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For many years the age and correlation of late Paleozoic (post Meramecian) strata in the eastern Rocky Mountains and plains of western Canada and the northwestern United States have been difficult to establish, because the stratigraphy is complicated by at least three major angular unconformities. These occur at the Mississippian-Pennsylvanian boundary, the Pennsylvanian-Permian boundary and the Permian-Triassic boundary. The most controversial has been the one at the Mississippian-Pennsylvanian boundary, until Willis (1959) established it at the Heath (Big Snowy Group)-Tyler contact. In Alberta (Peace River area) the Mississippian-Pennsylvanian boundary was found to be at the Golata-Kiskatinaw contact. The Golata formation is very likely correlative with part of the Big nowy Group; the Kiskatinaw formation is believed to be the age equivalent of the Tyler formation. Fossil determinations have confirmed these lithological correlations.
To link equivalent formations from Peace River to Montana, the front ranges of the Rocky Mountains were included in the study. The Etherington formation (Mississippian Chester) here correlates with the Big Snowy Group and with the Golata formation. The Tunnel Mountain formation (Lower Pennsylvanian) is equivalent to the Tyler-Amsden (Kiskatinaw-Taylor Flat in Peace River) interval. A map showing the eastern edges of the Chesterian and Lower Pennsylvanian, cross sections through critical areas, and a nomenclature chart are included.
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