URBANA jf-.'-INOIS STATE GEOLOGICAL SURVEY 3 3051 00003 5240 Digitized by the Internet Archive in 2012 with funding from University of Illinois Urbana-Champaign http://archive.org/details/earlyordovicians100will 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 CIRCULAR 100 EARLY ORDOVIC1AN STRATA ALONG FOX RIVER IN NORTHERN ILLINOIS H. B. WILLMAN AND J. NORMAN PAYNE Reprinted from the Journal of Geology Vol. LI, No. 8, November-December, 1943 PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS URBANA, ILLINOIS 1943 EARLY ORDOVICIAN STRATA ALONG FOX RIVER IN NORTHERN ILLINOIS H. B. WILLMAN AND J. NORMAN PAYNE Illinois State Geological Survey ABSTRACT A nearly complete sequence of Ordovician strata along Fox River, southwest of Aurora, indicates the presence of the Kankakee arch—a major structure trending northwest-southeast across northeastern Illinois —and the probable location of the Sandwich fault, which parallels the arch for many miles and had been found previously by studies of well records. Outcrops of sandstone and dolomite which have long been corre- lated with the St. Peter and Galena-Platteville formations have been found to belong to the New Richmond sandstone and the Shakopee dolomite. Study of the outcrops and well records shows that the anticlinal struc- ture underwent major movements both before and after deposition of the St. Peter sandstone. INTRODUCTION subsurface data showed that this struc- ture, termed the "Kankakee arch," In the earliest geological studies of this (1) 2 had its greatest deformation before, rather area the sandstone and the dolomite out- than since, St. Peter time; (2) extends at crops along the 15 miles of Fox Valley least from Oregon, Illinois, southeast between Millbrook and Sheridan were through Momence, Illinois; and in correlated with the St. Peter sandstone (3) Indiana is probably a continuation of the and the "Trenton" (Galena-Platteville) west branch of the Cincinnati arch. 6 formations, respectively. The alternate Because of this structure, Cambrian stra- occurrence of dolomite and sandstone at ta are exposed along the axis of the Kan- the level of Fox River was first inter- kakee arch at Oregon 7 and directly un- preted as the result of deposition of the derlie glacial drift at Sandwich, about dolomite in erosional troughs in the top 4 miles northwest of Fox Valley. 8 How- of the sandstone 3 and later as due to up- ever, because the occurrence of St. Peter lift of the St. Peter sandstone along sev- and Galena strata along Fox Valley was eral "anticlinals." 4 Some years ago it not necessarily inconsistent with these was noted that the structure of the St. new structural conceptions, correlation Peter sandstone indicated an anticline of the strata was not seriously questioned with a northwest-southeast axis crossing 5 Fox Valley in the vicinity of Millington. 6 George E. Ekblaw, "Kankakee Arch in Illi- More recently a study of outcrops and nois," Bull. Geol. Soc. Amer., Vol. XLIX (1938), pp. 1425-30. Reprinted as ///. Slate Geol. Surv. Circ. 40 (1938). 2 H. C. Freeman, "Geology of La Salle Coun- ty," in Geology and Paleontology, III. Geol. Surv., 7 A. C. Bevan, "Fault Block of Cambrian Strata Vol. Ill (1868), pp. 257-87; H. M. Bannister, "Geol- in Northern Illinois" (abst.), Bull. Geol. Soc. Amer., ogy of Kendall County," in Geology and Paleontol- Vol. XL (1929), p. 88; "Cambrian Inlier at Oregon, ogy, III. Geol. Surv., Vol. IV (1870), pp. 136-48. Illinois," Kan. Geol. Soc. Guidebook, gth. Ann. Field Conf. (1935), pp. 383-85; "Cambrian Inlier in 3 Freeman, p. 279 of ftn. 2 (1868). Northern Illinois," Bull. Amer. Assoc. Pet. Geol., Vol. XXIII (1939), pp. 1561-64; Ekblaw, p. 1426 of ftn. 6 (1938). * Bannister, pp. 145-46 of ftn. 2 (1870). 8 J. N. Payne, in "Geology and Mineral Resour- 5 G. H. Cady, "The Structure of the La Salle ces of the Marseilles, Ottawa, and Streator Quad- Anticline," ///. State Geol. Surv. Bull. 36 (1920), rangles," ///. Stale Geol. Surv. Bull. 66 (1942), p. 127. P- 57- S3 1 — 532 H. B. WILLMAN AND J. NORMAN PAYNE until a study of samples from a well STRATIGRAPHY drilled at the Illinois School for Boys, As the outcrops are widely scattered, mile south of Sheridan, revealed that \ the stratigraphic sequence is not com- Shakopee dolomite there lay immediately pletely exposed. Consequently, much of 9 below the surface. As a result of this dis- the information about the general charac- covery, a detailed examination of the ter, the thickness, and the stratigraphic area in was immediately undertaken relations of the formations, shown in December, as a project of the Illi- 1940, Table 1, is derived from study of samples nois State Geological Survey to supple- of cuttings from near-by wells." The ex- ment the authors' recent work on the