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Secular distribution of highly metalliferous black shales corresponds with peaks in past atmosphere oxygenation

Citation

Johnson, SC and Large, RR and Coveney, RM and Kelley, KD and Slack, JF and Steadman, JA and Gregory, DD and Sack, PJ and Meffre, S, Secular distribution of highly metalliferous black shales corresponds with peaks in past atmosphere oxygenation, Mineralium Deposita, 52, (6) pp. 791-798. ISSN 0026-4598 (2017) [Refereed Article]

Copyright Statement

Copyright Springer-Verlag Berlin Heidelberg 2017

DOI: doi:10.1007/s00126-017-0735-7

Abstract

Highly metalliferous black shales (HMBS) are enriched in organic carbon and a suite of metals, including Ni, Se, Mo, Ag, Au, Zn, Cu, Pb, V, As, Sb, Se, P, Cr, and U ± PGE, compared to common black shales, and are distributed at particular times through Earth history. They constitute an important future source of metals. HMBS are relatively thin units within thicker packages of regionally extensive, continental margin or intra-continental marine shales that are rich in organic matter and bio-essential trace elements. Accumulation and preservation of black shales, and the metals contained within them, usually require low-oxygen or euxinic bottom waters. However, whole-rock redox proxies, particularly Mo, suggest that HMBS may have formed during periods of elevated atmosphere pO2. This interpretation is supported by high levels of nutrient trace elements within these rocks and secular patterns of Se and Se/Co ratios in sedimentary pyrite through Earth history, with peaks occurring in the middle Paleoproterozoic, Early Cambrian to Early Ordovician, Middle Devonian, Middle to late Carboniferous, Middle Permian, and Middle to Late Cretaceous, all corresponding with time periods of HMBS deposition. This counter-intuitive relationship of strongly anoxic to euxinic, localized seafloor conditions forming under an atmosphere of peak oxygen concentrations is proposed as key to the genesis of HMBS. The secular peaks and shoulders of enriched Se in sedimentary pyrite through time correlate with periods of tectonic plate collision, which resulted in high nutrient supply to the oceans and consequently maximum productivity accompanying severe drawdown into seafloor muds of C, S, P, and nutrient trace metals. The focused burial of C and S over extensive areas of the seafloor, during these anoxic to euxinic periods, likely resulted in an O2 increase in the atmosphere, causing short-lived peaks in pO2 that coincide with the deposition of HMBS. As metals become scarce, particularly Mo, Ni, Se, Ag, and U, the geological times of these narrow HMBS horizons will become a future focus for exploration.

Item Details

Item Type:Refereed Article
Keywords:highly metalliferous black shale (HMBS), atmopsheric oxygen, metal enrichments, pyrite
Research Division:Earth Sciences
Research Group:Oceanography
Research Field:Chemical Oceanography
Objective Division:Mineral Resources (excl. Energy Resources)
Objective Group:Other Mineral Resources (excl. Energy Resources)
Objective Field:Mineral Resources (excl. Energy Resources) not elsewhere classified
Author:Johnson, SC (Mr Sean Johnson)
Author:Large, RR (Professor Ross Large)
Author:Steadman, JA (Dr Jeffrey Steadman)
Author:Meffre, S (Dr Sebastien Meffre)
ID Code:116773
Year Published:2017
Web of Science® Times Cited:1
Deposited By:CODES ARC
Deposited On:2017-05-18
Last Modified:2018-04-23
Downloads:0

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