Paleozoic EraCambrian and Ordovician Periods
Although very little is known of the conditions existing in western Kansas during early Paleozoic time, it is believed that Scott County, along with a large part of west-central United States, was a land surface during early Cambrian time. In the middle part of Cambrian time there began the development of an interior sea with a resultant change to marine conditions. Submergence of the land continued through most of Ordovician time with extensive deposition of lime sediments that were later indurated to form limestones and dolomites. The sandy, cherty dolomite that forms the Arbuckle limestone or "siliceous lime" of Cambrian and Ordovician age was deposited in the earlier part of this interval. In Scott County the Arbuckle is encountered in one well at a depth of about 5,470 feet.
A well in the Shallow Water oil pool penetrates the Viola limestone and Simpson group of Ordovician age. The Viola is a sugary, dolomitic, and very cherty limestone at the top, but becomes finer grained and non-cherty below, grading into the Simpson group at a depth of about 5,450 feet.
Silurian and Devonian Periods
There is little or no evidence that rocks of Silurian and Devonian age are present under Scott County. Either they were never deposited in this area or they were removed by erosion prior to the deposition of the overlying Mississippian strata.
Mississippian and Pennsylvanian Periods
During early Mississippian time there was extensive deposition of marine dolomitic limestone and some shale. According to the logs of oil wells in the Shallow Water pool, Mississippian strata are present under Scott County, the top being encountered at a depth of about 4,650 feet. When production was found initially in the Shallow Water pool it was believed that the producing limestone was of Chesterian (upper Mississippian) age (Ver Wiebe, 1938, p. 138). Norton (1938), however, reports that this oolitic limestone is probably the equivalent of the Ste. Genevieve limestone of middle Mississippian age. In later Mississippian time there was an uplift, during which the surface of the early Mississippian strata was subjected to erosion.
A long period of erosion intervened between the deposition of the youngest Mississippian rocks and the oldest Pennsylvanian rocks. During this interval the limestone of Chesterian age, if deposited originally, may have been removed in Scott County. Alternate subsidence below and emergence above sea level were repeated many times during the Pennsylvanian, giving rise to both marine and continental deposits consisting of sandstone, shale, coal, and limestone. This sequence of deposition was interrupted at times when the land surface was elevated and subjected to erosion. The Pennsylvanian rocks are approximately 1,400 feet thick in Scott County. According to Ver Wiebe (1938, p. 138) the top of the Topeka limestone lies at a depth of 3,600 feet and the top of the Lansing group is approximately 350 feet lower. Below the Lansing-Kansas City-Bronson sequence of limestones are shales and limestones, which may correspond to the Marmaton group and Cherokee shale of eastern Kansas. In Scott County these shales are subordinate to coarse-grained limestones of gray to black color. The composition of the lower Pennsylvanian rocks is somewhat different also, notably in the presence of considerable chert. The basal conglomerate may be represented by red and green shales near the base of the system.
A transitional period intervened in which marine conditions during early Permian time were somewhat comparable to those existing during late Pennsylvanian time, and alternate successions of limestones, dolomites, and shales (Wolfcampian Series) were deposited. Following this there was an interval when beds of continental origin were deposited alternately with beds of marine origin. Gradually continental deposition became the dominant mode of origin for late Permian sediments. Most of the deposition took place in shallow water, so that subsidence must have kept pace with deposition during this interval. It is probable that an arid climate prevailed and evaporation must have taken place in shallow basin, giving rise to extensive deposits of salt and anhydrite interbedded with deposits of gypsum of the Leonardian Series. According to the logs of oil wells in the Shallow Water pool the top of the Permian is encountered at a depth of approximately 1,150 feet. Gypsum of the Blaine formation is encountered at a depth of about 1,430 feet, and anhydrite of the Stone Corral dolomite lies at a depth of about 2,100 feet. Beneath the red beds, the gray shales and anhydrites of the Wellington formation are encountered and these beds continue to a depth of about 2,800 feet where the first dolomite of the Wolfcampian Series appears.
At the close of the Paleozoic, deposition was terminated by an uplift that brought the region above water. This condition probably prevailed throughout most of Triassic time and through Jurassic time, during which there was no deposition and probably considerable erosion. Rocks of Triassic and Jurassic age are not known to occur in Scott County.
As the result of an early Cretaceous uplift there was at first a land surface followed by a shallow-water body in Comanchean time during which the sandstone and shale of the Cheyenne sandstone were deposited. The deposits were laid down either by streams or in a shallow sea or perhaps they were deposited in part on the beach by wind, suggesting that the place of deposition was not far above or far from a shore line (Twenhofel, 1924, pp. 19-21).
Following this there was a change from continental to marine conditions as a result of submergence of the land surface during which time the Kiowa shale was deposited. It is believed that Cheyenne sandstone and Kiowa shale underlie at least a part of Scott County, but in subsurface studies of oil-well samples no attempt has been made to segregate either of the formations from the underlying Dakota. None of the test holes drilled by the State and Federal Geological Surveys in Scott County were drilled deep enough to penetrate strata below the Niobrara formation.
In late Cretaceous time there was a return to conditions similar to those under which the Cheyenne sandstone was deposited and the sandstones, shales, and clays of the Dakota formation were laid down. The Dakota formation is a freshwater deposit that was laid down on beaches and near the shore during an uplift in which the sea retreated far to the south. The top of the Dakota formation is encountered at a depth of about 700 feet in Scott County. The combined thickness of the Dakota formation, the Cheyenne sandstone, and the Kiowa shale in Scott County is approximately 550 feet.
After the Dakota formation was laid down there was a rapid change in the conditions of sedimentation to those under which several thousand feet of shale, lime, and chalk were deposited, beginning with the Graneros shale and including the Greenhorn limestone, the Carlile shale, the Niobrara formation, and the Pierre shale. This marks the beginning of very extensive later Cretaceous submergence, in which marine conditions prevailed over a large area for a long time. Sedimentation was interrupted from time to time by emergence of the land to a point at or near sea level. According to the logs of oil wells in the Shallow Water pool, the base of the Niobrara formation is encountered at a depth of about 310 feet, and the top of the Greenhorn limestone is found at about 540 feet, indicating a thickness of about 230 feet for the Carlile shale.
Kansas Geological Survey, Scott County Geohydrology|
Comments to email@example.com
Web version March 2003. Original publication date July 1947.