Onset of oxidative weathering of continents recorded in the geochemistry of ancient glacial diamictites

Richard M. Gaschnig, Roberta L. Rudnick, William F. McDonough, Alan J. Kaufman, Zhaochu Hu, Shan Gao

Research output: Contribution to journalArticlepeer-review

32 Citations (Scopus)

Abstract

Glacial diamictites deposited in the Mesoarchean, Paleoproterozoic, Neoproterozoic, and Paleozoic eras record temporal variations in their average compositions that reflect the changing composition of the upper continental crust (UCC). Twenty six of the 27 units studied show elevated chemical index of alternation (CIA) and low Sr abundances, regardless of their age, documenting pervasive weathering of the average UCC. Lower abundances of transition metals reflect a shift towards more felsic crustal compositions after the Archean. Superimposed on this chemical difference is the signal of the rise of oxidative weathering of the continents, recorded by changes in the absolute and relative abundances of the redox sensitive elements Mo and V. Neoproterozoic and Paleozoic diamictites show pervasive depletion in Mo and V, reflecting their loss from the continents due to increasing intensity of oxidative weathering, as also recorded in some of the Paleoproterozoic diamictites. A few of the Paleoproterozoic diamictites deposited after the Great Oxidation Event show no depletion in Mo and V (e.g., Gowganda), but such signatures could be inherited from their provenance. In contrast, the pre-GOE Duitschland diamictite (ca. 2.3-2.5 Ga) from South Africa reveals evidence of intense oxidative weathering (i.e., large depletions in Mo), supporting a growing body of observations showing the presence of measurable atmospheric oxygen prior to permanent loss of the mass independent fractionation signal in sulfur isotopes.

Original languageEnglish
Pages (from-to)87-99
Number of pages13
JournalEarth and Planetary Science Letters
Volume408
DOIs
Publication statusPublished - 2014 Dec 15
Externally publishedYes

Keywords

  • Diamictite
  • Glaciation
  • Great Oxidation Event
  • Oxygen
  • Precambrian
  • Upper continental crust

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

Fingerprint Dive into the research topics of 'Onset of oxidative weathering of continents recorded in the geochemistry of ancient glacial diamictites'. Together they form a unique fingerprint.

Cite this