|Original published in D.F. Merriam, ed., 1964, Symposium on cyclic sedimentation: Kansas Geological Survey, Bulletin 169, pp. 57-62|
Oklahoma Geological Survey, Norman, OklahomaRepetition of rock types is recognizable in several systems in Oklahoma. Customarily the Simpson Group is thought of as consisting of four or five formations, each consisting of a basal sandstone, a middle shale, and an upper limestone, and each disconformably overlain by the succeeding formation. In fact, the sequence is not so regular nor is the existence of disconformities so certain. Ham (1955, Fig. 10) has shown that the Joins and Tulip Creek wedge out to the northeast and that the basal sandstones are not everywhere present. In subsurface, sections are known in which three sandstones occur in the McLish and two each in the Oil Creek and Bromide. It is probable that cyclicity in the Simpson is highly imperfect because of lateral facies changes (Fig. 1).
Figure 1--Regional stratigraphy of the Simpson Group in Arbuckle Mountains (after Ham, 1955).
In the thick Mississippian sequence of the Ouachita Mountains certain rock types are repeated, although no general cyclicity is apparent. Siliceous shale units occur within the formations of the Stanley and Jackfork Groups. Exotic boulders occur in the Wesley Formation and at two levels in the Johns Valley (Cline, 1960).
At the top of the section cyclical units are prominent in the Permian redbeds, primarily in the evaporite units (Jordan and Vosburg, 1963).
Well-developed cyclicity is so prominent in the Pennsylvanian System of the United States that in several areas, such as Missouri, Illinois, and Ohio, geologists divide the rocks into named cyclothems. Because Oklahoma has littIe platform area and much basinal area (Fig. 2), few cyclothems can be recognized in the state. Cyclicity however is apparent in the platform facies of the Desmoinesian and to a lesser extent in the Upper Pennsylvanian and Lower Permian (Gearyan).
Figure 2--Platform and basinal areas in part of northeastern Oklahoma.
In the platform area the Desmoinesian contains 24 coal beds, many of local distribution. Of these only eight are in a sequence of rock types well developed enough to be termed a cyclothem, and even these are far from uniform. Other characteristic and easily recognizable units besides coal are limestones, each of which has a caprock position, underclays, and black fissile shales. In the Krebs and Cabaniss Groups, 10 coal beds of fairly wide distribution occur. Five of these have a limestone caprock and two have black radioactive fissile shale over them. Division into cyclothems is not practical in a section in which so few sequences are well developed and so few have wide distribution.
Markers of cyclicity in the Desmoinesian disappear basinward. Of the principal platform coals, seven extend into the Arkoma Basin; no black fissile shale is persistent, but three caprock limestones have significant distribution in the basinal sediments (Fig. 3). Marmaton rocks in Oklahoma contain but one coal, known at two places, but one fissile black shale, and seven persistent limestones. One recognizable cyclothem is present in one county.
Figure 3--Extension of coals from platform into Arkoma Basin.
Table 1--Coal beds in the Krebs and Cabaniss Groups.
|Cabaniss Group||Iron Post coal|
|Croweburg coal||Croweburg coal|
|Krebs Group||Bluejacket coal||Secor coal|
|Drywood coal||Witteville coal|
|unnamed coal||Stigler coal|
|unnamed coal||McAlester coal|
|Riverton coal||U. Hartshorne coal|
|unnamed coal||L. Hartshorne coal|
Sequences containing recognizable cyclical units together with coal and underclay are few.
|1.||Spaniard Limestone||(in Savanna Fm.)|
|unnamed coal, local, thin||(in McAlester Fm.)|
|2.||Doneley Limestone||(in Savanna Fm.)|
|3.||caprock limestone, one locality||(in Savanna Fm.)|
|4.||Inola Limestone (lowest, fusulinid-bearing)||(in Boggy Fm.)|
|5.||black shale with ironstone concretions||(in Boggy Fm.)|
|lnola Limestone (upper, marginiferid-bearing)|
|6.||black shale with ironstone concretions||(in Senora Fm.)|
|black fissile shale|
|7.||Verdigris Limestone||(in Senora Fm.)|
|black fissile shale|
|shale, siltstone, sandstone|
|McNabb Limestone (underlime position, but marine)|
|8.||Excello black shale||(in Senora Fm.)|
|Breezy Hill Limestone|
|Iron Post coal|
|9.||Mine Creek Limestone||(in Marmaton Group)|
|Anna Shale, black fissile|
|Lexington coal (two exposures)|
|10.||caprock limestone||(in Seminole Fm.)|
|black fissile shale|
|11.||Hogshooter Limestone||(in Skiatook Group)|
No other sequence has significant distribution, and of the above only the Croweburg coal cycle occurs in as many as five counties; most occur in but one. The dominantly marine "cycles" of Osage and Pawnee Counties (Virgilian and above) are baffling in that many elements are local.
