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Geology of Mitchell and Osborne Counties

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Rocks Not Exposed

By J. W. Ockerman


The following discussion of the subsurface formations in Mitchell and Osborne counties is based largely on information derived from drillers' logs. Samples from a few of the wells were secured and studied and the writer is indebted to the Midwest Exploration Company and the Phillips Petroleum Company for the use of their samples. He is especially grateful to Mr. Robert Roth, of the Indian Territory Illuminating Oil Company, for aid rendered in the correlation of the lower Pennsylvanian formations.

Cretaceous System

The Cretaceous rocks, as shown by well cuttings, are variable lithologically, being clayey and sandy shale of different colors, sandstone and chalky limestone. The Cretaceous cannot be subdivided into small units as at the outcrop, and in this part of the report only the Colorado group and the "Dakota" sandstone will be recognized.

The Colorado group consists of chalky limestone beds which appear to belong to the Fort Hays, and dark gray to black, in part chalky, shale which is very probably Benton. The shale series is characteristically uniform in color and lithology, and can be recognized in logs without difficulty.

The "Dakota" sandstone includes the sandstone, red, gray, and white shale, and limestone in the lower part of the Cretaceous. At the present time it seems inadvisable to attempt to separate the Comanchean from the Cretaceous, although detailed work should give some results on this problem. The sandstone beds in this series are usually friable; the grains are very poorly sorted and range from coarse and rounded to fine and angular. The sands are usually light gray to white in color, but red sands are not uncommon in the section. Abundant pyrite in zones in the "Dakota" sandstone is characteristic, and "iron" or "pyrite" is found in many of the drillers' logs in this part of the section. Red shale zones are found interbedded with the sandstone along with gray and white shale. Thin beds of limestone are logged by the drillers in the lower part of the section. The "Dakota" series ranges in thickness from 320 feet in Mitchell County to 450 feet in western Osborne County. It rests unconformably on the Permian red beds. Sandstones of the "Dakota" are not safe to use as datum planes for subsurface structure because, though they follow the contour of the Permian red beds fairly well, they vary too much locally for accurate detailed work.

Permian System

The Permian ranges from approximately 1,500 feet in thickness in western Osborne County to 1,000 feet in Gish No. 1 well of the Wilcox Oil and Gas Company in sec. 23, T. 6 S., R. 9 W., in eastern Mitchell County, which shows rapid thinning to the north and east. Two distinct lithologic divisions are represented in the Permian, an upper red-bed series known as the Cimarron group, which is composed of nonmarine red shale and sandstone with minor amounts of gypsum and anhydrite, and a lower series, known as the Big Blue group which includes the Sumner, Chase and Council Grove formations. The Big Blue group is made up of salt, gray shale, anhydrite, and gypsum with a few thin dolomitic limestones and thin red beds. Definition of the lower boundary of the Permian presents a problem because of the lithologic similarity that exists between the lower Permian beds and those of the upper Pennsylvanian and also because of the lack of a break or unconformity between the Permian and Pennsylvanian formations. The writer believes that a detailed study of the microfossils will help materially in the solution of this boundary question. Fragments of what appears to be Fusulina sp., probably F. longissimoidea Beede, were found in cuttings from the well, Vickers No. 1 Luhman, in sec. 11, T. 9 S., R. 16 W., Rooks County, at a depth of 2,350 to 2,358 feet. Fusulina longissimoidea is reported to be confined to the upper part of the Wabaunsee formation and should be an excellent fossil for determination of the top of the Pennsylvanian. This particular determination puts the base of the Permian at the base of the lowest fairly thick red beds, which accords with current practice.

The Cimarron group, which lies unconformably below the Cretaceous, is a thick series of red shale and sandstone beds that arc usually logged as red rock. A bed of gypsum averaging about 40 feet in thickness is found below the top red bed in the more westerly wells (see sections) and is an excellent marker where found. It is probably equivalent to the Medicine Lodge gypsum, but is usually logged as a limestone, as is most of the gypsum and anhydrite in the Permian section. Below the gypsum layer is another thick red bed and some gray shale containing small amounts of gypsum. The thinning that takes place in the Permian is due to the truncation of the Cimarron beds as they rise eastward. The thickness of this group varies from 600 feet in the Stearns-Streeter Matheson No. 1 test, in sec. 28, T. 10 S., R. 16 W., eastern Rooks County, to 100 feet in the Royal Union Gurley No. 1 well, in sec. 27, T. 9 S., R. 7 W., in eastern Mitchell County. The manner of this thinning may be seen in Plate 9 by noting the anhydrite bed as it approaches the top of the Cimarron and is cut off in the Alcorn Oil Company well, Beeler No. 1, in sec. 19, T. 9 S., R. 8 W., Mitchell County. The bottom of the Cimarron is placed at the base of the red bed above the salt or the gray shale, occupying the approximate position of the salt if it is absent. This is usually the third major red bed.

