Age of Amsden Formation, Cherry Creek, Wind River Mountains, Wyoming: GEOLOGICAL NOTES

Abstract

Six new collections of fossils from the lower part of the at Cherry Creek, Wind River Mountains, Wyoming, place the Mississippian-Pennsylvanian boundary more than 48 feet and less than 63 feet above the Madison limestone. The lower faunas are Chesteran in age, and the upper faunas are tentatively dated as Atokan. The name Sacajawea formation is rejected for the Mississippian beds at Cherry Creek. The presence of two sandstones in the Amsden, both of which have been called Darwin sanstone, is inferred, and it is pointed out that the at Cherry Creek contains beds that are specifically excluded farther north in the Wind River Mountains. Until the faunas of the type are made known it will be impossible to decide which use of the name Amsden is correct in the Wind River Mountains.