Early Wuchiapingian (Lopingian, late Permian) drowning event in the South China block suggests a late eruptive phase of Emeishan large Igneous Province

Abstract

Abstract Although the precise age and magnitude of the end-Guadalupian biodiversity crisis is still debated, this “mass” extinction has been customarily linked with the onset of massive volcanism in the Emeishan Large Igneous Province (ELIP) in south China. The onset of ELIP eruptive activity at least partly coincides in time with episodes of regional subsidence interrupting the predominant regime of carbonate platforms during Capitanian times. Here, we present a strikingly similar but younger (early Wuchiapingian) subsidence episode from the Pingtang syncline in southern Guizhou, termed the Mapojiao Event. Shallow-marine, light-grey, thick-bedded bioclastic limestone of the Wuchiaping Formation (Unit A) are overlain by deep-marine radiolarian-sponge spicule, thin-bedded black limestone (Unit B). The latter is followed by volcaniclastic distal turbidites (Unit C). The base of the next overlying unit consists of cherty, nodular limestone (Unit D) rich in radiolarians and sponge spicules, whose respective abundances decline up-ward within a few meters. Concomitant replacement by a shallow marine benthic fauna documents the uplift that terminates the event. A total of five index species of Clarkina conodonts indicating an early Wuchiapingian age were obtained from Units A and B. Brachiopods of Wuchiapingian age were also documented in units A, B and D. Compilation of drowning events in the Guadalupian-Lopingian (G-L) interval suggests clustering into three episodes; 1: middle Capitanian, 2: possibly latest Capitanian, 3: early Wuchiapingian. The first drowning event is overlain by ELIP volcanics in sections near the center of the volcanic province. In peripheral areas, the first drowning is intercalated within carbonate platforms (e.g. Maoershan). A second drowning event cannot be excluded close to G-L boundary but it is obscured by the unconformity associated with an eustatic regression and by ambiguous conodont age control. Overlying this unconformity, the Wangpo Shale, which contains ELIP-derived volcanic materials, rests on the first (e.g. in Chaotian) drowning event. The striking similarities of the facies architecture shared by the first and third drowning events suggest a similar driving mechanism. Hence, we propose that the Mapojiao Event represents the youngest, early Wuchiapingian, burst of ELIP eruptive activity. There is no one-to-one correlation between these episodes related to ELIP eruptive activity and extinction phases of marine clades. Only the end-Guadalupian extinction has been correlated with the first eruptive episode. In marked contrast, the newly discovered Mapojiao drowning episode occurred within a diversification phase, which undermines any causal relations between the younger phases of ELIP volcanism and additional extinctions.