The Furongian (late Cambrian) Steptoean positive carbon isotope excursion (SPICE) in Avalonia

Abstract

The Steptoean Positive Carbon Isotope Excursion (SPICE) of earliest late Cambrian (Furongian) age is identified in England. The excursion is found within a c. 145 m thick siliciclastic succession within the middle and higher part of the Outwoods Shale Formation of Warwickshire, and reaches a maximum 13Corg amplitude of 4.1 at values of –25.6. Biostratigraphical data show that the excursion occupies the greater part of the Olenus Biozone, an equivalent of the Glyptagnostus reticulatus Biozone that marks the base of the Furongian and coeval base of the Steptoean in North America. The amplitude of the excursion approaches that recorded in limestone-dominated Laurentian successions, and is greater than that recently documented for organic-rich mudstones of palaeocontinental Baltica in southern Sweden. A minor positive excursion above the SPICE may equate with a similar excursion recognized in Siberia. The SPICE in the Outwoods Shale Formation seems closely linked to the widely recognized early Furongian eustatic sea-level rise. There is no evidence in the English succession for slightly later regression, elsewhere considered coincident with the peak of the excursion and pivotal to some previous models explaining the SPICE. Supplementary material: Analytical results, including total organic carbon (TOC) values for each sample, are available at www.geolsoc.org.uk/SUP18455