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Contents
Introduction
Definition
Subdivision
Summary
Des Moines series
Missouri series
Virgil series
Carboniferous

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Introduction

The state of Kansas contains an extremely interesting succession of marine and continental deposits of Pennsylvanian age. These deposits offer exceptional opportunity not only for studies bearing on classification of Pennsylvanian rocks in North America, but for investigations that have general application on principles of stratigraphic classification, on sedimentation, on the paleoecology of faunas and floras, and on the operation of diastrophic forces in the earth's crust. The area of Pennsylvanian outcrops occupies approximately the eastern one fourth of Kansas and is continuous with extensive exposures in the neighboring states of Missouri, Nebraska, Iowa, Oklahoma, and Arkansas. The strata dip gently outward from the Ozark uplift and in eastern Kansas the direction of dip is thus to the west and northwest. Because of the simple structure and the presence of numerous stratigraphic horizons that can be traced long distances it is possible to determine with accuracy and a fair degree of completeness the stratigraphic column of various parts of the Pennsylvanian system in the district.

Perhaps the outstanding feature of the Pennsylvanian rocks of Kansas is the large number of alternating limestone, shale and sandstone units, part of which are marine and part continental. It is evident that these represent conditions of sedimentation almost continuously changing as represented by the vertical succession, but remarkably similar for long distances horizontally, as shown by lateral persistence of many of the formational and smaller divisions. The relation of faunas and floras to these lithologic types permits study of changing ecologic conditions. The characters of the Pennsylvanian stratigraphic column and the recognition of unconformities at certain horizons provide a basis for conclusions as to the stability of the continental platform in this region during the Pennsylvanian period.

It is not the purpose of this report to describe in detail the Pennsylvanian formations of Kansas and adjacent parts of the northern Mid-Continent region, but rather to consider the problems of stratigraphic classification and nomenclature that are needed for description of the system and for treatment of the historical geology of Pennsylvanian time in this region.

Previous Work

[Note: Specific references to the rather voluminous literature on the Pennsylvanian rocks in the northern Mid-Continent region are omitted from this section of the report, since detailed citations are given subsequently for each stratigraphic unit.]

The presence of Carboniferous or Coal Measures strata in the northern Mid-Continent region was recognized more than a century ago, but the beginning of stratigraphic investigations of these rocks may be placed in the early 1850's when the first geological survey of Missouri was organized. The application of names to various rock units has been a matter of gradual development. The most prominent scarp-forming limestones were among the first units to receive geographic designation, in part taken from the name of towns where the rocks were quarried for commercial uses or from other geographic features that were locally well known. Examples are "Manhattan stone" and Cottonwood limestone. It was almost certainly in this sense rather than as formal proposal of stratigraphic names that G. C. Swallow, state geologist of Kansas in 1865, used the names Fort Scott, Stanton and Fort Riley as applied to limestone beds described in sections. Swallow did not use geographic names for other equally prominent units described by him, and he miscorrelated the Stanton with beds (Burlingame) 750 feet or more stratigraphically above the limestone at Stanton, Kan. Introduction of these now well-known names is, however, credited to Swallow. F. B. Meek, in 1865 and subsequently, published descriptions of "Coal Measures" rocks and fossils of Kansas and Nebraska, but did not apply definite stratigraphic names. The first really noteworthy early work on Pennsylvanian stratigraphy in the Missouri-Kansas-Nebraska region is that of G. C. Broadhead, who prepared a series of remarkably accurate general sections. Most of the stratigraphic units, designated by numbers, are readily identifiable, and reference to them by modern workers is still not uncommon. In 1868 to 1872 Broadhead published certain proposed major groupings of the Pennsylvanian rocks of Missouri. Some of these groups, designated mostly by letter symbols, are practically identical with divisions now recognized, but Broadhead largely avoided use of geographic names as applied to the rocks. Another early worker in the Kansas Carboniferous area is Robert Hay who, in the period from 1887 to 1896, published several short papers describing these rocks. He proposed names for some stratigraphic units but these have been largely overlooked. Charles R. Keyes, in the period from 1888 to the present, has contributed many papers to the subject of Carboniferous stratigraphy and nomenclature in the Mid-Continent, but the value of most of this writing is lowered by lack of first-hand field knowledge.

The work of Erasmus Haworth and assistants (especially Bennett and Kirk), of the University Geological Survey of Kansas, organized in 1895, is of outstanding importance. A number of east-west cross-sections of the Pennsylvanian strata of Kansas were measured and many stratigraphic units were traced in reconnaissance mapping across the state. A large number of formation names that are now in common use were introduced by Haworth in 1898 or before. Schrader, in 1908, and Haworth, in 1909, added and revised various formational units. The larger stratigraphic divisions, Cherokee, Marmaton, Pottawatomie, Douglas, Shawnee, and Wabaunsee, were introduced by Haworth in the period 1895-1898, and excepting Pottawatomie, have remained unchanged in subsequent publications. The 1909 report of the University Geological Survey (volume 9) contains a rather detailed faunal study of the Kansas Pennsylvanian by Beede and Rogers, which distinguishes faunal divisions with boundaries corresponding almost precisely with the stratigraphic divisions recognized by Haworth. This coincidence is, indeed, surprising, indicating an exceptionally prescient subdivision by Haworth, or perhaps an unrecognized adjustment of paleontologic testimony to fit existing classificatory units. Some of these boundary lines are plainly of physiographic or cartographic significance only.

Studies of much importance on the Upper Pennsylvanian and "Permian" strata of Kansas are reported in papers by Charles S. Prosser published in the period from 1894 to 1910. Many stratigraphic units are described and named in these contributions which laid the groundwork of classification that has been followed for many years. Associated with Prosser in part of his work, but in part independent, is J. W. Beede who, from 1898 to 1914, published additions to knowledge of the stratigraphy of the northern Mid-Continent area. Beede is the author of numerous stratigraphic names. One of Haworth's assistants in the early geologic work on the Carboniferous of Kansas was George I. Adams, whose most important papers are a general summary of the stratigraphy of these rocks (with paleontologic notes by G. H. Girty and David White) published in 1903 and a description of the rocks of the Iola quadrangle, issued in 1904. Various new stratigraphic units are described and named in these papers.

Hinds and Greene, in 1915, published a very important contribution to knowledge of Pennsylvanian stratigraphy of Missouri. The Kansas classification developed by Haworth was mainly used, but certain miscorrelations were corrected and Haworth's "Pottawatomie" formation was divided into two parts, the lower termed Kansas City, and the upper, Lansing. The Marmaton formation, also, was subdivided into the Henrietta formation, below, and the Pleasanton formation, above. The group terms, Des Moines and Missouri, proposed by Keyes, were adopted for "lower Coal Measures" and "upper Coal Measures," respectively, as used in the Kansas reports.

Some work was done on the Pennsylvanian of Iowa during the nineties and subsequently, the most recent studies being contributed by J. L. Tilton, who differentiated and named certain units in southwestern Iowa.

For many years G. E. Condra, state geologist of Nebraska, has been at work on the Pennsylvanian stratigraphy of southeastern Nebraska, and in the course of his investigations has made extended trips into adjacent Pennsylvanian areas. In 1927 the results of Condra's stratigraphic studies were published as a report of the Nebraska Geological Survey. Many measured sections were described in detail and the rocks were correlated with named units in neighboring states. A feature of the Nebraska report is the proposal of many new stratigraphic names, drawn chiefly from localities in Nebraska and northern Kansas, for seemingly minor units, which, however, were shown to be amazingly uniform and persistent. A chief reason for the addition of these many names is the need for detailed stratigraphic zoning in connection with paleontologic studies and precise correlation with sections in various distant places where the same units may be recognized. Condra's work is a step in the direction of more painstaking, detailed and accurate stratigraphic correlations. Because of the disconnected outcrops of Pennsylvanian strata in southeastern Nebraska stream valleys (intervening areas being deeply mantled by glacial draft), because of the existence of an unrecognized structural uplift along Platte river, and because of a peculiarly deceptive repetition of sequences of beds, the section of the Platte river valley was erroneously correlated in the 1927 Nebraska report. Condra subsequently discovered and corrected the error, making necessary revision of the nomenclature of a number of units.

