Summary of Stratigraphy
[Note: The stratigraphic classification used in this report is that of the State Geological Survey of Kansas and does not necessarily follow the nomenclature of the U. S. Geological Survey.]
The areal geology of Clay County is shown on Plate 1. The rocks cropping out in the county are of sedimentary origin. The oldest rock exposed at the surface is the Barneston Limestone of the Chase Group, Wolfcampian Series, Permian System. It is exposed in the valley wall of Republican River in the vicinity of Wakefield. Successively younger Permian rocks are exposed west of the outcrop of the Barneston Limestone. The Wellington Formation, the youngest Permian formation in Clay County, is exposed in a wide belt extending across the county from north to south.
The Kiowa Shale is known to overlie the Wellington Formation in southwestern Clay County, but it is so poorly exposed that it is mapped with the Dakota. The Dakota Formation, the youngest Cretaceous rock unit in the county, crops out over a large part of western and northern Clay County.
Much of the upland area is blanketed by eolian silt or loess of Pleistocene age. Extensive Pleistocene alluvial deposits occur in the valleys.
A generalized section of the outcropping rock units of Clay County is given in Table 1. More detailed descriptions of these units are given in the section on rock units and their water-bearing characteristics.
Table 1--Generalized section of outcropping geologic rock units in Clay County.
|Physical character||Water supply|
|0-35||Fine to medium quartz sand, and some silt.||Above the water table, and does not yield water to wells in Clay County.|
|Alluvium||0-70||Stream-deposited clay, silt, sand, and gravel. Generally graded, the coarser materials at the base.||Yields large quantities of water to wells in Clay County.|
|Wisconsinan||Sanborn||Peoria||0-20||Wisconsinan terrace deposits and the Crete formation consist of stream-deposited beds of silt, clay, sand, and gravel. Loveland and Peoria formations consist of massive eolian deposits||Wisconsinan terrace deposits yield large quantities of water in Republican River valley and smaller amounts along tributary streams. Silt units yield little or no water to wells. Crete formation yields small to moderate quantities of water to wells in Clay County.|
|Kansan||Meade||Sappa||0-5||Gray clay and silt.||Does not yield water to wells in Clay County.|
|0-10||Locally derived gravel.||Yields moderate amounts of water to wells in Clay County.|
|0-165||Varicolored silty and sandy shale and massive sandstone beds.||Yields moderate amounts of water to wells in Clay County.|
|0-50||Dark fissile shale containing a few thin streaks of sand and silt.||Does not yield water to wells in Clay County.|
|0-250||Chiefly gray shale; some red and green shale in lower part. Contains discontinuous beds of gypsum and impure limestone.||May yield small quantities of somewhat Mineralized water to wells in Clay County.|
|18-23||Sandy and dolomitic yellowish-gray limestone and gray and red shale.||Yields small to moderate quantities of water to wells in Clay County.|
|20-24||Chiefly gray shale, varicolored in the upper part.||Does not yield water to wells in Clay County.|
|21-25||Massive fossiliferous upper limestone, gray and yellow-gray shale, and lower cherty limestone.||Yields small to moderate quantities of water to wells in Clay County.|
|65-70||Gray and varicolored shale and impure limestone.||May yield small quantities of water to wells in Clay County.|
|Fort Riley Ls.
|75-85||Thick, massive limestone members separated by a thin shale member; lower limestone very cherty.||Yields moderate amounts of water to wells in Clay County.|
Pre-Cenozoic Geologic History
Although, exposed rocks in Clay County total only a few hundred feet in thickness, a great deal is known about the much thicker sequence of deeply buried rocks through the interpretation of deep tests for oil and gas. The geologic history during the Paleozoic Era, as it is discussed here, is based chiefly on reports by Jewett (1949) and by Lee, Leatherock, and Botinelly (1948).
Clay County, like the rest of Kansas, is underlain by a basement complex of Precambrian crystalline rocks. The area that is now Clay County was invaded by the sea during Cambrian time, and remained an area of marine deposition during most of the Paleozoic Era. Rocks representing each of the systems of the Paleozoic Era are present, but leveling by erosion of certain beds indicates that the area was not always stable and was elevated above sea level from time to time. Clay County is in the central part of the early Paleozoic North Kansas Basin and on the eastern flank of the late Paleozoic Salina Basin. Sedimentary rocks present under Clay County total about 3,000 feet in thickness.
The Paleozoic Era was brought to a close by uplifting of the entire area by the end of Permian time. The area was above sea level and subjected to erosion throughout all of Triassic and Jurassic time. Erosion continued through Early Cretaceous time until the deposition of the Kiowa Shale during a brief invasion by the sea. As the sea retreated from the area, the Dakota Formation was deposited in shallow fresh water. The sea again invaded the area and marine deposition was resumed.
At the end of the Cretaceous Period an area far to the west was uplifted, forming the Rocky Mountains. The Mississippi Valley area also was uplifted at about the same time, resulting in a northwest regional dip of Cretaceous and older rocks in eastern and central Kansas.
Cenozoic Geologic History
After the withdrawal of the Cretaceous sea and the tilting of Cretaceous and older rocks, there was a long period of erosion. The Cretaceous rocks overlying the Dakota Formation were eroded from the area that is now Clay County. Late in the Tertiary Period (Pliocene Epoch) the area to the west of Clay County was receiving deposits of sand and gravel from the eroding Rocky Mountains. These sand and gravel deposits, the Ogallala Formation, may not have reached as far east as Clay County, but they are found in several scattered areas a few miles west of Clay County.
Quaternary Period--Pleistocene Epoch
The major events of the Pleistocene Epoch in this area were the establishment of new drainage lines and downcutting by existing streams, aggradation of the major streams, and the deposition of loess. The relation of the Pleistocene deposits is shown in Plate 3.
At the beginning of the Pleistocene Epoch, Clay County probably was drained by a system of small streams, none of whose headwaters were very far from the county. Climatic changes associated with the advance of the glacial ice fronts during the Pleistocene Epoch resulted in increased streamflow and downcutting by streams. There was little or no deposition along streams in Clay County during the first glacial stage, the Nebraskan. The second glacial stage, the Kansan, continued much as the Nebraskan stage had been. In early Illinoian time, the ancestral Republican River became blocked by ice or choked by sediments. The ancestral Republican River followed approximately the course of the present Republican River from its headwaters to the city of Republic in Republic County. From this point the ancestral river flowed northeastward into Nebraska (Lohman, in Fishel, 1948). After the damming of the ancestral Republican River in early Illinoian time, the impounded waters spilled over the lowest part of a divide between Republic and Scandia in Republic County, and the present course of Republican River was established from Republic to Junction City. Republican River and several smaller streams in Clay County have alternated since late Kansan time between periods of deposition and periods of downcutting, so that the valleys now contain terrace and alluvial deposits of Kansan, Illinoian, Wisconsinan, and Recent age.
During Recent time, sand has been carried from the flood plain of Republican River by the prevailing westerly winds and has been deposited in several places as sand dunes on the alluvium and Wisconsinan terraces.
Kansas Geological Survey, Geology
Placed on web April 7, 2009; originally published June 1959.
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