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Freshwater limestones comprise a significant portion of the Upper Pennsylvanian and Lower Permian strata of the northern Appalachian basin. In some areas, the Monogahela Group consists of as much as 50% freshwater limestones. These limestones are clayey to silty, iron-bearing, sparsely fossiliferous, micritic, and thinly bedded or nodular and are presumed to be lacustrine in origin. They are part of a recurring sequence of beds that include coal, sandstone, shale/clay, and marine limestone. The initial goals of this study are to develop a stratigraphic framework for these freshwater limestones and to determine, their lateral continuity, thickness variability, and relation to other beds in this section, in particular the coals, on a regional scale. The Pittsburgh coal and Ames limestone are very persistent regionally and are used as a datum. Regional correlations show that possibly 20 freshwater limestone beds are persistent and widespread; some cover at least 5,000 mi{sup 2} in eastern Ohio, western Pennsylvania, northern West Virginia and western Maryland. Cross sections and fence diagrams constructed from drill logs and measured sections indicate that the thickness of these limestone beds varies laterally and between beds, ranging from less than 1 to 150 ft thick. Correlations also show stratigraphic and paleogeographicmore » relationships between the coals and freshwater limestones. Many of the limestones underlie coal beds, directly in some places. The coals and limestones are better developed in the northern part of the Appalachian basin. These associations may hold significant clues to the depositional and the paleoclimatic setting of the freshwater limestones and the coals.« less |