Mar- posed formations are described below. seilles, Ottawa, and Streator quad- 10 RICHMOND rangles. This study determined that NEW SANDSTONE the sandstone exposed near Sheridan Outcrops of New Richmond sandstone was part of the New Richmond sand- occur along Fox Valley west of Sheridan stone and that the dolomite cropping out (Fig. 1). The sandstone is well exposed a short distance south of Sheridan and in the west bluff of the valley and along near Millington belonged to the Shako- the tributary ravines in Section 7 and the pee formation. south part of Sec. 6, T. 35 N., R. 5 E., especially near the highway bridge west of GEOGRAPHIC SITUATION Sheridan. On the east side of the valley the sandstone crops out in the bluffs and portion of the valley of That Fox River in a tributary ravine in the SW.j Sec. 8. considered in this study extends from Approximately the upper 40 feet of the miles north of south- about 1 1 Millbrook formation is exposed. The sandstone is west to a mile south of Sheridan (Fig. 1). mostly fine-grained (sample 4, Table 2) The valley is 75-100 feet deep, and the but contains thin lenticular streaks of valley floor \-1 mile wide—consists of coarse sand, especially along the bed- terraces in which the river is entrenched ing-planes. The coarse sand streaks in a narrow channel. The valley bluffs contain scattered but conspicuous grains and terraces are composed largely of of secondary white opaque silica which dis- glacial drift, which mantles a much is penetrated by some of the surround- sected bedrock surface. Fox River has ing quartz grains. The sandstone is eroded its valley to a level at which it thin-bedded, almost laminated in places, truncates some of the higher buried bed- but locally appears massive on weathered rock ridges, so that bedrock outcrops surfaces. Commonly the sandstone is locally extend as high as feet the 30 above much cross-bedded (Fig. 2), but at some river. Rapids occur in the river near places the beds are mostly parallel. Some most of the outcrops. Several long sec- beds are ripple-marked. tions of the valley in which there are no The heavy minerals in the New Rich- bedrock outcrops mark the position of mond sandstone are characterized by an major preglacial drainage channels. abundance of tourmaline, usually more than 50 per cent, and the presence of gar- 9 L. E. Workman, personal communication. net, especially a diagnostic brownish- 10 H. B. VVillman and J. N. Payne, "Geology pink variety, and of ferromagnesian min- and Mineral Resources of the Marseilles, Ottawa, erals. The heavy minerals in samples of and Streator Quadrangles," ///. State Geol. Snrv. Bull. 66 (1942). 11 Payne, pp. 53-69 of ftn. 8 (1942). EARLY ORDOVICIAN STRATA ALONG FOX RIVER, ILLINOIS 533 the upper part of the formation, omit- This sandstone is similar to the lower ting the upper 3-5 feet, collected from fine-grained part of the St. Peter sand- each foot of an outcrop at the mouth of stone (sample 1 , Table 2) but it is some- the ravine on the east side of Fox Valley what finer grained, more cemented, much R6E ORDOVICIAN SHAKOPEE rOofid ONEOTA |>psp..| ST. PETER l<Pnr„ NEW RICHMOND SCALE 2 Fig. i.—Location of outcrops and areal distribution of formations along part of Fox Valley west of the Boys School, in the SW. \ thinner bedded, more poorly sorted, and Sec. 8, T. 35 N., R. 5 E., are as given in more cross-bedded, and the grains are 12 Table 3. more angular and less frosted than those 12 Mineral analyses by Paul Herbert, Jr. in the St. Peter sandstone. 534 H. B. WILLMAN AND J. NORMAN PAYNE SHAKOPEE DOLOMITE On the east side of Fox Valley the Shak- The Shakopee dolomite crops out opee dolomite crops out along the south along Fox Valley near Sheridan and Mil- side of a ravine in the SW. \ SW. \ Sec. lington (Fig. i). Near Sheridan, 15-20 8, T. 35 N., R. 5 E., in washes on the sur- feet of the dolomite is exposed on the face of the terrace south of the ravine west side of Fox Valley in and near an and along the bank of the river south to TABLE 1 Geologic Formations in Area along Fox Valley from Aurora to Wedron Approximate Normal System Series Formation Material Thickness (Feet) Pleistocene Glacial drift Niagaran Joliet Dolomite Silurian Unconformity Alexandrian Kankakee 60 Dolomite Edgewood Dolomite Major unconformity Cincinnatian 1 Maquoketa IS© Shale, limestone, dolomite Unconformity Galena Dolomite, limestone *Decorah 35° Dolomite, limestone, shale Mohawkian *Platteville Dolomite, limestone Ordovician Unconformity Chazyan 1 St. Peter 175 Sandstone Major unconformity Shakopee 5° Dolomite Prairie du Chien New Richmond 60 Sandstone *Oneota I4S Dolomite (cherty) Unconi *Jordan 3° Dolomite, sandstone, shale *Trempealeau 200 Dolomite *Franconia 140 Sandstone, dolomite, shale (glauco- Cambrian St.