Lisa L. Varga

Date of Award


Degree Name

Master of Science


Geological and Environmental Sciences

First Advisor

Dr. William B. Harrison III

Second Advisor

Dr. Thomas Straw

Third Advisor

Dr. John Grace

Access Setting

Masters Thesis-Open Access


The Lower Silurian Brassfield Formation which outcrops in the Tri-state area of Ohio, Indiana and Kentucky is a transgressive sequence consisting of a series of interbedded shales, limestones and dolostones. Evidence from depositional environments, petrography and spatial relationships of dolomitized and undolomitized rock suggests dolomitization in southwestern Ohio was a two-stage process. Initial dolomitization was restricted to the basal Belfast Member and probably occurred penecontemporaneously on small supratidal islands in a manner analagous to that which occurs in the modern sabkha environment of the Persian Gulf. Regional dolomitization was a later diagenetic event related to the formation of a fresh-seawater mixing zone beneath a landmass created by upwarping of the Cincinnati Arch at the close of the Silurian. Intensity of dolomitization in the outcrop belt is controlled by the proximity of the original carbonate to the source of dolomitizing fluids in the mixing zone.

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