View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Illinois Digital Environment for Access to Learning and... l<i.6S STATE OF ILLINOIS DWIGHT H. GREEN, Governor DEPARTMENT OF REGISTRATION AND EDUCATION FRANK G. THOMPSON, Director DIVISION OF THE STATE GEOLOGICAL SURVEY M. M. LEIGHTON, Chief URBANA REPORT OF INVESTIGATIONS—NO. 118 PREGLACIAL EROSION SURFACES IN ILLINOIS LELAND HORBERG Reprinted from The Journal of Geology, Vol. LIV, No. 3, 1946 |tUNO' Q 3G1CAL SUR v ARY PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS URBANA, ILLINOIS 1946 ORGANIZATION STATE OF ILLINOIS HON. DWIGHT H. GREEN, Governor DEPARTMENT OF REGISTRATION AND EDUCATION HON. FRANK G. THOMPSON, Director BOARD OF NATURAL RESOURCES AND CONSERVATION HON. FRANK G. THOMPSON, Chairman NORMAN L. BOWEN, Ph.D., D.Sc, LL.D., Geology ROGER ADAMS, Ph.D., D.Sc, Chemistry LOUIS R. HOWSON, C.E., Engineering CARL G. HARTMAN, Ph.D., Biology EZRA JACOB KRAUS, Ph.D., D.Sc, Forestry ARTHUR CUTTS WILLARD, D.Engr., LL.D. President of the University of Illinois GEOLOGICAL SURVEY DIVISION M. M. LEIGHTON, Chief [500-7-46 ILLINOIS STATE GEOLOGICAL SURVEY 3 3051 00005 7335 PREGLACIAL EROSION SURFACES IN ILLINOIS 1 LELAND HORBERG Illinois State Geological Survey, Urbana ABSTRACT A generalized map of buried erosion surfaces in Illinois, compiled from detailed maps of the bedrock topography, provides regional perspective for recognition and correlation of erosion surfaces within the state. A correlation of the Lancaster peneplain of northwestern Illinois, the Calhoun peneplain of western Illinois, and the Ozark peneplain of northern Illinois is suggested; an independent lower surface which developed on the weak rocks of the Illinois basin is described and named the "Central Illinois peneplain"; and possible straths along major preglacial valleys are recognized and named the "Havana strath." INTRODUCTION tures of the bedrock surface. The original Because of the cover of glacial drift, maps for about half the state were com- studies of erosion surfaces in the Missis- piled on topographic sheets and con- sippi Valley region have been restricted toured with intervals of 10, 20, and 25 largely to the Driftless Area and to the feet. For the remainder of the state, uplands lying outside the limits of where less control was available," 50-foot glaciation. Studies in Illinois, which con- contours were drawn on a base map hav- cern (i) the Driftless Area of north- ing a scale of 4 miles to the inch. The western Illinois, (2) Calhoun County in final map of the entire state was drafted western Illinois, and (3) the southern un- on the latter scale. glaciated section, are summarized briefly The generalized map of the erosion in the following pages. A few attempts surfaces was drawn from the detailed have been made to correlate buried bed- map by connecting points of equal eleva- rock uplands in local areas within the tion on interstream areas. It thus shows glaciated region, but there has been no the general form of the uplands before regional treatment of the problem. In the dissection and could be considered an at- present study a groundwork for regional tempted reconstruction of a late Tertiary interpretation was provided by a de- land surface somewhat modified by later tailed bedrock-surface map of Illinois, fluvial and glacial erosion. The element which was compiled in connection with of personal judgment enters into the se- ground-water studies. A generalized con- lection of broad valleys that are to be tour map of the erosion surfaces (Fig. 1) shown or eliminated, otherwise the con- summarizes the essential features re- tours are closely controlled by numerous vealed by the detailed map. points on the divides. This method ap- The detailed bedrock-surface map was plied to the upland terraces of southern compiled from about 60,000 records of New England was found to show the borings within the state and from all available data on the location of bedrock same major features as those revealed by exposures. In areas where the drift is thin, multiple projected profiles of the same 2 the present topography, shown by topo- area. graphic maps, revealed the major fea- 2 George F. Adams, "Upland Terraces in South- 1 Published with the permission of the chief of ern New England," Jour. Geo!., Vol. LIII (1945), the Illinois Geological Survey, Urbana, Illinois. p. 309. 179 i8o LELAND HORBERG PREVIOUS STUDIES OF EROSION In the Illinois section of the Driftless SURFACES IN ADJOINING Area two prominent upland surfaces are DRIFTLESS AREAS present. The upper surface, termed the 6 "Dodgeville peneplain," is represented NORTHWESTERN ILLINOIS by the tops of narrow ridges and isolated The upland surfaces in the Driftless mounds capped by Silurian dolomite Area of the upper Mississippi Valley which are 1,000-1,150 feet above sea- have been studied intensively for the last level and 350-450 feet above drainage. fifty years and are better known than The lower surface, called the "Lancaster other erosion surfaces in the interior of peneplain," 7 lies about 200 feet below the the continent. 