A record of the Steptoean Positive Carbon Isotope Excursion (SPICE; Cambrian, Paibian) from the Cow Head Group, western Newfoundland

Abstract

Analysis of biostratigraphically dated boulders demonstrates that the Steptoean Positive Carbon Isotope Excursion (SPICE) is recorded in debris flow conglomerates of the Downes Point Member of the Shallow Bay Formation in western Newfoundland. Fifteen boulders composed of bioclastic carbonates were assigned to five faunas based on assemblages of agnostids and trilobites. The Glyptagnostus reticulatus and “ Innitagnostus” inexpectans faunas correlate into strata that record the rising limb of the SPICE in its type area of Nevada and Utah, whereas equivalents of the Acmarhachis kindlei Fauna lie in the interval that records peak δ 13 C values. The Crepicephalus and Triorygma burkhalteri faunas correlate into pre- and post-SPICE strata, respectively. δ 13 C values for boulders from the three faunas correlative with the SPICE are significantly higher than “background” levels of the pre- and post-SPICE boulders, but the maximum value in the A. kindlei Fauna (1.5‰) is less than half of the peak values recorded in Nevada and Utah. The values are, however, in line with those reported from the Port au Port Peninsula of Newfoundland, which reach 2.2‰. The differences in magnitude between Newfoundland and Nevada–Utah hint at differences in the expression of the SPICE in different geographic regions of the Laurentian continent that might reflect oceanographic conditions.