Summary of Stratigraphy(This report is a cooperative product of the U.S. Geological Survey and the State Geological Survey of Kansas. The classification and nomenclature of the rock units accord for the most part with those of the two surveys but differ somewhat from those of the U.S. Geological Survey.)
The rocks that crop out in Reno County are of sedimentary origin and range in age from Paleozoic to Cenozoic (P1. 1). The oldest rocks that crop out in the county are a part of the Ninnescah shale of the Leonardian Series, Permian System. The Ninnescah shale crops out in the northeastern and southeastern parts of the county and along the valley of the Ninnescah River in the southern part of the county where the river has cut through younger deposits. The Stone Corral dolomite crops out in northern Reno County and along the Ninnescah River valley in south-central Reno County. The youngest rocks of Permian age exposed in the county are rocks classified as the Harper sandstone, which crop out along the valley of Ninnescah River west of the outcrop of the Stone Corral dolomite. Cenozoic deposits of the Pleistocene Series ranging in age from the Blanco formation of the Nebraskan glacial stage to Recent alluvium unconformably overlie the Permian rocks over most of Reno County. These include unconsolidated deposits of sand and gravel in both the valleys and most of the upland area, and eolian silt occurring principally in the upland area. Information on the unexposed rocks that lie beneath the surface in Reno County has been obtained from test holes and from logs of oil wells drilled in the county.
A generalized section of the rocks cropping out in Reno County is given in Table 2. The configuration of the pre-Pleistocene surface and the locations of the test holes in the county are shown in Figure 7, and the geologic cross sections based on these test holes are shown in Plate 3.
Geologic HistoryPaleozoic Era
Over the basement igneous and metamorphic rocks were deposited marine rocks of Paleozoic (Cambrian and Ordovician) age. Silurian and Devonian rocks were probably deposited over the area and later removed by erosion after the pre-Mississippian uplift of the Ellis arch, known also as the Central Kansas arch. This ancestral arch extended from Chautauqua County northwestward through Ellis County. Rocks of Mississippian age were deposited over the arch and lie unconformably on the Cambro-Ordovician rocks. Post-Mississippian folding raised these rocks in Reno County, and parts of the upper Mississippian strata were eroded. Subsequent to this erosional period the area was submerged again and Pennsylvanian and Permian rocks totaling about 3,500 feet in thickness were deposited. After the deposition of the Permian rocks there was another long period of erosion.
The Mesozoic Era in Kansas is represented by rocks of the Triassic, Jurassic, and Cretaceous systems. Reno County was probably a part of the land area during Triassic and Jurassic time; deposition in the county was renewed during Cretaceous time. No Cretaceous rocks crop out or were penetrated in the test drilling, but these rocks are present only a few miles west in Stafford County and to the north in Rice County. A considerable thickness of Cretaceous rocks probably was deposited in Reno County and later removed by erosion during early Tertiary time.
Reno County was probably subjected to erosion during most of Tertiary time. No Tertiary deposits were found in the county during this investigation, but Ogallala rocks have been identified in Rice County. Thin deposits of the Ogallala formation probably were laid down in Reno County and later removed by erosion. In late Tertiary time Reno County was an area of low relief, but renewed erosion in early Pleistocene time dissected the land surface and cut deep valleys into the Permian beds. These valleys were later filled with alluvial deposits. Four major periods of erosion and deposition in the Pleistocene are evident in the county. Climatic changes during the four major glacial epochs effected the four major periods of erosion and deposition in Reno County.
History of DrainageAt the close of the Tertiary the surface of Reno County was an area of low relief. During the Nebraskan stage of Pleistocene time, streams traversing the county increased their rate of cutting and deepened their channels. The maximum relief in the county at the close of this cutting was about 160 feet.
Three main early Nebraskan valleys enter Reno County. One channel enters southwestern Reno County near the center of the west line of Township 26 South and extends eastward along this tier of townships nearly two-thirds the distance across the county. A second channel enters the county near the northwest corner and extends eastward about halfway across the county, where it is joined by the third--the Chase channel (Fent, 1950). From this junction the main channel trends southeastward and leaves the county near the center of the east county line.
After the period of valley cutting in Nebraskan time, a period of valley filling took place. The deposits, the Blanco formation of the Nebraskan stage, range in thickness from a few feet along the flanks of the valleys to more than 100 feet in the channel entering the county at the northwestern corner. Figure 8 shows the areas in Reno County in which the Blanco formation of the Nebraskan stage crops out or is buried in the subsurface.
Late Wisconsinan downcutting by the streams removed the Crete sand and gravel member of the Illinoian stage and the Meade formation from the valleys; subsequent filling produced younger Wisconsinan terrace deposits. In the Ninnescah River valley the stream cut into Permian rocks as much as 100 feet below the base of the Meade formation. Since the deposition of the Late Wisconsinan terrace deposits the streams have remained in the same channels, and stream activity has consisted of minor downcutting and filling. Prominent low terraces in the valleys of the major streams are remnants of the Wisconsinan surface. The present Arkansas River has a braided channel. The channel becomes choked with sand and gravel during times of flood, and in low-water stages the stream flows through, rather than over, the pervious material making up much of the stream bed. The Ninnescah River, in a part of its course, and its tributaries are eroding their channels fairly rapidly, as indicated by the relatively rugged topography bordering these streams. Figure 11 shows the areas in Reno County in which Wisconsinan and Recent alluvial deposits are found.
Kansas Geological Survey, Reno County Geohydrology|
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Web version Feb. 2001. Original publication date Aug. 1956.