Coupled sedimentary and δ13C records of late Mississippian platform-to-slope successions from South China: Insight into δ13C chemostratigraphy

Abstract

Variability in stratigraphic accumulation rates and distribution of stratal hiatuses along with strong endemism of index fossils hinder regional to global stratigraphic correlation of the Visean–Serpukhovian (V–S) boundary interval (late Mississippian) and thus geological inferences regarding the onset of the late Paleozoic ice age. Here we integrate high-resolution δ13C time series with detailed sedimentary facies analysis of late Visean–early Serpukhovian (V–S) carbonate platform-to-slope successions from South China to evaluate the influences of local depositional and diagenetic processes on δ13Ccarb and to address the correlation issue.Analysis of 11 sedimentary facies from 5 outcrop sections indicates a restricted platform setting (Yashui section) dominated by bioclastic wacke-packstone to lime mudstone in which paleokarst developed, and contemporaneous carbonate slope settings dominated by thin-bedded lime mudstones intercalated with slumps and calciturbidites. Based on vertical facies assemblages, three depositional units are recognized, recording a significant sea-level drawdown across the V–S boundary. Multiple negative δ13C excursions (>1‰) can be correlated across the V–S boundary interval in several slope sections (Naqing, Luokun, and Narao sections). Variability in the V–S boundary δ13C record in some sections is interpreted to record truncation physically by submarine erosion by slumps or chemically during karstification. A long-term decrease in δ13C values through the Serpukhovian of the Yashui section likely records local influences on carbon cycling in the restricted platform setting. This negative δ13C trend and associated depositional facies at the Yashui section can be correlated to the Arrow Canyon section, USA, which, together with other coeval global sedimentary and geochemical records, indicate a widespread eustatic drawdown in the late Visean with initial buildup of Gondwanan ice sheets. We conclude that integrated sedimentary facies analysis and δ13C chemostratigraphy can be used for stratigraphic correlation when interpreted within a well-constrained sedimentary and carbon-isotope regional framework.