Geologic History (1)Although the oldest formation exposed at the surface in Ford County is the Dakota formation, it is known from the records of several deep tests for oil and gas in the county that the exposed. mocks are underlain by older sedimentary rocks of Paleozoic age, which in turn rest upon crystalline rocks of pre-Cambrian age. (2)
(1) Parts of the following discussion are taken from: Darton, N.H., Geology and underground waters of the Arkansas valley in eastern Colorado: U.S. Geol. Survey, Prof. Paper 52, pp. 45, 48, 1906.
(2) Logs and information regarding the several deep test wells for oil and gas in Ford County were furnished by Raymond Keroher of the Kansas Geological Survey.
Paleozoic EraCambrian and Ordovician periods
During early Cambrian time Ford County was a land surface along with a large part of west-central United States. In middle Cambrian time there began the development of an interior sea with a resultant change to marine conditions. Submergence of the land continued with similar shore lines through part of Ordovician time with extensive deposition of lime sediments that were later indurated to form limestones and dolomites. During this interval was deposited the sandy cherty dolomite that forms the Arbuckle limestone or "Siliceous lime." Several of the deep tests in Ford County were drilled into this formation, the top being encountered at depths ranging from about 5,600 to 6,000 feet, although its exact thickness is not known.
Limestones and dolomites that have been correlated with the Viola and Simpson formations of Ordovician age are also known to be present, the top of the Viola being encountered at a depth of about 5,400 feet.
Silurian and Devonian periods
There is little or no evidence that rocks of Silurian and Devonian age are present under Ford County, either they were never deposited in this area or they were removed by erosion prior to the deposition of the overlying Mississippian strata.
Carboniferous periodDuring early Mississippian time there was extensive deposition of marine dolomitic limestone and some shale. According to the logs of several deep tests, Mississippian strata are present under Ford County between the depths of about 4,900 and 5,400 feet. In later Mississippian time there was an uplift, during which time the surface of the early Mississippian strata was subjected to erosion. Following this there was a return to marine conditions at which time the so-called Chester "lime" of late Mississippian age was deposited on the weathered surface of older Mississippian strata.
A long period of erosion intervened between the deposition of the youngest Mississippian rocks and the oldest Pennsylvanian rocks next above. 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. Based on the logs of the several deep tests in Ford County, the thickness of the underlying Pennsylvanian strata averages about 1,500 feet, the top being encountered at a depth of about 3,400 feet.
Permian periodThe transition from rocks that are regarded as Pennsylvanian to those that have been classed as Permian is apparently unbroken. Marine conditions during early Permian time were somewhat similar to those existing during late Pennsylvanian time, and alternate successions of limestones, dolomites, and shales 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 there must have been subsidence that kept pace with deposition during this interval. Presumably an arid climate prevailed and evaporation took place in shallow basins giving rise to extensive deposits of salt and anhydrite interbedded with deposits of gypsum correlated with the Guadalupe series. According to the logs of the several deep tests in Ford County approximately 3,000 feet of Permian sediments are known to underlie the area, including both lower and upper Permian rocks. Permian redbeds have been reported as shallow as 400 feet in one test.
Kansas Geological Survey, Ford Geohydrology|
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Web version April 2002. Original publication date Dec. 1942.