Acknowledgments

The studies on which this paper is based include work by Dr. N. D. Newell, of the University of Kansas, Dr. R. G. Moss, now of the Phillips Petroleum Company, and Prof. J. M. Jewett, of the University of Wichita, carried on as members of the Kansas Geological Survey under my direction. Critical points in the field investigations of these men have been checked by me. Introduction and definition of several new stratigraphic units that will be credited to these men in forthcoming publications come from phases of the general study assigned to them, and have been developed in part as a result of collaboration. Acknowledgments are also due Mr. F. C. Greene, of the Missouri Bureau of Geology and Mines, and especially to Dr. G. E. Condra, state geologist of Nebraska, who have joined me in field investigations of problems involving stratigraphic classification and nomenclature, and who in many other ways have contributed to progress of the work.

Stratigraphic Definition of the Pennsylvanian System in the Northern Mid-Continent Region

The Mississippian-Pennsylvanian Boundary

The base of the Pennsylvanian system is very clearly defined in Missouri, Iowa, Nebraska, and Kansas. The lowermost Pennsylvanian beds, called Cherokee, consist of shale, sandstone, thin limestone, coal, and conglomerate that rest unconformably on a somewhat uneven surface of massive Middle or Lower Mississippian limestone. Extensive subsurface data, as well as outcrop observations, indicate that there was a long period of nondeposition and of considerable erosion between the time of formation of the youngest Mississippian rocks still present and the oldest Pennsylvanian rocks observed in the area, Prior to the beginning of Cherokee deposition, Mississippian rocks that were once continuous over the Ozark uplift were removed, so that Pennsylvanian rocks now are found resting directly on Devonian, Silurian or Ordovician strata. Information from deep wells in the central part of Kansas and southeastern Nebraska shows that Pennsylvanian strata overlap Mississippian rocks and are in contact with Devonian (?), Silurian, Ordovician, Cambrian, and pre-Cambrian rocks.

Northeastern Oklahoma and northern Arkansas contain outcrops of Late Mississippian (Chester) strata overlain unconformably by rocks called Morrow, which in turn are unconformably overlain by beds equivalent to the Cherokee. The Morrow beds are classed as Early Pennsylvanian.

The Pennsylvanian-"Permian" Boundary

The upper boundary of the Pennsylvanian rocks in the northern Mid-Continent region has been arbitrarily placed at various horizons by different workers at different times. The transition from rocks that are regarded by all as Pennsylvanian to those that have been classed as Permian is apparently unbroken. The practice of the United States Geological Survey and of state surveys in drawing the boundary at the base of the Cottonwood limestone has served for many years to fix an arbitrary boundary in official geologic reports. Beede has called attention to paleontologic evidence indicating that the base of the "Permian" should be drawn at least 70 to 75 feet lower than the Cottonwood, so as to include the Neva limestone, which contains the first appearance of Schwagerina. [Beede, J. W., The Neva limestone in northern Oklahoma: Oklahoma Geol. Survey, Bull. 21, 1914. Species of the genus Schwagerina and their stratigraphic significance: Texas Univ. Bull. 2433, 1925.] Similarly, on a basis of fossils and of distinctive lithologic features, I have advanced the opinion that the Pennsylvanian-"Permian" boundary should be drawn still lower, at least so as to include in the "Permian" the beds classed as Foraker and Elmdale. [Moore, R. C., Reclassification of Pennsylvanian rocks in the northern Mid-Continent region: Kan. Geol. Soc. Guidebook, Sixth Ann. Field Conf.; p. 89, 1932.] Subsequently evidence has been discovered pointing to a discontinuity in sedimentation that appears to be coincident with the most marked faunal and lithologic changes in this part of the stratigraphic column, and which indicates that perhaps the most logical boundary is located above the Brownville limestone and below the Aspinwall limestone. [Moore, R. C., and Moss, R. G., Pennsylvanian-Permian boundary in the northern Mid-Continent area: Geol. Soc. America, Proc, for 1933, p. 100, 1934.] In the present paper the upper boundary of the Pennsylvanian system in the northern Mid-Continent is placed at this disconformity.

Subdivision of the Pennsylvanian System in Kansas

Objectives of Classification

For many years I have been interested in the stratigraphy of the Pennsylvanian rocks. The conclusion was reached very soon after the beginning of my studies in Kansas in 1916, that the major grouping of these beds in the northern Mid-Continent region was apparently lacking in any very definite relation to the historical geology of the period. That is to say, the previous grouping of beds had been established primarily on the basis of conveniently spaced, persistent and prominent mappable escarpments. This was certainly a desirable or necessary procedure in the initial classification and tracing of the rock strata. There is a close relationship, of course, between lithology and the topographic expression of beds, but it does not follow that because one bed is slightly thicker and more resistant than another, the topographically prominent stratum defines a major plane of division in the stratigraphic succession. It may be selected arbitrarily as a cartographic datum, but it is possible that an inconspicuous horizon may be really much more important in the light of paleontologic studies or of physical evidence of widespread disconformity. The validity of this approach to the subject of stratigraphic classification is evident.

It may be added that the long accepted grouping of Kansas Pennsylvanian beds, if determined by physiographic or lithologic coni siderations, as seems to be the case, is inconsistent. For example, the Douglas formation, as defined by Haworth, begins with a shale (Weston) and ends with a prominent scarp-making limestone (Oread) at the top. The succeeding Shawnee formation begins with a shale (Kanwaka) but also ends with a shale (Scranton) at the base of a prominent scarp-making limestone (Burlingame). This matter is not of very much importance, even though it has definite bearing on areal mapping.

The fact that paleontologic zonal boundaries, defined subsequent to the differentiation of formational or group units, coincide with lines of division between formations or groups has little real significance, especially when the nature of the faunal evidence, as presented by Beede and Rogers, is analyzed. The faunal distinctions in Pennsylvanian stratigraphic divisions that are now being recognized, depend largely on a close study of mutations in a few groups, such as the fusulinids, the chonetid brachiopods, and (in Texas) the ammonoid cephalopods.

Despite the conviction that the major grouping of Pennsylvanian beds introduced by Haworth was arbitrary and artificial in several particulars, it has seemed unwise to make changes until a thorough general restudy had been made. The immediate purpose of recent Pennsylvanian studies in Kansas has been to determine the correctness of previous stratigraphic correlations and mapping, and to supply needed additional information for a new geological map of the state on a scale of 1:500,000. Most of the mapping of the Haworth survey has been found good, especially considering conditions of field work at the time the maps were prepared. The recent field studies have made use of some hundreds of detailed plane-table maps by oil-company geologists and independent petroleum geologists. In areas little studied by commercial workers the survey geologists have carried on detailed field work. Field work done by me includes the measurement and study of hundreds of stratigraphic sections, mapping and correlation of strata in all parts of the Pennsylvanian section, and the supervision and checking of work done by assistants in various areas. Opportunity to examine typical sections in Missouri, Nebraska and Oklahoma has aided in reaching an understanding of certain Kansas stratigraphic problems. General familiarity through personal field study in Texas, Arkansas, southern Oklahoma, the Rocky Mountain region and parts of the East, has also aided in formulating the proposed major divisions of the Kansas Pennsylvanian section.

Consideration of the subject of Pennsylvanian classification in the northern Mid-Continent region should be prefaced by a brief statement of some of the principles of stratigraphic classification that apply.

