https://ir.uiowa.edu/igs_ofm/1028/thumbnail.jp

Anderson, Raymond R

Bunker, Bill J

Ludvigson, Greg A

Witzke, Brian J

English

Iowa Research Online

DIGITAL GEOLOGIC MAP OF IOWA
PHASE 5:  SOUTHWEST IOWA
BEDROCK GEOLOGY OF SOUTHWEST IOWA
prepared by
Brian J. Witzke, Raymond R. Anderson,
Bill J. Bunker, and Greg A. Ludvigson
Iowa Geological Survey
September 2003
0 5 10 15 20 25 Miles
0 7 14 21 28 35 Kilometers
scale: 1:250,000
(when printed at 36" x 42" format)
R32W
R34W R33WR35W
R36WR37W
R38WR39W
R40WR41W
R42WR43W
    I
R44W
T68N
T69N
T71N
T72N
T73N
T74N
T75N
T76N
T77N
T78N
T79N
T80N
T81N
T82N
T83N
T84N
T85N
       I
R45W
    I
R46W
    I
R46W
    I
R47W
R43W R42W
R41W R40W R39W R38W R37W R36W R35W R33WR34W
T85N
T84N
T83N
T82N
T81N
T80N
T79N
T78N
T77N
T76N
T75N
T74N
T73N
T72N
T71N
T70N
T69N
T68N
T67N
R44W
R45W
R46W
R47W
R33W R32W
T67N
T70N
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Index Showing Area of Geologic Map
Prepared by the Iowa Department of Natural Resources
Iowa Geological Survey
Open File Map 03-1
Rock Exposures in the Study Area
Areas of bedrock exposure or bedrock surface within the soil horizon
Prepared under the STATEMAP program, in cooperation with the
U.S. Geological Survey, Department of Interior, Supported by
Cooperative Agreement 02HQAG0034
LEGEND
Description of Rock Units
Lansing Group.  Upper Pennsylvanian (upper Missourian).  Thickness 45  to  78 ft
(14-24 m).  Primary lithologies: limestone, fossiliferous; shale, gray.  Secondary:
limestone, coated grain; mudstone to siltstone.  Minor: black shale, phosphatic.
K ansas City Group.  Upper Pennsyl vanian (middle Missourian).  Thickness 100
to 140 ft (30-43 m).  Primary lithologies: limestone, fossiliferous; shale, gray.
Secondary: limestone, coated grain; mudstone.  Minor: chert ; coal; black shale,
phosphatic
B ronson G roup .  Pennsylvanian (lower Missourian-uppermost Desmoinesian).
Thickness 100 to  130 ft (30-40 m).  Primary lithologies: limestone, fossiliferous;
shale, gray.  Secondary: limestone, coated grain; black shale, phosphatic ;
mudstone to siltstone, gray.  Minor: chert; coal; sandstone.
Marmaton G roup.  Middle Pennsylvanian (upper Desmoinesian).  Thickness 125
to 170 ft (38-52 m).  Primary lithologies: shale, gray; limestone, fossiliferous.
Secondary: mudstone, gray, green-gray, red; sandstone, very fine- to  medium-
grained.  Minor: coal; siltstone; pyrite.
CRETACEOUS
Dakota Formation:  mid Cretaceous (upper Albian).  Maximum thicknesses of
100 to 200 ft (30-60 m).  Primary lithologies: sandstone, very fine- to coarse-
grained, part pebbly to conglomeratic, part cemented by iron oxide.  Secondary:
chert/quartz gravel and conglomerate; mudstone, gray to variegated, part with
siderite pellets.
Cherokee Group.  Middle Pennsylvanian (Atokan-Desmoinesian).  Thickness
variations over entire m ap area 100 to 750 ft (30-230 m); area of Pc bedrock
surface 300-400 ft (90-120 m).  Primary lithologies: shale, gray, part silty to
sandy; sandstone, very fine- to coarse-grained.  Secondary: mudstone; black shale,
carbonaceous; limestone; coal.  Minor: siderite/ironstone concretions; cone-in-
cone limestone; pyrite.
M ISSISSIPPIAN
 “St. Louis” and Pella Formations.  Middle Mississippian (Meramecian).
Thickness generally 40 to 80 ft (12-24 m); locally truncated beneath Pc.  Primary
lithologies: dolomite, part sandy; limestone, part fossiliferous to sandy.
Secondary: shale, green-gray, calcareous; oolitic limestone; limestone breccia ;
sandstone.  Minor: chert, chalcedony.
Augusta G roup.  Middle Mississippian (Osagean).  Thickness 135 to 240 ft (41-
73 m).  Primary lithologies: dolomite; dolomitic limestone.  Secondary:  limestone,
fossiliferous; shale, gray; glauconitic dolomite; chert.  Minor: chalcedony; quartz
geodes.
Gilmo re City F ormation.  Mississippian (lower Osagean-uppermost
Kinderhookian).  Thickness 20 to 90 ft (6-27 m).  Primary lithologies: limestone,
