Black shales of the late Neoproterozoic Gwna Group (570-580 Ma), UK, contain enrichments of tellurium (Te), selenium (Se) and cobalt (Co) relative to average shale compositions. The Te and Co enrichments bear comparison with those of ferromanganese crusts in the modern deep ocean. Gwna Group deposition coincides with the Second Great Oxidation Event, which had a significant effect on trace element fixation globally. Selenium and Te concentrations within these black shales indicate increased continental weathering rates, high biological productivity and corresponding increases in atmospheric O2 concentrations. Cobalt, nickel (Ni) and arsenic (As) enrichments in this succession are secondary mineralisation phases. Demand for many of the trace elements found enriched in the Gwna Group black shales make their mechanisms of accumulation, and variations through the geological record important to understand, and suggests that new resources may be sought based on black shale protoliths from this period.
Bibliographical noteWe are grateful to John Still for his skilled technical support and the ACEMAC facility at the University of Aberdeen. Research funded by NERC grant NE/M010953/1 and NERC facility grant IP-1631-0516. AJB is funded by NERC support of the Isotope Community Support Facility SUERC. The authors thank Eva Stüeken, Ross Large and one anonymous reviewer for their constructive feedback on the original manuscript.
- black shales
- atmospheric oxygentation
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John Still (Manager)Geology and Geophysics
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