The Big Blue group, comprising the Sumner, Chase and Council Grove formations, ranges from 800 to 900 feet in thickness in the area studied. The upper part, Wellington, is made up of salt, gray shale and anhydrite. The bed of rock salt varies both in thickness and lithologic character, thinning to the north and east rapidly, as can be seen in Plate 9, and changing from a pure salt bed to one made up of interbedded gray shale, gypsum and salt. The purer salt beds are recognized by the drillers, but those in which there is a great deal of shale and gypsum are usually logged as shale or limestone. This uncertainty in recording the salt series makes it inadvisable to use either the top or the bottom of the salt as a basis for structural mapping. Below the salt are thin-bedded deposits of gray shale, red shale, anhydrite, gypsum, and dolomitic limestone. It is important to note that the anhydrite and gypsum beds are logged as limestone, giving the Big Blue group the appearance on the plotted logs of being largely limestone, whereas there is very little true limestone in the section. The base of the Big Blue is placed at the bottom of the lowest fairly thick red bed, until further evidence locates it more definitely.

Pennsylvanian System

Conformably below the Permian lies a thick series of Pennsylvanian limestone and shale which ranges from about 1,700 feet in thickness in eastern Mitchell County to about 1,200 feet in western Osborne and eastern Rooks counties. The exact top of the Pennsylvanian is difficult to place because of the lack of a marked lithologic change or an unconformity. In this report it is assumed that red-bed deposits are essentially confined to the Permian and lacking in the Pennsylvanian, and the division of the two groups is based in part on this assumption. The base of the Pennsylvanian is usually distinct, being recognized by the variegated shales, in a large part reddish, and the conglomeratic material, as well as an abrupt, well-marked change in lithology in the pre-Pennsylvanian formations. There is weathered detritus in the basal shales that is indicative of an unconformable condition.

The Pennsylvanian is divided into four parts in this report, the topmost including the Wabaunsee, Shawnee, and Douglas groups, the next the Lansing and Kansas City groups, below this the Marmaton group and at the bottom the Cherokee group. No attempt has been made to separate and identify the Wabaunsee, Shawnee, and Douglas groups. The division of the lower part of the Pennsylvanian into the Lansing-Kansas City, Marmaton, and Cherokee is based on lithologic and paleontologic evidence. The writer is indebted to Robert Roth, of the Indian Territory Illuminating Oil Company, for correlations in the lower Pennsylvanian based upon a careful study of fossil ostracodes and fusulinids. The lower Pennsylvanian section given differs from the usual classification in that it puts the "big lime," which occurs above the Oswald, in the Lansing-Kansas City group instead of correlating it with the Topeka limestone of the Shawnee group. This change, of course, lowers the assigned stratigraphic position of the Oswald lime, placing it in the upper part of the Marmaton formation instead of the Lansing.

The Pennsylvanian series shows a gradual thinning to the west, and all the formations decrease in thickness, especially the Cherokee. For example, in the Marland test, the Kyle No. 1A, sec. 11, T. 7 S., R. 10 W., Mitchell County, the formations in the Pennsylvanian have the following thicknesses: The Wabaunsee-Shawnee-Douglas group, 680 feet; the Lansing-Kansas City, 280 feet; the Marmaton, 420 feet; and the Cherokee, 340 feet; a total of 1,720 feet. In the Midwest-Skelly well, Jones No. 15, in sec. 28, T. 7 S., R. 16 W., Rooks County, the Pennsylvanian is only 1,180 feet thick, the group thicknesses being as follows: Shawnee- Wabaunsee-Douglas group, 560 feet; Lansing-Kansas City, 250 feet; Marmaton, 260 feet; and Cherokee, 110 feet. It can readily be seen that the greatest thinning is in the Cherokee, although the other members show a decrease in thickness also. Lithologically the Pennsylvanian series is made up in a large part of shale, with considerable limestone and but little sandstone. The shale units of the Pennsylvanian are characteristically gray to dark gray in color, and in many parts of the section are quite soft and calcareous. Variegated shale is not uncommon in the Pennsylvanian, especially at the contacts or unconformities between individual groups. This is especially marked in the Oswald producing zone. The limestones are generally soft, compact, and light gray or yellowish in color. Many of the beds are fossiliferous, containing abundant fusulinids and ostracodes which are of value for correlative purposes. A few of the beds are oolitic, and some of the thicker beds are cherty. The sandstones are rather scarce in the section and are usually micaceous and contain fine, angular grains.