The purpose of subdivision of rocks in a stratigraphic succession is to differentiate major and minor portions of unlike lithology, faunal content, or both, as a basis for mapping, for correlation with rocks of the same age in other areas, and for economic development, Subdivision on a purely lithologic basis may differ radically from that outlined on paleontologic data, and it is clear that a classification established on purely economic considerations may have little relation to these other lines of study. An almost endless variety of arbitrary and artificial classifications might be formulated. The geologist presumably seeks to ascertain and apply the most "natural" classification, however; that is, one that expresses with maximum fidelity and completeness the nature of the sedimentary, paleontologic and diastrophic history of the portion of geologic time recorded by the stratigraphic section. Such a classification will have largest significance in historical geology. It should also conform, with special emphasis on certain features, to requirements of economic geology.

Criteria for Designation of Major Stratigraphic Units

The larger divisions of geologic time, and some of the smaller ones, are characterized by paleontologic features that are readily determined by the trained student of fossils. Thus distinguished, characters of fauna and flora furnish definite basis for differentiation of geologic systems, even though there are in some cases questions as to the precise definition of the intersystemic boundaries. Paleontologic changes of lesser moment may be expected to define the series within a system, and this is commonly the case. The faunas of the marine Pennsylvanian rocks, however, appear to have undergone comparatively little change during the period, and accordingly no definite, readily applicable subdivision of Pennsylvanian rocks on a paleontologic basis has been advanced. Nevertheless, it appears that close study will lead to differentiation of significant and definite faunal stages.

Lithologic characters vary regionally and have no necessary relationship to major subdivisions within a geologic system. They do furnish certain evidence of importance, however, indicating, for example, times of prominent elevation of the land, or protracted times of marine sedimentation. Evidence from lithologic characters is secondary as regards major stratigraphic units. It merely supplements information obtained from other sources.

The structural attitude of rocks, and especially the existence of widespread unconformities, may be very important in differentiating major stratigraphic units. Deformation of the earth crust, involving folding or warping of previously deposited strata, is commonly accompanied by the recession of seas and the occurrence of erosion on lands, and this serves to limit clearly the rocks formed prior to deformation from those deposited subsequently. Either because of accelerated biologic changes at times of diastrophism or because of considerable lapse of time during which no sedimentary formations are laid down in a given region, unconformities of the type described commonly coincide with major changes in the paleontologic record. This combined diastrophic and paleontologic evidence furnishes punctuation points in the geologic record that provide the basis for definition of geologic systems as now recognized, and within the system, similar punctuation points of lesser magnitude define series.

Series

Whether the Pennsylvanian rocks should be regarded as constituting a geologic system, presumably depends on whether these and equivalent rocks are deemed to constitute a natural division of the geologic column recognizable in all parts of the world and whether the boundary separating Pennsylvanian strata from contiguous parts of the stratigraphic column have major importance in historical geology and are recognizable very widely. [See G. H, Ashley and others, Classification and nomenclature of rock units: Geol. Soc. America, Bull., vol. 44, pp. 429-445, 1933.] The major subdivisions of a system, called series, are presumably recognized on the same qualitative criteria as those that define systems, but they are of lesser magnitude. Such subdivisions may be well defined and clearly recognizable in a given province or in a continent, but it is generally believed that they are not necessarily recognizable in other parts of the world. The same type of physical evidences, consisting of stratigraphic and structural relations, general lithologic characters, and of organic evidence consisting of the nature of faunas and floras, may be used to differentiate successive series as are employed in definition of systems.

The Pennsylvanian rocks of the Mid-Continent region are divisible into major parts based on the recurrence of diastrophic movements in the geosynclinal regions, accompanied by widespread interruption of sedimentation and in some cases by gentle deformation and more or less erosion in the adjacent stable platform areas. The Pennsylvanian rocks are here regarded as constituting a geologic system, and the major subdivisions of the Pennsylvanian are classed as series.

Groups

A group is "a local or provincial subdivision of a system, based on lithologic features. It is usually less than a standard series and contains two or more formations." [Classification and nomenclature of rock units: Geol. Soc. America, Bull., vol, 44, p. 429, 1933.] Properly determined, these aggregates "express the natural relations of the formations of a particular region." [Classification and nomenclature of rock units: Geol. Soc. America, Bull., vol, 44, p. 437, 1933.] They are useful units of stratigraphic classification for purposes of description and in some cases for mapping. Since lithologic characters are accepted as the controlling basis in defining formations and are also the main feature in establishing groups, a group may well be regarded as a sort of "super-formation."

The Pennsylvanian rocks of the northern Mid-Continent region are conveniently divisible into a number of lithologic aggregates that are of larger order than formations and smaller than the divisions classed as series. These intermediate units may be termed groups. The groups here defined are based both on dominance of certain kinds of rocks and on differences in the development of cyclic rhythms of sedimentation. There is a general correspondence between most of these groups and the larger stratigraphic units previously recognized in the northern Mid-Continent area, but there are differences in many of the boundaries, and some of the groups here proposed are subdivisions of former larger aggregates. The question of revision of existing nomenclature so that well known terms, such as Shawnee, Wabaunsee, and others, might be retained, and the alternative of abandoning a majority of these familiar names to make way for entirely new terms has been considered carefully. This consideration has included conference with many of the geologists who are working in the northern Mid-Continent region. The conclusion has been reached that it is decidedly preferable to revise and redefine at this time the stratigraphic units that are already established than wholly to discard the old and construct a new classification from previously unused names. We have purposely delayed modifications of stratigraphic definition of various parts of the Pennsylvanian column in Kansas until extended general studies had been completed. There seems now a fair prospect of reasonably stable classification on the basis of these studies, and after a transition in which there may be need for explicit statement of stratigraphic boundaries, it is expected that the old names will become employed in their revised application.

Criteria for Designation of Minor Units

Minor stratigraphic units in a system like the Pennsylvanian may be defined in different ways. Presumably, lithologic and faunal characters are of special importance. Each compact group of beds of similar lithologic nature and faunal content should be classed as a formation, or perhaps in some cases as a member of a formation.

Formations

It has been a common practice in the Mid-Continent region to define as formations the strata lying between two readily mappable beds, such as scarp-making limestones or sandstones. Defined on this basis, the boundary between adjacent formations should be drawn at the base of resistant strata. This is illustrated in the accompanying diagram (formations M, N, O, fig. 1). It is obvious, however, that there is no necessary relation between "formations" that are based on convenience in mapping and the "natural" relationship of the beds.

Figure 1--Generalized diagram of formation boundaries. A to G, limestone and shale members. M to O, formations defined from base of one hard member to next. X to Z, formations defined from top of one hard member to next. Clearly, the boundaries between units C and D, E and F, are the most readily mapped.

The recognition of a cyclic rhythm in sedimentation in the Pennsylvanian section of the Eastern Interior and Appalachian coal field basins, and the discovery likewise of a somewhat dissimilar but very definite sedimentation cycle in different parts of the Mid-Continent region, have an important bearing on stratigraphic classification. In Illinois each of these cycles is separated from adjacent ones by disconformities. Weller and his associates of the Illinois Geological Survey propose logically to regard each of the cyclic groups of beds as a formational unit. It is certainly true that each unit in these sequences of beds has definite relation to others in the same sequence. The sedimentation cycle in the Mid-Continent region differs from that of Illinois and other eastern states in the greater prominence of the marine deposits, especially limestone, and in the absence in most cases of definitely recognizable disconformities. There is perhaps some question as to the lines of division between certain cycles of the Kansas Pennsylvanian, but there is no doubt as to the definite relationship of each element in the succession of beds comprising the cycle.

Tha lateral continuity of beds as observed in the Pennsylvanian of the Mid-Continent region is a factor that bears on stratigraphic classification. The general persistence of beds, including many minor stratigraphic units, provides basis for differentiation of units which are certainly different from those that would be recognized if the deposits were highly variable along the strike.

