Gilmore City Formation

Interval includes lower Marble Valley Member, upper Humboldt Member; “Iowa Falls Dolomite” (dolomite facies); formation shares partial regional facies relationships with Burlington Formation; not present in southeastern Iowa. Primary Lithologies: limestone, primarily coated grain/oolitic to peloidal, variably fossiliferous to intraclastic. Secondary Lithologies: dolomite; dolomitic limestone; limestone, dense, “sublithographic.” Minor: shale, gray, calcareous; oncolitic limestone; glauconite; chert; breccia. Maximum thicknesses in northern Iowa 150-170 ft (45-52 m); interval thins to south and southeast 20-70 ft (6-21 m).
State Iowa
Name Gilmore City Formation
Geologic age Lower Mississippian, upper Kinderhookian to Middle Mississippian, lower Osagean
Lithologic constituents
Sedimentary > Carbonate > Limestone (Bed)primarily coated grain/oolitic to peloidal, variably fossiliferous to intraclastic; minor dolomitic limestone; incidental oncolitic
Sedimentary > Carbonate > Dolostone (Bed)
Sedimentary > Chemical > Chert (Bed)
Sedimentary > Clastic > Mudstone > Shale (Bed, Calcareous)gray, calcareous
Sedimentary > Clastic > Sedimentary-breccia (Bed)

Witzke, Brian J., Anderson, Raymond R., and Pope, John P., 2010, Iowa Geological and Water Survey, DNR, Bedrock Geologic Map of Iowa, OFM-2010-1. Scale 1:500,000.

NGMDB product
Counties Boone - Buena Vista - Calhoun - Cherokee - Franklin - Grundy - Hamilton - Hardin - Humboldt - Jasper - Marshall - Monona - Pocahontas - Sac - Story - Webster - Woodbury - Wright