GO 548 Field Stratigraphy

James S. Aber
Emporia State University

The identification and interpretation of upper Paleozoic strata in eastern Kansas through field experiences. This course requires that students be available for field trips during the fall break, Oct. 9-12, 2008.

http://academic.emporia.edu/aberjame/strata/
Course Information

Course requirements Summary of field project
Cyclothem blog 2008 Introduction to stratigraphy

ESU syllabus attachment.

Course availability

This course will be taught in fall semester, 2008. Regular (on-campus) students should enroll through normal procedures. The course is also available for distance learning from Emporia State University. Off-campus students should enroll through lifelong learning. In order to receive university credit, students must be enrolled officially and must be in contact with the instructor for course materials and directions. BIS students must have the prerequisites noted above.

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GO 548 requirements

  1. Participation: Each student is expected to attend and participate in all class meetings and field trips. Notes, maps, photographs, samples, and measurements that are made on field trips will form the basis for preparing final reports.

  2. Report: Written report of findings based on field trips and on published or unpublished information relevant to the project. Report should include pertinent observations, data, calculations, maps and illustrations to support your interpretation of the stratigraphic problem. Report must follow standard scientific style and include a bibliography of all references cited--see guidelines for geologic reports.

  3. Grading: The grading scheme for GO 548 follows: participation = 20%, report = 80%. Final grades are given in letters (A-F) with +/- designations, according to current university policy. The ESU student academic dishonesty policy is observed in this course.

Each student should make or acquire a Jacob's staff. This is a simple measuring pole that also serves as a walking stick. The typical Jacob's staff is five feet (1.5 m) long and is marked in one-foot (30 cm) intervals. This staff is used to measure strata thickness. In this example, the Jacob's staff stands on limestone and shale beds of the Neva Limestone, Chase County, Kansas. Image date 6/02, © J.S. Aber.

Field materials: Each student should have a field notebook and small bag to carry materials. A Jacob's staff is recommended. A tape measure or folding ruler could also be utilized for measuring stratigraphic sections. For marking on outcrops, a large waterproof marking pen is useful. A digital camera would be valuable for photographing rock exposures. Instructor will supply topographic maps, field compass, and any other necessary supplies.

Semester schedule

Several one-day field trips will take place on weekends during the semester. Students should be available for 2 or 3 field trips depending on weather conditions and other factors. Students should bring lunch/beverage and field notebooks. A camera is recommended. Wear appropriate clothing and foot gear. Your instructor will supply necessary field equipment.

Primary field trips are scheduled during the fall-break period, October 9-12th
If needed, additional trips may be scheduled later.

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Summary of field project

The project region for this course is the Flint Hills, primarily in Chase, Morris, Riley, and adjacent counties in east-central Kansas. The Flint Hills are underlain by a classic sequence of lower Permian bedrock that consists primarily of interbedded limestone and shale units. Course projects involve selected formations from the Council Grove and Chase groups. These include such well-known units as the Neva Limestone, Eskridge Shale, Cottonwood Limestone, Speiser Shale, Threemile Limestone, Florence Limestone and Fort Riley Limestone. The course project will focus on the Neva Limestone Member of the Grenola Limestone and Cottonwood Limestone Member of the Beattie Formation, as well as intervening and adjacent formations of the Council Grove Group (see map below).

Surficial geology of Butler County, Kansas.

Map of surficial geology of Butler County, Kansas. Based on Aber (1994a, b). The Chase Group is reddish purple (central and western), light blue depicts the Council Grove Group (eastern margin), and purple-blue shows Pennsylvanian strata (easternmost edge). The Neva and Cottonwood limestones outcrop along the easternmost edge of the county.

Taken from Kansas Geological Survey.
See geologic maps of Kansas.

The Butler County geologic map depicts the general outcrop pattern of bedrock units in the study region. Formations are distributed in N-S belts, and strata dip gently toward the west. This results in older formations outcropping to the east and younger formations appearing toward the west. The regional dip is interrupted in places by anticlines and synclines particularly over the crest of the buried Nemaha Uplift and Humboldt Fault zone, which trend NNE-SSW across the middle of Butler County.

Lower Permian strata of the Flint Hills region are arranged in repetitive sequences of interbedded limestone and shale. Such repeated intervals in sedimentation are called cyclothems. The bedrock stratigraphy of eastern Kansas is famous for cyclothems in the upper Pennsylvanian and lower Permian bedrock. These cyclic repetitions of strata are interpreted as results of marine transgressions and regressions across a broad and stable continental shelf environment. With each transgression-regression cycle, a new sequence of sedimentary deposits accumulated to form a cyclothem.

Flint Hills Permian geology.

