STATEMAP Williamson County-BG Bedrock Geology of Williamson County, Illinois W. John Nelson 2020 615 East Peabody Drive Champaign, Illinois 61820-6918 (217) 244-2414 http://www.isgs.illinois.edu © 2020 University of Illinois Board of Trustees. All rights reserved. For permission information, contact the Illinois State Geological Survey. R. 4 E. R. 1 E. R. 2 E. R. 3 E. Pond Crk Freeman Pond ver k Spur Cree Creek Pond Bush 148 57 Big M Hurst Big Muddy Ri ud dy Rive r Lake Cree 149 k Johnston T. 8 S. Wade City Pond Creek Madison Prairie Lake Colp ek B r H re ushy u C Creek r Herrin r Johnston e i L ak c Bear Cree a City Lake n e C 37 r e k White Pittsburg Cambria e k Energy Ash Spillertown Buckley Carterville Herrin Reservoir Rock Cree Cree Crainville k k P 13 ig e Li o ttl ab Orcha ek n e Cr rd re Marion C C k Rock Creek r T. 9 S. e e k Cana Cr 13 Crab Crab Bankston For Or char d Orchard k Lake k 1 Caplinger Cree rd Pond rcha Brier Crab O C r e e k W k olf For S k ali e Marion h n k Cree Sou t e h ee re nc r a C C Reservoir 37 r k r B st y a k 166 o s g L s R a u iv r k e e S r G e r 57 L 148 k itt C h l e c k e Cana Cree n Cree e r r a e v sy r C e R i s B n a i r y l T. 10 S. G e a Sugar n S a C South Fork k Little Devils olf Herrin Cree Lake W W Lake h Kitchen Grassy Tacoma i eek te Brushy Cree Lake r O Creal Springs Lake Little C G a e k Stonefort n Lake r i assy l Cree Cre a S of k e k e k l Grassy t Egypt 45 t i 37 L Interstate Route PLSS Township N 0 5 Miles & Range U.S. Route Water body 0 10 Kilometers State Route Stream Local road Figure 1 Map of Williamson County showing towns, Town roads, railroads and bodies of water. Railroad Introduction and Shaw and Savage (1912) mapped the Herrin 15-minute quadrangle, which includes the De Soto and Herrin 7.5-min- Geographic and Geologic Setting ute quadrangles. Cady (1916) mapped and described coal One of 102 counties in Illinois, Williamson County is located resources. Lamar (1925) mapped the Carbondale 15-minute in the southern part of the state (Fig. 1). Land area of the quadrangle, which includes southwestern Williamson County county is 444 square miles (1,150 km2) and population as of and parts of neighboring Jackson and Union Counties. His 2019 was 66,597(https://www.census.gov/quickfacts/william- accompanying report describes in detail bedrock and surficial soncountyillinois). The county seat and largest city is Marion, deposits, structural features, and mineral deposits. All of the population 17,413 (https://en.wikipedia.org/wiki/Williamson_ above maps were produced at scales of 1:62,500 or smaller. County%2C_Illinois, https://cityofmarionil.gov/grow/). Wil- liamson County was carved out of Franklin County in 1839 The “modern” era of geologic mapping in southern Illinois, and its name was transferred from a county in Tennessee just at 1:24,000 scale, began during the 1980s and continues southwest of Nashville. Until recently, coal mining was the today with financial support from the U.S. Geological Sur- dominant industry in the county. This activity continues today, vey. Five maps published during the early 1990s (Trask and but a more diverse economy based on mixed light industry Jacobson 1990; Nelson and Lumm 1990; Jacobson 1991; Ja- and agriculture has taken hold. Marion is a regional center for cobson and Weibel 1993; Weibel and Nelson 1993) take in a retail and wholesale business and for medical services. narrow strip along the southern border of Williamson County (Fig. 2). The major effort specifically targeted at Williamson Williamson County straddles the border between the Mt. County entailed data collection during 2001 to 2003, with the Vernon Hill Country of the Central Lowland Province on bedrock geologic maps published several years later (Nel- the north and the Shawnee Hills Section of the Interior Low son 2007b, 2007c, 2007d, 2007e, 2007f, and 2007g). Also Plateaus Province on the south (Horberg 1950). Essentially, during this effort the surficial geology of much of the county the physiographic boundary is the border between glaciated was mapped, publication being further delayed (Follmer and terrain on the north and unglaciated bedrock hills on the Nelson 2010a, 2010b, 2010c, 2010d, 2010e, 2010f). The six south. The southernmost advance of continental glaciers in “core” quadrangles covered during this project lie entirely the Northern Hemisphere took place near Lake of Egypt in or largely in Williamson County, but strips along the eastern Williamson County. Mt. Vernon Hill Country is characterized and western edges of the county were left unmapped. These by broad lowlands underlain by relatively