Carbon-isotope stratigraphy of the uppermost Cambrian in eastern Laurentia; implications for global correlation

The delta (super 13) C profile from an interval of the Martin Point section in western Newfoundland (Canada) spans the upper Furongian (uppermost Cambrian). The interval ( approximately 90 m) is a part of the Green Point Formation of the Cow Head Group and consists of the Martin Point (lower) and the Broom Point (upper) members. It is formed of slope marine carbonates alternating with shales (rhythmites) and conglomeratic interbeds. The preservation of the investigated micritic carbonates was meticulously evaluated by multiple petrographic and geochemical screening tools. The delta (super 13) C and delta (super 18) O values (-0.5+ or -0.8 ppmVPDB and -7.1+ or -0.3 ppmVPDB, respectively) exhibit insignificant correlation (R (super 2) =0.002) and similarly the correlation of delta (super 13) C values with their Sr and Mn counterparts, which supports the preservation of at least near-primary delta (super 13) C signatures that can be utilized to construct a reliable high-resolution carbon-isotope profile for global correlations. The delta (super 13) C profile exhibits two main negative excursions, a lower broad excursion ( approximately 3 ppm) that reaches its maximum at approximately 70 m below the Martin Point/Broom Point members boundary and an upper narrow excursion ( approximately 2.5 ppm) immediately below the same boundary. The lower excursion can be correlated with the global latest Furongian HERB event (TOCE), which is also recognized in the C-isotope profile of the GSSP boundary section at Green Point whereas the upper excursion matches with that of the Cambrian-Ordovician boundary in the same section. The peak of the HERB delta (super 13) C excursion is correlated with positive shifts on the Th/U and Ni profiles (redox and productivity proxies).