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Stratigraphy
Sedimentary rocks of Paleozoic age and unconsolidated sediments of Quaternary age overlie the Precambrian basement complex in western Shawnee County and vicinity. Granite was penetrated in one well.
The unexposed sedimentary rocks of Late Cambrian to Late Pennsylvanian age, as much as 3,300 feet thick, were lithologically described by use of sample logs from five wells in the north half of the area (pl. 4), Supplemental data on the general distribution and thickness of these stratigraphic units were obtained from drillers' logs of 12 other wells in the area. Rocks of the Arbuckle Group (Upper Cambrian and Lower Ordovician) were drilled through their entire thickness in only one well; the upper part of the Arbuckle was drilled in three other wells. The lower part of the Severy Shale contains the youngest unexposed strata in the area. The color terms used to describe the unexposed sedimentary rocks are those used in the sample logs and do not necessarily conform to those of the "Rock-Color Chart."
The exposed sedimentary rocks in the mapped area are about 600 feet thick and are classified in the Wabaunsee Group of Late Pennsylvanian (Virgil) age and in the Admire and Council Grove Groups of Early Permian age. The nomenclature and classification of the stratigraphic units are shown on plate 3. The derivation of the nomenclature and the specific location of the type locality of each formation and its members were discussed in detail by Mudge and Burton (1959, p, 16-58) and by Johnson and Adkison (chap. A, this report); only reference to the first use of each name is included in this chapter.
In the Wabaunsee Group, fairly thick shale formations of claystone, siltstone, and sandstone and alternating relatively thin resistant limestone formations (pl. 3) record a distinctive cyclic pattern of sedimentation (Moore, 1936a, p. 25-26). The Lower Permian rocks also show cyclic sedimentation (Jewett, 1933; Elias, 1937). In those rocks the lithologic units are similar to those of the Wabaunsee Group except that sandstone and coal are less abundant and red and green mudstones are more abundant. 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.
In this study the cyclothems were not mapped or described. The boundaries of the cyclothems were difficult to determine because many units of the theoretical cyclic sequence are missing and because the cyclothemic boundaries occur within the shale members or formations.
The unconsolidated sediments of Quaternary age include glacial till and outwash and more recent deposits of loess and colluvium that mantle much of the northern two-thirds of the mapped area. Stream valleys are filled with terrace deposits and alluvium.
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
Rocks of the Arbuckle Group were drilled in the Musgrove Heiland 1 well, where they are 28 feet thick. Thirty-three feet of the Arbuckle was drilled in the W. M. McKnab Fritz 1 well, in the NW sec. 4, T. 12 S., R. 14 E. The Arbuckle is generally pale-yellowish-brown, gray, or buff finely to coarsely crystalline, in part slightly sandy, dolomite. The dolomite contains much white to medium-light-gray dense chert and oolitic chert. In the Murchison Federal Land Bank 1 well, a thin medium-gray to greenish-gray shale occurs near the top of the Arbuckle.
Simpson Group
The Simpson Group is about 90-125 feet thick. The lower two-thirds of the group is mainly white to gray fine- to medium-grained sandstone that has rounded frosted grains, and the upper third is mainly brown medium-crystalline partly sandy and vuggy cherty dolomite, limestone, and shale. A few very thin layers and stringers of green and dark-gray to black shale are intercalated in the sandstone. In the Musgrove Heiland 1 well, the sandstone and shale in the lower half of the Simpson are overlain by slightly sandy, dolomitic limestone. Dark-gray, greenish-gray, and in part black platy subwaxy shale occurs at or near the top of the Simpson in some wells and at the base of the Simpson in others.
Viola Limestone
The Viola Limestone, about 75-115 feet thick, is mostly brownish-gray to pale-yellowish-brown very finely to medium-crystalline dolomite commonly containing abundant very light gray to medium-gray dense opaque somewhat spicular chert in its upper part. Near the northwest corner of the area, mottled gray coarsely crystalline limestone occurs at the base, Locally the upper part has a few very thin beds of medium-gray shale,
Maquoketa Shale
The Maquoketa Shale, about 60-90 feet thick, is dominantly medium- to dark-gray and gray-green commonly dolomitic shale but contains a few thin beds of shaly dolomite. In the Kaiser-Francis and Shawver-Armour Adams "A" 1 well, however, the dolomite beds are thicker and more numerous; some are slightly cherty (pl. 4).
Silurian and Devonian Systems
The Silurian and Devonian Systems are represented in the mapped area by the Hunton Formation. The Hunton ranges in thickness from 125 to 285 feet and is thickest in the northwestern part of the area. According to Lee (1943, p, 44, 45, 51), the lower part of the Hunton is of Early Silurian age, and the upper part is of Middle Devonian age. Light-gray to medium-light-gray and buff-gray finely to medium-crystalline dolomite, in places containing light-gray dense chert and a few thin beds of medium-gray and gray-green shale, composes the lower 55-235 feet of the Hunton.
The upper part of the Hunton Formation, about 55-85 feet thick, is light-gray, buff, or very pale orange very finely to finely crystalline partly sandy dolomite containing sparse to abundant chert. The chert is light gray to medium light gray and pale yellowish brown, dense, and opaque; it occurs in zones that differ in stratigraphic position from well to well. The sand is fine to medium, rounded, and frosted. Euhedral quartz occurs in the dolomite locally, Some medium-gray shale is interbedded with the upper beds of the Hunton in the northeastern part of the area.
Devonian and Mississippian Systems
The Chattanooga Shale of Devonian and Mississippian age ranges from about 130 to 260 feet in thickness but averages about 150 feet thick. The shale is mainly medium to dark gray in the eastern part of the area and greenish gray in the western part. In places dolomitic siltstone and shaly dolomite occur near the top. Most well samples from the lower part of the Chattanooga contain abundant dark-brown to dark-gray spore cases. The basal unit of the formation--the Misener sand of economic usage--is recognized only in the eastern part of the area. It may occur elsewhere but, because it probably does not exceed 2 feet in thickness, it was not recognized by drillers. The sandstone is light to medium gray, fine to coarse grained, dolomitic, and pyritic. Locally it contains very light gray to medium-light-gray calcareous quartzose chert.
Mississippian System
The Mississippian rocks in the area are those of the Lower Mississippian Series. The strata, which range in thickness from about 210 to 290 feet and average about 235 feet thick, are composed mainly of thick units of limestone and dolomite in nearly equal amounts. The Lower Mississippian rocks in eastern Shawnee County (chap. A, this report) were divided into formations, but those formations could not be recognized with certainty in western Shawnee County and vicinity. The Lower Mississippian limestone is pale yellowish brown, light to medium gray, or brownish gray, and is very finely to coarsely crystalline. Crinoid fragments are common throughout, and white to light-gray chert is commonly present in the upper part. Euhedral quartz is locally abundant in limestone near the middle of the unit, and glauconite occurs in some beds in the upper part. The dolomite is pale yellowish brown, very pale orange, grayish brown, or buff; it is very finely to finely crystalline and commonly contains abundant light- to medium-gray and white dense chert, Thin black shale beds are locally intercalated in the limestone and dolomite, and white fine- to medium-grained cherty sandstone occurs in the upper part in the Kaiser-Francis and Shawver-Armour Adams "A" 1 well (pl. 4),
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Kansas Geological Survey, Geology
Placed on web October 2005; originally published 1967.
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