Nonskeletal Aragonite and pCO2 in the Phanerozoic and Proterozoic

  1. E.T. Sundquist and
  2. W.S. Broecker
  1. Philip A. Sandberg

Published Online: 18 MAR 2013

DOI: 10.1029/GM032p0585

The Carbon Cycle and Atmospheric CO: Natural Variations Archean to Present

The Carbon Cycle and Atmospheric CO: Natural Variations Archean to Present

How to Cite

Sandberg, P. A. (1985) Nonskeletal Aragonite and pCO2 in the Phanerozoic and Proterozoic, in The Carbon Cycle and Atmospheric CO: Natural Variations Archean to Present (eds E.T. Sundquist and W.S. Broecker), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM032p0585

Author Information

  1. Department of Geology, University of Illinois, Urbana, Illinois 61801

Publication History

  1. Published Online: 18 MAR 2013
  2. Published Print: 1 JAN 1985

ISBN Information

Print ISBN: 9780875900605

Online ISBN: 9781118664322

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Keywords:

  • Carbon cycle (Biogeochemistry)—Congresses;
  • Atmospheric carbon dioxide—Congresses;
  • Geological time—Congresses;
  • Paleothermometry—Congresses;
  • Geology, Stratigraphic—Congresses

Summary

Calcitized, originally aragonitic nonskeletal carbonates may be recognized by a combination of textural and compositional properties including: disruptive replacement textures, relic aragonite inclusions, and elevated strontium content. Temporal distribution of once-aragonitic constituents appears to be discontinuous during the Phanerozoic. That suggests an alternation of “aragoniteinhibiting” conditions, in which nonskeletal carbonates formed only as calcite (of uncertain, but perhaps lower Mg2+ content), and “aragonite-facilitating” conditions, in which both aragonite and calcite (mainly high-magnesium calcite) formed. Fischer (1981, 1982) and Mackenzie and Pigott (1981) suggested that pCO2 changes are coupled to changes in plate tectonic mode. Control of nonskeletal carbonate mineralogy by the influence of pCO2 or some covariant factor most probably oceanic Mg/Ca) is suggested by the close agreement between sea level curves and the presence-absence curves for nonskeletal aragonite. Times of aragonite inhibition by elevated pCO2 would probably also have been times of diminished non-skeletal carbonate precipitation and of some submarine occurrence of processes commonly regarded as meteoric, such as carbonate mud stabilization and molds or void-fill calcite casts of aragonite skeletons. A few examples of apparent nonskeletal aragonite occur in Precambrian rocks at least as old as -1.9 Ga. The inferred levels of pCO2 associated with apparent inhibition of nonskeletal aragonite precipitation in the Phanerozoic make it difficult to reconcile possible occurrences of Precambrian aragonite cements and ooids with standard interpretations of very high pCO2 throughout the Precambrian.