McGarry, Christopher S.

English

IDEALS @ Illinois

Bedrock geology of Carroll County, Illinois

Illinois Digital Environment for Access to Learning and Scholarship Repository

This map was prepared by the Illinois State Geological Survey,in cooperation with the Illinois Department of Commerce andCommunity Affairs and the Carroll County Board.  It is part ofa suite of maps created to assist county officials in addressinggeologic questions concerning capable sites for landfilldevelopment.  Maps produced for this study are intended forregional land use planning purposes.  More detailed mapping isneeded for site specific considerations.  This map has beenreviewed for scientific accuracy and has been edited to meetthe quality standards of maps in the ISGS Map Series.Data used to map the bedrock geology of Carroll County included ISGSwell logs, Illinois Department of Transportation borings, UnitedStates Department of Agriculture soil survey maps, previous studiesconducted by the Willman (1973), Kolata and Buschbach (1976), Willmanand Kolata (1978), Kolata and Graese (1983), and Larson et al. (1993),and project borings and field observations.  Grateful acknowledgementis given to Dennis R. Kolata for help identifying and differentiatingbedrock units.Bedrock geology is a significant consideration for land use planning.The dolomite and sandstone bedrock formations are important groundwaterresources in northern Illinois.  More than 90% of the water wells inCarroll County are finished in bedrock.  Therefore, land use decisionsshould be made with consideration for the protection of groundwaterresources from potential contamination.  In addition to groundwaterresources, dolomite and sandstone formations near land surface arecurrent or potential rock product resources.References:Kolata, D.R. and T.C. Buschbach (1976) Plum River Fault Zone of     Northwestern Illinois:  Illinois State Geological Survey     Circular 491, 20 p.Kolata, D.R. and A.M. Graese (1983) Lithostratigraphy and Depositional     Environments of the Maquoketa Group (Ordovician) in Northern     Illinois: Illinois State Geological Survey Circular 528, 49 p.Larson, T.H., A.M. Graese, and P.G. Orozco (1993) Hydrogeology of the     Silurian Dolomite Aquifer in Parts of Northwestern Illinois:     Illinois State Geological Survey Environmental Geology 145, 29 p.Nelson, W.J. (1995) Structural Features in Illinois:  Illinois State     Geological Survey Bulletin 100, 144 p.Willman, H.B. (1973) Rock Stratigraphy of the Silurian System in     Northeastern and Northwestern Illinois:  Illinois State Geological     Survey Circular 479, 55 p.Willman, H.B. and D.R. Kolata (1978) The Platteville and Galena Groups     in Northern Illinois:  Illinois State Geological Survey Circular     502, 75 p.ExplanationSILURIAN SYSTEMundifferentiated  (0 - 150 feet thick)     Brownish gray dolomite; some beds contain white chert; veryargillaceous at base.  This cliff- forming rock outcrops in the uplands insouthern Carroll County and north of the Plum River Fault Zone where it hasbeen relatively downthrown 100- 400 feet.  These rocks are exposed in theMississippi River bluffs north of Savanna.ORDOVICIAN SYSTEMMaquoketa Group  (0 - 200 feet thick)     Dolomitic greenish- gray silty shale with argillaceous dolomite lensesin the lower half.  This slope- forming rock occur in road and railroad cutsin the western part of the county.Galena and Platteville Groups  (0 - 300 feet thick)     Brown and gray dolomites; some cherty beds; some argillaceous beds;clay (K- bentonite) beds.  Platteville Group is finer grained and thinnerbedded than the Galena Group.  These cliff forming- rocks are exposed inthe ravine of Carroll Creek in Mt. Carroll and many quarries throughoutthe county.Ancell Group  (100 - 200 feet thick)     Chiefly composed of pure fine to medium grained, well sorted quartzsandstone.  The upper 25 feet is composed of interbedded dolomite, fineto medium grained sandstone and shale.  These rocks are exposed along thecrest of the Forreston Dome in eastern Carroll County.Plum River Fault Zone (Tail on down-thrown side)Surface topography in feet above mean sea levelContour interval 25 feetUS HighwayState HighwayStreamsMunicipalityWater Bodies

https://www.ideals.illinois.edu/bitstream/handle/2142/55473/ofs1997-13d.pdf?sequence=2

Bedrock geology of Carroll County, Illinois

Abstract

Similar works

Full text

Available Versions

IDEALS @ Illinois

Illinois Digital Environment for Access to Learning and Scholarship Repository