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

Geology
By: , and 

Links

Abstract

The globally recognized Late Cambrian Steptoean positive C-isotope excursion (SPICE) is characterized by a 3???-5??? positive ??13C 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 (Corg) and pyrite. We analyzed ??18O values of apatitic inarticulate brachiopods from three Upper Cambrian successions across Laurentia to evaluate paleotemperatures during the SPICE. ??18O values range from ~12.5??? to 16.5???. Estimated seawater temperatures associated with the SPICE are unreasonably warm, suggesting that the brachiopod ??18O values were altered during early diagenesis. Despite this, all three localities show similar trends with respect to the SPICE ??13C curve, suggesting that the brachiopod apatite preserves a record of relative ??18O and temperature changes. The trends include relatively high ??18O 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 ??18O values during the global extinction at the onset of the SPICE suggests seawater cooling and supports earlier hypotheses of upwelling of cool waters onto the shallow shelf. Decreasing and low ??18O 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 O2 concentrations, which enhanced the preservation/burial of Corg causing the positive ??13C shift. ?? 2011 Geological Society of America.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Oxygen-isotope trends and seawater temperature changes across the Late Cambrian Steptoean positive carbon-isotope excursion (SPICE event)
Series title Geology
DOI 10.1130/G32109.1
Volume 39
Issue 10
Year Published 2011
Language English
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Geology
First page 987
Last page 990