Abstract

Critical comparisons of Montanan sequences in southern Alberta and various parts of Montana permit some conclusions on north–south, as well as east–west, correlation. The Lower Milk River sandstone of Alberta is the equivalent of the Lower Eagle sandstone of northwestern Montana but both differ from the type Virgelle Sandstone, with which they have been equated. The Pakowki Formation of Alberta represents the Claggett of Montana plus lower parts of the Judith River Formation. The remainder of the Judith River Formation is equivalent to the Foremost and Oldman Formations of Alberta. The Bearpaw Formation thins markedly from east to west, and uppermost shales pass into marine sandstones and these in turn into non-marine formations. Of the various formational boundaries, the top of the Lower Milk River and Lower Eagle sandstone, the base of the Pakowki and Claggett Shale, and the top of the Oldman and Judith River Formations, are also time boundaries throughout large parts of the region.

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