Abstract
Calcitic shells of three species of the ostreid pelecypods, Exogyra cancellata, E. costata (Late Cretaceous) and Crassostrea virginica (Recent) were analyzed for Mg and Sr. Shells of Exogyra contain 0.5-1.5 mole per cent MgCO3, 0.04-0.13 mole per cent SrCO3; shells of Crassostrea-1.0-1.6 mole per cent MgCO3, 0.08-0.09 mole per cent SrCO3. These calcites are not at equilibrium with the (aMg++) (aCa++) ratio as in the Recent sea water. The concentrations of Sr in the skeletons of these species and of Belemnitella americana (Late Cretaceous) can, at least in part, be accounted for by Nernst's distribution equilibria with respect to the Sr Ca ratio as in the Recent seas. A combined record of Mg and Sr, treated as an incomplete ternary free energy surface, may accentuate differences between geographically distinct populations. Interpretation of such differences is at present impeded by a lack of exact knowledge of the genetic and environmental effects on the skeletal chemistry. Approximate calculation of the activity coefficients of the components in magnesian calcites at 25°C is given in the Appendix.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 977-1002 |
| Number of pages | 26 |
| Journal | Geochimica et Cosmochimica Acta |
| Volume | 29 |
| Issue number | 8 |
| DOIs | |
| State | Published - Aug 1965 |
Funding
AckrtozuZedgement~-~rhis paper is based on a part of a doctoral dissertation done under the auspices of the Committee of Advisors, Profs. B. K~MMEL (chairman), R. SIEVER, H. B. WHIT-TINGTON, G. G. SI,VPSON, and supported by funds of the Division of Geological Sciences, Harvard University. Profs. R. SIEVER, R. M. GARRELS and J. B. THOMPSON discussed and helpfully criticized various stages of this work and preparation of the text. Prof. G. J’. WASSERBURC: (California Institute of Technology) discussed some of the problems outlined in the Appendix at the early stages of this work. Prof. H. D. HOLLAND (Princeton University) provided the result,s, some as yet, 7lnpubl~shed, of his work, read the m~uscript and offered critical comments. Prof. H. W. FAIRBAIRN (M.I.T.) made available the X-ray spectrometer. Prof. C. FRONDEL provided a sample of analyzed dolomite. Prof. W. H. WHEELER (University of xorth Carolina, Chapel Hill) gave a number of samples collected by him. Dr. G. MOORE (Department of Biology, University of New Hampshire, Durham) provided guidance and equipment for collecting the Recent, material. Messers. K. C. BECK and P. WILDE (Harvard University) participated in the eolleet,ing in xew Hampshire. The help and cooperat,ion of the above persons are grat,efully acknonlrdgcrl.
ASJC Scopus subject areas
- Geochemistry and Petrology