Summary of Stratigraphy
[Note: The geologic classification and nomenclature of this report follow the usage of the State Geological Survey of Kansas, which differs from that of the U. S. Geological Survey.]
The rocks that crop out in Harper County are of sedimentary origin and range in age from Paleozoic to Cenozoic (Pl. 1). The oldest rocks are a part of the Ninnescah Shale of the Leonardian Series, Permian System. Nearly all outcrops of the Ninnescah Shale in the county are in the eastern tier of townships. The Harper Siltstone, also of Permian age, crops out in a belt about one township wide that roughly coincides with R. 6 W. through the county. The Harper Siltstone is composed of two members, the Chikaskia Siltstone (lower) and the Kingman Siltstone (upper). The upper limit of this formation is not clearly marked, but the Kingman Siltstone member seems to be more resistant to weathering than the overlying Salt Plain Siltstone. The outcrop line of contact can be drawn only approximately between the Ninnescah and Harper, but roughly parallels the west line of R. 6 W. The youngest Permian rocks exposed in the county are rocks of the Salt Plain Siltstone, which crop out in approximately the western half of the county. Cenozoic deposits of the Pleistocene Series ranging in age from Nebraskan to Recent unconformably overlie the Permian rocks in much of Harper County. These deposits consist chiefly of silt, sand, and gravel, and are widely distributed in the valleys and over much of the upland area of the county. A generalized section of the geologic formations exposed in Harper County is given in Table 2. Configuration of the pre-Pleistocene surface is shown in Plate 4, and geologic cross sections based on the test-hole information are shown in Plate 2.
Table 2--Generalized section of stratigraphic units exposed in Harper County. Classification of the State Geological Survey of Kansas. The Pleistocene stratigraphic nomenclature is that of the State Geological Survey as adopted in January, 1959.
|Physical character||Water supply|
|Recent||Alluvium||30||Silt, sand, and gravel in major valleys.||Moderate supplies adequate for domestic and stock use may be obtained in some areas.|
|Dune sand||20||Medium and fine sand and some silt.||Generally above water table; yields little or no water to wells.|
|40||Clay, silt, sand, and gravel beneath terraces along principal streams.||Moderate supplies of water available for domestic and stock use.|
|10||Wind-deposited silt, locally clayey; in part composed of locally derived material.||Lies mostly above water table; yields no water to wells.|
|100||Silt, sand, and gravel; colluvium in part. Sand and gravel chiefly in deeper chanels; water-laid silt and colluvium in upper part.||Wells that penetrate channel deposits yield moderate to large supplies of water. Wells in areas where channels are absent yield little or no water.|
|20||Silt, sand, and gravel; some caliche in highest upland position.||Lies above water table and yields no water to wells.|
|25||Silt, sand, and gravel, and some volcanic ash. In upland position in northern part of area; in dissected terraces in southern part of area.||In northern part of area where there is sufficient thickness, water supplies adequate for industrial or irrigation use can be obtained. In southern part of area supplies adequate for domestic and stock use can be obtained.|
|20||Silt, clay, sand, and gravel underlying Kansan deposits in upland area.||Where sufficient thickness is penetrated, moderate to large quantities of water are obtained.|
|Tertiary (?)||Pliocene (?)||Undifferentiated
|25||Sand and gravel, minor amounts of silt and clay. Gravel derived chiefly from local material.||Lies above water table; yields no water to wells.|
|265||Chiefly red silty shale. Contains thin sandstone and siltstone beds throughout.||Yields small quantities of water from weathered zones. Quality of water variable. In some areas water is unsuitable for domestic use and inadequate for stock use.|
|80||Red silty shale, thin sandstone, and siltstone beds in upper part, reddish-brown siltstone and silty shale and some sandstone in lower part.||Yields small quantities of water of good to poor quality from weathered zone and from sandstone. In much of the area supplies are inadequate for domestic or stock use.|
|Runnymede||Siltstone||450||Varicolored calcareous, blocky clay shale, predominantly brownish red. Contains thin dolomitic and calcite-cemented zones of siltstone, limestone, and sandstone.||Yields small quantities of water of good to poor quality from weathered zone. In some areas supplies are inadequate for domestic or stock use.|
The rocks exposed at the surface in Harper County total only a few hundred feet in thickness. From these surface exposures the geologic history of the near-surface deposits may be interpreted, but the history of the deeply buried rocks must be studied through the use of drill-hole logs and samples obtained during exploration for oil and gas. The geologic history of the Paleozoic Era as it is discussed here is based chiefly on a report by Lee, Leatherock, and Botinelly (1948).
