DIAGENESIS OF THE COPPER RIDGE DOLOMITE (CAMBRO-ORDOVICIAN KNOX GROUP), CENTRAL ALABAMA

The Knox Group is an important sedimentary succession that covers a large swath of the southeastern United States. In Alabama it consists of five variably dolomitized formations that were deposited in a shallow shelf setting during the late Cambrian and early Ordovician. The Knox Group and equivalent strata are known throughout the southeast for hosting fresh water aquifers, Mississippi Valley Type ore deposits, hydrocarbon reservoirs, and potentially providing a trap for waste-water and to sequester CO₂. The purpose of this undergraduate honors study was to assess the petrographic characteristics and diagenesis of a portion of the Knox Group, particularly the Copper Ridge Dolomite, in central Alabama. Three cores comprised the bulk of the subject material in this study. These data were supplemented with samples collected from a Copper Ridge Dolomite field site approximately 40 km south of Birmingham, AL. A total of 57 thin sections were studied during the course of the project and reveal that the Copper Ridge Dolomite underwent extensive early to late diagenesis. Early sporadic silicification and pervasive dolomitization were followed by later multiple phases of fracturing, more silicification and dolomitization, and finally calcite precipitation and pressure dissolution. Specific cement fabrics include mosaic dolomite (now the dominant rock matrix), idiomorphic dolomite cement (also present as inclusions within chert), megaquartz, and spherulitic chalcedony. Bitumen lines many of the intercrystalline dolomite pores and was concentrated along stylolites during a burial phase of diagenesis. Porosity and permeability are low in the rocks we studied, victims of the complex diagenesis of the Knox Group.