bedrock geology of dixon west quadrangle · 2013-09-12 · structural geology the dixon west...
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STATEMAP Dixon West-BG
Bedrock Geology of Dixon West QuadrangleLee County, Illinois
Dennis R. Kolata
2013
Prairie Research InstituteILLINOIS STATE GEOLOGICAL SURVEY
615 East Peabody Drive Champaign, Illinois 61820-6964
(217) 244-2414http://www.isgs.illinois.edu
© 2013 University of Illinois Board of Trustees. All rights reserved.For permission information, contact the Illinois State Geological Survey.
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INTRODUCTION
The Dixon West Quadrangle is situated in northwestern Lee County, Illinois. It encompasses the western parts of the city of Dixon, which is the largest town in the county. Most of the land is used for agricultural purposes but a moderate amount of residential and commercial developments are present.
The quadrangle lies in the Rock River Hill Country of the Central Lowlands Province. The topography formed primar-ily by deposition of glacial sediments (clay, silt, sand, and gravel) in a till plain which was subsequently dissected by erosional processes of the Rock River and its tributaries. Bedrock in the Dixon West Quadrangle is largely concealed beneath the till plain except for local exposures along the riv-er bluffs and tributary ravines. The glacial deposits range in thickness from 0 to 50 feet throughout most of the quadran-gle but reach thicknesses of 100 feet in buried stream valleys in the southern parts of the quadrangle (Piskin and Berg-strom 1975). Bedrock formation contacts are largely inferred because of the widespread surficial cover. Surface elevations range from 820 feet near Palmyra to 650 feet along the banks of the Rock River.
Compilation of this map is based on examination of bedrock exposures in quarries, road excavations, railroad cuts, and natural exposures along streams and waterways. Subsurface information was obtained from water well records and drill cuttings filed at the Illinois State Geological Survey (ISGS). Wireline logs were not available in the Dixon West region during this field investigation. Two reference wells situated within three miles of the eastern boundary of the map in the adjacent Dixon East Quadrangle provided valuable insight to the stratigraphic succession. These include the City of Dixon water well No. 10 (IP 121032353400); SW SW NW Sec. 16, T21N, R9E; latitude N41° 489 3499 and longitude W89° 289 3599; total depth 1,748 feet) and the Dixon State School well No. 3 (IP 121030009200; SW SW SW Sec. 21, T22N, R9E; Latitude N41.874675 and Longitude W89.472851; total depth 1,965 feet). Drill cuttings and gamma ray logs are available for both wells.
The bedrock in Lee County was illustrated very generally on published state-wide geologic maps (Worthen 1875, Weller 1906, 1912, 1917, Weller et al. 1945, 1961, Willman et al. 1967, Kolata et al. 2005). One of the first concerted efforts to map in the area was done by Templeton (1940). His detailed report on the Woosung quadrangle (1:48,000 scale) includes bedrock descriptions for the northern parts of the Dixon West Quadrangle. The most recent effort to map the bedrock is the countywide work of McGarry (1999). Stratigraphic and structural investigations in the Dixon area include those by Templeton and Willman (1952, 1963), Kolata and Busch-bach (1976), Willman and Kolata (1978), and Kolata et al. (1978), Kolata and Graese (1983).
STRATIGRAPHY
Bedrock in the Dixon West Quadrangle consists largely of Ordovician dolomite and shale and a small area of Silurian dolomite in the southwestern part of the quadrangle. It has been standard practice of the ISGS during the past few decades to follow the Ordovician classification and nomen-clature proposed by Templeton and Willman (1963). Their stratigraphy was followed in large part by Willman and Ko-lata (1978) who made minor revisions to some members and documented the presence of nine widespread K-bentonite beds. These stratigraphic investigations have shown that the Upper Ordovician carbonate succession consists of distinc-tive rock units that can be traced over wide areas of the Midcontinent U.S. Correlation of rock units is based largely on 1) relative amount of disseminated clay, 2) chert content, 3) widely traceable K-bentonite beds, and 4) hardground omission surfaces. These were the primary features used to subdivide the Platteville and Galena carbonate succession into 1 megagroup, 2 groups, 3 subgroups, 10 formations, 32 members, and 9 beds. In the outcrop area of northern Illinois where the type sections for many of the subdivisions occur, the succession ranges from a mere 300 to 350 feet thick. Compared to other Paleozoic rock units, the Illinois Up-per Ordovician carbonate succession is one of most highly subdivided units in North America. Many of the formations are too thin to map at the current scale of 1:24,000, therefore do not meet the ‘test of mappability’ recommended in the North American Stratigraphic Code (1983). Furthermore, the ranks of ‘megagroup and subgroup’ are not recognized in the Code (1983). Based on these facts, adjustments in the ranks of the Illinois Upper Ordovician lithostratigraphic units are warranted. The simplest way to bring the Templeton and Willman (1963) and Willman and Kolata (1978) classifica-tion schemes up to code and to maintain the usefulness of the numerous recognized units is to reassign the ranks of the lithostratigraphic units. It is here proposed that the revised classification would:
• eliminate the megagroups and subgroups, • reassign Ottawa megagroup to the rank of group• reassign Platteville, Decorah, and Galena groups to
formations• reassign Pecatonica, Mifflin, Grand Detour, Nachusa,
and Quimbys Mill formations to members of the Plat-teville Formation
• reassign Spechts Ferry, Kings Lake and Guttenberg formations to members of the Decorah Formation
• reassign Dunleith, Wise Lake, and Dubuque forma-tions to members of the Galena Formation
• reassign all 32 corresponding members to beds• keep the nine named K-bentonite beds (Willman and
Kolata 1978) at bed rank (fig. 1).
