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

een caused by alternating humid and arid clinaates.e containing whitetau At some localitiesin western Kentucky and southern Indiana, basalPennsylvanian strata consist almost entirely of whitequartz pebbles in a ferruginous f ine-grained sandstonematrix. The abundance of white quartz pebbles withinbasal Pennsylvanian sandstone will be observed at severallocalities in the basin. The depositional history ofthe sandstone and its similarity to the Millstone Grit ofEngland will be considered.e gradual increase ike argillaceousflakes with decreasing age of ciastig: rocks. This increasesuggests a gradual change in provenance of sediments inmiddle and late Pennsylvanian time. Evidences of sucha change will be considered at several field trip stops.limestone members as much as 50 feet thick have beenrecognized. Coal, one of the least abundant tiahic unitsof the Pennsylvanian System, constitutes no more thantwo percent of rock strata in most areas.More than 500 units sf sandstone, si6tstone, shale,limestone, coal, and clay are distinguishable in thePennsylvanian strata of the liiirnoisness and great number of vertical cindicate that changes in depositioria! environment wereecause of the relativefy large number oh lithicsomewhat complex stratigraphic nomenclaturehas developed (figs, 1 and 2), Although some cornmonalityin nomenclatures exists between Illinois,Indiana, and Kentucky, many different names havealso been adopted ii-1 each state, ML~c~ hasto establish equivalance of stratigraphic nomenciaturein each state.balls occur in 17 coals aPliinois Basin Coal Field. An opportunity will be affordedat one or more stops on the field trip to obtaincoal ball samples.ennsylvanian stratiPennsylvanian rocks have a maximum thickness ofm) in Union County,western Kentucky, where the thickest section occurs inaben block downthrown more than 1,QOm). Douglass (this Guidebook, part 2) hasfied Permian (Wolfcampian) strata in the uppermostpart of the graben block. Elsewhere in the lllinoisBasin, the maximum thickness of the PennsylvanianSystem is slightly more than 2,s 8 feet (762 m). Theformations are generail y thickest in southeastern P llinoisand western Kentucky. Some lower strata arepresent only in the southern part of the basin and areoverlapped by younger formations in the north.About 90 to 95 percent of the PennsylvanianSystem in the lllinois Basin consists of elastic rocks(figure 2, Peppers and Popp, this u idebook, part 2).Siltstone, shale, and underclay nstitute about 40percent of the lower part of the system and 65 to 70percent of the middle and upper parts.particularly well developed in the lowthey constitute about 6 percent of strata; in the middleand upper parts, they constitute only about 25percent of the strata. Limestone is rare, but in someareas constitutes as much as 5 to 10 percent of theupper two-thirds of the system. Limestone is especiallycommon in the Bond Formation of lillinois, whereennsylvanian Systert? in the illinsisasin were deposited in a subsiding trsrsgh open at itssouthern margin and batuplifts to the north, east,times, bordering structural features were at or belowdepositional base level, and some lithic emits were depositedwithout substantial interruption in an areaextending from Pennsylvania to Kansas (Wanless, 1935,Part 8, p. 72). The lllinois Basira was strMany major structurai features of the Biiinois Basinoriginated or experienced important growtlr and developmentduring the Pennsylvanian Period. "The La SalkAnticlinai Belt (fig. 1, which extends from 1-a SalkCounty in northern Illinois to Lawrencesoutheastern Bilirrcsis, a distance of more tha(320 km), was substantialiy uplifted prior to depositionof Pennsylvanian rocks. Much of the area of theLa Salle An.ticlinai Belt must have been a penirlsula orarchipelago during early ennsyivanian time, becauseno Caseyvilie strata vvere deposited, and .the Abbottand Spoon Formations are rnhach thinner there thanelsewhere. CIegged that progressivemovement took plPe13r1sylvanian time,and intensive upliftanian strata occurredlvanian or post-Penrisylvanian time.Monocl ine arm' associated Sakmines (fig. 3) extend along the westernmargin of the Fairfield(160 km). The monocline farms a hinge line separatinggently dipping strata to the west from more steeplydipping rocks at the margin of -the Fairfieldmonodine has iocal structural relief sf abo(I52 m) at the Herrin (No. 6) Coal and more thanINTRODUCTION