Relation to cyclothems--The deposits that form a sedimentary cycle are designated by Weller as a cyclothem. [Weller, J. M., Geol. Soc. America, Bull., vol. 43, p. 1003, 1932.] The cyclothem is regarded by Weller as equivalent in rank to formation, as this term is commonly used in stratigraphic nomenclature, and geologists of the Illinois Geological Survey have employed cyclothems as cartographic units. It is doubtless true that the grouping together of the sandstone, shale, coal and various types of limestone beds of a cyclothem expresses an exceedingly important genetic relationship, and this grouping is of decided value in stratigraphic study. The fitness of a cyclothem to serve as the fundamental unit of stratigraphic nomenclature may be doubted, however, for in practical use, rocks are to be classified and named on the basis of characters that can be observed readily in the field. The boundaries between cyclothems, as these are known in the Mid-Continent area, are not always precisely determinable even in well-exposed sections, and they are almost without exception extremely ill-suited for mapping. On the other hand, certain lithologic units of the cyclothem, such as the escarpment-forming limestones, are readily differentiated from associated less resistant strata. It is these clearly defined lithologic entities that seem to be the natural units of classification and nomenclature. Boundaries between them can be determined precisely and they can be mapped without difficulty. Because they are evident and definite they are best suited to general requirements of description, mapping and economic use.

If we reject the cyclothem as the basic unit of classification and nomenclature, it is nevertheless possible and desirable to take due account of the cyclic relationships of the beds in defining formational units. Most of the limestone formations as previously classified, and as I shall define them, comprise the calcareous deposits of one cyclothem, but the intervening shales generally include parts of two cyclothems. In a majority of cases no change in the boundaries of established formations is necessary, but in some a revision of boundaries has been deemed advisable in order to include in a limestone formation a bed that previously had been considered as belonging in the adjoining shale. A reliable guide in such reclassification is furnished by knowledge of cyclic relationships.

Comparison of classification by formations and by cyclothems in part of the Wabaunsee group
Formations	Index No.	Members	Cyclothems
Dry shale	.8-.9	Shale	Dover cyclothem
Dover limestone	.7	Limestone, algal (local)
	.6	Shale (local)
	.5	Limestone, fusulinid
	.4	Shale, molluscan fauna
	.3	Limestone, molluscan (generally absent)
Table Creek shale	.2	Shale, molluscan fauna
	.1	Shale, nonmarine, and coal
	.0	Sandstone, nonmarine
	.9	Shale, nonmarine	Maple Hill cyclothem
	.8	Shale, molluscan fauna
Maple Hill limestone	.7	Limestone, algal (generally absent)
	.6	Shale, molluscoid fauna
	.5	Limestone, fusulinids
	.4	Shale, molluscoid fauna
	.3	Limestone, molluscan (generally absent)
Pierson-Point shale (upper part)	.2	Shale, molluscan fauna
	.1	Shale, nonmarine, and coal
	.0	Sandstone, nonmarine

For consideration of the genetic relations of stratigraphic elements in the Pennsylvanian section of the Mid-Continent region, it is certainly important to recognize the cyclothem. Reference to cyclothems is useful in describing the rocks and, as indicated under discussion of members, in the informal numerical indexing of cyclic subdivisions. Since it is believed that formations should be defined primarily on lithologic characters, this means that classification by cyclothems for purpose of recognizing genetic relationships is to be superimposed on the classification by formations. There is seemingly no source of ambiguity in such dual classification, providing use of the word formation is restricted to aggregates of beds having general lithologic similarity (that is, cartographic units) and of the word cyclothem to the cyclic succession of beds of all sorts. It does not seem desirable, however, to introduce a separate list of names for the cyclothems. Therefore, we propose to designate the cyclothems of the northern Mid-Continent Pennsylvanian by the name of the limestone formation that each contains. This use of terms is illustrated by reference to part of the Wabaunsee group (fig. 2).

Figure 2--Diagram showing two typical cyclothems in the Wabaunsee group. The relation of formational stratigraphic divisions to the cyclothems is also indicated.

Members

Any lithologic or paleontologic subdivision of a formation that has stratigraphic significance and reasonable persistence may be classed as a member of the formation. Many such members in the Pennsylvanian section of the northern Mid-Continent area have received formal stratigraphic names. To some extent this is desirable, but the number of named units is already so great that even one who is familiar with the section has difficulty in remembering them. Surely, the addition of scores of new names for members now recognized but unnamed is to be avoided, even if the lack of names necessitates some circumlocution or perhaps an arbitrary letter or number symbol in order to designate them exactly in descriptions. This informal method of designating members, based on the typical succession of units in a formation or cyclothem, may be extended advantageously to include members that have received formal stratigraphic names. The classification and designation of members that has been found most flexible and best adapted to field use is a sort of Dewey system. Thus far it has been employed as a convenient supplement rather than as a substitute for geographically named subdivisions. One of its main advantages is the indication contained in the index number of the type of rock and place in the ideal cyclothem of the member catalogued. The index numbers for members are given in the form of decimals because this suggests the subordinate status of the subdivision and because the decimals can be combined with whole numbers assigned to indicate a given complete cyclothem.

In dividing the cyclothem and in assigning index numbers to subdivisions, effort has been made to formulate a scheme that, with appropriate modification of detail, will be applicable to all cyclothems in the Pennsylvanian and "Permian" of the Mid-Continent region. Each of the subdivisions noted can be split into as many elements as may appear desirable, but it is intended uniformly to indicate corresponding parts of different cyclothems by the same index figures. The members are numbered in upward order.

Members of an ideal cyclothem
.9.	Shale (and coal).
.8.	Shale, typically with molluscan fauna.
.7.	Limestone, algal; molluscan, or with mixed molluscan and molluscoid fauna.
.6.	Shale, molluscoids dominant.
.5.	Limestone, contains fusulinids, associated commonly with molluscoids.
.4.	Shale, molluscoids dominant.
.3.	Limestone, molluscan, or with mixed molluscan and molluscoid fauna.
.2.	Shale, typically with molluscan fauna .
.1.	c.	Coal.
.1.	b.	Underclay.
.1.	a.	Shale, may contain land, plant fossils.
.0.	Sandstone.

Members .0 and .1 in the initial part of the cyclothem and .9 at the end are nonmarine. The remaining members are marine.

Members of formations and cyclothems in the Wabaunsee group. The simple type of cyclothem just described is well shown in the Wabaunsee group, which may be described briefly as follows, the members being numbered in upward order:

Members of typical Wabaunsee group cyclothem
.8-.9.	Shale, mostly unfossiliferous, marine or nonmarine.
.7.	Limestone, light-gray, algal, in many cases sandy to conglomeratic, or coquinoid, locally oolitic, laminated to Baggy, may contain numerous mollusks, brachiopods and bryozoans or relatively unfossiliferous, marine.
.6.	Shale, commonly somewhat sandy, marine.
.5.	Limestone, blue to gray, weathers brown, granular to dense, massive, contains more or less abundant fusulinids with or without a varied assemblage of brachiopods, bryozoans, crinoid remains, and less commonly other fossils, marine.
.4.	Shale, clayey, in many cases with rich molluscoid fauna, marine.
.3.	Limestone, blue-gray, dense to shelly, contains numerous mollusks, especially pelecypods, and some brachiopods, crinoid remains, etc., marine.
.2.	Shale, clayey, commonly contains Myalina and other pelecypods, Derbya, Chonetes, Linoproductus and bryozoans, marine.
.1.	c.	Coal, continental.
.1.	ab.	Shale, sandy to clayey, top few inches in some cases constituting underclay of the coal, may contain plant fossils, continental.
.0.	Sandstone, shaly to massive, may contain fragments of plants, continental.

