The Significance of Stratigraphy and Lithology in Landform Development in Washington County, Oklahoma
THERE ARE A LOT OF ROCKY, TREE-COVERED HILLS AND FLAT GRASSY PLAINS IN THE COUNTY WHERE I LIVE. Washington County has interesting landforms. These landforms did not happen by accident; there was a reason. Two of the main factors controlling the shape of the land in my county are stratigraphy and lithology.
Stratigraphy is the description of rock layering. Usually, the oldest rocks are found at the bottom of a rock section, and the youngest are found at the top. In some cases the sequence can be flipped over and the rock layering is reversed, with the youngest rocks at the bottom and the oldest rocks at the top. This reversal can happen when continental plates shift and earthquakes occur or when mountains are formed. But in this area those situations occur very rarely, if at all, so the rocks are found in a normal sequence.
Because the rocks are dipping slightly to the west, the oldest rock outcroppings in Washington County are found in the eastern part of the county, and the youngest rocks are found in the west. Oakes's Geology and Mineral Resources of Washington County, Oklahoma provides a very complete description of the rocks in Washington County and is still the best reference available.
The rocks in my county are very old. They are from the Upper Pennsylvanian Series and are more than 250 million years old. In the Skiatook Group, which is the oldest rock sequence outcropping in this area, there are six different formations (Oakes 1940, pp. 22, 23). The deepest formation is the Seminole Formation. This formation generally contains sandstone and shale and is 10 to 20 feet thick. This formation is found only at the surface in the far southeastern corner of Washington County.
The next formation above the Seminole Formation is the Checkerboard Limestone Formation. This formation is only about 2 feet thick and is made up of limestone and calcareous shale.
The formation just above Checkerboard Limestone Formation is the Coffeyville Formation. This formation generally contains sandstone and shale. The Coffeyville Formation can be found in a wide band along the southeastern part of Washington County and extending northeast into Nowata County. The Coffeyville Formation is about 200 feet thick.
The formation overlying the Coffeyville Formation is the Hogshooter Formation. This formation generally consists of limestone and, occasionally, shale.
The next formation above the Hogshooter Formation is the Nellie Bly Formation. The Nellie Bly Formation is named after Nellie Bly Creek in Washington County (Oakes 1940, p. 47). The Nellie Bly Formation ranges from 80 feet to 180 feet in thickness. This formation most regularly consists of sandstone and shale.
The shallowest formation in the Skiatook Group is the Dewey Limestone Formation. The Dewey Limestone is about 6 feet thick. This formation generally consists of fossiliferous limestone.
In the overlying Ochelata group, five different formations outcrop in the Bartlesville area. The deepest formation is the Chanute Formation. This formation consists mostly of shale, sandstone, limestone conglomerate, and coal (Oakes 1940, p. 57). The Chanute is estimated to be 150 feet thick. It outcrops along the western side and in the northern part of the county.
The Inola Formation overlies the Chanute Formation. The main types of rocks found in this formation are limestone and shale. The Inola Formation is thin, only 1/2 to 2 feet thick, and it is found at the surface only in the southwest and northeast parts of the county.
Above the Inola Formation is the Wann Formation, which is composed of limestone, shale, and sandstone. The Wann is about 95 feet thick and outcrops, like the underlying Inola, in the north and southeast parts of the county.
The Torpedo Sandstone layer and Birch Creek Limestone layer overlay the Wann Formation. The Torpedo generally consists of sandstone and shale, and the Birch Creek is limey sandstone to shaley limestone. The Torpedo Sandstone and Birch Creek Limestone are found mainly in the northwest part of Washington County, near the Kansas border, but also exist in a narrow band along the western boundary of the county.
Washington County's rocks are really a lot more interesting than they might sound. The sand making up the sandstone beds was probably carried to the ocean through a series of rivers and streams that deposited sand and shale into the ocean.
