The thick section of the Bird Spring Formation near Lee Canyon, Clark County, Nevada, consists of more than 7000 ft. of predominantly carbonate beds that show no apparent major lithologic breaks. Megafossils collected from the basal 500 ft. indicate that the lower 100 ft. are Chesterian in age and that the Mississippian-Pennsylvanian boundary occurs within a transitional interval. Fusulinids collected from the remaining 6500 ft. of the formation indicate that all of the following divisions of the Pennsylvanian and Permian are represented: Morrowan, Atokan, Des Moinesian, Missourian, Virgilian, Wolfcampian, and Leonardian. The Pennsylvanian-Permian boundary is gradational. A total of 2600 ft. of Chesterian and Pennsylvanian beds are present, and 4500 ft. of Permian are present. The lack of important lithologic breaks and the presence of all major fusulinid zones indicate that deposition of the predominantly carbonate Bird Spring Formation was continuous from late Mississippian time, through all of Pennsylvanian time, and into at least the Leonardian part of the Permian Period. The upper limits of the Bird Spring formation could not be determined because of truncation by faulting. Fusulinids representing Wolfcampian and Leonardian from the upper 3800 ft. of the formation were identified by Christy and include several species of Schwagerina and one species each of Pseudoschwagerina, Pseudofusulina, and Parafusulina. Fusulinids representing the Pennsylvanian and part of the Wolfcampian were identified in the present study from the lower 3300 ft. of the formation and are listed.

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