The sandstone (.0) may rest disconformably on underlying beds and appears definitely to represent the initial deposits of the cyclothem. Locally a thin conglomerate may occur at the base of the sandstone. The succeeding shale and coal (.1) are clearly continental in origin and indicate deposits made on an extremely low, flat coastal plain. The mollusk-bearing shale and limestone (.2 and .3) indicate the submergence of the coal swamps or coastal plain by a very shallow sea, and the overlying shale (.4) marks continued marine transgression that culminates in making the offshore fusulinid-bearing limestone (.5). The succeeding parts of the cyclothem appear to signify marine regression which leads to shoaling waters inhabited by mollusks and favoring growth of algae (.6, .7 and .8). The terminal unit of the cyclothem (.9) is generally an unfossiliferous shale, but it may contain remains of land plants (see fig. 2). The entire cyclothem thus records a single marine pulsation, and it may be divided into an initial emergent phase (.0-.1) a transgressive marine phase (.2-.4), a culminating marine phase, (.5), a regressive marine phase (.6-.8) and a terminal emergent phase (.9). This nearly symmetrical or harmonic sort of rhythm might be expressed numerically by the sequence 0-1-2-3-4-5-4-3-2-1-0. That is, the index numbers .6 to .9 as previously given correspond to .1-.4, but they are arranged in reverse order. The Illinois cyclothems, as described by Weller and Wanless, seem to differ from this in representing mainly, if not entirely, the first half (transgressive hemicycle) of the complete rhythm, the latter half (regressive hemicycle) being absent or so foreshortened as to be as yet unrecognized.

The stratigraphic names that have been applied to limestones and shales of the Wabaunsee group will in most cases serve with little or no change of application to define formations. The placing of all of the limestone (and intervening shale) members of each cyclothem in a limestone formation and the assignment of remaining members to shale formations calls for revision of the boundaries of certain formations in various places, but these are mostly matters of detail. Application of stratigraphic names in this way leaves almost all of the several scores of individually recognizable members of Wabaunsee formations and cyclothems without formal names. It is seemingly an entirely unnecessary and undesirable step in this case to propose formal names even for the limestone members.

Members of formations and cyclothems in the Shawnee group. The succession of lithologic and faunal units that is seen in the Shawnee group differs mainly from that in the Wabaunsee group in the more complex character of the sequence of members and in the greater development of fusulinid-bearing limestones. It was in this part of the Pennsylvanian section of the northern Mid-Continent region that I first recognized clearly a cyclic repetition of beds, and because of the definite nature of stratigraphic relationships and apparent completeness of members that are developed this has served as a type in previous study and description of the Mid-Continent Pennsylvanian cyclothems. [Moore, Raymond C., Pennsylvanian cycles in the northern Mid-Continent region: Ill. Geol. Survey, Bull. 60, pp. 247-257, 1931; A reclassification of the Pennsylvanian system in the northern Mid-Continent region: Kan. Geol. Soc., Guidebook, Sixth Ann. Field Conf., pp. 79-97, 1932.] Present knowledge indicates that the Shawnee cyclothem contains certain significant elements that have not yet been described and that it may be of composite rather than simple character.

The outstanding elements in the Shawnee cyclic sedimentary rhythm are the three or four different types of limestone that appear in the same order in each of the four limestone formations of the group, which in upward order are called Oread, Lecompton, Deer Creek, and Topeka (see fig. 10). The limestone members have come to be designated commonly as "lower," "middle," "upper" and "super," respectively. All of the limestone members, except in some cases the fourth or topmost ("super") of each of these limestone formations, are typically fusulinid-bearing. The thin shale members that separate the limestones differ from one another in various characters and the order of succession of these is constant in each formation. Black fissile shale, for example, belongs invariably between the "middle" and "upper" limestone members and does not occur elsewhere.

These limestone formations, in which a cyclic succession is so very evident, are separated by relatively thick shale formations that are mostly rather sandy, and are mainly nonmarine. They are the Kanwaka shale, Tecumseh shale, and Calhoun shale, named in upward order. When attention is directed more closely to the content of these shales it is observed that each is typically divisible into a nonmarine shale in the lower part, one or two beds of limestone with or without fusulinids in the middle part, and a nonmarine shale, sandstone and at least locally a coal bed in the upper part. There is thus a cyclic repetition of elements in the shale formations as well as in the limestones.

Having made these observations, the problem of defining the character of unit cyclothems and the proper lines of division between contiguous cyclothems is presented. Approach to this problem calls for recognition of the genetic significance of each type of sedimentary deposit that is here encountered and for an acceptable correlation of members in the Shawnee succession with members in the seemingly more simple Wabaunsee type of cyclothem. Present knowledge of sedimentation, especially as regards the conditions responsible for the very different lithologic characters of the several limestone units, is certainly too meager for a satisfactory understanding of the genetic significance of all cyclothem members, but it is possible to distinguish homologies of elements in the Wabaunsee and Shawnee successions. Let us undertake to apply the Wabaunsee or ideal cyclothem as a yardstick in classifying and arranging a partition of the Shawnee rocks.

The ideal cyclothem, as previously described and as seen more or less typically developed in the Wabaunsee group, begins with nonmarine sandstone, shale and coal, is followed by marine shale and limestone with a molluscan fauna, attains a culminating marine phase in fusulinid-bearing limestone, that is succeeded by shale and limestone containing mollusks and algae, and closes with nonmarine shale. We find in the upper part of the Lawrence shale, Kanwaka shale, Tecumseh shale and Calhoun shale a persistent sandstone member that at least locally is conglomeratic at the base, and in each case this sandstone is overlain by sandy shale with land plant remains and by coal (fig. 10). These nonmarine deposits may be identified as equivalent to the initial members of the Wabaunsee cyclothem. Above the coals in the Shawnee group and upper Lawrence shale are a few feet of shale, un fossiliferous or containing a molluscan or molluscoid marine fauna; no limestone member with a molluscan fauna is recognized. Then comes (a) the relatively thick, fusulinid-bearing "lower" limestone, (b) shale, (c) the thin, also fusulinid-bearing "middle" limestone, (d) black fissile shale, (e) yellow or gray clay shale, and (f) the thick light gray, wavy-bedded "upper" limestone which contains fusulinids. If the fusulinid limestones, taken together, are correlated with the middle (fusulinid-bearing) member of the Wabaunsee cyclothem, the Shawnee group may be considered as distinguished by a great and somewhat complex development of the inferred culminating marine phase of the cyclothem--that part marked by presence of fusulinids. Most of the "super" limestones of the Shawnee group correspond very well to the receding molluscan and algal limestone member of the Wabaunsee cyclothem, and both are followed by nonmarine shale. There remains to consider the marine, in part fusulinid-bearing limestones, that occur in the middle or upper part of the thick shale formations of the Shawnee group. This definitely indicates a marine invasion that followed a considerable time of continental sedimentation and that was in turn followed by continental sedimentation. Seemingly these limestones and a portion of the contiguous strata must be considered as a separate cyclothem. If that is accepted, we have an alternating sequence of complex major and simple minor cyclothems, the former characterized by presence of numerous members including three or in some cases four different fusulinid limestones, and the latter marked by similarity to the simple ideal cyclothem. This repeated succession of cyclothems of differing character indicates a rhythm of larger order than that shown in the individual cycles and suggests the desirability of a term to designate a combination of related cyclothems. The word "megacyclothem" will be used in this sense to define a cycle of cyclothems. The interpretation of the Shawnee members just discussed is indicated in tabular form below.

