An 17O record of late Neoproterozoic glaciation in the Kimberley region, Western Australia

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We have recently reported non-mass-dependent 17O depletion in sulfate deposited after the Marinoan glacial meltdown at ca. 635 million years ago. Further investigation linking the Δ 17O of barite to its sedimentological-geological context in Marinoan South China reveals that the 17O depletion in sulfate is most pronounced at sites near paleo-continents, supporting the hypothesis that atmospheric O 2 was the source of the depletion which was transferred to sulfate via oxidative weathering of sulfides. Host minerals or rocks for the Marinoan 17O depletion have been limited to barite (southern China and western Africa) and carbonate-associated sulfate (CAS) in limestone lenses within a diamictite (Svalbard). If the Marinoan 17O depletion event is indeed related to an extraordinary atmospheric condition, the signal should be global in its distribution. The Kimberley region of Western Australia was close to a continent in the late Neoproterozoic and will serve as a test of our hypothesis that the anomalous 17O depletion may be widely recorded in the rock records of this time period.We report here that the CAS in the Moonlight Valley (MV) cap dolostones, Texas/Mabel Downs (TMD), the eastern Kimberley region, Western Australia is anomalously depleted in 17O (Δ 17O value as low as -0.68‰). The magnitude of the anomaly decreases gradually toward the overlying Ranford mud-silt-sandstones. This finding not only expands the geographic distribution of the depleted 17O signal, but also the type of host rocks or minerals that the anomalous sulfate resides. The CAS in the MV cap dolostones in Palm Spring (PS) section, ∼150km south of TMD, however, does not bear a 17O depletion. Neither does the CAS in the Egan cap dolostones. The presence and absence of pronounced 17O anomalies in the two time-equivalent yet spatially different MV cap dolostones are consistent with the paleogeography that indicates TMD was close to the continent while PS was at an open-ocean environment. While sharing some of the same sedimentological features with that of the MV cap dolostones at TMD, the Egan cap has distinct δ 13C and δ 18O values for dolostones and distinct Δ 17O, δ 34S and δ 18O values for CAS, supporting an earlier assignment of the Egan glaciation to be younger than Marinoan in the late Neoproterozoic. © 2012 Elsevier B.V.

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Precambrian Research

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