In many basins, Upper Cambrian carbonate successions display intervals with a positive carbon isotope excursion (CIE) of up to +5‰. In North America, this marks the boundary between the Sauk II-III super-sequences. A Steptoean Positive Carbon Isotope Excursion (SPICE) locality previously identified in the Port-au-Port peninsula, western Newfoundland, has been revisited and an additional potential SPICE locality found. In both locations, a CIE is found to be associated with a prominent bioherm and sandstone layer within a sequence of carbonate rocks. At March Point, columnar stromatolites occur while at Felix Cove thrombolites can be seen. In the latter, the sandstone immediately overlies the thrombolites coincident with the CIE, while at March Point a dolomitized grainstone occurs above the stromatolites. The sandstone at this locality post-dates the CIE. Although lower than the SPICE in some localities, a positive CIE is present in both sections, March Point (+1.1 ‰) and Felix Cove (+1.8 ‰). Additionally, δ13Corg rises from –30.0 ‰ to –22.0 ‰ at March Point, and from -27 ‰ to –24.0 ‰ at Felix Cove and, in accordance with previously published work, we suggest that this could be the SPICE. Comparison of the stratigraphy and petrography between the two localities suggest that both depositional and diagenetic factors could have influenced the nature of the interpreted SPICE in Newfoundland. It is also possible that the local carbon isotopic signature may have been influenced by a semi-restricted depositional and early diagenetic environment, related to the paleogeographic configuration, rather than the global marine excursion.
Bibliographical noteThis work is a part of the PhD of the first author, developed at Universidade Federal do Rio Grande do Sul (UFRGS) and University of Aberdeen (UoA). The authors gratefully acknowledge support from Shell Brasil through the “BG05: UoA-UFRGS-SWB Sedimentary Systems” project at UFRGS and the strategic importance of the support given by ANP through the R&D levy regulation. BGS and LAMIR staffs are also acknowledged for assisting with stable isotope analysis. We also would like to tank Dr. Duncan McIlroy for all his help during the field work, and Dr. Marc Laflamme, Dr. Pedro Jose Marenco and an anonymous reviewer for their help in improving the manuscript.
- Port au Port Group
- Stable Isotopes