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Classification of Rocks in Kansas (1968)

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Introduction

The State Geological Survey of Kansas has issued summaries from time to time indicating current classification and nomenclature of rock units in the State. These summaries have proved of value in unifying and clarifying Stratigraphic usage in the State and have served as an easily accessible reference for those unfamiliar with Kansas stratigraphy.

A chart entitled "Graphic Column of Kansas Rocks" (Moore et al., 1952) showed graphically the relationship of the stratigraphic sequence in Kansas. A revised chart, "Graphic Column and Classification of Rocks in Kansas," by J. M. Jewett was published in 1959.

The present report is similar to "The Kansas Rock Column," Bulletin 89, and "Tabular Description of Outcropping Rocks in Kansas," Bulletin 52, Part 4, inasmuch as it describes a generalized composite rock section in the State. The text is supplemented by a graphic representation (Pl. 1).

The classification used in this paper, like that in other tables of classification of rocks, is dual: (1) rocks are classified as to their origin within a commonly used and accepted geologic time scale, and (2) geographic names are applied to parts of the earth's crust that are regarded as rock-stratigraphic units.

Time Classification

Geologic time is divisible as shown in Table 1. Judgment for the making of a geologic time classification is based on observation of the superposition and fossil content of the rocks.

Table 1. Conceptual relationship between geologic time, time-stratigraphic units, and rock-stratigraphic units.

Geologic time Time-stratigraphic unit Rock-stratigraphic unit
Eon  
Era  
PeriodSystem 
EpochSeries 
AgeStage 
EpochSeries 
  Group
  Formation
  Member
  Bed

Time-Stratigraphic Classification

Rocks that were formed during the periods of geologic time are called systems and bear the same names as those of the periods (Table 2). Hence, rocks of the Permian System were deposited during Permian time or in the Permian Period; rocks of the Cambrian System were formed during the Cambrian Period, etc. It is possible and useful to assign rocks to smaller divisions than those listed in Table 2. Rocks that are placed within a major division of a system are said to constitute a series, which may be called lower, middle, upper, or which may be given a geographic name. In parts of the geologic section it seems advisable to assign strata to still smaller divisions, and hence stages are used as smaller and usually more local divisions within a series (Table 1).

Table 2. Classification and relationship of geologic time and time-stratigraphic units. (Time-scale in millions of years from Kulp, 1961).

Time units Beginning of period, in millions of years Time-stratigraphic units
Cenozoic Era Quaternary Period 1 Quaternary System
Tertiary Period 63 Tertiary System
Mesozoic Era Cretaceous Period 135 Cretaceous System
Jurassic Period 181 Jurassic System
Triassic Period 230 Triassic System
Paleozoic Era Permian Period 280 Permian System
Pennsylvanian Period 320 Pennsylvanian System
Mississippian Period 345 Mississippian System
Devonian Period 405 Devonian System
Silurian Period 425 Silurian System
Ordovician Period 500 Ordovician System
Cambrian Period 600 (approx.) Cambrian System
Precambrian

Rock-Stratigraphic Classification

A rock-stratigraphic unit is a subdivision of rocks that is delimited on the basis of lithologic characteristics (American Comm. Strat. Nomenclature, 1961). Rock-stratigraphic units are divided into groups, formations, members, and beds. A formation is the most fundamental and useful unit in this division. A group is the next higher ranking unit and may include two or more formations. A member is a subdivision of a formation. A bed is the smallest subdivision in rock-stratigraphic classification.

Acknowledgments

Many persons have contributed to the revised description of the stratigraphy of Kansas. We are especially indebted to the authors of Bulletin 89, R. C. Moore, J. C. Frye, J. M. Jewett, Wallace Lee, and H. G. O'Connor, for the fund of information upon which this bulletin is based. Thanks are extended to P. H. Heckel, A. L. Hornbaker, P. L. Hilpman, of the State Geological Survey of Kansas, S. M. Ball and P. C. Franks, formerly of the State Geological Survey of Kansas, and M. E. Bickford, of the Department of Geology, The University of Kansas, for information and special assistance, and to Lila Watkins, JoAnne Crossfield, Diana Coleman, Karyl Higbie, and Anita Sloan for help in the preparation of final copy.

Many helpful suggestions were given by D. F. Merriam, of the State Geological Survey of Kansas, who reviewed the manuscript. Scribing of Plate 1 was done by Larry Hensiek. Preparation of copy for Plate 1 and the illustrations were by Sharon Hagen. Doris Zeller was responsible for the layout of Plate 1.

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Kansas Geological Survey, Stratigraphic Succession in Kansas
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Web version August 2005. Original publication date Dec. 1968.
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