Through the Eyes of a Stratigrapher
Exploring the Upper Cretaceous Hell Creek Formation, Montana

This page was written by Jen Aschoff as part of the DLESE Community Services Project: Integrating Research in Education.

Part 1: Outcrop Description

Detailed outcrop descriptions are a fundamental component of stratigraphy. Bedding character, architecture, color, sedimentary structures and grain size aid depositional environment interpretation.

A. Describe the macroscale features of the rocks in the photo below. Use the following questions as a guide.

1. Where are the bedding surfaces?

2. How do you distinguish individual beds?

3. What is the overall architecture of these beds? Are strata laterally continuous or channelized?

Helpful resources for more information:

• Boggs (2000)
• USC Sequence Stratigraphy website
• Geology Links
• Monterey Bay National Marine Sanctuary: Geology (more info)

B. This is a close-up view of part of the broad outcrop belt in the last photo. Describe the these strata.

1. Where are the bedding surfaces in this outcrop?

2. Describe the nature of the bedding surfaces? Planar? Sharp? Erosional?

3. Where would you go to look for sedimentary structures in this outcrop?

Helpful resource for more information:

• Boggs (2000)

C. Describe the microscale features of these strata.

1. What sedimentary structures are present?

2. What flow conditions are required to produce these sedimentary structures in this medium-grained sand?

3. How does this limit the number of possible depositional environments?

Helpful resources for more information:

• USGS Bedform Sedimentology (more info)
• USC Sequence Stratigraphy Web (more info)
• Geology Online Laboratory Manual (more info)
• Boggy's Geology Links - Sedimentology (more info)

D. List and describe all of the different layers in this outcrop using the photos above (i.e., lithofacies).

1. Some layers reappear or repeat throughout the section, explain.
2. List some possible depositional processes and environments for each of the lithofacies you defined.

Helpful resources for more information:

• USC Sequence Stratigraphy Web (more info)
• Geology Online Laboratory Manual (more info)

Photos: Courtesy of Dr. J. Schmitt, Montana State University

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Finished with Part 1?
Proceed to Part 2: Generating and Testing Hypotheses