Purpose and Scope of Investigation
Cyclothems, especially in Pennsylvanian rocks, have provoked much study and discussion. They present problems of correlation which can be resolved only by detailed studies that lead to paleoecological interpretations. Once their stratigraphy and paleoecology are understood, the problems concerning their origin remain. Understanding of the broader aspects of the origin of cyclothems and, specifically, of Permian cyclothemic history cannot be expected until most or all of the Lower Permian cyclothems of Kansas have been examined carefully.
The objective of this study was to interpret the sedimentary and ecological setting that yielded lithofacies and biofacies recognizable as the Red Eagle cyclothem in Kansas. This approach entailed explanation of certain facies patterns that have hindered attempts by earlier stratigraphers to trace the cyclothem across Kansas. Moreover, this investigation supplied information supplementary to the work of others toward an understanding of Permian cyclothems and geologic history in the classic Midcontinent region of Kansas and Nebraska.
This investigation of the Red Eagle cyclothem was the outgrowth of the author's interest in the Red Eagle Limestone itself. Preliminary work showed that this formation could not be understood properly unless the underlying Johnson Shale and overlying Roca Shale were studied also.
The Red Eagle cyclothem, named for its principal limestone formation, includes the Johnson Shale, Red Eagle Limestone, and Roca Shale formations (Table 1). These rocks occur in the Council Grove Group of the Lower Permian (Wolfcampian) about 150 feet stratigraphically above the base of the system. Red shale within the Roca and Johnson Formations marks the upper and lower limits, respectively, of the Red Eagle cyclothem (Elias, 1937).
Table 1.--Stratigraphic placement of Red Eagle cyclothem units (marked by asterisks) in Lower Permian rock succession of Kansas.
|Council Grove Group|
|Blue Rapids Shale|
|Easly Creek Shale|
|Salem Point Shale|
|*Red Eagle Limestone|
|Long Creek Limestone|
|Hughes Creek Shale|
|Virgillan Stage (Pennsylvanian System)|
Some of the earliest scientific explorers of America noted the distinctive Permian and Pennsylvanian rocks of the Midcontinent, sampled their profuse fossil remains, and measured and described sections. Swallow and Hawn (1858) published the earliest reference to Permian rocks in Kansas. Meek and Hayden (1860) provided additional information, as did Swallow (1866) when he placed the lower boundary of the Permian at a horizon included in the Grenola Limestone of present classification. This position is stratigraphically above the Red Eagle cyclothem.
In the 65 years following Swallow's (1866) publication, a series of renamings and reclassifications of Upper Pennsylvanian and Lower Permian rocks appeared in geologic literature. The newer, more positive correlations led to revision of the older classifications. Rocks of the Red Eagle cyclothem were included by Prosser (1902) in the "Elmdale Formation," which embraced rocks ranging upward from the top of the Americus Limestone Member of the Foraker Limestone, to the base of the Neva Limestone Member of the Grenola Limestone. Bass (1929) did not alter this classification essentially when he added the Neva Limestone to Prosser's Elmdale Formation. By moving the Pennsylvanian-Permian boundary upward to the base of the Cottonwood Limestone Member of the Beattie Limestone, he left the Red Eagle rocks in the Upper Pennsylvanian. Moore and Moss (1934) defined the Pennsylvanian-Permian boundary at the base of the Indian Cave Sandstone, which is the lowest unit of the Admire Group. Thus, the Johnson, Red Eagle, and Roca Formations were transferred to the Lower Permian.
The Johnson Shale and Roca Shale, named by Condra (1927), have presented no serious correlation problems because they lie between widely persistent, readily recognizable units. The Red Eagle Limestone was named by Heald (1916) from exposures in Osage County, Oklahoma. It was thought to be part of the Elmdale Formation of Prosser (1902). Condra (1927) named the Glenrock, Bennett, and Howe units from exposures in southeastern Nebraska. Subsequently, Condra traced them southward into Kansas, where he was able to recognize them near Manhattan and elsewhere.
O'Connor and Jewett (1952, p. 333) summarized the work of Bass (1936) in establishing the correlation of the Glenrock, Bennett, and Howe of Nebraska with the Red Eagle Limestone of Oklahoma as follows:
Bass (1929, pp. 54-55) identified the Red Eagle limestone in Cowley County, Kansas, and expressed the belief that it is continuous into central Kansas in the Cottonwood River Valley. Later, Bass (1936, pp. 41-42) stated that he recognized as members of the Red Eagle limestone beds in Cottonwood River Valley bluffs east of Elmdale that Moore and Condra had identified as equivaIents of the Glenrock limestone, Bennett shale, and Howe limestone of northern Kansas and southern Nebraska. Thus, correlation of the Red Eagle limestone, Bennett shale, and Howe limestone in southern Nebraska was indicated.
The work of O'Connor and Jewett (1952) verified the correlations indicated by Bass (11936), and added some detailed stratigraphic descriptions useful in tracing the Red Eagle Formation across Kansas.
Jewett (1933) recognized the cyclic nature of certain Permian rocks of Kansas. This view was greatly amplified by Elias (1937) when he described the faunas associated with the sequences of lithologic units making up the many cycles of the Lower Permian ("Big Blue Series") of Kansas. Elias' principal postulate was that the repeated lithologies and especially the faunas of the cycles were controlled primarily by water depth during deposition. Moore (1959) lucidly summarized the present understanding of cyclic sedimentation as manifested in Pennsylvanian and Permian rocks of Kansas. His conclusions emphasized the need for more study of cyclothems.