Suggested grouping of members of a typical Shawnee megacyclothem
Minor cyclothem
.8-.9.	Shale, marine or nonmarine (thick).
.7.	Limestone, light-gray, algal, sandy to conglomeratic, oolitic, may contain mollusks, brachiopods, bryozoans, etc.
.6.	Shale, may contain abundant mollusks, brachiopods, bryozoans, etc.
.5.	Limestone, contains fusulinids.
.2-.4.	Shale, marine, thin or absent.
.0-.1.	Shale and sandstone, nonmarine, not definitely differentiated.
Major cyclothem
.9.	Shale, nonmarine, thick, commonly with plant fossils.
.8.	Shale, with molluscan fauna.
.7.	Limestone, dark-blue or gray, like .7 member of Wabaunsee cyclothem, but less persistent and more irregular in thickness (the "super" limestone of field classification).
.6.	Shale, thin or absent.
.5.	h.	Limestone, blue or gray, even-bedded, contains fusulinids, absent in many sections (and where present it has generally been classed with the "fourth" or "super" limestone).
.5.	g.	Shale, commonly somewhat sandy, marine.
.5.	f.	Limestone, light-gray, fine-grained, wavy-bedded, locally cherty, thickness generally 12 feet or more, contains abundant fusulinids and other fossils, at top in some cases contains algal? "super" type limestone lacking in fusulinids (the "upper" limestone).
.5.	e.	Shale, yellow or gray, clayey.
.5.	d.	Shale, black, fissile.
.5.	c.	Limestone, dark-blue, dense, single massive bed, 1 to 2 feet thick, vertical joints, contains numerous fusulinids and other fossils (the "middle" limestone).
.5.	b.	Shale, gray, clayey, 10 feet or more, in southern areas contains a red zone and subordinate thin sandstone and nodular limestone beds.
.5.	a.	Limestone, blue-gray weathering strongly brown, ferruginous, somewhat sandy or earthy, massive, 5 to 10 feet in average thickness, contains numerous fusulinids and other fossils (the "lower" limestone).
.2-.4.	Shale, sandy to clayey, contains brachiopods and mollusks, may include zone with brachiopods and pelecypods at base of 5a.
.1.	c.	Coal, thin and very local.
.1.	ab.	Shale, yellowish, sandy, may contain plant fossils.
.0.	Sandstone, yellow-brown, fairly persistent, 5 to 10 feet in average thickness, base locally conglomeratic.

If this characterization of cyclothems most accurately depicts the stratigraphic relationships in the Shawnee group, the reasons for the alternating succession of major and minor cyclothems are to be formulated, and it is also to be explained why the fusulinid phase of the so-called major cyclothem is divided into contrasting parts as noted.

An alternative classification of the Shawnee members remains to be considered. It is possible that the three or four fusulinid limestones of the limestone formations and the fusulinid limestone of the shale formations each represent the culmination of several more or less completely developed cyclothems. This would mean that instead of a major and a minor cyclothem we have to do with a succession of associated and related cyclothems of slightly differing characters. This suggested cycle of cyclothems comprises the same units that have previously been designated as a megacyclothem. The following tabulation arranges the members according to this plan, introducing certain members that are only locally developed, but that may be very important in reaching an understanding of the succession as a whole. The five cyclothems that are tentatively identified are indicated by the letters A-E and the members are designated by index numbers corresponding to those employed in describing the Wabaunsee cyclothem (see fig. 3). The most prominent, persistent and definitely recognized stratigraphic units are indicated by an asterisk (*).

Subdivisions of a typical Shawnee megacyclothem
Cyclothem E
*E.9.	Shale, sandy, plant fossils, thick.
E.8.	Shale, marine.
*E.7.	Limestone, oolitic or pebbly, contains algae and few mollusks.
*E.6.	Shale, molluscan and molluscoid fossils.
*E.5.	Limestone, contains fusulinids and molluscoids.
E.4.	Shale, molluscan and molluscoid fossils.
E.3.	Limestone, shaly, thin, molluscan fossils.
E.2.	Shale, marine, molluscan fossils.
*E.1-E.0.	Shale and sandstone, plant fossils, thick.
Cyclothem D
D.9.	Shale, plant fossils (in general without definite upper boundary).
D.8.	Shale, molluscan fossils.
*D.7.	Limestone, oolitic or flaggy, molluscan fossils, locally prominent ("super" limestone).
D.6.	Shale, thin or absent.
D.5.	Limestone, blue or gray, even-bedded, granular, contains abundant fusulinids, 1 to 4 feet thick, but absent in many exposures (generally included in the so-called "super" limestone).
D.2-D.4.	Shale, calcareous, molluscan and molluscoid marine fossils.
D.0-D.1.	Sandstone and shale, mostly unfossiliferous, locally with land plant fragments.
Cyclothem C
C.9.	Shale, grades without definite boundary into next higher member.
C.8.	Shale, marine molluscan fossils, mostly thin or unrecognized.
C.7.	Limestone, blue or gray, granular, impure, may be algal, lacks fusulinids, clearly recognized in some outcrops (included in the "upper" limestone).
C.6.	Shale, generally absent.
*C.5.	Limestone, light-gray, wavy-bedded, locally chert-bearing, in general thick (5 to 25 feet), contains fusulinids and molluscoids ("upper" limestone).
*C.4-C.2.	Shale, molluscan and molluscoid fossils.
*C.1.	Shale, black fissile, contains conodonts, scanty brackish water molluscan fauna, locally insects, abundant macerated plant fragments.
C.0.	Absent or not recognized.
Cyclothem B
B.9-B.8.	Absent or not recognized.
B.7.	May be represented in top of "middle" limestone by zone of abundant molluscan fossils.
B.6.	Absent or not recognized.
*B.5.	Limestone, dark-blue, dense, a single massive bed with vertical joints, contains fusulinids and molluscoids except commonly in thin zones at top and bottom ("middle" limestone).
B.4.	Absent or not recognized.
B.3.	May be represented at base of "middle" limestone by zone of molluscan fossils.
B.2.	Shale, marine, generally molluscan fossils.
B.1.	Shale, nonmarine, in most cases not definitely recognized, coaly streak may be present.
B.0.	Sandstone or red shale.
Cyclothem A
*A.9-A.8.	Shale, generally unfossiliferous.
*A.7.	Limestone, oolitic or granular, molluscan fauna, locally 3 or 4 feet thick.
A.6.	Shale, generally not differentiated.
*A.5.	Limestone, blue-gray weathers brown, ferruginous, impure, massive or uneven thick beds, contains fusulinids and molluscoids ("lower" limestone) .
A.4.	Generally absent or not recognized.
A.3.	May be represented at base of "lower" limestone by zone of molluscan fossils.
*A.2.	Shale, marine, generally molluscan fossils.
A.1.	c.	Coal, thin or absent.
A.1.	b.	Underclay, generally recognized where coal is present.
*A.1.	a.	Shale, sandy, plant fossils.
*A.0.	Sandstone, nonmarine, locally contains plant fragments, may be conglomeratic at base.

Figure 3--Diagram showing typical megacyclothem of the Shawnee group.

Careful analysis of this succession of units leads to the conclusion that we are dealing here not with a single unbroken rhythm in types of sedimentation, marked by the uniform direction of changes in what might be termed respectively transgressive and regressive hemicycles, but there is indication rather of oscillations that are superposed on a large cyclic movement. The actuality of existence of the lesser rhythms is marked by the repetition in varying degrees of distinctness and prominence of elements that are restricted to a single part of the ideal simple cyclothem. For example, it may be noted that oolitic limestone with a strongly molluscan fauna is a typical near-end member of the receding phase of the simple cyclothem (fig. 3). The occurrence of such rock (A.7) between the "lower" (A.5) and "middle" (B.5) limestones, both of which contain: fusulinids, is expectable on the hypothesis of a group of related cyclothems, but is seemingly inexplicable otherwise. The same may be said of other members. The coal A.1e is definitely recognized in many places and occurs in its proper relationships as compared to the ideal simple cyclothem. The carbonaceous or coaly streak in B.1 fits properly in the cyclothem that contains the "middle" limestone (B.5) as its central member, but is anomalous otherwise. It is nevertheless true that in different parts of the megacyclothem certain members of the supposed simple cyclothems are characteristically suppressed and it is also true that certain members are strongly developed in a particular supposed simple cyclothem but little developed or absent in others. These facts, in conjunction with the difference in physical characters that distinguish the fusulinid-bearing members and their repetition in constant order, give definite basis for the grouping designated as a mega cyclothem. Indeed, the cyclic character of the larger rhythm is much more evident and striking than that of the indicated lesser rhythm. The arrangement of megacyclothem members in five cyclothems, as shown in the second table, is tentatively accepted as more completely and naturally representing essential relationships than a grouping in two very unequal cyclothems, as indicated in the first table.

