Spatial variation in carbonate carbon isotopes during the Cambrian SPICE event across the eastern North China Platform

Abstract

The Cambrian SPICE (Steptoean Positive Carbon Isotope Excursion) event is widely reported from the late Miaolingian to the early Furongian, but recent studies imply that the synchroneity and magnitude of the SPICE may be controversial. In order to test the spatial variation of the SPICE, here we present 367 carbonate δ13C data from six outcrop sections across a ~700 km transect along the eastern North China Platform. The SPICE is present in all the studied sections, but showing different features regarding the duration and magnitude. An abrupt increase in δ13C from ~1.5‰ to 3.5‰ occurs in three Shandong sections, with maximum value present only in a thin (0.5–1.2 m thick) transgressive lag deposit (crudely wave stratified, bioclastic grainstone). In contrast, the δ13C record of the Baijiashan and Shashan sections in the Liaoning region displays a gradual increase (~20 m thick) from ~1.5‰ to the maximum value of 4.7‰. Both facies analysis and trilobite collections suggest that the spatial variation of the SPICE in the North China Platform most likely resulted from missing of sedimentary record (with high δ13C values) in the Shandong sections as a result of erosion and non-deposition during sea-level lowstand, a possible coeval hiatus prior to the Sauk III transgression in the Laurentian basins. Further high-resolution, integrated studies of sedimentology, biostratigraphy, and sedimentary geochemistry on the SPICE event are required to better understand its nature.