Large variations in the stoichiometry, perfection of order, and substitution of iron for magnesium in sedimentary dolomite make precise interpretation of the trace-element and isotopic chemistry of this complex mineral difficult.

Redetermination of phosphoric acid fractionation factors yields values of of 10³ 1n ^prop between 11.4 and 11.9 for most sedimentary dolomites (the redetermined value for calcite is 10.5). A few dolomite types apparently yield values of about 12.5, but the reasons are unknown.

Mathematical modeling of the diagenetic behavior of the trace element strontium, in conjunction with oxygen isotopic changes during the diagenesis of limestones, substantiates recent suggestions that experimentally determined partition coefficients for calcite may not apply under actual diagenetic conditions. Presumably, an analogous situation exists with respect to dolomite.

At the present state of the art, quantitative interpretation of absolute isotopic and/or trace-element values is tenuous at best. Qualitative interpretation of regional or stratigraphic gradients in either or both of these variables appears to be of far greater utility.

End_of_Article - Last_Page 485------------