fossiliferous; limestone, coated grain.  Secondary: dolomite.
Kd
Pm
Pb
Pk
Pl
Mg
Ma
Msp
Pc
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Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Pd
Pd
Pd
Pd
Pd
Pd
Pd
Pd
Pd
Pd
Pd
Pd
Pd
Pd
Pd
Pd
Pd
PdPd
Pd
Ps
Ps
Ps
Ps
Ps
Ps
Ps
Ps
Ps
Ps
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
KdKd
Kd
Kd
KdKd
Kd
Kd
Kd Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd Kd
Kd
Kd
Kd
Kd
Pk
Pk
Pk
Pk
Pk
Pl
Pl
Pl
Pl
Pd
Pd
Pd Pd
Pd
Pd
Pd
Pd
Pd
Pd
Pd
Pd
Pd
Pd
Pd
Ps
Ps
Ps
Ps
Ps
Ps
Ps
Ps
Ps
Ps
PsPw
Pw Pw
Pw
Pw
Pw
Pw
Pw
Pm
Pd
Pd
Pd
Pd
Pd
Pd
Pd
Pd
Pk
Pl
Pl
Pl
Pl
Ps
Ps
PsPs
Ps
Ps
Ps
Ps
Ps
PsPs
Ps
Ps
Ps
Ps
Ps
Ps
Ps
Ps
Ps
Ps
Ps
Ps
Ps
Ps
Pw
Pw
Pw
Pw
Pw
Pw
Pw
Pw
Pw
PwPw
Pw
Pw
Pw
Pw
Pw
Pw
Pw
Pw
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Kd
Pw
Pw
Pw
Pw
Pw
Pw
Pw
PwPw
Pw
Pw
Pw
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Pw
Pw
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Pw
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Pw Pw
Pd
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Pd
Pd
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Pd
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Ps
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Pk
Pk
Pk
Pk
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Pl
Pl
Pl
Pl
Pl
Pl
Pb
Ps
Ps
Ps
Ps
Ps
Ps
Ps
Ps
Ps
Ps
Ps
Ps
Ps
Pl
Pl
Pl
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Pd
Pd
Pd
Pd
Pd
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PsPs
Ps
Ps
Ps
Ps
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Pw
Pw
Pw
Pw
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Pw Pw
Pw
Pw
Pw
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Pw
Pw
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Pw
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Pw
Pw
Pw
Pw
Pw
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Pw
Pw
Pw
Pw
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Pw
Pw
Pw
Pw
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Pw Pw
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Ps
Ps
Ps
Ps
Ps
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Ps
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Ps
Ps
Ps
Ps
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Ps
Ps
Ps
Pl
Pl
Pd
Pd
Pd
PdPd
Pw
u
d
d
u
d
u
d
u
Pb
Pb
Pl
#
#
Description of Map Symbols
BEDROCK WELL DATA  POINTS
GEOLOGIC UNIT CONTACTS
COUNTY OR TOWN BOUNDARY
MAJOR HIGHWAYS
LAKE, RIVER, OR STREAM
TOWNSHIP BOUNDARY
FAULT ZONE
        (dashed where inferred)
Interstate Route
U S. Route
State Route
#
25
34
29
u
d
d
u - identifies up-thrown block
- identifies down-thrown block
Pw
Ps
Pd
PENNSY LVANIAN
Wabaunsee Group.   Upper Pennsyl vanian (upper Virgilian).  Maximum
thickness 320 ft (98 m) in Fremont County.  Primary lithologies: shale, gray;
mudstone, gray, part laminated silty to sandy.  Secondary: limestone, fossiliferous,
part coated grain; mudstone, part red, part calcareous/nodular; siltstone to very
fine sandstone.  Minor: black shale; coal.
Shawnee Group.  Upper Pennsylvanian (middle Virgilian).  Thickness 190 to 220
ft (58-67 m).  Primary lithologies: limestone, fossiliferous; shale, gray.
Secondary:  mudstone, part calcareous/nodular, part silt-laminated; limestone,
coated grain.  Minor: chert; coal; black shale, phosphatic; very fine sandstone.
Douglas Group.  Upper Pennsylvanian (lower Virgilian-uppermost Missourian).
Thickness 90 to 135 ft (27-41 m).  Primary lithologies: Shale and mudstone, gray,
part silt-laminated.  Secondary: limestone, fossiliferous, part coated grain;
siltstone to very fine sandstone; mudstone, part red, part calcareous/nodular.
Minor:  coal; black shale.


Bedrock geology of southwest Iowa, Digital geologic map of Iowa, Phase 5: Southwest Iowa

https://ir.uiowa.edu/cgi/viewcontent.cgi?article=1028&amp;context=igs_ofm

Bedrock geology of southwest Iowa, Digital geologic map of Iowa, Phase 5: Southwest Iowa

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