PETROFACIES AND DIAGENETIC ALTERATION IN THE CAMBRO-ORDOVICIAN KNOX GROUP OF CENTRAL ALABAMA

The Cambro-Ordovician Knox Group is a thick sequence of shallow marine carbonate strata that crops out over a large portion of central and northern Alabama. In the vicinity of Tuscaloosa, these strata are flat lying. Exposure quality is variable. River incisions provide the best exposure, but the disposition of the strata limits the thickness of sedimentary sections possible at any one location. Fortunately, several petroleum exploration and water wells have been drilled in the area and some of the cored intervals have penetrated the Knox Group. The intent of this study is to describe and interpret the sedimentary and petrographic characteristics of the Knox Group and to resolve the diagenetic history of these strata in central Alabama. At this point in the project, three cores have been examined. Core 1 (AL Permit X1586), consisted largely of nodular gray mudstone/wackestone, the entire core was crisscrossed with veins and microfractures filled with multiple phases of calcite. Core 2 (AL Permit X1132) was composed of alternating layers of fine grained massive, and dark gray, nodular/mottled dolostone. Core 3 (AL Permit X1586), was also composed of nodular dolostone, but contained interbeds of wackestone. The entire examined interval followed the bedding direction of the strata implying near vertical orientation at this location. The core likely encountered a thrust fault below the surface. As in core 1, there was significant fracturing in core 3, however, mineral-fills consisted of quartz and dolomite rather than calcite. Data collected to date suggests that fracturing played an important role in the transport of fluids responsible for much of the dolomitization and silicification in subsurface intervals of the Knox Group. Future work, which will comprise the bulk an Honors dissertation, will explore the role of fractures in the diagenesis of surface exposures of the Knox group in the study area.