PETROGRAPHIC OBSERVATIONS OF DIAGENETICALLY ALTERED STROMATOLITIC FABRICS OF THE KNOX GROUP, CHATSWORTH, GEORGIA

Stromatolitic fabrics from the Proterozoic are typically associated with early diagenetic black chert deposits. These black chert nodules can contain well-preserved microfossils; however, it is unclear whether similar nodules and deposits exist later in the Cambrian when silica-utilizing organisms evolved. Stromatolites from the Copper Ridge Dolomite of the Knox Group were deposited within the late-Cambrian to early Ordovician and are associated with large nodules and layers of black chert. Unlike older stromatolite samples of the Proterozoic, these Copper Ridge stromatolites from NW Georgia do not preserve many individual microfossils. The carbonate of the Knox Group has been diagenetically altered during the formation of the Valley and Ridge province. Petrographic observations indicate that diagenesis involved the injection of multiple, complex episodes of fluids. Stromatoltic fabrics contain evidence of silicification and dolomitization episodes with silica crosscutting through the surrounding fabric, dolomite rhombs recrystallized as silica, and a rectilinear pattern indicative of a silica gel precursor. This study investigates the mineralogy and chemical composition of these Copper Ridge stromatolites using SEM and CL data in an attempt to establish a paragenetic sequence for the mineral and fluid phases preserved in the samples.