Carbon and oxygen isotopes across Devonian and Carboniferous boundary in the Funing area of Yunnan Province and the response to sea-level changes

Youjiang Basin in which continuous strata from Devonian to Carboniferous were deposited is the key area for the study of Hangenberg biological extinction event between Devonian and Carboniferous in China. The Upper Devonian to Lower Carboniferous strata of Funing area in the western margin of the Youjiang Basin were selected to systematically study carbon and oxygen isotopic compositions of carbonate rocks based on the litho-stratigraphic research. Negative shifts of δ¹³C and δ¹⁸O with different amplitudes exist in the Upper Devonian to Lower Carboniferous in the Funing area, especially near the Devonian-Carboniferous boundary. The layers in which δ¹³C and δ¹⁸O shifts are consistent with the sequence of stratigraphic transformation and paleontological extinction events, which reflected the decline of sea level during the Famennnian stage of the Late Devonian and the transgression events in the Early Carboniferous. The negative δ¹³C shift near the Devonian-Carboniferous boundary in the study area is similar to the evolutionary shift of δ¹³C values in Youjiang Basin. The δ¹³C values in other typical sections in South China all show negative shifts of different magnitudes. The evolutionary sequence of carbon isotopes near the Devonian-Carboniferous boundary is consistent with the sea-level decline events reflected by the offset of δ¹³C values in Europe and North America, which shows global correlation significance.