1. Searching for the Great Oxidation Event in North America

    Map showing the distribution of the Huronian Supergroup and other Paleoproterozoic successions in the Great Lakes area. The two studied drill cores (150–4, 156–1) are located ca. 10 km north of the city of Elliot Lake, Ontario, Canada. Modified from the work of Rasmussen et al. (2013). Image credit: None
    Map showing the distribution of the Huronian Supergroup and other Paleoproterozoic successions in the Great Lakes area. The two studied drill cores (150–4, 156–1) are located ca. 10 km north of the city of Elliot Lake, Ontario, Canada. Modified from the work of Rasmussen et al. (2013).

    Members of the NASA Astrobiology Institute University of Wisconsin Team have reported the first in situ analysis of all four S isotopes in metasediments of the Paleoproterozoic Huronian Supergroup and examined sulfur isotope evidence for the Great Oxidation Event (GOE). The early study of Papineau et al. (2007) argued for placement of the GOE within the lower Huronian. However, this interpretation is not supported by the improved precision, analysis of 36S, and new textural interpretations of this study. Values of Δ33S are uniformly from -0.07 to 0.38‰ in the lower Huronian. The most commonly analyzed sulfide mineral of both studies is pyrrhotite, whose textures indicate it to be metamorphic rather than authigenic, potentially homogenizing mass-independent fractionations and obscuring the placement of any transition to mass-dependent processes that would mark the GOE.

    The study Searching for the Great Oxidation Event in North America: A Reappraisal of the Huronian Supergroup by SIMS Sulfur Four-Isotope Analysis was published in Astrobiology. The work was supported in part by the NASA Astrobiology Institute.