Geochemistry of pyrite from diamictites of the Boolgeeda Iron Formation, Western Australia with implications for the GOE and Paleoproterozoic ice ages

Abstract

Sediments of the ca. 2400Ma Turee Creek Group of Western Australia are coincident with the oxygenation of Earth's surface associated with the ‘Great Oxidation Event’ (GOE). Diamictite within the Boolgeeda Iron Formation from the Boundary Ridge section at the Duck Creek Syncline was previously correlated to the glaciogenic sediments of the Meteorite Bore Member of the Turee Creek Group at the Hardey Syncline (Martin, 1999). The Meteorite Bore Member is considered correlative and time-equivalent with the Paleoproterozoic glacial diamictites of the 2.45–2.22Ga Huronian Supergroup in North America. If the diamictite units at Boundary Ridge correspond to worldwide Paleoproterozoic glaciations, they should also record the disappearance of mass independently fractionated (MIF) sulfur. Triple S-isotope compositions for pyrites from the Boundary Ridge sections were measured in situ by a multi-collector ion microprobe and yielded both mass dependently fractionated (MDF) and MIF sulfur isotope values (Δ33S values from −0.44 to +6.27‰). Trace element heterogeneities are indicated by measurements at multiple spatial scales within rounded pyrites in the Boundary Ridge section, consistent with multiple generations of pyrite that incorporated sulfur processed in an anoxic atmosphere. A compilation of S-isotope data from pyrite in the Boundary Ridge diamictites analyzed in this study and previous work (Williford et al., 2011) defines multiple δ34S vs. δ33S arrays, consistent with an origin of detrital pyrite from the underlying Hamersley and Fortescue groups. Sulfides in a shale unit from the Boundary Ridge section plot along the terrestrial fractionation line but still retain positive MIF-S. This and detrital pyrite suggest low atmospheric oxygen immediately before the initiation of Paleoproterozoic Ice Ages. This data is inconsistent with a correlation to glacially-influenced successions within the North American Huronian Supergroup, in which the MIF-S signal permanently disappears. The diamictites at the Duck Creek Syncline are older than the Meteorite Bore Member because their stratigraphic position is within the Boolgeeda Iron Formation that underlies the Turee Creek Group, which is separated from the Meteorite Bore Member by nearly 1000m of the Kungarra shale at the Hardey Syncline.