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Eastern Shawnee County

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Sedimentary rocks of Paleozoic age and unconsolidated sediments of Quaternary age overlie the Precambrian basement complex in eastern Shawnee County and vicinity. White to pink biotite granite was penetrated in two wells.

The unexposed sedimentary rocks of Late Cambrian to Late Pennsylvanian age are as much as 2,700 feet thick and are lithologically described on the basis of sample logs prepared by W. L. Adkison (pl. 2). Supplemental data on the general distribution and thickness of these stratigraphic units were obtained from drillers' logs and electric logs of 15 other wells in the area. Rocks of Cambrian and Ordovician age--older than the Simpson Group--were drilled through their entire thickness in only two wells. The Toronto Limestone Member of the Oread Limestone is the youngest unexposed unit in the area.

The exposed sedimentary rocks, about 725 feet thick, are classified in the Shawnee and Wabaunsee Groups of Late Pennsylvanian (Virgil) age. The classification and nomenclature of these stratigraphic units are shown on plate 1.

Fairly thick shale formations of claystone, siltstone, and sandstone and alternating relatively thin resistant limestone formations (pl. 1) record a distinctive cyclic pattern of sedimentation (Moore, 1936a, p. 26-34). The deposits of each sedimentary cycle are a cyclothem (Wanless and Weller, 1932, p. 1003), and each cyclothem contains a limestone formation and parts of the overlying and underlying shale formations. The cyclic succession of lithologic units is markedly exemplified in the limestone formations of the Shawnee Group by the repetition of three or four types of limestone and shale that appear in the same order in each of the four limestone formations of the group (pl. 1). The cyclic repetition in the Wabaunsee Group is less complex than that in the Shawnee; fewer limestone and shale members are present.

In this study the cyclothems were not mapped or described. Their boundaries were difficult to determine because many units of the theoretical cyclic sequence are missing and because the cyclothemic boundaries occur within the shales.

The unconsolidated sediments of Quaternary age include glacial till and outwash and more recent deposits of loess and colluvium. Stream valleys are filled with terrace deposits and alluvium.

Cambrian System

The Cambrian System in the study area comprises the Lamotte Sandstone and the Bonneterre Dolomite of the Upper Cambrian Series.

Lamotte Sandstone.--The Lamotte Sandstone (equivalent to the Reagan), about 5-25 feet thick, is composed chiefly of white fine to medium subangular to subrounded sand. The basal 5 feet which is probably "granite wash" is white to pink coarse to very coarse sand containing granules of angular quartz and granite.

Bonneterre Dolomite.--The Bonneterre Dolomite, about 85-125 feet thick, is medium-light-gray to medium-gray finely to medium-crystalline dolomite. It contains scattered fine to medium, in part frosted, sand and much glauconite and pyrite, especially in the lower half of the formation.

Cambrian and Ordovician Systems

The Cambrian and Ordovician Systems are represented in the mapped area by the Arbuckle Group of the Upper Cambrian and Lower Ordovician Series, the Simpson Group of the Middle Ordovician Series, the Viola Limestone of the Middle and Upper Ordovician Series, and the Maquoketa Shale of the Upper Ordovician Series.

Arbuckle Group.--The Arbuckle Group, 365-400 feet thick, consists primarily of medium-light-gray and pale- to moderate-yellowish brown finely to medium-crystalline dolomite. In the upper part of the group the dolomite contains abundant white to medium-gray dense oolitic chert, and near the middle of the group it contains white and tripolitic chert. Quartz crystals also occur in the dolomite near the middle of the group. Several thin beds of medium-light-gray and greenish-gray glauconitic and pyritic shale are in the lower part, and several thin beds of white fine- to coarse-grained sandstone, composed of rounded and frosted grains, occur near the top and in the lower half. The position of the contact between rocks of the Arbuckle Group and the underlying Bonneterre Dolomite is questionable.

Simpson Group.--Rocks of the Simpson Group are about 70-125 feet thick and consist chiefly of white fine- to medium-grained sandstone in which the grains are rounded and frosted. The upper part of the Simpson contains brownish-gray to medium-dark-gray partly sandy fine- to medium-crystalline dolomite. The sandstone is dolomitic near the top of the group. A few thin beds mainly of gray, greenish-gray, and Mack shale occur near the top and base.

Viola Limestone.--The Viola Limestone, uniformly 110-120 feet thick, is mainly pale-yellowish-brown to brownish-gray (locally very pale orange and medium-gray) finely to medium-crystalline dolomite. The upper part of the unit contains very light gray to medium-gray dense opaque and partly spicular chert, some of which has black specks. The lower part locally contains chert and scattered fine to medium rounded and frosted sand.

Maquoketa Shale.--The Maquoketa Shale, which ranges in thickness from about 20 to 70 feet, is principally medium-light-gray to medium-gray partly dolomitic shale but includes some olive-gray shale. Locally the formation contains medium-light-gray to medium-gray dolomitic siltstone.

Silurian and Devonian Systems

The Silurian and Devonian Systems are represented in the mapped area by the 85- to 200-foot-thick Hunton Formation. The lower part of the Hunton is of Silurian age, and the upper part is of Devonian age.

