Mississippian Stratigraphy of North-Central Iowa

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Proceedings of the Iowa Academy of Science

Volume 80 Number Article 3

1973

Mississippian Stratigraphy of North-Central Iowa

Donald L. Koch Iowa Geological Survey

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Recommended Citation Koch, Donald L. (1973) "Mississippian Stratigraphy of North-Central Iowa," Proceedings of the Iowa Academy of Science, 80(1), 1-3. Available at: https://scholarworks.uni.edu/pias/vol80/iss1/3

This Research is brought to you for free and open access by the Iowa Academy of Science at UNI ScholarWorks. It has been accepted for inclusion in Proceedings of the Iowa Academy of Science by an authorized editor of UNI ScholarWorks. For more information, please contact [email protected]. Koch: Mississippian Stratigraphy of North-Central Iowa

Mississippian Stratigraphy in Southeastern Iowa

MARY C. PARKER1

PARKER, MARY C. Mississippian Stratigraphy in Southeastern Iowa. west portion of southeast Iowa and occur locally within the basal Proc. Ia. Acad. Sci., 80(1):4-7, 1973. Osage. Siltstone occurs within the lower portion of Kinderhook SYNOPSIS: All formational units of the Kinderhook, Osage and strata. The maximum thickness of the Mississippian System across Meramec Series are represented in Iowa. No rock units of the south-central Iowa represents the main axis of Mississippian de Chester Series are present in the state. The Mississippian sequence position. of rocks is dominated by cherty marine carbonates, but thin fossili INDEX DESCRIPTORS: Stratigraphy, Mississippian, Iowa, Meramec ferous shale units occur in the Osage and Meramec. Sandstone and Series, Osage Series, Kinderhook Series. sandy carbonate are dominant within the Meramec in the north-

Mississippian formations constitute the bedrock in a diag outcrop belt in eastern Iowa. The general thinning to the onal belt twenty to forty miles wide from Lee and Des northwest reflects the transgressive conditions present in the Moines Counties in the southeast corner of the state north early Mississippian. westward to southern Cerro Gordo and Hancock Counties in The stratigraphic succession of the Mississippian rocks in north-central Iowa. southeastern Iowa is shown in Table 1. The thickness of The standard sections of Mississippian age rock units are the Mississippian sequence and the thickness of each series along the Mississippi Valley from southeastern Iowa into in southeastern Iowa is shown in Figure 1. southern Illinois and southeastern Missouri. All formational units of the Kinderhook, Osage and Meramec Series are rep resented in Iowa. Because the Kinderhook varies lithologi SERIES GROUP FORMATION MEMBER cally from place to place and many of the formations orig ;:,re. \.:7enev1eve inally correlated as Mississippian are now placed in the De Meramec ~r, LOUIS vonian, no standard section has been established for the ~pergen vvarsaw Kinderhook. The type sections of the Burlington and Keo i<.eOKUK kuk Formations are located near those cities in southeast Osage Cedar Fork Iowa. The Warsaw Formation derives its name from ex Burlington Haight Creek posures at Warsaw, Illinois, nearly opposite Keokuk, Iowa. Dolbee Creek The Spergen, St. Louis, and Ste. Genevieve Formations are I I I I I I I I I represented in Iowa by marginal facies of formations which are thicker and more uniform in composition farther south Hampton I 11 11 v assonv1 e in the Mississippi Valley. Kinderhook ~rarrs ._ave None of the Chester Formations are represented in the North Hill rrospec1 n111 state and it is probable that the Chester seas never extended McLraney this far north. The Mississippian-Devonian boundary is placed at the base Table 1. Stratigraphic succession of the Mississippian rocks in of the North Hill Group by the Iowa Geological Survey. A southeastern Iowa. discussion of the Mississippian-Devonian boundary in Iowa has been presented by Dorheim, Koch, and Parker (1969) . Along the eastern and northeastern edge of the outcrop STRATIGRAPHY-KINDERHOOK SERIES belt, Kinderhook strata occur above formations of the Yellow Spring Group (uppermost Devonian) . Along the northern The Kinderhook Series in southeastern Iowa includes the boundary in Hancock and Kossuth Counties, Kinderhook North Hill Group and the overlying Hampton Formation. strata occur above the Lime Creek Formation (lower Upper The Kinderhook is composed dominantly of carbonate rocks. Devonian). In western Iowa and eastern Nebraska, Kinder Siltstone occurs in the North Hill Group and chert in the hook strata occur above Middle Devonian rocks. For the Hampton. most part, the boundary is a transgressive, nonconformable The North Hill Group (Workman and Gillette, 1956) in contact. cludes in ascending order: McCraney Limestone, Prospect The Mississippian System is unconformably overlain by Hill Siltstone, and Starrs Cave Formation. The McCraney Lower Pennsylvanian (Cherokee Group) sediments in most Limestone is dominantly a very pale-orange to pale yellow of southeastern Iowa. Jurassic (?) (Fort Dodge Beds) and ish-brown, sublithographic limestone. Brown medium-grained Lower Cretaceous units were deposited upon the eroded dolomite occurs in irregular horizontally and vertically ori Mississippian surface in north-central and northwestern Iowa. ented planes. The McCraney is sparingly fossiliferous except Pleistocene deposits mantle the Mississippian rocks along the for the basal portion which consists of an oolitic, crinoidal limestone that locally contains a coarse brachiopod coquina composed almost entirely of Chonetes. The Prospect Hill 1 Iowa Geological Survey, 16 West Jefferson Street, Iowa City, Siltstone is dominantly a light greenish-gray, medium silt Iowa 52242. stone with discontinuous green shaley seams. The Prospect

