Ar-40/Ar-39 dating of exceptional concentration of metals by weathering of Precambrian rocks at the Precambrian-Cambrian boundary

John Parnell*, Darren F Mark, Robert Frei, Anthony E Fallick, Rob M Ellam

*Corresponding author for this work

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Abstract

The sub-Cambrian surface, including diverse metalliferous deposits, shows evidence of intense weathering of Precambrian rocks to form supergene-enriched ores and metalliferous placers, followed by widespread peneplanation. Much of the metal would have been flushed to the Cambrian ocean during peneplanation. An Ar-40/Ar-39 age of 542.62 +/- 0.38 Ma (1 sigma, full external precision, Renne et al., 2011) for metalliferous alteration clays in Scotland shows that this event occurred immediately prior to the Precambrian-Cambrian boundary. A negative delta Cr-53 isotopic signature for the clay is consistent with mobilization on land of redox sensitive metals by oxidative terrestrial weathering. This unprecedented flushing of metals from the weathered Precambrian surface would have contributed to the chemistry of the earliest Cambrian ocean at a time of marked faunal evolution. (C) 2014 Elsevier B.V. All rights reserved.

Original languageEnglish
Pages (from-to)54-63
Number of pages10
JournalPrecambrian Research
Volume246
DOIs
Publication statusPublished - Jun 2014

Keywords

  • Precambrian
  • Precambrian-Cambrian boundary
  • great unconformity
  • ore deposits
  • weathering
  • Metazoan
  • Fish Canyon sanidine
  • K-40 decay constants
  • isotopic composition
  • joint determination
  • chromium isotopes
  • improved accuracy
  • geochronology
  • constraints
  • supergorup
  • transition

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