Wabaunsee-Shawnee-Douglas Groups

The upper division of the Pennsylvanian is a thick series of limestone and shale ranging from 1,020 feet in thickness in the Gurley Abercrombie No. 1 well, in sec. 32, T. 9 S., R. 7 W., Mitchell County, to 560 feet in the Midwest-Skelly well, the Jones No. 15, in sec. 28, T. 7 S., R. 16 W., eastern Rooks County. It comprises the three major groups of the Pennsylvanian of Kansas, namely, the Wabaunsee, Shawnee and Douglas groups. It does not seem advisable on the basis of evidence at hand to attempt to distinguish these groups, but detailed paleontological study will probably make such division possible. The Douglas group is apparently very thin or lacking in this region and there seems to be evidence in many of the wells of an unconformity between the upper division and the Lansing-Kansas City below. Lithologically the group is not markedly different from the Permian above, except in the absence or near absence of red beds. The shale is generally moderately soft and gray, with little or no red shale present in the section. The limestone beds are generally fairly soft, gray to yellow in color, and in a few places are oolitic. They often yield numbers of fusulinids as well as ostracodes and shell fragments.

Lansing-Kansas City Groups

This thick limestone series below the Wabaunsee-Shawnee-Douglas group is fairly uniform in thickness but gradually thins toward the west. The series ranges from 250 to 300 feet in average thickness. This group, known as the "big lime," is an excellent marker and is clearly defined in all wells. It has been variously placed in the Pennsylvanian stratigraphically, but the lithologic and paleontologic evidence leads the writer to regard it as belonging in the Lansing-Kansas City group. The series consists predominantly of limestone, which is usually a soft, gray, compact crystalline rock with abundant fusulinids and many ostracodes, as well as shell and bryozoan fragments. In places the limestone contains much chert of a light gray to brown color. Very little shale is found in the section, but at the base there is usually red or variegated shale which marks the contact between the Lansing-Kansas City and the Marmaton. In a few of the wells fine micaceous sandstone is found, but it is neither abundant nor common in this series.

Marmaton Group

Unconformably below the Lansing-Kansas City group there is a series of limestone and variously colored shale beds that is assigned to the Marmaton. In the upper part of this lies the Oswald horizon, which is a distinct zone in southwestern Osborne County but becomes indeterminate to the north and east. The Oswald has generally been placed higher in the section, but evidence from fusulinids bears out the correlation in this report.

It may be added here that any controversy arising out of this correlation will be of value if it stimulates greater interest in a careful study of the fossils found in this part of the Pennsylvanian. The Marmaton is not as constant in thickness as the Lansing-Kansas City and ranges from 260 to 400 feet, also gradually thinning to the west. The series is characterized by variegated shale near the top and by the' presence in some cases of a porous limestone member which probably coincides with the Oswald porous pay in' Russell County and southwestern Osborne County. The series usually has a red or variegated shale at both top and bottom. The limestones are also variable, ranging from soft white and crystalline to brown and porous. Fusulinids and ostracodes are quite abundant and an occasional small brachiopod is also found.

Cherokee Shale

The Cherokee formation below the Marmaton consists predominantly of shale, but there are a few limestone beds. It is variable in thickness, mainly because it rests unconformably upon a pre-Pennsylvanian erosion surface. The formation thins to the west very markedly, being about 300 feet thick in Mitchell County wells and about 100 feet or less in the western Osborne and eastern Rooks County wells. The Cherokee shows a preponderance of reddish and variegated shale, not only at the top and bottom, but also scattered through its section. The limestone beds are generally soft and light gray in color and contain many fusulinids. Shell fragments are not uncommon, but are of little value for identification purposes. The base of the Cherokee often contains beds of conglomerate associated with red and black shale making, wherever present, a definite marker for the base of the Pennsylvanian. There is also a distinct change in the lithology of the pre-Pennsylvanian rocks which aids in identifying the base of the Cherokee.

Pre-Pennsylvanian Rocks

Several of the wells in Mitchell and Osborne counties have penetrated formations older than the Pennsylvanian. Notable among these wells are the Stearns-Streeter Carlin No. 1, in sec. 18, T. 6 S., R. 13 W., the Phillips Grieve No. 1, in sec. 6, T. 7 S., R. 12 W., the Mid-Kansas Boyce No. 1, in sec. 18, T. 6 S., R. 13 W., and the Gurley et al. Abercrombie No. 1, in sec. 32, T. 9 S., R. 7 W. The prePennsylvanian formations are Mississippian limestone (?), undetermined Ordovician limestone, Decorah shale, Arbuckle limestone, and pre-Cambrian granite.