Published by UNI ScholarWorks, 1973 1 Proceedings of the Iowa Academy of Science, Vol. 80 [1973], No. 1, Art. 3

MISSISSIPPIAN SOUTHEASTERN low A 5

THICKNESS OF MISSISSIPPIAN ROCKS THICKNESS OF KINDERHOOK ROCKS IN SOUTHEASTERN IOWA IN SOUTHEASTERN IOWA

contour interva I 100 feet contour interval 50 feet

THICKNESS OF OSAGE ROCKS THICKNESS OF MERAMEC ROCKS IN SOUTHEASTERNIOWA IN SOUTHEASTERN IOWA

contour interval 50 feet contour interval 50 feet

Figure I. Thickness maps of Mississippian series in southeast Iowa.

Hill contains fish teeth, brachiopods, and pelecypods. The tive of the Hampton Formation (Laudon, 1931) in south Starrs Cave Formation is a very pale orange to pale gray, eastern Iowa. The Wassonville consists of pale to dark yel oolitic limestone which contains fragmented brachiopods, lowish-orange, dolomitic limestone and pale yellowish-brown corals, and crinoids. dolomite. Over most of the area of its occurrence, the Was The Wassonville Limestone Member is the only representa- sonville contains appreciable amounts of light gray, fossilif- https://scholarworks.uni.edu/pias/vol80/iss1/3 2 Koch: Mississippian Stratigraphy of North-Central Iowa

