Some carbonate concretions in the Alberta oil sands contain calcite with
quite high carbon isotope values.  See: Dimitrakopolous and Muehlenbachs
(1987) Chemical Geology 65, p. 283-291; Longstaffe et al. (1992),
Proceedings of the 7th International Symposium on Water-Rock Interaction,
Balkema Publishers, p. 955-958; Longstaffe (1994) in Quantitative
Diagenesis, Recent Developments and Applications to Reservoir Geology, p.
223-274.  Kluwer Academic Publishers; and brief mention in Hornibrook and
Longstaffe (1996), Clays and Clay Minerals 44, p. 1-21.  So far, our
group's highest value for calcite from the oil sands has been +23 permill.



==============================================================================
Fred J. Longstaffe                      ph:  519-661-3177
Department of Earth Sciences            fax:  519-661-3198
University of Western Ontario           e-mail:  [log in to unmask]

London, Ontario N6A 5B7