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Upper Paleozoic Shales

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Conclusions

In this study, Kansas shales were found to consist of six major facies (based on the combined mineralogical, geochemical, and petrological data), each corresponding to a separate depositional environment.

  1. A sandstone and siltstone facies corresponding to deltaic sands and siltstones with a source in the Ouachita Mountains of Oklahoma and Arkansas and, occasionally, the lowlands of Iowa, Nebraska, and Missouri. This facies contains abundant quartz, feldspar, and detrital zircons and is, therefore, enriched in SiO2, Al2O3, and Zr.
  2. A clayey shale facies corresponding to prodeltaic marine muds, the seaward extension of the previous facies. The shales are rich in quartz and feldspar and have an increased clay mineral content. Ga, Li, and K2O may also be enriched in these shales.
  3. 3A black shale facies that is a product of a restricted marine environment (Heckel, 1972a, 1977, 1978). The regular stagnation of bottom waters, leading to development of reducing conditions in the sediments, may be caused by tectonic uplifts of a barrier at the mouth of the epeiric sea, a thermocline developed in a quasi-estuarine cell, or a shallow-water lagoonal formation. These shales are enriched in the trace elements Cd, Cr, Cu, Be, Mo, Ni, Pb, V, and Zn by the chemical action of organic matter.
  4. A calcareous grey shale facies that represents open-marine, shallow-water deposits that are characterized by abundant brachiopods, bivalves, fusulinids, and bryozoans. These shales have high calcite, CaO, MnO, Sr, Sn, Ge, and Bi content.
  5. A shale partings in limestone facies equated to diastemic conditions but mineralogically and geochemically similar to the calcareous facies.
  6. A facies of minor importance is a red and purple shale facies that occurs in certain sections of Lower Permian shales and possibly represents a calcareous equivalent of facies 2.

These facies equate to the lithologic divisions noted by Schwarzacher (1969), Davis and Cocke (1972), and Heckel and Baesemann (1975). By combining facies 1 and 2, a group of deltaic shales is obtained that occurs primarily in the thick shale formations separating limestone formations (outside shales). Discussing the stratigraphy and tectonic framework of Kansas, it was conjectured that the appearance of these deposits may be related to tectonic uplifts of the Ouachita foldbelt resulting from cyclic movement along subduction zones (Bott and Dean, 1973). Facies 3 and 4 generally occur as shale members separating individual limestone beds in a limestone formation (inside shales). The black shales are normally located above the second limestone bed. Facies 5 (equivalent to inside shales) and 6 (equivalent to outside shales), however, are only of minor importance as they represent a small number of shale samples. Stratigraphically, these facies were found to be distributed in a number of zones:

  1. In the Pleasanton, Kansas City, and Lansing Groups, there are regular alternations of limestones and inside shales separated into formations by thick beds of deltaic outside shales;
  2. The succeeding Douglas Group, however, appears to contain only outside shales;
  3. The Shawnee Group reverts to the limestone-inside shale alternation with outside shales separating limestone formations;
  4. The Upper Pennsylvanian culminates in the Wabaunsee Group with outside shales and occasional limestones; and
  5. In the Admire, Council Grove, and Chase Groups of the Lower Permian, a general increase in the carbonate content of all rocks is manifest in the development of calcareous outside shales (red and purple shale facies) separating the alternations of inside shales and limestones. Towards the top of this division evaporites are developed, although the geochemical data show no evidence for increasing salinity.

A number of different oscillatory patterns can be detected in these deposits. First, in the Pleasanton, Kansas City, Lansing, Shawnee, and Lower Permian Groups, a succession of alternating inside shales and limestones constitutes a limestone formation. The limestone formations are separated by outside shales, thereby outlining a set of sedimentary deposits approximately equivalent, in thickness, to a cyclothem (Moore, 1950). However, there is no firm evidence for such cycles in the stratigraphic distribution of the facies. The only corroborative support is obtained from the statistical analysis of mineral and element distributions. Fourier analyses of the stratigraphic distribution of quartz, SiO2, Al2O3, CaO, MnO, Ba, Cr, Ni, Mo, Cu, and Ga indicate the presence of 70-foot cycles in the shales. This agrees with the thickness attributed to cyclothems by Moore (1950), although no evidence for the lithological complexity of cycles presented by Moore (1950) can be found. It is, therefore, suggested that the 70-foot cycles recognized in this study match the mathematically derived oscillations noted by Schwarzacher (1969) and Davis and Cocke (1972) and are possibly manifestations of a simplified "ideal" cyclothem. It can also be inferred that, in terms of detecting cyclicity, Fourier analysis is a more appropriate and sensitive tool than multivariate analysis. Dunn (1974) also recognized this potential.

In the intervening Douglas and Wabaunsee Groups no evidence for cycles was noted. The beds are primarily deltaic clastics and may represent the products of important tectonic events in the orogenic belts to the South. The Douglas and Wabaunsee Groups are also recognized by Moore (1964) and Schwarzacher (1969) as distinct zones although they distinguish poorly developed or incomplete cyclothems in the formations.