3 Yet there is no general Dodgeville plain and is of greater extent agreement as to the number of cyclical than the older surface. It coincides close- surfaces present or their age. Interpreta- ly with the top of the Ordovician Galena tions have ranged from noncyclical de- dolomite and slopes southwestward from velopment during a single period of about 950-800 feet above sea-level 4 erosion to recognition of five distinct 8 (Figs. 3 and4). cyclical surfaces. 5 Most writers have Gravels of the Windrow formation are identified remnants of either one or two found on remnants of the Dodgeville peneplains. peneplain in adjoining states, 9 but only 3 O. H. Hershey, "Preglacial Erosion Cycles in scattered pebbles, occurring at various Illinois," Amer. Geol., Vol. XVIII 10 Northwestern elevations, have been found in Illinois. (1896), pp. 72-100, and "The Physiographic develop- Nebraskan drift is reported to be present ment of the Upper Mississippi Valley," ibid., Vol. XX (1897), pp. 246-68; U. S. Grant and E. E. on both upland surfaces in Iowa but has Burchard, "Lancaster-Mineral Point Folio, Wis- not been discovered in valleys eroded consin-Iowa-Illinois," U.S. Geol. Surv. Geol. Atlas, below the Lancaster plain. This relation Folio 145 (1907), p. 2; A. C. Trowbridge, "Some 11 Partly Dissected Plains in Jo Daviess County, led Trowbridge to conclude that the Illinois," Jour. Geol., Vol. XXI (1913), pp. 731-42; lower surface was undissected at the E. W. Shaw and A. C. Trowbridge, "Galena- Elizabeth Folio, Illinois-Iowa," U.S. Geol. Surv. Geol. 6 Named from the upland near Dodgeville, Wis- Atlas, Folio 200 (1916), pp. 9-10; A. C. Trowbridge consin, by Trowbridge (p. 64 of ftn. 3 [1921]). Trow- and E. W. Shaw, "Geology and Geography of the bridge now regards the Dodgeville plain as part of Galena and Elizabeth Quadrangles," 77/. Geol. Surv. the lower Lancaster peneplain rather than as an in- Bull. 26 (1916), pp. 136-46; U. B. Hughes, "A Cor- dependent erosion surface (personal communication relation of tjie Peneplains of the Driftless Area," [1946]). Proc. Iowa Acad. Sci., Vol. XXIII (1916), pp. 125- 32; A. C. Trowbridge, "The Erosional History of the 7 Named from Lancaster, Wisconsin, by Grant Driftless Area," Iowa Univ. Studies, 1st ser., No. 40 and Burchard, p. 2 of ftn. 3. ("Studies in Nat. Hist.," Vol. IX, No. 3 [1921]), 8 Both surfaces are well shown on the Galena and of the problem; PP- 55—127 (the most detailed study Elizabeth quadrangle maps. contains a complete bibliography up to 192 1); 9 "Preglacial on the Lawrence Martin, "Physical Geography of Wiscon- R. D. Salisbury, Gravels Quartzite Range near Baraboo, Wisconsin," Jour. sin," Wis. Geol. Surv. Bidl. 36 (2d ed., 1932), pp.69- Geol, Vol. Ill pp. 665-67; Trowbridge, 77; A. C. Trowbridge, in Kansas Geological Society (1895), ftn. F. T. Thwaites and Guide Book, Ninth Annual Field Conference, Upper pp. 111-13 of 3 (192 1); W. H. Twenhofel, "Windrow Formation: An Upland Mississippi Valley (Wichita : Kansas Geological Soc, Gravel Formation of the Driftless and Adjacent 1935), pp. 62, 75; F.T. Thwaites, in Kansas Geological Areas of the Upper Mississippi Valley," Bull. Geol. Bates, Society Guide Book , pp. 105-26; R. E. "Geomorphic History of the Kickapoo Region, Soc. Amer., Vol. XXXII (1920), pp. 293-314. Wisconsin," Bull. Geol. Soc. Amer., Vol. L 10 (1939), Trowbridge, p. 112 of ftn. 3 (1921); H. B. 820-41. pp. Willman, personal communication (1946). 4 Martin, ftn. 3. "Pp. 123-25 of ftn. 3 (1921) and pp. 62, 75 of 5 Hershey, ftn. 3. ftn. 3 (1935). PREGLACIAL EROSION SURFACES IN ILLINOIS 181 time of Nebraskan glaciation. However, lower upland about 600 feet above sea- the possibility of subsequent removal of level south of the flexure in the southern 14 the drift from the valleys cannot be tip of the county (Fig. 1). This relation eliminated altogether, and the surface raises the question of whether there was may have been dissected at an earlier important movement along the Cap date. This alternative is indicated by the au Gres fault after deposition of the occurrence of Kansan and possibly gravels, as concluded by Rubey, 15 or Nebraskan drift within deep bedrock whether gravels, possibly of different valleys of the ancient Mississippi and its age, were deposited on two distinct sur- tributaries (Fig. 5) in the central part of faces. the state. 12 A compromise view that the SOUTHERN ILLINOIS deep valley of the ancient Mississippi in The driftless section of southern the Driftless Area is younger than the Illinois roughly includes the area lying deep valley to the south has not been south of the Pennsylvanian (Caseyville) supported preliminary subsurface by escarpment, which extends east-west studies in the intervening area.