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Geology
Summary of Stratigraphy
[Note: The terminology used in this report is that of the State Geological Survey of Kansas as of the publication date and differs in some respects from that of the United States Geological Survey and current use.]
The rocks that crop out in Pawnee and Edwards counties are sedimentary, ranging in age from Cretaceous to Recent (Pl. 1). The oldest rocks exposed in this area are Cretaceous, comprising the Dakota formation, Graneros shale, Greenhorn limestone, and Carlile shale. The terrace deposits that cover large areas adjacent to Pawnee River are believed to be Pleistocene in age but may be in part Tertiary. The alluvium in the principal valleys probably is Pleistocene and Recent. Most of the area south of Arkansas River is covered by a thin deposit of dune sand which is largely Recent but which may be in part Pleistocene.
Information on rocks that are not exposed in Pawnee and Edwards counties but which lie beneath the surface in that area has been obtained from test holes drilled during the course of the investigation and from logs supplied by drillers (Pl. 3).
A generalized section of the geological formations of this area is given in Table 2 and the geologic time scale is given in Table 3.
Table 2--Generalized section of the geologic formations of Pawnee and Edwards Counties, Kansas.
| System | Series | Subdivision | Thickness (feet) |
Physical character | Water supply |
|---|---|---|---|---|---|
| Quaternary | Recent and Pleistocene | Dune sand | 0-50 | Fine to medium grained quartz sand. | Lies above the water table and hence does not yield water to wells in this area, but serves as a catchment area for rainfall. |
| Uncomfortable on older formations | |||||
| Alluvium | 0-100 | Coarse sand and gravel containing silt and clay. | Yields large quantities of water to wells in Pawnee and Arkansas Valleys. Principal source of ground water for irrigation. | ||
| Uncomfortable on older formations | |||||
| Pleistocene | Terrace deposits | 0-150 | Principally silt and clay. May contain sand and gravel in the lower part in some places. | Yields small to moderate quantities of water to domestic and stock wells and to a few irrigation wells. | |
| Uncomfortable on older formations | |||||
| Meade formation | 90-300 | Sand, gravel, silt, and clay. | Yields moderate to large quantities of water to domestic stock, and irrigation wells south of the Arkansas River. | ||
| Uncomfortable on older formations | |||||
| Tertiary | Middle Pliocene | Ogallala formation | 0-70+ | Silt, sand, gravel, and caliche. | Yields no water to wells in this area. |
| Uncomfortable on older formations | |||||
| Cretaceous | Gulfian1 | Carlile shale | 0-100 | Chalky shale containing thin beds of chalky limestone. | Yields small quantities of water to wells in this area. |
| Greenhorn limestone | 0-120 | Chalky shale containing thin beds of crystalline limestone at base and granular to chalky limestone in upper part. | Yields small quantities of water to dug wells in northern Pawnee County. | ||
| Graneros shale | 20-35 | Dark-grey shale containing sandy shale and lenses of sandstone. | Yields little or no water to wells in this area. | ||
| Dakota formation | 0-225 | Varicolored sandy shale and clay containing beds of fine-grained lenticular sandstone. | Yields small to moderate quantities of water to domestic and stock wells. | ||
| Comanchean | Kiowa shale | 100-200 | Dark-gray to black shale containing lenses of sandstone. | Yields little or no water to wells in this area. | |
| Cheyenne sandstone | 25-50 | Gray, tan, and white fine to medium grained sandstone. | Does not yield water to wells in this area owing to its considerable depth, but is a potential source of ground water. | ||
| Uncomfortable on older formations | |||||
| Permian | Leonardian and Guadalupian1 | Undifferentiated redbeds | 1,000+ | Red sandstone and siltstone containing beds of gypsum,anhydrite, and dolomite. | Does not yield water to wells in this area owing to its considerable depth and to the relatively high mineral content of its water. |
| 1. Classification of the State Geological Survey of Kansas. | |||||
Table 3--The geologic time scale. Adapted from Moore (1933, p. 52).
| Major divisions of geologic time | Estimated duration in years | ||
|---|---|---|---|
| Eras | Periods | Epochs | |
| Cenozoic | Quaternary | Recent | 2,000,000 |
| Pleistocene | |||
| Tertiary | Pliocene | 58,000,000 | |
| Miocene | |||
| Oligocene | |||
| Eocene | |||
| Paleocene | |||
| Mesozoic | Cretaceous | 65,000,000 | |
| Jurassic | 32,000,000 | ||
| Triassic | 28,000,000 | ||
| Paleozoic | Permian | 38,000,000 | |
| Pennsylvanian1 | 48,000,000 | ||
| Mississippian1 | 38,000,000 | ||
| Devonian | 45,000,000 | ||
| Silurian | 27,000,000 | ||
| Ordovician | 67,000,000 | ||
| Cambrian | 105,000,000 | ||
| Proterozoic | Together constitute the Pre-Cambrian | 900,000,000 | |
| Archeozoic | 550,000,000 | ||
| 1. The Pennsylvanian and Mississippian periods together make up the Carboniferous System of the U. S. Geological Survey. | |||
Geologic History
Pawnee and Edwards counties ar underlain by thick deposits of sedimentary rocks consisting of shale, limestone, sandstone, clay, silt, sand, and gravel and smaller amounts of salt, anhydrite, and gypsum. The character, appearance, and relationships of these rocks as studied in well cuttings and at outcrops reveal much of the geologic history of the region.
