Sedimentary rocks of Paleozoic and Quaternary age underlie Douglas County. The Paleozoic rocks are of Pennsylvanian, Mississippian, Devonian, Ordovician, and Cambrian age and overlie the Precambrian basement. The thickness of the Paleozoic rocks ranges from about 2,400 feet in the southeast corner and the northeast corner along Kansas River to about 3,000 feet in the northwest corner of the county. The general thickness and character of the subsurface rocks are known through the study of logs and samples of drill cuttings from oil and gas wells in the area. The sequence and attitude of the major rock units are shown in a cross section on Plate 1.
An excellent discussion of the stratigraphy and structural development of the Forest City Basin, which includes the area of this report, was prepared by Lee (1943). More recently Lee and Merriam (1954) prepared north-south and east-west cross sections through Douglas County, which depict the Paleozoic structural movements that affected the area.
Quartzite, schist, slate, marble, porphyry, and granite have been reported from wells drilled into the Precambrian in Kansas. Lee (1943) identified as pink granite the Precambrian rock in the R.F. Duffens No. 1 Stanley well (NW NE NW sec. 3, T. 14. S., R.21 E.) and the C. J. Neuner et al No. 1 Emmett well (SE NW sec. 6, T. 14 S., R. 18 E.).
The Precambrian topography slopes to the northwest across Douglas County from about 1,400 feet below sea level in the southeast corner to approximately 2,000 feet below sea level in the northwest corner (Jewett, 1954, fig. 9).
The Lamotte Sandstone of Late Cambrian age underlies the Arbuckle Group and overlies Precambrian rocks. Throughout Douglas County it is believed to be generally less than 30 feet thick, and locally may be absent. It is reported to be 7 feet thick in the Duffens No. 1 Stanley well in central eastern Douglas County and 15 feet thick in the Neuner No. I Emmett well in central western Douglas County. The Lamotte is a fine- to coarse-grained sandstone composed chiefly of quartz or quartz and feldspar.
Cambrian and Ordovician rocks
In Douglas County the Arbuckle Group, of Early Ordovician and Late Cambrian age, consists of five recognizable subdivisions. The upper three, of Ordovician age, and their thickness in east-central Douglas County (Duffens No. 1 Stanley well) are as follows: (1) undifferentiated Cotter and Jefferson City Dolomites, 106 feet; (2) Roubidoux Dolomite, 167 feet; and (3) undivided Gasconade Dolomite and Van Buren Formation [including a slight thickness of Gunter Sandstone in the basal part], 206 feet. The lower two subdivisions of the Arbuckle, of Late Cambrian age, and their reported thickness in this well are, (1) the Eminence Dolomite, 175 feet, and (2) the Bonneterre Dolomite, 19 feet (Lee, 1943, fig. 5). Except for the Roubidoux Dolomite, which thickens slightly to the northwest across the county, all the subdivisions of the Arbuckle thin to the north and west. The thickness of the Arbuckle ranges from about 750 or 800 feet in the southeast to about 500 feet in the northwest.
Late Ordovician rocks in eastern Kansas are represented by the Maquoketa Shale, and Middle Ordovician rocks by the Viola Limestone. Both Middle and Early Ordovician rocks are included in the Simpson Group.
The Maquoketa Shale is present only in the northwestern part of the county (Lee, 1943, fig. 11), where it ranges in thickness from a featheredge to nearly 50 feet and consists of greenish-gray silty dolomitic shale and silty dolomite. The Viola Limestone is present throughout the area and consists of slightly more than 100 feet of limestone.
The Simpson Group is distributed throughout the county and comprises the Platteville Formation and the underlying St. Peter Sandstone. The upper beds include gray lithographic limestone, gray shale, brown cherty dolomite, and green shale. Lower beds are chiefly medium- to coarse-grained, well-rounded white sandstone and some shale (Lee, 1943; Moore and others, 1951). The Simpson Group has a thickness of about 50 to 100 feet. According to Lee (1943, fig. 13), Silurian rocks are absent in Douglas County.
In Douglas County the Devonian rocks are believed to be present directly below the Chattanooga Shale everywhere except in a small area in the east-central and southeastern parts (Lee and Merriam, 1954, fig. 2), where Viola Limestone directly underlies the Chattanooga Shale. A maximum of slightly less than 100 feet of Devonian limestone and dolomite is present in the northwest (Lee, 1943, fig. 12). Undifferentiated Silurian and Devonian rocks are commonly termed the "Hunton" Group in eastern Kansas.
Mississippian or Devonian rocks
The Chattanooga Shale of Mississippian or Devonian age ranges in thickness from slightly less than 50 feet to about 100 feet and is thickest in the northwestern part of the county (Lee, 1943, fig. 14). It is greenish-gray, dark-gray, and black shale, and is silty and pyritiferous in part. Locally a thin sandy shale or sandstone in the, lower part is correlated with the Misener Sandstone member in parts of eastern Kansas.
Lee (1943, fig. 16) indicated that the Mississippian rocks bad a thickness range of about 250 to 400 feet, thinning in the southern part of Douglas County and in Franklin County (Lee, 1939, p. 36). The Spergen(?) and Warsaw Limestones of Meramecian age, the Burlington Limestone of Osagian age, and the Sedalia and Chouteau formations of Kinderhookian age are believed to be present in the county (Lee, 1940, pl. 6). The Mississippian rocks are chiefly limestone and dolomite.
The Pennsylvanian rocks are represented by the Virgilian Series, the Missourian Series, and the Desmoinesian Series. The Wabaunsee, Shawnee, and Douglas Groups make up the Virgilian Series. The Missourian Series consists of the Pedee, Lansing, Kansas City, and Pleasanton Groups. The Marmaton and Cherokee Groups compose the Desmoinesian Series. Pennsylvanian rocks exposed in Douglas County are discussed in more detail in the following pages.
Kansas Geological Survey, Geohydrology of Douglas County
Web version Aug. 1999. Original publication date Dec. 1960.
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