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General Geology
Summary of Stratigraphy
The rocks that crop out in Morton County are all of sedimentary origin and their areal extent is shown on plate 1. The rocks that supply water to wells in this area range in age from Permian to Recent. The principal water-bearing beds are the unconsolidated silts, sands, and gravels of Tertiary and Quaternary age (including the Ogallala formation) that overlie the Mesozoic and Paleozoic rocks. For simplicity of treatment the Pliocene and undifferentiated Pleistocene deposits are referred to in this report under the name Ogallala formation.
The character and ground-water supply of the geologic formations in Morton County are described briefly in the following generalized section (table 3) and in more detail under "Water-bearing formations."
Table 3--Generalized section of the geologic formations in Morton county. [Classification of the State Geological Survey of Kansas]
| System | Series | Subdivision | Thickness, (feet) | Physical character | Water supply |
|---|---|---|---|---|---|
| Quaternary | Pleistocene and Recent | Alluvium. | 0-75 (?) | Sand and gravel containing some silt and clay. | Yields adequate supplies of hard water to stock wells in the Cimarron river valley. |
| unconformable on older formations. | |||||
| Dune sand. | 0-75 (?) | Medium-grained, well-rounded quartz sand. | Does not yield water to wells in Morton county, but serves as catchment area for rainfall. | ||
| unconformable on older formations. | |||||
| Loess. | 0-15 | Silt and some sand and clay. | Does not yield water to wells in Morton county. | ||
| unconformable on older formations. | |||||
| Tertiary and Quaternary | Pliocene and Pleistocene | Pliocene (including the Ogallala formation) and Pleistocene undifferentiated. | 30-600 | Predominantly silt, but also sand, gravel, caliche, and some clay. | Principal water-bearing formation in Morton county. Yields adequate supplies of moderately hard water to domestic, stock, municipal, and irrigation wells. |
| unconformable on older formations. | |||||
| Cretaceous | Dakota group* | Cockrum sandstone. | 40-160 | Fine-grained, buff sandstone and buff to brown clay. | Yields adequate supplies of moderately hard water to domestic, stock, and irrigation wells in the northwestern part of the county. |
| Kiowa shale. | 30-85 | Dark-gray and blue-gray shales and beds of sandstone. | Yields little or no water to wells in Morton county. | ||
| unconformable on older formations. | |||||
| Cheyenne sandstone. | 0-125 | Medium-to coarse-grained gray and white sandstone. | Yields adequate supplies of moderately hard water to wells in the northwestern part of the county. | ||
| Jurassic (?) | Morrison (?) formation. | 0-50 | Bluish-green marl containing thin beds of gray and buff sandstone. | Yields little or no water to wells in Morton county. | |
| unconformable on older formations. | |||||
| Triassic (?) | Undifferentiated redbeds. | ±300 | Buff and red fine-grained sandstones and red siltstones. | The upper beds yield adequate supplies of moderately hard water to wells near Point Rock. The lower beds yield moderate quantities of very hard water to artesian wells near Point Rock. | |
| unconformable on older formations. | |||||
| Permian | Leonard and Guadalupe* | Undifferentiated redbeds. | ±1100 | Red sandstones and siltstones and some beds of gypsum, anhydrite, and dolomite. | Yields large quantities of strongly mineralized water to flowing wells in the vicinity of Richfield. |
Geologic History
The geologic history of Morton County is similar to that of much of the High Plains section. Morton County is underlain by thick deposits of limestone, sandstone, shale, clay, sand, and gravel and lesser amounts of salt and gypsum. The character, appearance, and relationships of these rocks as studied in well cuttings and at outcrops reveal considerable of the geologic history of the region.
Paleozoic Era
Very little is known of the early Paleozoic sediments in this county for they do not crop out and have not been reached by deep test drilling. According to Darton (1920, p. 7) the seas covered a large part of western Kansas during most of the Paleozoic era except possibly during the Silurian and Devonian periods. Marine deposits of Cambrian and Ordovician age crop out along the Front Range in Colorado and have been penetrated by test wells in central and eastern Kansas. It is probable that these sediments also underlie southwestern Kansas.
