Carbon-isotope stratigraphy of the SPICE event (Upper Cambrian) in eastern Laurentia: implications for global correlation and a potential reference section

The delta 13C profile from the lower interval of the Martin Point section in western Newfoundland (Canada) spans the Upper Cambrian (uppermost Franconian - lowermost Trempealeauan). The investigated interval (similar to 110 m) is a part of the Green Point Formation of the Cow Head Group and consists of the upper part of the Tucker Cove Member (topmost part of the Shallow Bay Formation) and the lowermost part of the Martin Point Member (bottom of the Green Point Formation). It is formed of rhythmites of marine carbonates alternating with shales and minor conglomeratic interbeds. Multiscreening petrographic and geochemical techniques have been utilized to evaluate the preservation of the investigated lime mudstones. The delta 13C and delta 18O values of the sampled micrites (-4.8 parts per thousand to +1.0 parts per thousand VPDB and -8.2 parts per thousand to -5.3 parts per thousand VPDB, respectively) have insignificant correlation (R2 = 0.01), as similarly do the delta 13C values with their Sr counterparts (R2 = 0.07), which supports the preservation of at least near-primary delta 13C signatures that can be utilized to construct a reliable high-resolution carbon-isotope profile for global correlations. The delta 13C profile exhibits two main negative excursions: a lower excursion (similar to 4 parts per thousand) that reaches its maximum at the bottom of the section and an upper narrow excursion (similar to 6 parts per thousand) immediately above the boundary of the Tucker Cove/Martin Point members (Shallow Bay Formation - Green Point Formation boundary). The lower excursion may be correlated with the global SPICE event, whereas the upper excursion may match with a post-SPICE event that has been also recognized in profiles of equivalent sections on different palaeocontinents.