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Southeastern Geology


Middle and Upper Cambrian strata (Cambrian Series 3 and Furongian) in the southernmost Appalachians (Tennessee to Alabama) comprise the Conasauga Formation or Group. Heretofore, the youngest reported Conasauga beds in the Valley and Ridge Province of Georgia were of the late Middle Cambrian (Series 3: Drumian) Bolaspidella Zone, located on the western state boundary in the valley of the Coosa River. Two new localities sited eastward in the Conasauga River Valley, yield a diagnostic suite of trilobites from the Upper Cambrian Aphelaspis Zone. Very abundant, polymeroid trilobites at the primary locality are referable to Aphelaspis brachyphasis, which is a species known previously in western North America. A second locality has produced a few identifiable specimens of the aphelaspine Eugonocare (Olenaspella) separatum. Specimens at these two localities are generally complete individuals compressed in tan mudstones. The primary locality features abundant body cluster accumulations, implying mass mortality by bioimmuration. The trilobite assemblage also includes the agnostoids Glyptagnostus reticulatus, Agnostus inexpectans, and Aspidagnostus rugosus, all correlated to the global Paibian agnostoid Glyptagnostus reticulatus Zone. These localities contain the southeastern-most Late Cambrian faunule in the Appalachians. The trilobite species and carbonate-free, mudstone lithology, lacking evidence of infaunal bioturbation and burrowing, suggest accumulation eastward of a paleotopographic shelf-to-basin break, which is interpreted to be east of the Alabama Promontory and in the Tennessee Embayment. The preservation of abundant aphelaspine specimens by bioimmuration events may have been the result of mudflows down the shelf-to-basin slope.