Likewise, the Maquoketa group is reassigned to rank of formation and the Cape, Scales, Fort Atkinson, Brainard, and
Cowen
Sinsinawa
Wyota
Wall
Sherwood
Rivoli
Mortimer
Fairplay
Eagle Point
Beecher
St. James
Buckhorn
Glenhaven
GarnavilloGlencoe
Castlewood
Strawbridge
Shullsburg
Hazel Green
Everett
Elm
Eldena
Forreston
Oglesby
Medusa
New Glarus
Dane
Chana
Hennepin
Stillman
Stewartville
Sinsinawa
Wyota
Wall
Sherwood
Rivoli
Mortimer
Fairplay
Eagle Point
Beecher
St. JamesBuckhorn
Glenhaven
Garnavillo
Glencoe
Castlewood
Strawbridge
Shullsburg
Hazel Green
Everett
Elm
Eldena
Forreston
Oglesby
Medusa
New Glarus
Dane
Chana
Hennepin
Victory
Hely
Clement
Stillman
Walgreen
Dement
Briton
Hazelwood
Establishment
Brickeys
Blomeyer
Stewartville
Guttenberg
Wise Lake
Dunleith
Quimbys Mill
Nachusa
Grand Detour
Mifflin
Pecatonica
Dubuque
Spechts Ferry
Gal
ena
Pla
ttin
Dec
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Kim
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Pla
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Otta
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Tre
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FORMATION MEMBERK-BENTONITE BED
Gal
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Pla
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Dec
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Pla
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Otta
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Tre
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Guttenberg
Wise Lake
Dunleith
Quimbys Mill
Grand Detour
Mifflin
Pecatonica
Dubuque
Spechts Ferry
Nachusa
Love
s P
ark
Dygerts
HaldaneNassetConoverCalmar
DickeyvilleElkport
Millbrig
Deicke
SE
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STA
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ATIO
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MEMBER BEDK-BENTONITE BED
Guttenberg
Wise Lake
Dunleith
Quimbys Mill
Grand Detour
Mifflin
Pecatonica
Dubuque
Spechts Ferry
Nachusa
Gal
ena
Dec
orah
Pla
ttevi
lle
Otta
wa
Cowen
Sinsinawa
Wyota
Wall
Sherwood
Rivoli
MortimerFairplayEagle Point
Beecher
St. James
Buckhorn
Glenhaven
Garnavillo
Glencoe
Castlewood
Strawbridge
Shullsburg
Hazel Green
Everett
Elm
Eldena
Forreston
Oglesby
Medusa
New Glarus
Dane
Chana
Hennepin
Stillman
Stewartville
Dygerts
HaldaneNassetConoverCalmar
DickeyvilleElkport
Millbrig
Deicke
Love
s P
ark
Moh
awki
an
Ed
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ian
Ch
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Templeton and Willman (1963) Willman and Kolata (1978) Present Report
Figure 1 Comparison of the proposed lithostratigraphic classification of the Platteville and Galena carbonate rocks in northern Illinois with that of Templeton and Willman (1963) and Willman and Kolata (1978).
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Neda formations to rank of members. The series and stage names as well as boundaries are also updated in recognition of the recent advancements in Ordovician chronostratigra-phy.
The stratigraphic units that are known to occur at the bed-rock surface in the quadrangle include the Upper Ordovician Platteville, Galena, and Maquoketa Formations and Silurian Mosalem Formation. All were deposited in intertidal to subtidal marine environments. The Platteville and Galena Formations consist mainly of dolomite. Several hardground omission surfaces within the Galena and Platteville are wide-spread and persistent. They are readily identified in outcrop and drill core and are useful in correlating this part of the stratigraphic column. These planar surfaces are character-ized by irregular solution cavities, mainly less than 2 inches across. They penetrate the bedding planes to depths of 2 to
3 inches, are stained by iron-rich minerals, and are back-filled with sediment from the overlying unit (Kolata et al. 1998, 2001). Some of the more significant surfaces include 1) approximately 15 to 20 surfaces in the lower part of the Dunleith Member, 2) top of the Guttenberg Member, 3) top of the Quimbys Mill Member 4) top of the Mifflin Member, 5) top of the Pecatonica Member and 6) two or three surfaces in the lower 10 feet of the Pecatonica.