The stratigraphic zones 1 to 4, therefore, form an alternation of cyclothem-bearing and non-cyclothem-bearing deposits, i.e., the Pleasanton, Kansas City, and Lansing Groups contain cyclothems whereas the succeeding Douglas Group does not contain cycles and similarly the Shawnee Group contains cycles and the Wabaunsee does not. The oscillation of stratigraphic zones may represent a large-scale cyclic development, possibly related to tectonism. These cycles roughly correspond to hypercyclothems (Merriam, 1963), but have been described in detail only in this project.

The cyclic development of outside shales and black shales has been accounted for by orogenic events in the Ouachita foldbelt. Major tectonic periods may also account for the differences between zones containing cyclothems and those without. Although the basic cause of the oscillation remains unknown, several tectonic controls have been proposed:

  1. Varying rates of subsidence allowing transgressions and regressions (Matthews, 1974);
  2. Repeated eustatic changes in sea level and variation in clastic influx, controlled by climatic changes (Wanless and Shepard, 1936); and
  3. Diastropic uplift and subsidence of source area (Weller, 1956).

In the light of modern theories of global tectonics and sea-floor spreading, it would seem likely that a combination of controls such as (a) and (c) may provide the answer.

A multivariate statistical analysis has elucidated the geochemical and mineralogical evolution of the Upper Pennsylvanian and Lower Permian shales and has indicated that the stratigraphic variation in the mineralogical and geochemical data is controlled by nine components--a carbonate component, a black shale component, a clay mineral component, a dolomite component, a shallow- versus deep-water environment component, a manganese component, and three uninterpretable components. These carbonate and black shale factors may be related to the orogenic controls of outside and inside shales and, similarly, the manganese component is related to marine conditions of the inside shales. The dolomite component indicates that diagenetic activity has affected the shales, particularly in the Lower Permian.

In conclusion, therefore, the concept of a 10-component "ideal" cycle envisaged by Moore (1936) is not supported in detail by mineralogical, geochemical, or petrological data from the Upper Pennsylvanian and Lower Permian shales of Kansas. However, a simplification of the clastic classification to three components--calcareous marine shales, restricted-marine black shales, and finally deltaic and prodeltaic shales, sandstones and siltstones--suggests cycles at approximately 70-foot intervals in the Pleasanton, Kansas City, Lansing, and Shawnee Groups. This classification matches the mathematically derived lithological divisions observed in the Kansas City Group by Davis and Cocke (1972). The calcareous shales equate to inside shales and similarly deltaic shales to outside shales. Black shales are in both cases equivalent.

However, a major limitation of this research project is the extensive number of interpretations and conclusions made from such a small data set. In retrospect, a more satisfactory data set could have been obtained by sampling at a fixed interval within the clastic deposits. It would also have been more appropriate to have chosen a smaller section, for example the Shawnee and Wabaunsee Groups, and to have analyzed both the limestones and shales. The sampling interval should be related to the oscillatory patterns noted in this study, i.e., less than 70 feet.

A further constraint on generalizing the results obtained was the relatively subjective decision to sample on a bed-by-bed basis. In retrospect, it would have been more desirable to have sampled extensively within beds (on a fixed-interval scale) and also along the strike of the beds, producing another level of replication and information for the project. Despite the inherent limitations due to these problems, it can be inferred that Moore's "ideal" cyclothem is not developed in the stratigraphic section examined but that a simplified cycle may be.

Acknowledgments

This manuscript was developed from research conducted for a Ph.D. at Leicester University in England.

The author would like to thank:

Dr. W. Hambleton, G. Waldron, and the staff at the Kansas Geological Survey for financial support for 20 months, field expenses, laboratory equipment, editorial, secretarial, drafting, and photographic services.

The Department of Geology at the University of Leicester for providing laboratory equipment and assistance.

Dr. J. C. Davis, without whose supervision, encouragement, advice, and friendship this project could never have been completed.

Dr. A. Khan for critically reading this manuscript.

Professor D. F. Merriam, who initiated the project, provided invaluable assistance with fieldwork, and produced the final stimulus for completion of this task.

Dr. J. G. Wilkinson, for his assistance and most helpful discussions about electron spin resonance.

Dr. C. H. James and Miss V. Rutherford, for providing assistance with the Emission Spectrometer at Leicester University.

Dr. R. J. King for providing a selection of mineral samples for analysis by electron spin resonance.

Drs. T. D. Ford, P. H. Heckel, W. Read, C. D. Conley, and B. Bassett for encouragement, discussion of the manuscript, and for their constructive advice.

Professor Symons, for the use of the electron spin resonance spectrometer.

The Leicester Computer Laboratory and Syracuse University Computing Center, for their assistance to the author during the tenure of his research.

Mr. M. Sackin and the Medical Research Council Unit for use of the computer programs ITBNTOMT and ITBNCLST.

His parents and parents-in-law for their constant encouragement and help.

And lastly to his wife, Cynthia, who advised and assisted the author with laboratory work, with typing the first drafts of the manuscript, in the preparation of diagrams, and to whose endless enthusiasm and encouragement the work is indebted.

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Kansas Geological Survey, Geology
Placed on web May 6, 2009; originally published December 1979.
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