Neva Limestone

The Neva Limestone Member is the uppermost portion of the Grenola Limestone (see fig. 2). It is overlain by the Eskridge Shale and underlain by the Salem Point Shale Member, which rests in turn on the Burr Limestone Member. The Neva includes relatively resistant fossiliferous limestone beds that form gray stone lines on slopes of the Flint Hills.

Roadcut section through the Neva Limestone, Eskridge Shale, and Cottonwood Limestone on K-150 highway west of Elmdale, Kansas.

Stratigraphic description of the Neva Limestone adapted from O'Conner et al. (in Zeller 1968, p. 46).

The Neva Limestone comprises gray limestone beds interlayered with gray and green shale. The basal bed is gray algal limestone ranging from ~10 cm to ~1 m thick, which is overlain by ~1 m of silty calcareous shale. Fusulinids, Orbiculoidea and Crurithyrus are present, and a thin limestone lens is found locally within this shale. Next above the shale is the main limestone interval of the Neva, consisting of massive, gray limestone beds varying from ~50 cm to 4.4 m in total thickness. This portion often displays a brecciated, porous appearance and contains diverse fossils of fusulinids, brachiopods, echinoids, and algae.

Above the main limestone interval, ~1 m of shale follows. This shale is gray to green in color and fossiliferous. The top of the Neva is marked by gray, fossiliferous limestone ranging from ~20 cm to ~2 m thick. Overall thickness of the Neva Limestone Member varies from slightly less than 3 m to 8½ m in south-central Kansas.

As the foregoing description suggests, the Neva Limestone is quite variable in thickness, facies and fossil content. In contrast to the usual constancy of lower Permian limestones in the Flint Hills, the Neva displays considerable changes over relatively short distances. It is this lateral variability that is the primary focus of our field investigation.

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Introduction to stratigraphy

Stratigraphy is the systematic organization and classification of rock layers (strata) based on their properties. Many different observed properties for rocks may be employed for stratigraphy, including lithology, fossils, magnetic polarity, chemical composition, and others. Rocks also may be classified according to interpretation of age and origin (genesis). In general, units classified on the basis of one property do not coincide with units determined from other properties. Three main categories of stratigraphy are commonly used by geologists (Hedberg 1976).

  1. Lithostratigraphy -- organization of rock strata into units based on their lithologic character.

  2. Biostratigraphy -- organization of rock strata into units based on their fossil content.

  3. Chronostratigraphy -- organization of rock strata into units based on their age relationships.

The scope of problems for this course involves primarily lithostratigraphy and to a lesser extent biostratigraphy, so these aspects will be emphasized for field observations and interpretations of lower Permian bedrock in the Flint Hills region. Also of concern are explanations for the depositional environments--genesis--of the stratigraphic units under investigation. The following stratigraphic terms are adapted from Hedberg (1976).

Lithostratigraphy

The organization of rock strata into units based on lithology is the foundation of stratigraphy on a local and regional basis. A lithostratigraphic unit should display a substantial degree of overall lithologic homogeneity ... as defined by observable physical features (Hedberg 1976, p. 31). Formal lithostratigraphic units are arranged in a hierarchy as follows. 

Group -- two or more formations.
  Formation -- primary unit of lithostratigraphy.
    Member -- named lithologic entity within a formation.
      Bed -- named distinctive layer in a member or formation.
The formation is the basic unit for lithostragraphy in all situations. No standard values exist for thickness or lateral extent of formations. The definition of a formation derives from practical application in a given geologic setting. In eastern Kansas, for example, upper Paleozoic formations are typically a few meters to 10s of meters in thickness. In contrast, some Mesozoic formations in western Kansas are 100s to 1000s of meters thick. The lithologic character of a formation is distinguished by two principal aspects.

  1. Composition -- This may refer to either mineralogy or chemical composition (or both).

  2. Texture -- This refers to the size, shape, and arrangement of constituent particles that make up the rock body. It includes such aspects as sorting, porosity, permeability, fabric, and other aspects of texture.

Some rock names are based on composition only--limestone, some depend only on texture--sandstone, and others are based on both composition and texture--chalk, granite, andesite, basalt, etc. Fossils may be part of lithology, in as much as they impart certain composition and texture to the rock body. The combination of composition and texture determines the bulk physical properties of a rock body, such as density, magnetic susceptibility, seismic response, hydrologic character, and many other aspects.

References

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This course is presented by the Earth Science department for the express use and benefit of students enrolled at Emporia State University. Anyone else may view and enjoy the information here. All course curriculum © by the author (2008).

Please send your comments to the course instructor.
J.S. Aber, e-mail: jaber@emporia.edu.

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Last update: June 2008.