Edited by James E. Palmer and Russell R. Dutcher - University of ...

Abbott and Caseyville formations, Upper Roaterstate 24Strata exposed here are divided into five distinctdepositional units (fig. I L-39). The strata include thefollowing depositional facies: channellpoint bar, peatswamp, interdistributary bay, distributary channel orcrevasse splay.The type location of the Reynoldsburg Coal Memberis about 6 miles (9.5 km) east of Stop 10 near thesmall town of Reynoldsburg. The coal is known tooccur only in a relatively small area in the central partof the outcrop belt of southern Illinois (Hopkins andSimon, 1975). The coal, which is as much as 3 feet(0.9 m) thick, varies locally in thickness. The coal hasbeen mined near Reynoldsburg.Two sandstone dikes are present in the ReynoldsburgCoal in the exposure on the east side of 1-24 (fig.I L-40). Sandstone dikes occur rarely in coalbeds, andtheir origin is not completely understood. The dikesconsist of sandstone similar to that directly overlyingthe coal, and the dikes pinch out downward toward thebase of the coal. The dikes probably were emplaced asintrusions of sand from the overlying sandstone duringcompaction of the unconsolidated sediments.ormation, Lower Roadcut, interstate 24The section exposed here is 170 feet (52 m) thickand consists of sandstone with lesser amounts of conglomerate,siltstone, and shale. The strata include thefollowing depositional facies: channellpoint bar, upperpoint bar/floodplain, interdistributary bay, distributarychannel, and abandoned channel.The outcrop has been divided into five depositionalunits. Descriptions of the rock units are listed infigure I L-41; inferred depositional environments aredescribed in the following paragraphs.IT 1. Sandstone and conglomerate. Fluvialldistributarychannel. Thickness of deposit and channelscours suggest that a meandering stream persisted inthis area.FluvialchannelDistributary'f luvialchannel orcrevasse splaySwampFaciesInterdistributarybay/ marshDistributaryf luvialchannelUnitNo.UNIT 5. Sandstone, white, weathers buff with iron-oxidestaining, finegrained to very fine-grained, grains are subangularto subrounded, well-sorted. Quartz is the dominant mineral;oxidized clay chips common. Unit is both planar cross-beddedwith asymmetrical, low-amplitude ripples where sorting is poor,and structureless where sorting is good. Paleocurrent directionssouth-southwest.UNIT 4. Sandstone and siltstone; sandstone, dark brown,weathers deep purple, fine- to mediumgrained, subroundedgrains, abundant quartz; some oxidized clay chips and woodfragment casts. Sandstone occurs as thick to thin lenses whichhave filled scours in siltstone. Siltstone, white, weathers lightgray, finegrained, silty, parts easily along bedding planes; thintovery thin-bedded; deposits draped over sandstone lenses.Ripple lamination common. Paleocurrent directions westsouthwest.Contact with overlying sandstone is sharp.UNlT 3. Coal (Reynoldsburg Coal Member), shale, and siltstone.Unit 3 fills paleotopographic depressions and is scouredby Unit 4; thickness is variable. The coal is bright banded and asmuch as 27 inches (70 cm) thick; partly stained yellow. Shale,black, carbonaceous, thin-bedded. Siltstone, dark brown, weathersrusty brown, grains subangular; siltstone occurs in very thinlenses which are rippled and which cut into the underlyingshale and grade into the overlying shale. Sharp contact with overlyingsandstone and siltstone.UNlT 2. Siltstone and shale; siltstone, light brown, weathersrusty brown and orange, subangular grains. Shale, gray, slightlysilty, carbonaceous, thin-bedded to laminar. Siltstone is thinbedded,ripple-bedded, and missing locally; fills an irregulareroded surface on underlying shale and grades into the overlyingshale. Sharp contact with overlying shale and coal.UNlT 1. Sandstone; white to pink, weathers rusty tan and buff,purple mottling, with red iron-oxide on bedding planes; finegrained,grains are subrounded, sorting is fair to good. Quartzis the dominant mineral; contains few clay chips. Lower part ofunit appears structureless due to good sorting of constituentgrains; upper part contains planar and trough cross-beds. Paleocurrentdirections south-southeast. Gradational contact withoverlying siltstone and shale. ISGS 1979Figure I L-39. Columnar section and description of units, Caseyville and Abbott Formations, Upper Roadcut, interstate 24, (IllinoisStop 10). (After Koeninger, 1978, and Koeninger and Mansfield, 1979.)