Many of the rocks have fossils of animals and plants that lived millions of years ago when the area was covered by a shallow ocean (Wilson 1975). The ocean was apparently very warm, since coral fossils are found here. It was also shallow, because there are fossilized pieces of algae. The fossils were formed during relatively calm and quiet periods when there was little sand being dumped into the ocean. The coral and algae had time to grow on the soft ocean bottom and remain undisturbed for a while. It is hard to believe that a community of organisms like those that grow in tropical seas today once inhabited this area.
Lithology is the collection of physical and chemical properties that make a rock unique. Some of these properties are composition, hardness, color, density, and bedding. The chemical and physical properties of a rock are related. For example, limestones are chemically reactive and are more easily dissolved than sandstones. Since limestone is more soluble, it is more easily broken down into small particles, which can be washed away.
Lithology plays a very important role in the shaping of the land. This is because harder rocks are more resistant to erosion and protect softer rocks below from weathering and erosion.
Several samples of different formations were collected from outcrops in and around Bartlesville, Oklahoma, for study. Sample Number 1 is a sample of the Coffeyville Formation collected on the banks of Hogshooter Creek in eastern Washington County in the SEA, NW/4, NW/4 of Section 21, Township 26 North, Range 14 East. The sandstone is light brown, moderately hard, and fine to very fine grained. The sand grains are subangular.
The next formation is the Hogshooter Formation. There are two samples that were collected from this formation. Sample Number 2 was taken from an outcrop in the far eastern part of Washington County in E/2, NE/4 of Section 17, Township 26 North, Range 14 East. This sample can be classified as a phylloid algal wackestone, according to the Dunham carbonate rock classification (Wilson 1975, p. 12). This sample of Hogshooter limestone is called a wackestone because it contains more than 10 percent grains (the algal platelets) supported in a lime mud matrix. The sample is brownish gray and hard.
The second sample of Hogshooter limestone was taken from the same place. It is also a phylloid algal wackestone, but it is grayish brown. It is also hard and argillaceous. However, the algal platelets are not as apparent in this sample.
The next formation is the Nellie Bly Formation. This formation is mostly shale. A sample of Nellie Bly shale was taken from an outcrop in W/2, SW/4 Section 9, Township 26 North, Range 13 East, in the eastern part of Bartlesville. It is light gray, soft, and thinly laminated. It is also micaceous and carbonaceous. Micaceous means that it contains tiny mica crystals within the composition. Sometimes the shale contains silt, which makes it harder. Carbonaceous means that it contains carbon particles or thin layers of coal.
The Nellie Bly Formation also contains sandstone in the upper and lower part. A sample of the lower sandstone was taken from S/2, SEA, Section 8, Township 26 North, Range 14 East, in the far eastern part of Washington County. The Lower Nellie Bly is a tan and moderately hard sandstone. The grain is also subangular and very fine. The sandstone is also poorly sorted, thin bedded, and micaceous. The sandstone contains argillaceous cement, which means that it is held together partly by clay.
The Upper Nellie Bly Sandstone is light brown and hard. A sample of this sandstone was collected from an outcrop in W/2, SW/4 Section 9, Township 26 North, Range 13 East, in the eastern part of Bartlesville. The sand grains are subangular and fine to very fine. The sandstone is poorly sorted, thin
bedded, and micaceous; it also contains argillaceous cement.
The Dewey Limestone Formation overlies the Nellie Bly Formation. Two samples of this formation were collected. The first sample is of a brachiopod shell wackestone. It was collected from an outcrop in W/2, NE/4, SE/4 Section 10, Township 26 North, Range 13 East, on Bison Road, just east of Bartlesville. It is grayish brown, hard, and argillaceous.
The second sample of Dewey Limestone was found in an outcrop behind the Bartlesville Mid-High School in S/2, SEA, NW/4, Section 10, Township 26 North, Range 13 East. It is a phylloid algal wackestone. The sample is brownish gray, hard, and also argillaceous.
