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There is remarkable similarity between the Devonian-Mississippian Sappington formation of western Montana and the Ohio shale-Bedford shale-Berea sandstone-Sunbury shale sequence of the Appalachian basin. The comparison is based on composition, color, and ordered succession of lithologic types, sedimentary structures such as channeled sand- and siltstones, ripple marks (oscillation, current, and interference), and cross-stratified sand- and siltstones, flow rolls (ball and pillow structures), paleogeographical and paleoecological interpretations, and fossils. Both areas bear a similar relation to the Cordilleran and Appalachian geosynclines, respectively.
In each case the strata involve a lower dark shale of late Devonian age, intermediate light-colored shales and siltstones or sandstones of Mississippian age, and an upper dark shale. This relationship can be summarized as follows:
One significant difference is in the presence of an algal (oncolite)--sponge biostrome (Unit E) which has wide distribution in the western area that is apparently absent in the Appalachian basin.
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