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Oil-field Areas of Ellis and Russell Counties

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Geologic History

The known geologic history of this area started with the erosion of the pre-Cambrian basement rocks that occur below the Paleozoic sediments. This surface was submerged below sea level and marine sediments were deposited upon it. Throughout much of Paleozoic time the area was successively submerged and elevated. Marine sediments accumulated during periods when the surface was below sea level, and these sediments were subsequently eroded during periods of emergence. The lower Paleozoic rocks consist for the most part of marine limestone, shale, and sandstone.

According to Moore and Jewett (1942) an important structural event occurred in this area during post Devonian-pre-Mississippian time. This consisted of a regional arching of the strata along a northwest-southeast axis and is indicated by the fact that preMississippian erosion truncated the earlier Paleozoic rocks and stripped off all of the beds down to the Arbuckle limestone. This period of uplift and subsequent erosion is believed to have been followed by marine inundation and resulting deposition of the Mississippian strata over this part of Kansas. The rocks of northwestern Kansas were again uplifted and warped along this same general structural trend at the close of Mississippian time or during early Pennsylvanian time to form the structural feature now recognized as the Central Kansas Uplift. It is this structure that has localized the accumulation of oil produced from these counties. The Mississippian strata believed to have existed across the top of this structure were stripped away by early Pennsylvanian erosion. As some places along the Central Kansas Uplift this early Pennsylvanian erosion cut away the rocks to such a depth as to expose the pre-Cambrian basement. Coarse clastic deposits accumulated along the flanks of the Uplift as a result of this period of erosion, and it is believed that they may have been contemporaneous with the denudation deposits that were spread out toward the east from the ancestral Rocky Mountains.

The sea again invaded the area and marine deposits accumulated across all of northwestern Kansas during Pennsylvanian time. During the latter part of the Paleozoic, marine conditions were less prevalent and at times sediment accumulated on the surface of the land. Thus marine and nonmarine deposits occur alternately throughout rocks representing upper Pennsylvanian and Permian time. Desiccation and continental type sediments became more prevalent throughout Permian time, indicating an intermittent but progressive withdrawal of the seas.

The sea withdrew completely from the area by the close of Paleozoic time and the surface was eroded, uplifted, and warped. Erosion proceeded throughout much of Triassic and Jurassic time and it was over this eroded land surface that the Cretaceous deposits were spread.

The contact between the Cretaceous and Permian rocks, where it can be observed in adjacent areas, is characterized by a weathered zone at the top of the Permian. This zone is several feet thick, gray in color, and transgresses the bedding planes, indicating a relatively long period of weathering. At many places a zone of pebbles or cobbles has been observed at the base of the Cretaceous deposits. These pebbles consist of quartzite and igneous rocks and probably represent the first phase of continental deposition. This zone may be equivalent to the gravel that occurs at approximately the same stratigraphic position northeastward from Kansas. It has been observed in Kansas at the base of the Cheyenne, Kiowa, and Dakota where these formations immediately overlie the Permian.

During much of early Cretaceous time Ellis and Russell counties were still above sea level, whereas marine deposits were accumulating to the south and southwest. As the early Cretaceous sea encroached northward, clastic sediments accumulated at and near the shore line as beach deposits, deltas, and off-shore bars. These deposits, in addition to near-shore channel and flood-plain deposits, constitute the Cheyenne sandstone. In central Kansas they probably accumulated during a period of stable sea level or when the shore line was moving slowly northward, and the Kiowa shale, which overlies and overlaps the Cheyenne, represents the sediments deposited under marine conditions as the sea more rapidly advanced and inundated this region.

The close of early Cretaceous time is marked by the withdrawal of the sea. It was not a continuous retreat but was marked by minor re-advances, and left interbedded marine and continental beds. Also it seems that the earth movements that occurred elsewhere at the close of Lower Cretaceous time may not have affected this area, because the Dakota formation, which is generally considered Upper Cretaceous in age, conformably overlies the Kiowa shale and is transitional with it. The Dakota formation is composed of continental and littoral beds deposited in channels, flood plains, beaches, lagoons and bars. Sand accumulated in stream channels or on beaches and bars, and clay, silt, and carbonaceous material were deposited on flood plains and in lagoons. The channel sandstones in general trend northeast, and the more evenly bedded bodies of sand that are believed to represent bar or beach deposits generally trend north or north-northwest. Thus the sandstones in the Dakota formation are elongate lenticular sand bodies interspersed through the clay and silt. This explains the fact that in some places one of two near-by wells will encounter several beds of sandstone and the other few or none. Also it can readily be seen why two near-by wells drilled into the Dakota sandstones yield water of different quality or water under a different hydrostatic head, and yet other wells more widely separated may have similar characteristics. This lattice work of lenticular sandstones is in part interconnecting, however, as shown by exposures where one lenticular sand body rests upon another.

Continental conditions existing throughout Dakota time again gave way to marine conditions and the upper part of the Dakota contains a larger percentage of even-bedded sand and silt suggesting beach or bar deposits, The sea completely transgressed the area for the last time and the Graneros shale and overlying marine formations of upper Cretaceous age were deposited.

Since the withdrawal of the Cretaceous sea this area has been continuously above sea level. It was subject to erosion during most of Tertiary time and was covered by a thin veneer of clastic sediments during the Pliocene. These sediments represent material eroded from the highlands to the west and transported to western Kansas by eastward flowing streams.

During the Pleistocene the major streams crossing this area from west to east cut wide valleys and spread a thick layer of gravel and silt over their valley floors. It was at this stage of valley development during the early Pleistocene that major changes occurred in the drainage pattern of central Kansas (Frye, Leonard and Hibbard, 1943) . Wilson valley in western Ellsworth county, which formerly had carried the Saline river drainage into the Smoky Hill valley, was abandoned. Also, the McPherson valley, which carried this western drainage southward to its junction with the Arkansas valley, was abandoned, and the major drainage way was established to the eastward across the flint hills in the position of the present Kansas river valley. Several minor periods of valley cutting followed and gave rise to the series of terraces now to be seen along the maj or valleys of this area. The present valleys of the major streams are quite narrow and are cut below the level of the lowest Pleistocene terrace.

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Kansas Geological Survey, Geology
Placed on web Jan. 26, 2017; originally published December 1944.
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