Oxygen-isotope trends and seawater temperature changes across the Late Cambrian Steptoean positive carbon-isotope excursion (SPICE event)

The globally recognized Late Cambrian Steptoean positive C-isotope excursion (SPICE) is characterized by a 3-5 per mil positive delta (super 13) C shift spanning <4 m.y. Existing hypotheses suggest that the SPICE represents a widespread ocean anoxic event leading to enhanced burial/preservation of organic matter (C (sub org) ) and pyrite. We analyzed delta (super 18) O values of apatitic inarticulate brachiopods from three Upper Cambrian successions across Laurentia to evaluate paleotemperatures during the SPICE. delta (super 18) O values range from approximately 12.5 per mil to 16.5 per mil. Estimated seawater temperatures associated with the SPICE are unreasonably warm, suggesting that the brachiopod delta (super 18) O values were altered during early diagenesis. Despite this, all three localities show similar trends with respect to the SPICE delta (super 13) C curve, suggesting that the brachiopod apatite preserves a record of relative delta (super 18) O and temperature changes. The trends include relatively high delta (super 18) O values at the onset of the SPICE, decreasing and lowest values during the main event, and an increase in values at the end of the event. The higher delta (super 18) O values during the global extinction at the onset of the SPICE suggest seawater cooling and support earlier hypotheses of upwelling of cool waters onto the shallow shelf. Decreasing and low delta (super 18) O values coincident with the rising limb of the SPICE support the hypothesis that seawater warming and associated reduced thermohaline circulation rates contributed to decreased dissolved O (sub 2) concentrations, which enhanced the preservation/burial of C (sub org) causing the positive delta (super 13) C shift.