The lower part is present with certainty only in the Murchison Federal Land Bank 1 well, in the SE cor. sec. 28, T. 10 S., R. 15 E., where it is 120 feet thick. The lower part may also he present as the lower 15 feet of the Hunton in the Forrester and others Hummer 1 well, in the SE NE SW sec. 14, T. 11 S., R. 16 E. The lower part of the Hunton is mostly light-gray and very pale orange very finely to medium-crystalline dolomite. A few thin beds of medium-gray shale occur in the lower half of the formation, and some light-gray dense chert is present in the lower quarter.

The upper part of the Hunton Formation, about 85-115 feet thick, is primarily light-gray, very pale orange, and pale-yellowish-brown very finely to finely crystalline, in part sandy, dolomite containing sparse to abundant very light gray to medium-gray and pale-yellowish-brown dense opaque chert. The chert is concentrated in zones that seem to vary in position from well to well. The sand is fine to medium, rounded, and frosted. Clear quartz crystals are also present locally in the dolomite. That part of the Hunton which is of Devonian age also contains--generally in its upper beds--medium-gray shales and a few thin beds of light-gray to medium-light-gray very fine grained or finely to medium-crystalline, in some degree very dolomitic, limestone. Some white glossy fine- to medium-grained, in part limy and dolomitic, sandstone occurs in the lower half of the part that is of Devonian age.

Devonian and Mississippian Systems

The Chattanooga Shale, of Devonian-Mississippian age, is about 80-150 feet thick and is composed mainly of medium- to dark-gray shale but includes some greenish- and brownish-gray shale and, in its upper part, some medium-light-gray dolomitic siltstone. Shales in the lower part of the Chattanooga contain dark-brown to dark-gray spore cases. The basal unit of the formation, called the Misener sand by drillers, is about 2 feet thick; it is composed of light- to medium-gray fine- to coarse-grained pyritic limy, or dolomitic, sandstone. Locally the sandstone contains very light gray to medium-light-gray limy quartzose chert.

Mississippian System

The Mississippian rocks in the area are those of the Lower Mississippian Series. These strata range in thickness from 205 to about 250 feet and are composed of limestone and dolomite. In the Murchison Federal Land Bank 1 well and in the J. J. Lynn Warner 1 well (pl. 2), these rocks were divided into those of Kinderhook age consisting, in ascending order, of the Chouteau Limestone, Sedalia Dolomite, and Gilmore City Limestone, and into those of Osage age consisting of the Burlington Limestone overlain by the Keokuk Limestone. The Burlington and Keokuk could not be differentiated in the J. J. Lynn Warner 1 well.

Chouteau Limestone.--The Chouteau Limestone, about 55-70 feet thick, is chiefly medium-light-gray to medium-gray and pale-yellowish-brown to brownish-gray very finely to finely crystalline limestone that is cherty in the upper half and dolomitic near the top. The chert is primarily light gray to medium gray, dense, and opaque. Locally some pale-yellowish-brown very finely crystalline cherty dolomite occurs at the top. Crinoid columnals are locally abundant in the lower part of the Chouteau.

Sedalia Dolomite.--The Sedalia, 10-15 feet thick, is chiefly medium light-gray to medium-gray and pale-yellowish-brown very finely crystalline fossiliferous dolomite that is cherty in part. In the J. J. Lynn Warner 1 well the lower part is medium-light-gray very fine grained slightly argillaceous dolomitic limestone. The chert is light gray to medium gray, dense, and opaque.

Gilmore City Limestone.--The Gilmore City Limestone, about 1015 feet thick, is predominantly pale-yellowish-brown to medium light-gray finely to medium-crystalline fossiliferous limestone. In the J. J. Lynn Warner 1 well (pl. 2), the limestone is dolomitic and in part glauconitic and contains some brownish-gray dense opaque spicular chert. Olive-gray very finely crystalline dolomite occurs at the top of the Gilmore City in this well.

Burlington Limestone.--The Burlington Limestone, the lower formation of Osage age, is about 35 feet thick and is mainly light-gray and very pale orange very finely crystalline to granular cherty limestone. It also includes cherty dolomite of the same color in its basal and upper parts. The chert is white to light gray, dense, and, commonly, opaque. Quartz crystals occur throughout the Burlington in the Murchison Federal Land Bank 1 well.

Keokuk Limestone.--The Keokuk Limestone, of Osage age, is about 90 feet thick in the Murchison Federal Land Bank 1 well. Its upper part consists of light-gray and pale-yellowish-brown very finely to finely crystalline partly dolomitic and glauconitic fossiliferous limestone that contains abundant white and light-gray dense chert and some spicular and tripolitic chert. Its lower part is mainly pale-yellowish-brown very finely to finely crystalline cherty dolomite but includes some dolomitic cherty limestone at the base. The chert in the dolomite resembles that in the limestone but is commonly darker. In the J. J. Lynn Warner 1 well, where the Keokuk and Burlington were not differentiated, the rocks are similar to those in the Federal Land Bank well except that the upper part is mainly cherty dolomite and lower part is limestone almost devoid of chert.

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Kansas Geological Survey, Geology
Placed on web October 2005; originally published 1967.
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