South China

Abstract

AbstractPennsylvanian (Late Carboniferous)–Early Permian cyclothems are documented for the first time from the shallow-marine carbonate succession on the Yangtze Carbonate Platform, South China. The Zongdi section in southern Guizhou Province comprises bioclast-rich grey limestones with dark-coloured intervals yielding macro- and microfabrics related to emergent events. We recognized 26 depositional sequences (consisting essentially of basal peritidal sediments, middle shallow subtidal sediments and upper peritidal sediments affected by meteoric diagenesis and subaerial exposure) separated by 25 lowstand events. These are interpreted as having been formed by alternating marine transgression and regression resulting from variations in the Gondwanan ice sheets. They are compared with the Midcontinent (Kansas-type) cyclothems in North America. However, the Zongdi cyclothems are relatively thin and consist entirely of very shallow-marine sediments formed above wave base, whereas the Midcontinent cyclothems reflect deposition far below wave base. The Zongdi depositional environment was an upper shelf area, on a platform within the epeiric sea on the South China Craton, where sedimentation occurred in a relatively small (shallow) accommodation space during the highest stands of sea level. They were formed by major (large-scale) transgressions that submerged high-shelf areas, and most of them correspond to the major cyclothems of the North American Midcontinent Basin. The fusuline biostratigraphical framework reveals an uneven stratigraphical pattern of the Zongdi cyclothems, reflecting subtle fluctuations of tectonic subsidence on the epeiric Yangtze Carbonate Platform. Less erosion and karstification on the tops of cyclothems in the Zongdi section, together with the presence of partly calcareous palaeosols, indicates that a dry climate prevailed on the South China Block during the Pennsylvanian–Early Permian when the Zongdi cyclothems were formed.