Geologic Formations and their Water-bearing Properties
Pre-Permian RocksComparatively meager data are available concerning the strata beneath the Permian rocks in Finney and Gray counties. The nearest outcrops of these older rocks are in the central and eastern parts of the state, more than 200 miles east of the area under consideration. These older rocks dip westward beneath younger strata and, therefore, are known in western Kansas only from deep oil and gas tests.
Only five wells have been drilled deep enough to penetrate pre-Permian strata beneath Finney and Gray counties. The oldest rocks encountered by deep drilling are sandy cherty dolomites (Arbuckle limestone) of Cambro-Ordovician age. Moss (1932, p. 39) states that the Arbuckle limestone probably is more than 300 feet thick beneath most parts of Ness and Hodgeman counties, but in places may be thin or entirely missing. The Champlin Refining Company's oil test in the NE 1/4 SW 1/4 sec. 34, T. 28 S., R. 29 W., Gray County, penetrated 119 feet of Arbuckle limestone at a depth of 6,386 feet to 6,505 feet. Two deep oil tests in Finney County encountered the Arbuckle limestone; the National Refining Company's test in the SW 1/4 sec. 13, T. 23 S., R. 30 W., penetrated the Arbuckle at a depth of 5,608 feet to 5,872 feet, and a test drilled in sec. 24, T. 22 S., R. 29 W., penetrated it at a depth of 5,470 feet to 5,556 feet (Ver Wiebe, 1938, p. 56). None of these tests were drilled through the Arbuckle limestone, so the total thickness is not known.
Rocks belonging to the Ordovician system were encountered above the Arbuckle limestone in the three deep oil tests mentioned above. The upper part of the Ordovician in this area, where present, consists of cherty, dolomitic limestone (Viola limestone), and the lower part consists of sand and sandy shale (Simpson group). It is doubtful whether these Ordovician rocks are present everywhere beneath Finney and Gray counties, for pre-Mississippian erosion has probably removed part or all of them locally. The Viola limestone was encountered at a depth of about 6,190 feet in the oil test drilled in sec. 34, T. 28 S., R. 29 W., and the Simpson group was penetrated at a depth about 6,350 feet. In the oil test drilled in sec. 13, T. 23 S., R. 30 W., the Viola was encountered at a depth of 5,405 feet and the Simpson at 5,580 feet (Ver Wiebe, 1938, p. 56). In sec. 24, T. 22 S., R. 29 W., the Viola was topped at 5,315 feet and the Simpson at 5,460 feet (Ver Wiebe, 1938, p. 56).
Rocks of Mississippian age are found unconformably overlying the Viola limestone. No strata of Silurian or Devonian age have been recognized in deep drillings in this area. The Mississippian system is characterized by massive limestone, which is sandy and oolitic near the top and contains cherty zones lower down (Ver Wiebe, 1940, p. 37). In the Atlantic Refining Company's Eva Nunn well, in sec. 27, T. 21 S., R. 34 W., the top of the limestone was reached at 4,616 feet. The well was drilled to a total depth of 4,718 feet but did not reach the base of the limestone. An oil test drilled in sec. 13, T. 23 S., R. 30 W., encountered the limestone at a depth of 4,742 feet to 5,405 feet, and an oil test drilled in sec. 24, T. 22 S., R. 29 W., encountered it at a depth of 4,655 feet to 5,315 feet (Ver Wiebe, 1938, p. 56). The oil test in southern Gray County in sec. 34, T. 28 S., R. 29 W., encountered limestone of Mississippian age between depths of about 5,125 feet and 6,180 feet.
Overlying the limestone of Mississippian age in this area is more than 1,200 feet of strata belonging to the Pennsylvanian system. The Pennsylvanian rocks consist predominately of limestone with interbedded gray, black, and red shales. Ver Wiebe (1938, p. 54) states that the upper part (Wabaunsee group) of the Pennsylvanian in this area is very limy, but contains thin shale beds and thin sandy zones. The next lower group of rocks (Shawnee group) consists predominately of limestone, which is cherty in the lower part. The Shawnee group is about 300 feet thick in most places in Finney County. The Shawnee group is underlain by a series of shales belonging to the Douglas group. Below these shales is from 400 to 500 feet of limestone (Lansing-Kansas City-Bronson age), which contains a great deal of chert.
Red rock, sandy shales, and thin limestone beds are found beneath the thick limestones. Ver Wiebe (1938, p. 54) believes that this shaly zone probably represents the Marmaton group* of eastern Kansas, but part may be equivalent to the Cherokee shale of southeastern Kansas. A conglomerate has been found at the base of the Pennsylvanian system in some wells (Ver Wiebe, 1938, p. 54).
(* - As defined by he Kansas Geological Survey.)
Kansas Geological Survey, Finney and Gray County Geohydrology|
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Web version April 2002. Original publication date Dec. 1944.