A pilot study of upper Yangtze shallow-water carbonates of the Paibian global marine euxinia: Implications for the late Cambrian SPICE event

Abstract

The SPICE (Steptoean Positive Carbon Isotope Excursion) is a significant event in the Late Cambrian, recording global carbon cycle perturbations. Its driving mechanism is still controversial, but mainly believed to be related to an increase of organic carbon burial caused by ocean anoxia. The shallow-water platform carbonates of the Upper Cambrian Loushanguan Formation of Yankong outcrop (Upper Yangtze) spans the event interval. Their primary geochemical proxy signatures (trace elements, carbon and strontium isotopes), have been utilized to better understand the driving mechanism of the SPICE event. The variations of paleoenvironmental proxies in the upper Loushanguan Formation exhibit a rapid transformation of redox conditions similar to those of deep-water regions, thus reflecting an expansion of anoxic seawater to shallow-water column. The increase of 87Sr/86Sr, Al, and ∑REE during the SPICE suggests an enhancement in nutrient inputs from continental weathering that might have promoted primary productivity, which preferentially consumed light 12CO2 of surface waters, resulting in 13C-enriched DIC. The occurrence of PGMEE (Paibian global marine euxinia event), immediately before the enhancement of continental weathering, suggests that it was the onset-driving mechanism of the SPICE event and the increase in continental weathering might have promoted primary productivity to further intensify carbon burial and play a superimposed effect on that of the SPICE event.