The formations of the Shawnee group, as previously noted, have been defined to consist of closely associated limestones and intervening thin shales on the one hand, and of thick shales and included thin limestone and sandstone on the other (see fig. 10). These two types of formations are arranged in alternating succession. In terms of megacyclothem members, as given above, the Oread limestone includes members A.5 to D.7, inclusive; the Kanwaka shale contains the remainder of this mega cyclothem, D.8 to E.9, and in addition the basal part of the next following one, A.0 to A.4; the Lecompton limestone includes members A.5 to D.7 of this second megacyclothem, the Tecumseh shale members D.8 to E.9 and the following A.0 to A.4, and so on. This stratigraphic classification which is based essentially on lithologic features is the most natural and practical, but does not coincide with the limits of either the cyclothems or of the megacyclothems. Arguments in favor of defining formation boundaries so as to coincide with the limits of megacyclothems have some merit but are open to the objections that a complete revision of stratigraphic nomenclature would be required, that boundaries would be difficult to map, and that in order to be logical the group boundaries would have to be modified. Furthermore, if adopted for one part of the system, the cyclic basis of classification should be applied to the remainder, and such action seems definitely inexpedient. Finally, it is certain that although some features of the cyclic development are very definitely known, others remain to be worked out.

Members of formations and cyclothems of the Douglas group. The Douglas group consists mainly of clastic deposits in which only one or two cyclothems with persistent limestones are developed, but there are alternations of sandstone, shale and coal beds that indicate the existence of other partially complete cyclothems (see fig. 9). Much study of the Douglas beds remains to be done.

Members of formations and cyclothems of the Missouri series. The cyclothems of the Missouri series are generally similar to those of the Shawnee group, but the succession of different members is less complete. There is seemingly greater irregularity than in the Shawnee group, which makes classification of some parts of the Missouri series doubtful as yet. Equivalents of cyclothems B and C as listed under the Shawnee megaeyclothem are definitely recognized again and again in the Missouri series, but cyclothems corresponding to A, D, and perhaps E are either absent or not clearly identified. Therefore, we may tentatively distinguish megacyclothems in the Missouri series with the differentiation and grouping of members as shown in the following table. The most prominent and characteristic members are designated by an asterisk (*).

Subdivisions of a typical Missouri series megacyclothem
Cyclothem C
C.9.	Shale, unfossiliferous or with plant fossils.
C.8.	Shale, molluscan fossils.
*C.7.	Limestone, oolitic, or very siliceous, cherty, or fragmental, molluscan fossils or algae ("super" limestone).
C.6.	Shale, molluscan and molluscoid fossils, well developed in some cases but typically absent in others.
*C.5.	Limestone, light-gray, wavy-bedded, locally chert-bearing, in general thick, may contain fusulinids ("upper" limestone).
C.4-C.2.	Shale, molluscan and molluscoid fossils.
*C.1.	Shale, black fissile, contains conodonts, scanty brackish water molluscan fauna and abundant macerated plant fragments.
C.0.	Sandstone, mostly lacking or unrecognized.
Cyclothem B
B.9-B.8.	Absent or not recognized.
B.7.	May be represented in "middle" limestone by abundant Osagia, pelecypods and worm borings, brecciated limestone.
B.6.	Absent or not recognized.
*B.5.	Limestone, dark-blue, dense, a single massive bed with vertical joints, may contain fusulinids but commonly molluscoids and mollusks are dominant ("middle" limestone).
B.4-B.2.	Shale, molluscan and molluscoid fossils.
B.1.	Coal, thin but persistent in some cases, absent in others, underlain by nonmarine shale, locally bearing plant fossils.
B.0.	Sandstone or red clay shale, may be absent.

Next below the cyclothem B, as listed above, mainly distinguished by the "middle" limestone (B.5), is a cyclothem of the C type with prominent "super" and "upper" limestones. The peculiarities of the Missouri series cyclothems may be related to the more dominantly marine character of these deposits in the northern Mid-Continent region. Southward tracing of the beds shows that in general the limestones become thin and eventually disappear, the shales become thicker and more sandy, beds of sandstone and coal appear. Clastic sediments were evidently borne mainly from the south, and in Oklahoma sandstone and shale far outweigh limestone. The deposits are mostly marine, however. Careful study of southern Kansas and Oklahoma beds belonging in the Missouri series, with special attention given to cyclic sequences, has not been undertaken, but no indication has yet been seen that members characteristic of the A cyclothem make appearance in this region. In the case of the Stanton limestone, at least, there are three distinct cyclothems, each containing fusulinid members and other typical elements of the ideal cyclothem, but the lowest of these three cyclothems is typically representative of the "B cyclothem," characterized by presence of a "middle" (dense blue, vertically jointed) limestone.

Formations and members of the Missouri series have been defined wholly on the basis of lithologic characters. Some formations embrace most of the beds in a megacyclothem, as defined above, but others include relatively small parts of two adjacent cyclothems or megacyclothems and a few comprise the limestone or shale portion of a single cyclothem. The recognition and definition of cyclic elements has value in indicating the relationship of beds, but it has not been applied uniformly to stratigraphic classification of the Missouri series (see figs. 7 and 8).

Members of formations and cyclothems of the Des Moines series. In the Des Moines series, the existence of a number of cyclothems is definitely determined, but detailed stratigraphic investigation of this part of the section remains to be undertaken. The Marmaton-group cyclothems closely resemble those of the Missouri series. Persistent limestones are well developed. The Cherokee cyclothems, as yet little known in Oklahoma, Kansas and Missouri, appear to be very similar to those described by Weller and Wanless in Illinois. Here the sandstone, shale and coal of the nonmarine part of the cycle are approximately, equal in importance to the marine, or the nonmarine may be better developed than the marine (see fig. 6).

Some Problems of Stratigraphic Nomenclature

The application of names to the stratigraphic units recognized in the Pennsylvanian of the Mid-Continent states offers a number of vexing problems. In the first place, it is necessary to determine as accurately as possible the prior use of stratigraphic names, and in several cases difficulty and confusion are encountered here. The availability or suitability of names, in a number of cases, depends on the accuracy of correlation between outcrops at distant points.

A problem encountered in regional stratigraphic study of any system is that concerning the use of names in relation to lateral changes in the character of the beds. No stratum or group of strata is laterally continuous indefinitely. Ultimately, a limestone grades into sandstone or shale, or it pinches out. Thus, a sharply defined stratigraphic boundary between limestone and shale in one section may be lost entirely where the limestone disappears. Some of the difficulties and complexities in the application of names as encountered in eastern Kansas are represented diagrammatically in the accompanying sketches (figs. 4A, 4B). Ideally, contemporaneous deposits of different lithologic character may be recognized by continuous faunal horizons. A horizon in the midst of thick shale may carry a distinctive group of fossils that represents exact equivalence in age wherever the faunal horizon is identified. The shale may grade laterally into limestone or sandstone, but if the faunal horizon persists in the latter, fairly exact correlation of beds in the shale and limestone or sandstone is possible (fig. 5). Examples of this type of faunal and lithologic relationships are encountered in the Mesaverde sandstone-Mancos shale sections of the Cretaceous in the Rocky Mountains region, in the Elmdale shale-Foraker limestone of the Kansas-Oklahoma region, in the Ordovician and Devonian of New York, and many other cases. Such occurrences are of much stratigraphic value and interest, but it is generally quite impossible to map the line defined by fossils. The beds are divided, rather, on lithologic bases. Stratigraphic names must have practical application.

Figure 4A--Diagrammatic representation of stratigraphic units in the Missouri series along the strike of outcrops in eastern Kansas. (For DeKalb read Westerville; for Elm Branch read Ladore; for Sniabar read Hertha.)

Figure 4B--Same as Fig. 4A, showing stratigraphic nomenclature. (Definition of the Swope formation is modified to exclude beds below Middle Creek limestone. (See page 83.)

