Terreneuvian bio- and chemostratigraphy of the South Sichuan Region (South China)

Classical sections, such as the Maidiping and Daqiao Mine sections of South Sichuan (China), expose early Cambrian deposits that are crucial for understanding the biological and environmental evolution of Yangtze Craton. These sequences are rich in Terreneuvian small shelly fossils, which can be assigned to assemblages I and III from South China. The Anabarites trisulcatus-Protohertzina anabarica Assemblage Zone (Assemblage I) is recognized at the lower Maidiping Formation. The second assemblage (Paragloborilus subglobosus-Purella squamulosa Assemblage Zone) cannot be verified in South Sichuan, although previous reports claimed its existence based on the occurrence of Paragloborilus subglobosus. The third assemblage (Watsonella crosbyi Assemblage Zone) is confirmed in the upper Maidiping Formation. The abundant bioclasts in this interval indicate abrasions and bioerosions by winnowing or starved sedimentation. Carbon isotope values from the Maidiping section present no negative excursion at the presumed Ediacaran-Cambrian transition. A positive carbon isotope excursion is observed in the Upper Maidiping Formation (Assemblage III) which is correlated to the ZHUCE excursion in the Dahai Member of eastern Yunnan. The shallow-water deposits of South Sichuan can be correlated with the South China, western Mongolia and Siberia successions based on biozonations and carbon isotope trends.

Automated summary

Classical sections in South Sichuan, such as the Maidiping and Daqiao Mine sections, reveal early Cambrian deposits rich in Terreneuvian small shelly fossils. The carbon isotope values in these sections show different anomalies, with a positive excursion observed in the Upper Maidiping Formation. These shallow-water deposits can be correlated with successions in South China, western Mongolia, and Siberia based on biozonations and carbon isotope trends.