The seeming absence of any deposits of Silurian or Devonian age in this area suggests a widespread land area at that time. If any sediments were laid down at that time they were removed by later erosion, probably during early Mississippian time.
In 1925 a well was drilled in southern Hamilton county to a depth of 5,486 feet. It encountered thick deposits of marine limestone and shale of Mississippian, Pennsylvanian, and early Permian age as well as deposits of salt, gypsum, and redbeds of late Permian age. The marine character of the limestone and shale indicates widespread invasions by the sea. These invasions probably were interrupted by many short periods of emergence.
In Late Permian time there was general emergence that produced shallow basins and broad mud flats in which the redbeds were deposited. The red color of these beds together with the presence of thick deposits of gypsum and salt indicate an arid climate in Late Permian time.
Mesozoic Era
Triassic (?) Period
The conditions during the Triassic (?) period were probably not much changed from those in Late Permian time, for the Triassic (?) deposits are very similar in character to the Upper Permian deposits. They consist of redbeds, buff to white sandstones, and a very small amount of gypsum.
Not all of the Triassic system is represented in Morton County. The absence of part of these rocks indicates either that they were never deposited or that they were deposited and subsequently removed by erosion.
Jurassic Period
Rocks of Jurassic age (Morrison formation) crop out at Two Buttes in southern Prowers county, Colorado, about 50 miles northwest of Richfield. Test hole 4, in the southeastern earner of see. 36, T. 31 S., R. 42W) penetrated 40 feet of blue-green marl and buff sandstone that probably is equivalent to the Morrison formation. Other test holes drilled in the county by the State and Federal Geological Surveys failed to encounter these beds. Fossil remains of dinosaurs and other land animals have been collected from the Morrison beds in other areas. During the Jurassic period Morton County was part of a large land mass upon which the fluviatile Morrison beds were laid down. Subsequent erosion removed much of these beds.
Cretaceous Period
The sandstones of the Cheyenne formation were deposited in this area in Early Cretaceous time. According to Twenhofel (1924, p. 19) they were deposited in shallow seas or by streams. Then followed an invasion of the sea and the deposition of the dark, very fossiliferous Kiowa shale. At the beginning of Late Cretaceous time sandstones and clays were laid down probably under both fluviatile and near-shore marine conditions. These beds were formerly known as the Dakota sandstone, but for reasons given later, are called the Cockrum sandstone in this report. In certain areas the sandstone contains salt water and marine fossils and is well stratified, but fossil plants found in the Cockrum sandstone in other areas suggest a fresh-water origin. Moore (1933, p. 443) suggests that the Cockrum sandstone is a stream-laid and sea-worked deposit. Marine sediments of Late Cretaceous age probably were deposited in all or part of Morton County and removed by erosion during late Cretaceous and early Tertiary time.
Cenozoic Era
Tertiary Period
The Cretaceous period was followed by great uplifts that produced the Rocky Mountains and uplifted the High Plains section. This orogeny was followed by a long period of erosion that lasted until Late Tertiary (Pliocene) time. During Late Tertiary and Early Quaternary (Pleistocene) time sediments from the Rock Mountains were carried eastward by streams and deposited as the Ogallala formation and younger undifferentiated Pleistocene beds on the eroded surface of Permian and Mesozoic rocks. The nature of the vertebrate fossils found in these beds in southwestern Kansas suggests that the climate was cooler and more moist than at the present time.
Quaternary Period
Conditions similar to those of Pliocene time existed in Morton County during the early part of the Quaternary period. Great dust storms during the Quaternary period deposited a blanket of loess over much of the county north of Cimarron River, and dune sand was laid down in the area south of the river. Erosion during the Quaternary period stripped the area of some of its cover of Tertiary sediments, exposing, in places, part of the underlying Mesozoic rocks. The Cimarron valley and other topographic features of the area were developed in Quaternary time, and alluvium was deposited by Cimarron River and some of its tributaries.
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Kansas Geological Survey, Morton County Geohydrology
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Web version Sept. 2004. Original publication date March 1942.
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