thick glacial and bedrock maps were completed independently later, again glacial-fluvial and lacustrine sediments that partly mask the with financial support from the U.S. Geological Survey (Nel- pre-glacial topography. Rounded hills are largely cored by son 2007a, 2013a, 2019; Nelson and Denny 2015). bedrock that is mantled with loess and thin, patchy drift. In the Shawnee Hills, resistant sandstone layers of Pennsylva- Knitting these 15 quadrangle maps into a coherent whole nian age (and Mississippian age south of Williamson County) took place in late 2019 and early 2020. Dee Lund and Emily are inclined gently northward, forming a series of south-fac- Bunse electronically combined existing maps into a single ing escarpments near the south border of the county. sheet covering the entire county, revealing glaring and not so obvious mismatches and discrepancies among the 15 maps. Geologically, Williamson County lies along the southern Most of these entailed simple oversight or errors on the part margin of the Illinois Basin (or Eastern Interior Basin), of previous authors and cartographers, but larger problems which encompasses much of Illinois together with south- needed to be corrected by working up new data, chiefly western Indiana, part of western Kentucky, and small areas of from borehole records. Largest among these changes, the Missouri and Tennessee (depending upon precise definition). Shelburn and Patoka Formations, previously undivided, have The Illinois Basin is an interior cratonic basin that underwent been differentiated across the Herrin, Johnston City, and active subsidence and sedimentation from Cambrian through Pittsburg Quadrangles. Also, the Bond Formation has been Pennsylvanian time (Leighton et al. 1991; Kolata and Nimz remapped extensively in the Pittsburg Quadrangle. Some 2010). Regional dip throughout the county is northward, earlier edge-matching problems in the southern part of the exemplified by the north-facing cuestas of the Shawnee Hills. county had been addressed by outcrop study circa 2001 to Trending east-west across the northern part of the county is 2003, but these problems all reside within the Tradewater the Cottage Grove Fault System, a zone of strike-slip faulting Formation, which is not subdivided on the present product. that probably was active primarily during Late Pennsylvanian and Permian time (Nelson and Krausse 1981) Method of study Three primary sources of geologic data are available for Wil- Previous geologic mapping liamson County: outcrops, coal mines, and well records. Several detailed geologic maps that cover part or all of Wil- liamson County were published during the first quarter of the Outcrops Bedrock outcrops are numerous in southern Wil- 20th century. These include Cady (1910), who mapped geol- liamson County. This area lies largely south of the limit of ogy and mineral resources of an area including the Johnston glacial drift and includes resistant sandstone units, which City and Pittsburg 7.5-minute quadrangles. Savage (1910) commonly form cliffs and ledges. Non-resistant rocks such 2 Herrin Johnston City Pittsburg Harco De Soto A B Crab Orchard Marion Crab Orchard Lake Carbondale C Carrier Mills D Lick Creek E Goreville F Creal Springs G H A Mapped, 1912 D-H Mapped, 1990s Makanda Stonefort B Mapped, 1910 Not mapped prior to 2007 C Mapped, 1925 Figure 2 Diagram showing geologic mapping in Williamson County prior to 2007. A. Shaw and Savage (1912), B. Sav- age (1910), C. Lamar (1925), D. Jacobson and Weibel (1993), E. Weibel and Nelson (1993), F. Jacobson (1991), G. Trask and Jacobson (1990), and H. Nelson and Lumm (1990). as shale, coal, and limestone crop out in steep ravines and mines are reclaimed in accordance with law, leaving no rock gullies. I traversed southern Williamson County thoroughly, exposed. Rock is still visible on the highwalls of a few strip walking out mappable units and contacts. My work load was mines that pre-date reclamation law, but such exposures lightened by the fact that I and other ISGS geologists had are difficult of access and seldom yield useful information. already mapped all of southernmost Williamson County at Fortunately, observations made by ISGS geologists in active scale 1:24,000. Thus a stratigraphic framework was already mines are archived and provide a wealth of information, in place, awaiting extension into new areas. especially on faults. Room-and-pillar underground mines expose faults both in map and cross-sectional view for thou- Northern Williamson County is mantled by thick Quaternary sands of feet along strike. Faults were mapped extensively deposits.