Mississippian formations were found in three wells, the Boyce, Abercrombie and Grieve. The thickness ranged from 270 feet in the Abercrombie well to 110 feet in the Grieve well. The Mississippian strata consisted of hard white chert and white to cream-colored dolomite containing a single thin white oolitic limestone bed. Basal Mississippian shale was present in the Abercrombie well. This may be Kinderhook, but as no fossils have as yet been found correlation is uncertain.

The Upper Ordovician limestone studied in the well cuttings was not definitely identified. It was a soft, white to cream-colored dense limestone, with minor amounts of sand present. Edson (1929) correlates the Ordovician limestone immediately below the Pennsylvanian in the Carlin well with the Trenton limestone. Other workers in the area report the presence of Viola limestone and the Simpson formation. The Decorah shale, which has been identified in several of the wells, is distinguished by its fauna. It is usually a soft green or greenish gray shale. Bryozoans, especially Rhinidictya mutabilis Ulrich, are abundant in the cuttings.

The Arbuckle limestone is characterized by its crystalline dolomite, which ranges from white to brown in color, and an associated coarse sub angular sand.

The pre-Cambrian was encountered in the Boyce well at a depth of 3,700 feet; and 160 feet of granite was penetrated. The cuttings were composed chiefly of feldspar and angular quartz, with a minor amount of hornblende and biotite.

The Mid-Kansas Boyce No. 1, in sec. 18, T. 6 S., R. 13 W., had the following lithology in the pre-Pennsylvanian:

Undetermined formation
3740-3810 Hard white opaque chert, small amount gray crystalline limestone.
3810-3820 White oolitic limestone, white chert.
3820-3845 Missing.
3845-3860 Cream-colored finely crystalline dolomitic limestone, small amount of white chert.
3860-3870 Coarse subangular to rounded sand, a little greenish shale.
3870-3885 Coarse subangular to rounded sand, white oolitic limestone.
3885-3895 Soft white crystalline limestone, coarse sand.
3895-3905 Soft greenish gray shale.
3905-3920 Soft white finely crystalline limestone. White chert.
3920-3955 Hard white chert, coarse sand, white limestone.
3955-3965 Missing.
3965-4000 Hard white chert, coarse rounded sand.
Undetermined limestone:
4000-4035 White dense limestone, a little green shale.
4035-4065 White crystalline limestone, small amount green shale.
4065-4085 Soft white dense limestone, a little green shale.
4085-4095 Hard sandy limestone.
4095-4110 Soft white dense limestone, small amount chert.
4110-4155 Hard sandy limestone.
4155-4195 Soft white crystalline limestone, a little green shale.
Decorah shale:
4195-4260 Soft green shale. Rhinidictya sp.
Arbuckle limestone:
4260-4350 Brownish crystalline dolomite.
4350-4360 Medium coarse subangular sand.
4360-4480 Yellowish crystalline dolomite. Medium coarse sand.
4480-4500 Medium coarse, subangular to round sand.
4500-4580 Yellowish crystalline dolomite.
4580-4640 White to cream crystalline dolomite.
4640-4700 Yellowish crystalline dolomite.
Pre-Cambrian (Archean?):
4700-4860 Granite.

The Gurley et al. Abercrombie No. 1, in sec. 32, T. 9 S., R. 7 W., penetrated several pre-Pennsylvanian formations, as may be seen in the following description of the deeper cuttings:

Undetermined formation
3380-3410 Hard crystalline dolomite, coarse sand.
3410-3425 Hard white chert, crystalline dolomite.
3425-3450 Hard crystalline dolomite, white chert.
3450-3533 Hard white chert, white crystalline dolomite.
3533-3570 Medium hard white oolitic limestone, sand.
3570-3580 Hard white finely crystalline limestone, chert.
3580-3650 Gray fissile shale.
Undetermined formation:
3650-3675 Hard white chert, much sand.
3675-3720 White dense limestone, green shale, sand.
3720-3750 White coarsely crystalline dolomite.
Decorah shale:
3750-3830 Soft green fissile shale.
Arbuckle limestone:
3830-3865 White coarsely crystalline limestone.
3865-3910 Gray coarsely crystalline limestone.
3910-3985 White dense limestone, some dolomite.
3985-4020 Gray crystalline dolomite, white limestone.
4020-4035 White crystalline limestone.
4035-4108 Missing.

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