Harper County, like the rest of Kansas, is underlain by a basement complex of crystalline rocks older than Paleozoic. The area that is now Harper County was invaded by the sea in Cambrian time and remained submerged most of the time until the end of the Mississippian deposition. Unconformities in the deposits older than Mississippian indicate that the area was probably a landmass for short intervals during pre-Mississippian time. Near the end of the Mississippian, the area became a landmass and remained so for a considerable time during which a large part of the Mississippian deposits was removed. Late in Mississippian time the Nemaha Anticline was formed. This major structural feature, which extends across Kansas from Nemaha County into Oklahoma, is east of Harper County, but the effects of the deformation were important in this area. The Sedgwick Basin to the west of the Nemaha Anticline was formed, and minor anticlinal ridges paralleling the Nemaha Anticline were formed in the basin. The Mississippian deposits were eroded to base level and the detritus was deposited in the Sedgwick Basin. These deposits are one of the most important oil producing zones in the Sedgwick Basin. After this period of erosion early in Pennsylvanian time, the area was again submerged and remained so until the end of Permian time. Rocks representing all the systems of the Paleozoic Era are present in Harper County, but the thinning of some units indicates that structural movements took place repeatedly throughout the Paleozoic Era.
The area that includes Harper County has remained above sea level since the emergence at the end of the Permian. Many of the late Permian deposits have been removed. During the Mesozoic Era, deposition was negligible, hence Cenozoic deposits rest directly on the remaining Permian deposits.
During early Tertiary time, the landmass in Kansas continued to be eroded, and very little if any deposition took place.
During late Tertiary (Pliocene) time, western Kansas was covered by a thick mantle of alluvial deposits. Some alluvial material probably was deposited in Harper County but was removed by later erosion. It is possible that remnants of deposits in four small areas capping hills in southeast Harper County, which are unlike later Pleistocene deposits in western Kansas, may be Pliocene (Pl. 1). A thin veneer of gravel resembling these deposits was observed farther west and may be the same age, but some of this material seems to have been reworked and may be slope wash from a higher deposit that has been removed entirely.
Quaternary System--Pleistocene Series
Widespread deposition during late Pliocene time was followed by a period of stability marked by extremely arid conditions; only local erosion and deposition occurred during this and period. An abrupt climatic change marked the end of the and period and the beginning of Pleistocene time.
Beyond the glaciated areas in Kansas, Pleistocene deposits consist of fluvial and eolian deposits that were laid down in a cyclic pattern during alternating glacial and interglacial stages. Four main glacial stages and the intervening interglacial stages are represented in these cycles. The glacial stages--the Nebraskan, Kansan, Illinoisan, and Wisconsinan--represent the advance and early retreat of the continental glaciers; the interglacial stages--the Aftonian, Yarmouthian, and Sangamonian--represent periods of relative stability when the glaciers were remote or had disappeared completely. The Wisconsinan Stage was interrupted by a major retreat or recession of the glacier, therefore the Wisconsinan Stage has been divided into an early Wisconsinan substage, a Bradian interglacial substage, and a late Wisconsinan substage. Deposits of all the Pleistocene divisions are present in Harper County. Distribution of these deposits was controlled chiefly by the drainage patterns during the various stages.
Nebraskan and Aftonian Stages
The climatic change at the Pliocene-Pleistocene time boundary caused a rejuvenation of streams, and during the early Nebraskan Stage eastward-trending streams deepened their valleys, some to a considerable depth. Downcutting probably continued until the maximum advance of the glacier. After the glacial maximum and during the retreat of the glacier, the valleys or channels cut during the glacial advance were filled with coarse clastic deposits. This early valley-filling phase probably took place rapidly as the streams became overloaded and dropped their coarse load. As the glacier retreated farther, the load carried by the streams in Harper County decreased, and the materials carried were finer. These finer materials were deposited over the older coarse materials. During the late glacial and interglacial phases much eolian material probably was deposited, but eolian deposits of the Nebraskan and Aftonian Stages have not been recognized in Harper County. The Nebraskan deposits in Kansas are represented by the Holdrege and Fullerton Formations.
Nebraskan deposits occur along the northern border of Harper County, where they are overlain by younger deposits in much of the area. Beds in Kingman County that have been classified as Nebraskan or early Aftonian in age, on the basis of molluscan and vertebrate faunas, can be traced laterally into Harper County, where the deposits consist of sand and gravel in the basal part and mostly silt in the upper part. A caliche bed occurs in the top of the silt. Both the Holdrege and Fullerton Formations of the Lower Pleistocene presumably are represented in these deposits, and the caliche is believed to represent the remnants of the Afton soil. These deposits were not differentiated from the overlying Kansan deposits on Plate 1.
