ABSTRACT

In a vertical, north-south trending, seemingly knife-edge dolomite to limestone contact in the Confusion Range of western Utah, the microscopic effects of alteration extend through a much broader interval than is indicated by the rocks at the contact. Within this interval nine petrographically distinct carbonates, six of which are in zones roughly parallel to the contact, are recognizable. Five to ten cm north of this contact the rocks are a medio-crystalline, brown-weathering dolomite containing white dolomite bodies, whereas 100 to 250 cm south of the contact the prevailing rock type is a limestone consisting of fossil fragments imbedded in an aphanitic lime matrix. Recrystallization of the limestone to fibrous calcite apparently preceded the dolomitization. The avenues followed by he dolomitizing solutions were the same as those of the calcite recrystallization, suggesting control was by a secondary permeability established with recrystallization. Cryptocrystalline calcite that occurs near the outer margin of incipient dolomite crystallization surrounds fossil fragments and residuals of limestone. These calcite-enclosed residuals and the enclosing material form the marble-like white dolomite bodies occurring on the dolomite side of the contact.