Elwood Atherton, Charles Collinson, and Jerry A. Lineback
The Pope Megagroup (Swann and Willman, 1961, p. 481-482), named for Pope County in southern Illinois.
The Pope Megagroup is roughly equivalent to the Chesterian Series, but it includes the Spar Mountain Member of the Ste. Genevieve (Valmeyeran) to the north and the Aux Vases (Valmeyeran) in most of its extent.
Extent and Thickness
The lateral extent of the Pope Megagroup in Illinois is the same as that of the base of the Ste. Genevieve Limestone to the north (fig. M-22) and that of the Aux Vases Sandstone to the south (fig. M-23). The outcrop area runs along and near the Mississippi and Ohio Rivers from Alton, Madison County, south to Grand Tower, Jackson County, and then eastward through Hardin County. The Pope thickens from its truncated edge on the north to about 1300 feet near its southern border, only slightly thicker than the Chesterian Series (fig. M-26).
Near its southeastern border the base of the Pope is locally a little higher than that of the Chesterian. The Pope is generally conformable on the Mammoth Cave Megagroup, except for minor erosional channels at the base of the Aux Vases Sandstone. It is separated from the overlying Pennsylvanian System by a major unconformity that has a relief of as 450 feet.
The Pope Megagroup comprises sandstone-shale units alternating with limestone-shale units of late Valmeyeran and Chesterian age that overlie the Mammoth Cave Limestone Megagroup and underlie the Pennsylvanian System and younger rocks (fig. 14).
SWANN, D. H., and H. B. WILLMAN, 1961, Megagroups in Illinois: American Association of Petroleum Geologists Bulletin, v. 45, p. 471-483; Illinois State Geological Survey Reprint 1961-N.
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