In Missourian rocks the Seminole Formation contains the Dawson coal and its overlying black fissile shale and concretionary caprock limestone. This unit is a cyclothem recognizable for 40 miles along strike. Above the Dawson coal cyclothem is no other unit which is of sufficient development or distribution to be considered a cyclothem. A few coal beds occur. The unnamed coal below the Hogshooter Limestone and the Cedar Bluff coal 11 to 40 feet below it are not in a recognizably cyclic sequence. The coal below the Paola Limestone and that below the Bowring Limestone are of extremely local distribution. In the Virgilian rocks a thin coal beneath the Turkey Run Limestone is known at but two localities. The Ralston coal, below the Brownville Limestone, is distributed across two counties.
The unit which is in Oklahoma called the Pawhuska Formation is in part in Kansas incorporated into a megacyclothem (Moore, 1949, Fig. 31). The rocks of the basin margin of the platform in Oklahoma show no pattern which could be considered that of a megacyclothem; indeed, beyond repetition of fusulinid limestones they have no discernible cyclic pattern (Fig. 4).
Figure 4--Nomenclature of some equivalent Pennsylvanian rock units in southern Kansas and northern Oklahoma.
In Oklahoma because of the narrow area of platform and of facies changes across the basin margin into the Arkoma Basin and because the structural strike more or less corresponds to the depositional strike, lithologic and biologic changes in the units are linear rather than vertical. We might facetiously refer to these as sidewise cyclothems. For instance, the Tiawah Limestone in Wagoner County contains a mytiloid coquina, in northern Wagoner County and southern Rogers County it is a fusulinid limestone, in central Rogers County a crystalline limestone containing gastropods and small brachiopods, in Craig County a siderite with Desmoinesia, in western Missouri a dense limestone with tabular algae. The Tebo coal is beneath, and phosphatic concretions occur both above and below the limestone.
The Higginsville Limestone is nowhere in Oklahoma underlain by the Summit coal or its caprock, but grades southward from a 30-foot fusulinid limestone with black shale partings to a fossiliferous gray shale in a black-shale section.
The Hogshooter Limestone is discontinuous and no more than 6 inches thick at Sapulpa, 40 feet thick at Lost City, 14 feet thick at Ramona where it contains a coral reeflike buildup, 10 feet in Nowata County, and 4 feet of sandy limestone in Cedar Bluff, Montgomery County, Kansas.
Basinward facies changes are rapid and profound. From Kansas southward the change in the rocks is reflected by the progressively simpler nomenclature. In the "Gearyan" the 19 formations of Kansas nomenclature are 14 in northern Oklahoma and one in central Oklahoma. The 26 Kansas Virgilian formations are 10 in northern Oklahoma and two in central Oklahoma. Many of these units have been considered cyclothems in Kansas (Fig. 5).
Figure 5--Upper Pennsylvanian rock units in north-central Oklahoma.
The southward change is to red dolomite and to sandstone. All units pass into deltaic redbeds and marker beds are gone or are not recognizable (Fig. 6).
Figure 6--Lower Permian (?) rock units in north-central Oklahoma.
In Oklahoma in the narrow platform area the cyclical units are insufficiently developed and are too limited in distribution to warrant designating any as cyclothems. It would only cause confusion to name any of them under cyclothem nomenclature. Areas of basinal facies are so greatly predominant that Oklahoma geologists must use mapping units discriminated in the basin rocks and must fit the platform units into that section.
Ham, W. E., 1955, Geology of the Arbuckle Mountain region: Oklahoma Geol. Survey Guidebook 3, p. 161.
Jordan, Louise, and Vosburg, D. L., 1963, Permian salt and associated evaporites in the Anadarko Basin of the western Oklahoma-Texas Panhandle region: Oklahoma Geol. Survey Bull. 102, p. 1-76.
Moore, R. C., 1949, Divisions of the Pennsylvanian System in Kansas: Kansas Geol. Survey Bull. 83, p. 1-203. [available online]