STRUCTURAL GEOLOGY
The Dixon West Quadrangle is situated in a structurally complex area northern Illinois near the termination of the Sandwich Fault Zone, Plum River Fault Zone and the projected trend of the La Salle Anticlinorium (fig. 2). Lying parallel to and south of the Sandwich Fault Zone in Lee and Ogle Counties is the Ashton Anticline. This broad anticline
I l l inois BasinI l l inois Basin
LEE
Dixon WestQuadrangle
Ashton Ant ic l ine
Figure 2 Structural configuration of Cambrian Franconia Formation in northern Illinois showing Dixon West Quadrangle rela-tive to major structural features (compiled by Janis D. Treworgy and published in Kolata and Graese 1983). Note the regional southwestward dip within and adjacent to the Dixon West Quadrangle.
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brings Middle Ordovician and Upper Cambrian rocks to the bedrock surface along the south side of the Sandwich Fault Zone northeast of the Dixon West Quadrangle and is respon-sible for the subtle southwestward dip of bedrock within the quadrangle.
One of the more notable structures in the quadrangle is an anticline that strikes 340 degree NW. Dip on the NE limb was measured at 5 degrees but the dip of the SW limb could not be measured. The northeast trending dip is obvious in an abandoned quarry on the west side of Rock Island Road (NE Sec. 12, T21N, R8E) (fig. 3). The anticline is confirmed by the presence of the Platteville Formation at the bedrock surface in several water wells on the south side of Rock Is-land Road (SE Sec. 12, T21N, R8E) and on the north side of Rock River (SE Sec. 11, T21N, R8E). The Platteville-Galena contact is exposed at water level in the high bluff on the south side of Rock River (SW SE Sec. 11, T21N, R8E). The structure is here referred to as the Bloody Gulch Anticline in reference to Bloody Gulch Road which runs through the area of the anticline.
Bedrock fracture patterns indicate dominant northwest and subdominant southwest trends similar to other regions of northern Illinois (McGarry 2000).
ECONOMIC RESOURCES
DolomiteIn northern Illinois the Platteville and Galena dolomite is widely quarried for use as aggregate, road surfacing mate-rial, agricultural lime, and rip-rap. Active quarries in the Dixon West Quadrangle include those on the southwest side of Dixon, Illinois (N½ Sec. 7, T21N, R8E) and northwest of Palmyra (NW Sec.33 T22N, R8E).
GroundwaterResidential wells in the Dixon West Quadrangle recover groundwater largely from fractured dolomite in the Plat-teville and Galena Formations or from the underlying St. Peter Sandstone. Most of these wells are drilled in the range of 150 to 300 feet deep. Municipal wells in the area tend to draw water from Cambrian sandstone aquifers at depths of approximately 1800 feet.
ACKNOWLEDGMENTSWe thank the numerous landowners who allowed us onto their land for outcrop study. Jacquelyn L. Hannah provided field assistance. Special thanks go to Donald E. Luman for the Lidar maps and to Jane E. Johnshoy Domier for the graphic and cartographic layout and design.
Figure 3 Abandoned quarry on southwest side of Dixon (NE Sec. 12, T21N, R8E) showing prominent northeastward dip of Platteville rocks.
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This research was supported in part by the U.S. Geological Survey National Cooperative Geologic Mapping Program (STATEMAP) under USGS award number G12AC20408. The views and conclusions contained in this document are those of the authors and should not be interpreted as neces-sarily representing the official policies, either expressed or implied, of the U.S. Government.
REFERENCES
Kolata, D.R. (compiler), 2005, Bedrock geology of Illinois: Illinois State Geological Survey, 1:500,000.
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., T.C. Buschbach, and J.D. Treworgy, 1978, The Sandwich Fault Zone of Northern Illinois: Illinois State Geological Survey Circular 505, 26 p.
Kolata, D.R., and A.M. Graese, 1983, Lithostratigraphy and depositional environments of the Maquoketa Group (Or-dovician) in northern Illinois: Illinois State Geological Survey Circular 528, 49 p.
Kolata, D.R., W.D. Huff, and S.M. Bergström, 1998, Nature and regional significance of unconformities associated with the Middle Ordovician Hagan K-bentonite complex in the North American midcontinent, Geological Society of America Bulletin v. 110, no. 6, p. 723–739.
Kolata, D.R., W.D. Huff, and S.M. Bergström, 2001, The Or-dovician Sebree Trough: An oceanic passage to the Mid-continent United States: Geological Society of America Bulletin v. 113, no. 8, p. 1067–1078.
McGarry, C.S., 1999, Bedrock geology of Lee County, Il-linois: Illinois State Geological Survey, OFS 1999-1e Lee BG.
McGarry, C.S., 2000, Regional fracturing of the Galena-Platteville aquifer in Boone and Winnebago Counties, Illinois: geometry, connectivity and tectonic signifi-cance: Urbana, Ill., University of Illinois, unpublished M.S. thesis, 193 p.
North American Stratigraphic Code, 1983, American Asso-ciation of Petroleum Geology Bulletin, v. 67, p. 841–875
Piskin, K., and S.M. Bergström, 1975, Glacial drift in Illi-nois: Thickness and character: Illinois State Geological Survey Circular 490, 35 p.
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