6 PROC. lowA AcAD. Sc1. 80 ( 1973)

erous chert. In the extreme southeastern counties the Was kuk. To the north an::l west it decreases in thickness and is sonville is relatively chert free and is dominantly a Burlington Limestone exhibits gradational changes in County. South of Burlington the Prospect Hill Siltstone at lithology from the southeast to the north and west where tains a thickness of 30 to 40 feet. West of the Burlington dolomite content increases an ::1 both carbonates and cherts area the Prospect Hill becomes thinner and finer grained become darker in color. and appears to be absent in Monroe and Appanoose Coun The Keokuk Limestone consists of cherty limestone at the ties. In the Burlington area the Starrs Cave Limestone is 3 base, called "Montrose Cherts" by Keyes ( 1893), overlain to 5 feet thick. West of the Burlington area it increases in by fossiliferous limestones with interbedded fossiliferous thickness to approximately 65 feet at Albia in Monroe Coun shales. The "Montrose Cherts" are easily separated from the ty and 75 feet at Cincinnati in Appanoose County. relatively noncherty Cedar Fork Member of the Burlington An unconformity at the top of the Kinderhook in south Limestone. The top of the Keokuk cannot always be identi eastern Iowa has been described by Laudon ( 1937) and fied as readily. The upper portion of the Keokuk is com Harris and Parker ( 1964). Basal Burlington (Osage) rests posed of gray fossiliferous calcarenites with interbedded fos on units as old as the Starrs Cave Formation. Regional dis siliferous, calcareous shales. The shale beds increase in num tribution and thicknesses suggest the possibility of facies ber and thickness upward grading into the gray Warsaw equivalency between the Eagle City-Iowa Falls and the Gil shales, and dolomite beds replace the limestone. In subsur more City Formations (Kinderhook) in north-central Iowa face usage, the upper boundary of the Keokuk generally is with the lower Burlington in southeastern Iowa. Detailed placed at the top of the calcarenite. faunal studies are needed to clarify these Kinderhook-Osage In the extreme southeastern counties the thickness of the boundary relationships. Keokuk averages about 75 feet. To the west it thins to an average of 50 feet and to the north in Story and Marshall Counties it averages 25 feet. OSAGE SERIES The two units of the Keokuk are typified by light gray, medium to coarsely crystalline limestone grading into cal The Osage Series in southeastern Iowa includes the Bur carenite. Fossil fragments, especially of brachiopods and cri lington Limestone (Hall, 1857), Keokuk Limestone (Owen, noids, are commcm in well cuttings. Light gray to light olive 1852), and Warsaw Formation (Hall, 1857). The Osage is gray, fine to medium crystalline dolomite beds constitute composed dominantly of cherty carbonate rocks interstrati about 50 percent of the carbonates of the lower "Montrose" fied with minor amounts of fossiliferous shale. Quartz sand unit. Chert that is typically light gray and off-white, mottled stone occurs only locally at the base of the Burlington Lime and specked with black, gray, or brown is the dominant stone and has been noted in parts of Washington, Keokuk, lithology in well cuttings through the upper portion of the and Louisa Counties. The detailed stratigraphy of :md con Montrose unit. Spicular fragments of fossils are abundant in formable relationships between the Burlington and Keokuk the chert an:l serve to distinguish the Keokuk from the domi and the Keokuk and Warsaw in southeastern Iowa were de nantly crinoidal chert of the Burlington. The shales in the scribed by Harris and Parker ( 1964). upper portion of the Keokuk generally are gray, fossiliferous, The members of the Burlington Limestone are: Dolbee and calcareous. Glauconite, as scattered soft green spots, is Creek, Haight Creek and Cedar Fork. In general, the Dolbee associated with the Keokuk sediments, but no concentration Creek Member (Laudon's Cactocrinus zone in the type area, has been noted at a single horizon over a broad area, as it but including his underlying zones where the member is has in the Burlington. To the west the Keokuk is typically thick) is relatively pure, coarsely crystalline, crinoidal lime brown-dark in the upper portion and lighter below. The stone with a small amount of chert. Spirifer grimesi and frag most striking lithology is the brownish-gray chert which is ments Qf bryozoans are prevalent in this member. It rests un mottled white and contains white spicules. The carbonate in conformably on rocks which are more susceptible to weath the western portion is chiefly dolomite rather than limestone ering. This unit is thickest ( 17 feet) in the south near Keo- and is characteristically brown, finely crystalline, argi!laceous

Published by UNI ScholarWorks, 1973 3 Proceedings of the Iowa Academy of Science, Vol. 80 [1973], No. 1, Art. 3

