Date of Award


Degree Name

Master of Science


Geological and Environmental Sciences

First Advisor

Dr. William B. Harrison III

Second Advisor

Dr. Charles A. Sternbach

Third Advisor

Dr. B. Charlotte Schreiber

Access Setting

Masters Thesis-Open Access


The Richfield Member of the lower Middle Devonian Lucas Formation is represented in the subsurface of northeast Isabella County, Michigan as a 180-foot-thick sequence of Interbedded limestone, dolomite and anhydrite. Richfield lithofacies within the study area reflect deposition in a complex patchwork mosaic of evaporative supratidal, in tertid al, shoal, and subtidal environments.

The present variations in Richfield porosities were caused almost entirely by post-depositlonal diagenetic changes. The carbonate units have undergone pervasive dolomltlzation of mud matrix, leaching of allochems, and extensive anhydrite void -fillin g . The best porosity developments are associated with partial to complete dolomitizatlon of the carbonate mud. Replacement of dolomlcrite by anhydrite and later dissolution of replacement fabric anhydrite also contributed to secondary porosity within the carbonate reservoirs. Compaction and dewatering of the primary sulfates provided the source for the anhydrltizing solutions which produced diagenetic cements.

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