Isotope Signatures Associated with Early Meteoric Diagenesis

  1. Maurice E. Tucker3 and
  2. Robin G. C. Bathurst4
  1. J. R. Allan and
  2. R. K. Matthews

Published Online: 29 APR 2009

DOI: 10.1002/9781444304510.ch16

Carbonate Diagenesis

Carbonate Diagenesis

How to Cite

Allan, J. R. and Matthews, R. K. (1990) Isotope Signatures Associated with Early Meteoric Diagenesis, in Carbonate Diagenesis (eds M. E. Tucker and R. G. C. Bathurst), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304510.ch16

Editor Information

  1. 3

    Department of Geological Sciences, University of Durham, UK

  2. 4

    Derwen Deg Fawr, Llanfair DC, Ruthin, Clwyd, North Wales, UK

Author Information

  1. Department of Geological Sciences, Brown University, Providence, Rhode Island 02912, USA

  1. Chevron Oil Field Research Co., P.O. Box 446, La Habra, California 90631, USA

Publication History

  1. Published Online: 29 APR 2009
  2. Published Print: 21 AUG 1990

ISBN Information

Print ISBN: 9780632029389

Online ISBN: 9781444304510

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Keywords:

  • isotope signatures associated with early meteoric diagenesis;
  • isotopic analyses of Holocene and ancient limestones, suggesting isotope signature;
  • vadose-phreatic boundary;
  • carbonate sediments, undergoing mineralogical stabilization;
  • Barbados model, suggesting carbon and oxygen isotope data;
  • Horseshoe atoll consists of a build-up of cyclic carbonates;
  • Newman Limestone, shallow water carbonate shelf deposit

Summary

The environments in which carbonate diagenesis proceeds have been documented in previous studies of Holocene and late Pleistocene sediments and limestones on Barbados, West Indies. Variations in the carbon and oxygen isotopic composition of limestones, produced during early freshwater diagenesis, have been observed in this study to occur in specific patterns. Six potentially useful patterns emerge when one views stable isotope data within a stratigraphic framework: (1) the subaerial exposure surface is characterized by strongly 12C-enriched limestones. δ13C compositions of underlying limestones grow progressively heavier with increasing depth; (2) the subaerial exposure surface may also be marked by slight 18O-enrichment; (3) an abrupt shift in δ18O values may differentiate sediments above the exposure surface from those below; (4) sediments altered in the marine-meteoric mixing zone may be characterized by positive covariance between their δ18O and δ13C compositions; (5) the vadose-phreatic boundary may be marked by a sharp increase in δ13C values in the seaward portions of a fresh groundwater system; and (6) samples contemporaneously altered in a single fresh groundwater system within an areally restricted region should display a narrow range of δ18O and a wide range of δ13C compositions.

Analysis of samples from five Palaeozoic and Mesozoic formations, which contained petrographic evidence of early freshwater diagenesis, showed that isotope patterns similar to those observed in Barbados limestones have been preserved in rocks as old as Mississippian.

These isotope patterns could prove to be useful for identifying diagenetically induced porosity trends in carbonate rocks. They might be used to identify limestones diagenetically altered in meteoric environments, to identify mixing zone cements and dolomites, and to trace the regional and vertical distributions of early meteoric groundwater systems in ancient carbonate formations.