Devonian-Carboniferous boundary in China

The Devonian-Carboniferous transition is marked by major perturbations to the Earth's climate system and marine redox conditions, a first-order mass extinction, and the succeeding marine ecosystem recovery, recording a sequence of environmental and biotic events. In South China, there exist numerous well-preserved and continuous Devonian-Carboniferous boundary successions that were formed in low-latitude passive margin basin, and this presents a unique opportunity to decipher the strata along a proximal to basinal transect using integrated biostratigraphical, event-stratigraphical, and geochemical approaches. Our geochemical data (delta C-13(carb), delta N-15(bulk), delta U-238 and Mo/U enrichments, I/Ca ratio) indicated local and global C-N cycling perturbations and marine anoxia in the main phase of the Hangenberg Crisis interval (Middle Siphonodella praesulcata Zone), which coincided with a major regression in South China. Stromatoporoid biostromes and most typical Devonian faunas did not survive into the interval, and the deep-water black shales yield only opportunistic survivors, such as ammonoid Postclymenia cf. evoluta and bivalve Guerichina, along with miospores belonging to the LN Zone. The upper Hangenberg Crisis interval (Upper Si. praesulcata Zone, equal to the Protognathodus kockeli Zone) is marked by initial post-glacial transgression, a global delta C-13(carb) spike, and opportunistic faunal blooms, coincident with conodont biofacies shift to the polygnathid-protognathodid biofacies. The Protognathodus fauna, nearly absent from platform facies, is often found in the condensed upper crisis interval of the basin, slope, and platform margin facies within the Youjiang Basin, although the abundance is extremely low and the phylogenetic lineage of Pr. meischneri-Pr. collinsoni-Pr. kockeli cannot be recognised in most successions. In South China, the first occurrence of Pr. kockeli seems to correspond to lithofacies changes, recorded in the first level of transgression just above the Hangenberg Sandstone event. Multiple lines of evidence, including great spatial heterogeneity of delta C-13(carb) and delta N-15(bulk) records, extremes of redox proxies, and lack of macrofossils, suggest that marine habitats remained in a critical/turbulent state during the Upper Si. praesulcata Zone, triggering the opportunistic blooms and minor extinctions. Following the crisis intervals, radiation/recovery of many fossil groups did not occur until the upper part of the Siphonodella sulcata Zone to the Si. duplicata Zone. In particular, a negative shift of delta C-13(carb) to pre-crisis values occurring near the base of the Si. sulcata/Pr. kuehni Zone could be recognised worldwide. The research history, current status, and achievement of Devonian-Carboniferous boundary in China are briefly reviewed.