Area of Investigation
The Red Eagle cyclothem crops out in a narrow belt extending roughly north-south from Lincoln, Nebraska, through Manhattan, Kansas, to Burbank, Oklahoma (Fig. 1).
Figure 1.--Map of Red Eagle cyclothem outcrop belt showing locations of key sections and major structures.
Well-exposed sections are rare. Most of the limestone members form minor topographic benches, but the shales commonly lie beneath grassy slopes and are exposed in relatively few places. Fortunately, road cuts and quarries provide sections in areas where nature did not.
From Chase County, Kansas, northward to Lincoln, Nebraska, the more resistant (limestone) members of the Red Eagle assemblage are thin and, where exposed, form only minor benches on valley slopes below the major upland benches of the Neva and Cottonwood limestones. In southern Kansas and northern Oklahoma, where the Red Eagle becomes a thick limestone, it forms benches more conspicuous than the Neva and Cottonwood.
In northern Kansas, between the Nebraska border and Manhattan, beds belonging to the Red Eagle cyclothem are mostly hidden by glacial drift. This lack of exposure caused no correlation problem, because the sequences at Manhattan and Frankfort, Kansas, and Pawnee, Nebraska, are remarkably similar to one another. In southern Kansas, however, facies changes occur where there are few outcrops, so that correlations are less obvious. The best Red Eagle exposures are in southeastern Nebraska and between Manhattan and Emporia in Kansas.
The topography of the outcrop belt is dominated by gently rolling hills, locally supported by flatter limestone benches. The relief rarely exceeds 200 feet. Major valleys--such as those of the Nemaha, Kansas, Big Blue, Neosho, and Cottonwood Rivers--are wide and have alluvial floors. The many lesser tributaries derive most of their water from normal runoff, but a number are spring-fed. Vegetation ranges from grass on the uplands to woods in the valleys.
Methods of Investigation
During preliminary field reconnaissance for this project in the fall of 1956, study of the Red Eagle limestone formation was extended to include the Johnson and Roca Formations. For purposes of comparison, other cyclothemic rocks of the Council Grove Group were also studied. Detailed sampling and study of sections for this report was begun in the fall of 1958. Approximately 50 exposures were examined. Of these, 27 were measured, sampled, and described in detail.
Continuous shale samples were obtained by channeling through the section, extreme care being taken to avoid contamination. Samples of from 1 to 5 (rarely 10) pounds were usually taken. Thick beds with uniform lithologies were sampled at intervals of not more than 0.5 foot to avoid overlooking details of microfacies not observed in the field. Thus, at least one sample was taken from every lithologic unit thicker than approximately half an inch. Intervals as thin as 0.05 foot were sampled where field relations dictated.
Limestone was sampled by removing, where possible, a fresh, vertically oriented slab or elongate fragment from fractured portions of the outcrop. This was best accomplished in road cuts where blasting had provided freshly fractured limestone in place. Each sample was marked to indicate the top of the bed.
Every sample was examined under the binocular microscope to check and augment the field description.
Representative limestone samples were broken to pea size by means of mortar and pestle. A weighed quantity of each broken sample was then digested in dilute (10 percent) hydrochloric acid. Insoluble residues from each digested sample were weighed and later studied under the binocular microscope. The percentage (by weight) of insoluble material in each sample was computed and is expressed in bar graphs beside the graphic rock columns in the Appendix. A few selected limestone samples were digested in acetic acid to check against the results obtained from the same material in hydrochloric acid. Differences between the two were found to be insignificant. Microfossils were picked from the insoluble residues and identified as to genus.
Shale samples were boiled in a dispersant solution in order to liberate megafossils and microfossils. Dispersed silt and clay were usually decanted. Some dispersed clay was allowed to settle on microscope slides for use in x-ray studies. The dried shale samples also yielded microfossils and megafossils which were subsequently identified generically.
Limestone specimens were cut perpendicular to the bedding planes and polished. The polished surfaces were etched for 5 or 10 seconds in dilute (1 percent) hydrochloric acid. When the imperceptibly etched surfaces were dry, they were fixed in a level face-up position and wetted with acetone. The acetate film was pressed against them to obtain on the film an impression of the rock texture. These films were used to make magnified photographic prints (peel prints) of the textural details. The polished limestone surfaces were compared with and studied alongside the magnified peel photographs (see McCrone, 1963).
The laboratory procedures described above were supplemented by x-ray diffraction studies and differential thermal analyses of clay from selected samples. Fossil spore content of selected samples was also determined.
The assistance and advice of the following gentlemen is gratefully acknowledged. Harold L. Cousminer, Gulf Oil Corporation, New York City, identified the fossil spores. R. M. Proctor, Geological Survey of Canada, aided M. P. Bauleke, Kansas Geological Survey, in identifying the clay minerals. L. F. Dellwig, F. C. Foley, and H. A. Ireland, Geology Department, University of Kansas, made special facilities available to the author and reviewed the manuscript. R. C. Moore, University of Kansas, supervised and critically reviewed the entire study. J. M. Jewett, H. G. O'Connor, and D. F. Merriam, Kansas Geological Survey, and L. E. Speck, New York University, intensively reviewed the manuscript and offered many useful suggestions.
Kansas Geological Survey, Geology
Placed on web Jan. 4, 2007; originally published Dec. 1963.
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