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

from the Menard Limestone (upper Mississippian)to the Caseyville Sandstone (lower Pennsylvanian).Vertical displacement is about 500feet (152 m), downthrown to the north.Prominently slickensided sandstone is presentin a small outcrop at left side of road. TheRock Creek Graben, about 2 miles (3.2 km)wide here, is the easternmost of the two majordown-dropped blocks that transect the Illinoisfluorspar district. In this area the grabentrends approximately N 55' E and is boundedon the northeast by the Hogthief Creek andGoose Creek Faults, and on the southeast bythe Peters Creek Faults or by step-faultbranches of the Peters Creek Faults.7.7 Bridge over tributary creek to Rock Creek.Mt. Zion Church ahead on left.8.8 Abbott Formation (middle Pennsylvanian).Ten feet (3 m) of dark orange-brown sandstone,overlain by about 10 feet((3 rn) of darkgray to black shale and siltstone. A small fault( < 5 feet [I.5 m] vertical displacement,downthrown to north) is visible here (fig.I L-4). Horizontal slickensides occur in smallstream to right (east) of this exposure. Thefaulting appears to be compressional in origin,and evidently occurred when the RockGraben was formed.9.7 Sharp, wide curve to left (northwest). GooseCreek Fault. Vertical displacement about 5630feet (152 m), downthrown to the south. Slickensidedfault surface (sandstone) is exposedby natural erosion about 150 feet (46 m) westof the highway. Exposed interval in largeroadcut is mainly shale (fig. I L-5) with numerouschannel-fill sandstones (figs. IL-6, 7, and8). Two thin coals are present in the upperpart. Coals of the Caseyviile Formation aregenerally very thin and lenticular, and are lesscommon than those in overlying strata. Fieldtrip route here crosses from the Abbott Formationto middle part of the CaseyvilleFormation. Total section exposed is about140 feet (43 m), extending from just abovethe Battery Rock Sandstone Member to thePounds Sandstone Member.Two coals and associated strata in theupper part of this highway cut provide thefirst opportunity to observe cyclic sedimentationin Illinois. The lower coal, about 8 inches(20 cm) thick, is underlain by 1.4 feet (0.4 m)of medium gray, noncalcareous underclaywhich lies directly on a cross-bedded channelfillsandstone. A medium gray clay-shaleabout 4 feet (1.2 rn) thick overlies the coal;this clay-shale grades upward into light grayunderclay upon which the upper coal, about9.5 inches (24 cm) thick, was deposited.Apparently two successive coal swamps occupiedthe area, separated only by clay-shalewhich may have been deposited as lakebottomsediments. The upper coal is overlainby medium to dark gray, partly brittle, carbonaceousshale that grades upward into lightbrown,sandy shale which contains interbedsof sandstone in its upper part. The carbonaceousshale contains b~th fine clastic andFigure DL.-3.Figure I&-4.Siltstone and sandc;tone of the I-larclinsburgFarmatian. The lower unit is a lirrronitic,rippie-marked silzsroruc. The upper unit isa mediurn-grained, well-sorted sandstone withlocal lenticular (channel-fill beds.Flexures associated with small iault in shaleof the Abbcr~? F-ormation ill mileage 8.8.Wight (north) side is downthrown about 2feet (0.6 rn). (Scale: orae Foot and one inch~17its.Iorganic mattel and :8pparent$y was depositedimmediately after rhe coal swamp became inbaeiitlyche site was buried byFIELD TRIP 9/ROAD LOG