The Thayer coal is found within the Chanute Formation, above the Dewey Limestone. A sample of the coal was found at the side of the road in the W/2 of Section 12, Township 25 North, Range 12 East. It has a black, dull surface and is soft. The coal has a dark brown streak.
The last layer sampled is the Cottage Grove Member of the Chanute Formation. A sample of the Cottage Grove sandstone was found above the Thayer coal in the W/2 of Section 12, Township 25 North, Range 12 East. It is reddish brown and hard. The grain is very fine and subrounded. The sandstone is poorly sorted, micaceous, and laminated. Testing the rock with weak acid shows that it contains calcareous cement, which means that it is held together partly by calcite.
Landforms can be the result of millions of years of erosion. Stratigraphy plays a big part in the formation of landforms. For example, if there is an area with many hard rocks, that area will most likely remain higher because the harder rocks can resist erosion. But, if there is an area with softer rocks, erosion will weather the rocks away to create plains or valleys.
There are two types of weathering (Gerrard 1988, p. 107). The first kind is chemical, which is the breakdown of rock materials by chemical processes. Limestones are highly susceptible to weathering, because the calcite that makes up limestone is easily dissolved by acidic groundwater. Sometimes rocks are weathered by a chemical alteration from harder minerals to softer minerals. For example, the feldspars in granite can be chemically altered to form clay particles, which can then be easily dissolved by physical weathering.
The other type of weathering is physical. Physical weathering is the removal of rock particles by water, wind, or ice. Two examples are erosion caused by the movement of glaciers and the formation of valleys by rivers and streams.
In the Bartlesville area, weathering and erosion have produced several landforms. The Caney River Valley was produced by the Caney River and its tributaries. The river occupies a plain cut into the Nellie Bly Formation. To the west of the river valley there are several cuestas, which are hills capped by gently dipping resistant rocks (Bloom 1978, p. 262). The cuestas to the north and south of Bartlesville are capped by Torpedo sandstone and Birch Creek limestone. To the east of the river valley, several low hills are present, which are capped by the Dewey limestone.
How did the landforms seen today in the Bartlesville area form? Erosion can be described in five stages. In Stage One there has been no erosion. This is the starting point. The stratigraphic section consists of shales, sandstone, and limestone. By Stage Two, a lot of erosion has occurred. Streams have cut down through the shale and sandstone. The sandstone is hard, so that it is supporting the hills that are beginning to form. In Stage Three, erosion has already removed most of the top layer of shale, and streams have cut into the layer of limestone. The stream valleys have become wider as the hills have been eroded. By Stage Four, the top layer of shale is almost gone, and in some areas the limestone has weathered away to reveal the last layer of shale. In the last stage, Stage Five, the first layer of shale is gone, and the tops of the hills are supported only by a thin layer of sandstone. On one of the hills the only thing supporting it is a layer of limestone.
This paper has discussed the stratigraphy and lithology of the rock units outcropping near my home. The paper has shown the importance of these two factors in their interaction with the forces of erosion, such as wind and water, to shape the landforms we see today.
Bloom, A.L. Geomorphology. Englewood Cliffs, New Jersey: Prentice-Hall, Inc, 1978.
Curtis, N.M. Jr. and W.E. Ham. Geomorphic Provinces of Oklahoma. Oklahoma Geological Survey Educational Publication, 1979.
Gerrard, A.J. Rocks and Landforms. London: Unwin Hyman, 1988
Oakes, M.L. Geology and Mineral Resources of Washington County, Oklahoma. Oklahoma Geological Survey Bulletin No. 62, 1940.
USGS, Bartlesville South, Oklahoma 7.5 Minute Topographic Quadrangle, 1971.
USGS, Bartlesville North, Oklahoma 7.5 Minute Topographic Quadrangle, 1971.
Wilson, J.L. Carbonate Facies in Geologic History. Heidelberg: Springer-Verlag, 1975.
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