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Geology

  Seward County Geohydrology

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Table of Contents

Abstract

Introduction

Geography

Geology

Ground Water

Geologic Formations

Well Records

Logs of Test Holes

References

Plates

 

Geology

Summary of Stratigraphy

The geologic formations that have been recognized in Seward County either through surface outcrops or through the identification of the cuttings from test holes drilled by the Federal and State Geological Surveys are indicated in Table 7. The presumed relationships of the several stratigraphic units involved are indicated diagrammatically in Plate 3. The oldest geologic formations penetrated by the test holes were the redbeds of the Permian system. These do not crop out within the county, but are at the surface in Meade County. Several producing gas wells and oil- and gas-test wells (logs 12, 17, and 18) have been drilled to depths ranging from about 0.5 mile to almost 1 mile below the surface. The shallower of these either found production or drilling was stopped in formations near the base of the Permian system. The log of the deepest test well drilled to date is not now available so that no valid conclusions can be drawn as to what still older geologic systems are present below the Permian.

Table 7--Generalized section of the geologic formations in Seward County, Kansas.

System Series Formation Thickness (feet) Physical Character Water-supply
Quaternary Recent Colluvium 0-30 Sand, gravel, silt, and clay Does not yield water to wells in this area
Unconformable on older formation
Alluvium 0-75 (?) Coarse sand and gravel; contains silt and clay Yields adequate supplies of relatively hard water to domestic and stock wells
Unconformable on older formation
Dune sand 0-60 +/- Medium-grained sand containing fine grained sand and silt Does not yield water to wells in this area, but assists in recharge of underlying formations
  Unconformable on older formation
Recent and Pleistocene Terrace deposits 0-20 (?) Coarse sand and gravel Does not yield water to wells in this area
Unconformable on older formation
Kingsdown silt 0-40 +/- Silt and fine sand containing nodules of caliche
  Disconformity
Pleistocene Meade formation 75-100 (?) Sand and gravel at base; sand, silt, clay, and caliche in upper part. Locally contains volcanic ash. Yields moderately hard water to a few wells in the western part of Seward County
  Unconformable on older formation
Tertiary Pliocene Rexroad (?) formation* 15-150 (?) Sand and gravel at base; sand, silt, clay, and caliche in upper part. Cemented with calcium carbonate Yields abundant supplies of moderately hard water to dome wells
Unconformable on older formation
Laverne formation 300-500 (?) Sand, gravel, slit, and clay in lower part; micaceous sand, calcareous sandstone, silt, clay, caliche, and Limestone in upper part Yields water to very few wells in the southeastern part of this area. An important potential source of ground water
  Unconformable on older formation
Cretaceous Gulfian** Dakota formation 0-100 Brown, yellowish-brown, reddish-brown, buff and tan fine grained sandstone, and varicolored clay Locally is a potential source of ground water, but is practically unexploited in this area owing to its considerable depth
  Disconformity
Permian Guadalupian** and Leonardian Undifferentiated redbeds 1,500 +/- Brick-red sandstone and silt-stone containing salt, gypsum, anhydrite, and dolomite Locally is a potential source of ground water, but is practically unexploited in this area owing to its considerable depth and its generally high mineral content
* The fauna of the Rexroad (?) formation is believed to be the equivalent of the Blanco fauna of Texas. The Kansas and Nebraska Geological Surveys have adopted the term Blancan to include the deposits in the Central High Plains that contain the Blanco fauna and faunas of the equivalent age. At present there is not general agreement among paleontologists as to whether the Blancan is late Pliocene or early Pleistocene. We correlate the Seward County Rexroad (?) beds with the type Rexroad deposits in Meade County.

** The classification of Permian series is not adopted by the U.S. Geological Survey as applied to Kansas.

The Cretaceous formations which overlie the Permian redbeds do not crop out in Seward County, but have been found in surface exposures not far to the west in Morton County (McLaughlin, 1942), to the northwest in Stanton County (Latta, 1941) and to the south in Texas County, Oklahoma (Schoff, 1939). The nearest Cretaceous outcrops to the east are found in Clark County.

The oldest surface rocks in the county belong to the Laverne formation. Outcrops of the Laverne are restricted to the lower valley slopes along the southeasternmost part of Cimarron Valley in Seward County, but occur also in the adjacent part of Meade County and in Oklahoma. The Laverne formation is separated from the overlying Rexroad (?) formation by a prominent unconformity. Evidence to be presented later indicates that the geologic age of the Laverne is early Pliocene, but the exact age of the Rexroad (?) is still in doubt. The sediments here included in the Rexroad (?) formation crop out principally along the wall of the lower Cimarron Valley, but outcrops of beds as far west as Morton County are believed by us to belong to this formation. Both the Laverne and Rexroad (?) probably underlie all of Seward County.

It was not found practicable to separate the Meade formation from the somewhat younger Kingsdown silt; hence they were mapped as a single undifferentiated unit. The gravel and sand of the Meade crop out extensively along Cimarron Valley. The sand and silt of the Kingsdown directly underlie much of the upland surface north of Cimarron River except where they are concealed beneath relatively thin deposits of dune sand. Paleontologic evidence from this county and from Meade County confirms the Pleistocene age of the Meade formation and the Pleistocene and Recent age of the Kingsdown silt.

The youngest geologic formations in the county--alluvium, colluvium, and dune sand--are primarily Recent in age although part of the dune sand may be older. The alluvium is restricted to the valley bottoms, and the dune sand covers limited areas in Cimarron Valley and large parts of the upland surface.

The areal distribution of the exposed formations is shown in Plate 1, and all of the formations are described in greater detail in the section on geologic formations and their water-bearing properties.

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  Kansas Geological Survey, Seward County Geohydrology
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Web version Sept. 2001. Original publication date March. 1948.
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