Kansan and Yarmouthian Stages
After the relatively stable conditions of the Aftonian Stage, climatic changes at the start of the Kansan Stage again caused rejuvenation of the streams in Harper County. In the upland area in northern Harper County where the Kansan deposits lie on Nebraskan deposits, there is little evidence of downcutting, but in southern Harper County considerable downcutting must have occurred; the Kansan deposits in this area form terraces along the present streams, are below older rocks bordering the valley, and lie directly on Permian rocks.
In Harper County the Kansan deposits are represented by the Grand Island and Sappa Formations. The lower unit, the Grand Island Formation, consists of sand and gravel and minor amounts of silt and clay; the Sappa Formation consists principally of silt and minor amounts of clay but locally may contain sand, some caliche, and volcanic ash. The caliche generally is near the top of the formation and probably represents the remnants of the Yarmouth soil. During deposition of the Sappa Formation or during Yarmouthian time, a volcanic ash (Pearlette Ash) bed was deposited in the area. Two deposits of the Pearlette Ash are present in Harper County. One deposit, in the NW SW sec. 18, T. 31 S., R. 7 W., is on the upland, and the other deposit, in the NW NE sec. 28, T. 33 S., R. 6 W., forms a terrace along Bluff Creek.
The Upper Pleistocene Subseries of the Pleistocene Series consists of the Illinoisan Stage, Sangamonian Interglacial Stage, early Wisconsinan glacial substage, Bradian interglacial substage, and late Wisconsinan glacial substage. Climate during these stages of the Pleistocene was more arid than that during the Nebraskan, Aftonian, Kansan, and Yarmouthian Stages of Lower Pleistocene. Therefore the character and mode of occurrence of the deposits also differ. In much of western and northern Kansas the Upper Pleistocene contains thick eolian deposits. In the Upper Pleistocene the coarser clastic materials are generally in terraces along the present streams, although there are some sheet deposits. Eolian deposits in the Lower Pleistocene are lacking, but they may have been deposited and later removed by erosion. The coarser clastic deposits of the Lower Pleistocene in many places are sheet deposits or lie in very broad, relatively shallow channels unlike those of the Upper Pleistocene.
Illinoisan and Sangamonian Stages
The best developed Illinoisan fluvial deposits (Crete Formation) are in central Kansas and along Smoky Hill River in central and western Kansas. In central Kansas many of these seem to be sheet deposits overlying older Pleistocene deposits along Smoky Hill River; in east-central Kansas the Illinoisan deposits are generally in terraces along the present streams. In northern and western Kansas thick eolian deposits (Loveland Formation) of Illinoisan and Sangamonian age occur. Thinner eolian deposits are widespread in south-central Kansas but are difficult to identify in many places, because they have been to some extent removed or reworked, and the distinctive Sangamon soil where present at the top of these deposits merges into the modern soil. During the early part of the Illinoisan Stage, there seems to have been a major shift or change in drainage over much of east-central Kansas, including the Harper County area. In north-central Kansas, Republican River is believed to have abandoned its ancestral "Belleville" channel and established its present drainage pattern. In McPherson and Harvey counties the "McPherson" channel was abandoned and the drainage system of Smoky Hill River was diverted from the Arkansas River drainage system to the Kansas River drainage system.
In northwestern Harper County, deposits of sand and gravel overlying known Kansan deposits are thought to be Illinoisan in age. These deposits are present on the highest points along a part of the northern county boundary, but they have not been differentiated on Plate 1. Conditions seem to indicate that, after a short period of sheet deposition, structural movement or capture of an important trunk stream to the east and south caused an adjustment of drainage in this area. Sheet deposition ceased and a period of downcutting produced channels as much as 250 feet below Kansan deposits in the uplands area in central Harper County. The channel near the center of section B-B' and the deepest channels in section E-E', Plate 2, are believed to have been cut and at least partly filled during Illinoisan time.
The upper deposits in these channels and in adjacent areas differ from the lower deposits. These upper deposits are principally silt, but include sand and gravel at the top. This upper part is fairly widespread and is believed to be principally a slope-wash or colluvial material. The channels are not apparent from the surface, and all these deposits have been included in slope deposits of Illinoisan to Recent age on Plate 1.
During early Wisconsinan time most of the present drainage system in the state was established. In Harper County the upper part of Bluff Creek established its present course, parts of the deep channel trending eastward through the city of Harper were abandoned, and new streams, which headed farther east than the Illinoisan streams, were established. During the Wisconsinan Stage extensive tracts of dunes were deposited. Most of the dunes are now stable, but a few are still active. Probably much loess was deposited in the upland areas of Harper County during the Wisconsinan Stage, but most was derived locally and was moved only relatively short distances, hence is not easily distinguished from the weathered silty shale that underlies it in much of the county.
Kansas Geological Survey, Geology
Placed on web Feb. 27, 2009; originally published March, 1960.
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