Trace Element Composition of Dolostones and Dolomites and Its Bearing on the Dolomite Problem: ABSTRACT

Abstract

Three hundred specimens of primary and dolostones and 150 specimens of dolomite quantitatively analyzed in triplicate for 20 trace and minor elements statistically yield separate populations of the two major lithologic varieties of dolomitic carbonate rocks for certain trace elements. Histograms, probability plots and measure of the coefficient of variation suggest a lognormal distribution for the trace-element data, which when tested statistically at the 1 per cent level of significance, indicate higher concentrations of Al, Ba, Fe, K, Li, Zn, and Na in the primary dolostones. Sr is significantly concentrated in the secondary dolomites separated from the dolostones. On the basis of carbon-oxygen isotope ratios and crystallo-chemical considerations, the do omite is considered to be a replacement mineral after calcite or aragonite, and the abundance of Sr in dolomite is interpreted as a minor impurity originally derived from metastable aragonite and entrapped in the dolomite structure. For the samples studied, trace element patterns appear to suggest that primary dolostones (characterized by very fine and uniform grain size; complete absence of fauna, relict textures and phantom structures; lack of appreciable porosity; relatively light color; frequent fine lamination; conchoidal fracture; and association with evaporitic sequences) may represent the early replacement of predominantly calcitic limestones under conditions of somewhat above normal salinity; dolostones (characterized by relatively coarse and non-unifor grain size; euhedral dolomite rhombs; frequent oolith, pellet, and fossil relict textures; or organic fossil remains) may represent the early replacement of predominantly aragonitic limestones under normal marine conditions. A specific example of Ordovician Nittany dolostone comprising alternating zones of primary and dolostones confirms the relationship evident in samples differing widely in age and geographic location. End_of_Article - Last_Page 375------------