Abstract

In Jefferson County, in the Illinois coal basin, southern Illinois, the Pennsylvanian column between the Shoal Creek and Stonefort Limestones, an interval of about 900 feet, was divided into seven intervals separated by widespread coals or limestones readily recognized on electric logs, namely the Shoal Creek Limestone, coal No. 8, West Franklin Limestone, coal No. 7, coal No. 5, coal No. 4, coal No. 2, and the Stonefort Limestone listed in descending order. These intervals were determined from 578 electric logs in the county, an average of about one per square mile. Sand-shale ratios were determined for each interval and it was found than a "channel" sandstone of one age occurs in each interval except between the Shoal Creek Limestone and coal No. 8. Two ages of channels occur in one interval. Sandstone percentage maps were made of each interval. Thicknesses of each interval were compared in the "channel" areas and nearby, outside the channel, to avoid regional variations in thickness. Assuming that the coals and limestones were laid down nearly parallel to each other, variations in interval result from greater compaction of the shales than of the sandstones. Results show the following percentages of differential compaction for the six intervals with channels listed in descending order: 21, 34, 29, 35, 42 and 54 percent.

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