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Most of the sulfur and ash in the Pittsburgh coal of southeastern Greene County, Pennsylvania, are thought to be syngenetic. Variations in sulfur and ash
probably were controlled by paleoenvironmental factors. Northeast-trending belts of thin, low-sulfur, low-ash coal coincide with structurally high areas; and a belt of thicker, higher sulfur, higher ash coal coincides with the trough of a major syncline. The thickness relations suggest that folding was contemporaneous with peat accumulation, and that the folds produced linear northeast-trending paleotopography which was covered by the ancient peat-producing swamps. The slight local relief would have affected water depths and associated anaerobic conditions. Sandstone-filled stream channels in the rocks below and above the Pittsburgh coal trended northwest across the old topographic grain. Compositional variations in the coal are independent of variations in type of overlying rock.
Northeast of Pittsburgh, Pennsylvania, the upper Freeport coal has no partings on depositional and structural highs; it has one parting on the flanks of the highs; and it has two partings in lows. Between Pittsburgh, and Brookville, Pennsylvania, northeast-trending areas of high sulfur in the upper Freeport and lower Kittanning coals coincide with each other and with areas that were topographically and structurally low when the coals were deposited.
Penecontemporaneous structural control of coal thickness and composition is evident within and east of a northeast-trending zone on the east side of the Appalachian basin, across which 300-ft fold amplitudes increase abruptly to 600 ft. The control was not effective in areas west of the zone. Folds on the west probably are younger than those on the east, and they did not affect deposition of Upper Pennsylvanian coal.
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