MISSISSIPPIAN SOUTHEASTERN lowA 7

and highly siliceous. Brown, blocky, dolomitic shale is typi The average thickness is 50 feet, although thicknesses of over cal in the western counties. The lower part of the Ke:ikuk 125 feet have been recorded in the evaporite areas. contains a large amount of secondary siliceous material in The Ste. Genevieve is a pale yellowish-gray limestone the form of crystalline quartz and chalcedony, probably of with a high percentage of quartz sand in southern Iowa and geodal origin. is represented mainly by greenish-gray and pale rd shales The Warsaw Formation is characterized by shale, argilla in central Iowa. The Ste. Genevieve is conformable upon the ceous dolomite and chalcedonic chert. Shale is dominant in St. Louis, but varies greatly in thickness and distribution the upper portion whereas chalcedony tends to be concen because of post-Mississippian erosion. trated in the lower portion. In the southeastern counties the shale of the Warsaw is primarily very light gray to medium gray, chunky, and dolo SUMMARY mitic. Fenestrate bryozoans are common. Very light-gray to light medium-gray, finely crystalline, argillaceous dolomites The beginning of Mississippian time was a period of gen accompany the shales. To the west and north both the shales eral emergence with no evidence of localized uplift. The and dolomites are darker. The chalcedony is associated w:th region was a broad plain, modified somewhat by differen crystalline quartz and typically the color is light bluish-gray tial erosion. Shallow, restricted seas are evidenced bv the and bluish-white, but some is moderate re:ldish-orange or distribution of the formations of the North Hill Group: Nor moderate pink. mal marine seas during deposition of the Hampton are indi The carbonate rocks interstratified with shale are more cated by fossiliferous carbonate rocks. The nearly pure bio numerous in the lower portion of the formation. In the out clastic carbonate rocks of the Osage are the result of a crop area, these are calcarenites that are somewhat dolomitic. shallow shelf environment. The shales of the Warsaw are However, in most of southeastern Iowa they have been al the termination of a elastic wedge from the east. Carbonate tered to finely crystalline dolomite. Argillaceous carboniferous limestones of the Mississippi This interval is unconformably overlain by the Cherokee Valley: Am. Journ Sci., 2d Ser. 23:187-203. Group of Pennsylvanian age and by Pleistocene deposits. HARRIS, S. E., Jn., and M. C. PARKER. 1964. Stratigraphy of the The northward thinning is the result of truncation and over Osage Series in southeastern Iowa: Iowa Geol. Survey Rpt. lap at the base of the St. Louis. Inv. 1, 52 p. The Spergen (Salem) Limestone is a brownish-gray, mi KEYES, C. R. 1893. Geology of Lee County: Iowa Geol. Survey Ann. Rpt. 3:305-409. caceous dolomitic limestone with a minor quartz sand frac LAunoN, L. R. 1931. Stratigraphy of the Kinderhook Series of tion. It is restricted to southern Iowa by the pre-St. Louis Iowa: Iowa Geol. Survey Ann. Rpt. 35:333-451. unconformity. The Spergen often has been confused with __. 1937. Stratigraphy of the northern extension of Burlington the basal St. Louis. The average thickness is 20 feet, al Limestone in Missouri and Iowa: Am. Assoc. Petroleum Geol though as much as 35 feet has been recorded in wells in ogists Bull. 21: 1158-1167. Appanoose County. OwEN, D. D. 1852. Report on the geological survey of Wisconsin, The St. Louis Limestone in southeastern Iowa is domi Iowa, and Minnesota: Lippincott, Grambo and Co., Philadelphia, nantly a pale yellowish-brown limestone, often sublitho pp. 90-140. graphic, with a lower zone of brown areanaceous dolomite. SHUMARD, B. F. 1860. Observations on the geology of the county of Ste. Genevieve, Missouri: St. Louis Acad. Sci. Trans. 1 :404- It contains an upper shaley zone and a lower zone with a 415. high percentage of anhydrite and gypsum. The absence of ULRICH, E. 0. 1905. The lead, zinc, and fluorspar deposits of evaporites in the outcrop area may be due to ~olution, Western Kentucky: U.S. Geol. Survey Prof. Paper 36, 218 p. which would account for the brecciated nature of the car WORKMAN, L. E. and TRACY GILLETTE. 1956. Subsurface strati bonates. The shale content increases across southern Iowa graphy of the Kinderhook Series in Illinois: lllinois Geol. Sur with a sandy facies becoming prominent toward the north. vey Rpt. Inv. 189, 46 p.

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