Figure 5--Diagram showing gradation of shale into sandstone, with faunal horizons persisting through both types of rock.

It appears from our study that the only practical basis for differentiation of beds such as those of the Kansas Pennsylvanian, that are to be named and mapped, is a lithologic one. Thus, a limestone formation is considered to end where the limestone disappears. In the case of a formation name which applies to a group of beds, upper and lower limits of the formation may vary in different localities. The exact upper and lower limits may be indicated by reference to the names of the subordinate units that are recognizable in these particular places. In order to avoid numberless additions of stratigraphic names where the boundaries of formational units vary, usage adopted by the Kansas Geological Survey calls for expansion and in many cases hyphenation of the boundary units. For example, the Howard formation in part of central Kansas includes three limestone members (Bachelor Creek, Church and Utopia) and two shale members (Aarde and Winzeler),. the lower one containing the widely persistent Nodaway coal bed. The formation may be defined stratigraphically in this region by writing "Howard limestone (Bachelor Creek-Utopia)." Near Howard, Kansas, where the Utopia member is lacking, the exact designation becomes "Howard limestone (Bachelor Creek-Church)." In northern Kansas and southern Nebraska we find numerous sections which show the Utopia limestone and Nodaway coal but lack the Bachelor Creek member. The Howard limestone may be defined here by writing the names of the lower and upper members, as "Nodaway-Utopia." This usage of terms means that in places where the upper or lower members of a formation are absent or unrecognizable, the adjacent formation units are expanded actually a slight amount. For instance, the Severy shale in Greenwood County, Kansas, includes the strata between the top of the Topeka limestone, below, and the base of the Bachelor Creek member of the Howard limestone, above. Farther north, the top of the Severy may be defined at the base of the Church member of the Howard. It is recognized that equivalent shale deposits may thus be classed as belonging in the Howard limestone in some sections and as included in the upper Severy shale in other sections. The only alternative to this seems to be a departure from definition of formation and member units on lithologic bases and the drawing of arbitrary unrecognizable boundaries within shale bodies. These latter can be mapped only approximately and cannot be defined in sections.

South of the point where the Wyandotte limestone disappears, the Lane shale and the Bonner Springs shale, which occur below and above the Wyandotte, respectively, come together and no mappable horizon is found between the Iola limestone and Plattsburg limestone. The thick shale extending from the top of the Iola to the base of the Plattsburg may be designated as Lane-Bonner Springs shale. This usage seems preferable to introduction of a new name for this shale, (1) because the hyphenated name automatically defines the span of the shale body, (2) because adoption of the latter practice would require almost numberless additions to the existing long list of Pennsylvanian stratigraphic units, and (3) because the method of nomenclature is flexibly adapted to various types of changes along the strike of the beds. It is recognized that the middle part of the Lane-Bonner Springs shale may be stratigraphically equivalent to the Wyandotte limestone (see fig. 5).

Summary of the Revised Stratigraphic Classification of the Pennsylvanian Rocks of Kansas

Three divisions of series rank, separated one from another by unconformities, are now recognized in the Pennsylvanian section of Kansas. These are named, in upward order, the Des Moines series, the Missouri series, and the Virgil series. The Virgil beds are separated from the overlying Big Blue series, classed as "Permian," by an unconformity (see fig. 12). Because the boundaries of these series are defined by unconformities rather than by arbitrarily selected conformable contacts, there is necessary revision of the line between Des Moines and Missouri beds. The Missouri series is restricted to include only the lower part of deposits formerly designated by this name, and the boundary between Missouri and Virgil beds is an unconformity in the lower part of the Douglas group of previous usage (fig. 9). The upper boundary of the Virgil series is located at the break that occurs near the horizon of the Brownville limestone, and within the group of beds formerly known as Admire shale.

The Des Moines series in Kansas contains two groups, the Cherokee beds below, and the Marmaton group above. These groups are defined as previously, except that some rocks formerly classed as upper Marmaton are transferred to the Missouri series (fig. 6).

Figure 6--Diagram showing comparison of old and revised classification of Des Moines beds. This section, representing conditions in the latitude of the Kansas river, does not show the most typical development of the Marmaton beds. In southeastern Kansas the Lenapah limestone appears above the Altamont and beneath the disconformity that marks the base of the Missouri series, as redefined.

The rocks of the Missouri series are divided into five major segments which are clearly differentiated in east-central Kansas and western Missouri, but are not so definite in southern Kansas. At the base of the series is the Bourbon formation, including the deposits, chiefly shale and sandstone, that occur between the post-Des Moines unconformity and the base of the Hertha limestone. Conformably above the Bourbon beds comes the Bronson group, consisting chiefly of limestone and including the beds from the base of the Hertha limestone to the top of the Dennis limestone. This corresponds to the lower part of the Kansas City group as previously defined. The Bronson group is a compact assemblage of limestones that readily stand apart from the contiguous strata (fig. 7). The Kansas City group is redefined to include the middle and upper part of the old "Kansas City formation" as proposed by Hinds and Greene, and in addition it includes shale in the lower part of the previously defined "Lansing formation." It extends from the base of the Fontana shale to the top of the Bonner Springs shale. Thus the revised Kansas City group comprises the shale and included limestones, mostly thin or lenticular hard-rock bodies, that lie between the persistent and prominent Bronson and Lansing limestones. The Kansas City group contains much more shale than the next lower or higher groups. The Lansing group contains the Plattsburg and Stanton limestones, together with the mostly rather thin Vilas shale that lies between them. It is thus a limestone group that is persistent. Finally, a variable thickness of beds, chiefly shale, that occur between the top of the Lansing and the unconformity at the base of the Virgil series, is classed as the Pedee group. These rocks were, formerly included in the "Douglas formation" (fig. 8).

Figure 7--Diagram showing comparison of old and revised classification of lower Missouri beds (redefined).

Figure 8--Diagram showing comparison of old and revised classification of upper Missouri beds (redefined).

The Virgil series contains three groups as now classified in Kansas. Beneath the Oread limestone there is thick shale and sandstone, and rather unimportant thin limestone, that comprise the Douglas group. The Douglas beds are very dominantly clastic (fig. 9). The Shawnee group is defined to include the beds from the base of the Oread limestone to the top of the Topeka limestone, and thus is made up of alternating limestone and shale formations, each about 40 to 80 feet in thickness. These beds show best the characteristic features of the cycle of cyclothems which has been designated as a megacyclothem (fig. 10). The Wabaunsee group comprises the remainder of the Virgil series, in which there are numerous thin limestones and moderately thick shale bodies. Here is found a good development of simple cyclothems which, unlike those of the Shawnee group, are not evidently to be grouped in megacyclothems (fig. 11). There is possibly some ground for subdivision of the Wabaunsee group into two parts, as proposed (in manuscript) by G. E. Condra. If this is done, the line of separation belongs near the horizon of the Tarkio limestone, for in northern Kansas and in Nebraska the Tarkio and adjacent formations are well developed and fairly thick, whereas south of Emporia, Kan., the Tarkio disappears and the contiguous shales become markedly thin.

Figure 9--Diagram showing comparison of old and revised classification of lower Virgil beds. The unconformity that separates the Stranger formation from the Iatan, Weston, or Stanton beds was not recognized in earlier work.

The accompanying figures 6 to 12 show the revised classification of the Pennsylvanian rocks of Kansas, and for comparison, indicate its relation to older usage.

Figure 10--Diagram showing comparison of old and revised classification of middle Virgil beds.

Figure 11--Diagram showing comparison of old and revised classification of upper Virgil beds.

Figure 12--Diagram showing comparison of old and revised classification of beds now referred to the lower part of the Big Blue series of "Permian" age. This shows especially the revision of the boundary between the Pennsylvanian and "Permian" rocks.

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Kansas Geological Survey, Geology
Placed on web Sept. 28, 2016; originally published November 15, 1935.
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