Paleozoic Era
In the earliest part of the Paleozoic Era the area that now comprises Pawnee and Edwards counties was part of a land surface that extended over a large part of west-central United States. Submergence of the land began in Middle Cambrian time and the area remained inundated through the remainder of Cambrian and part of Ordovician time, during which the Arbuckle limestone or "Siliceous lime" was deposited. Limestone and dolomite comprising the Viola limestone and Simpson rocks were deposited in this area in Ordovician time.
Rocks of Silurian and Devonian age probably do not underlie Pawnee and Edwards counties. They either were not deposited in this area or were removed by erosion prior to the deposition of the overlying Mississippian strata. Deposits of marine dolomitic limestone and shale were laid down in this area during the early part of the Mississippian Period. The sea withdrew during part of Mississippian time and again covered the area in the last part of the period.
There was a long time of erosion between deposition of the youngest Mississippian rocks and the oldest Pennsylvanian rocks that overlie them. After this erosion there was alternate submergence by and emergence from the sea, causing the deposition of both marine and continental materials consisting of sandstone, shale, limestone, and coal. The alternating marine and continental deposition continued through Early Permian time but by Late Permian time continental deposition became dominant. These deposits consisted of redbeds containing gypsum, anhydrite, and salt, which indicate an arid climate.
Mesozoic Era
Cretaceous Period
The Cheyenne sandstone was deposited over all the Pawnee-Edwards area in Early Cretaceous time. These beds were laid down either in shallow sea water or by streams (Twenhofel, 1924, p. 19). The area was then covered by a sea in which the dark fossiliferous clay that formed the Kiowa shale was deposited. The sandstone and clay of the Dakota formation were laid down in Late Cretaceous time under both fluviatile and near-shore marine conditions. Marine deposits of limestone and shale which were laid down in this area after the deposition of the Dakota formation comprise the Graneros shale, Greenhorn limestone, and Carlile shale. Younger Cretaceous deposits probably covered at least part of this area but they have been removed by erosion.
Cenozoic Era
Tertiary Period
The Laramide revolution, which began in Late Cretaceous time and which continued into Tertiary time, probably caused the regional dip of the older beds in this area. After this major deformation (which uplifted the Rocky Mountains) the Ogallala formation of middle Pliocene age (Table 3) was deposited by streams that carried debris from the Rocky Mountains. These deposits mantled the bedrock in large areas in western Kansas. Much of these deposits has been removed by subsequent erosion but the formation still underlies small areas, mainly in northwestern Edwards County (Pl. 1).
Quaternary Period
Pleistocene Epoch--The thick deposits of silt, sand, and gravel that overlie the Cretaceous bedrock south of Arkansas River (Pl. 3) were laid down during the Pleistocene Epoch and represent stream-laid debris from the Rocky Mountains. Part of the material south of Arkansas River may be terrace deposits, which were also laid down during the Pleistocene Epoch.
The ancestral Pawnee River and its tributaries deposited fine-grained materials over a large area in Pawnee County and in northwestern Edwards County. These deposits consist primarily of silt and clay but contain lesser amounts of sand and gravel. They are shown on the map (Pl. 1) as terrace deposits and represent at least two stages of deposition by Pawnee River and its tributaries.
During late Pleistocene and Recent time Arkansas and Pawnee Rivers and their tributaries deposited alluvium in their valleys. Only the alluvium of the principal streams is shown on the map (Pl. 1). Part of the dune sand also may have been deposited in late Pleistocene time, but it is believed that most of the dune sand in the Pawnee-Edwards area is Recent in age.
Recent Epoch--During Recent time most of the dune sand south of Arkansas River was deposited, as is indicated by the presence of dune sand overlying alluvium. The present topography of Pawnee and Edwards counties was formed in part during the Recent Epoch. The principal valleys were eroded during the Pleistocene but most of the existing surface features are the result of Recent erosion.
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Kansas Geological Survey, Pawnee and Edwards Geology and Groundwater
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Web version June 2004. Original publication date March 1949.
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