Bedforms to Facies to Prediction: Walther's Law and Sequence Stratigraphic Analysis, Blackhawk Formation, Utah

Tom Morris
Brigham Young University
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This field exercise challenges students to apply their knowledge of bedforms to interpret facies within a vertical section of the Blackhawk Formation, Utah. The students draft a vertical succession of the outcrop identifying key sedimentary structures. Facies are interpreted from their observations and the importance of Walther's Law in predicting facies becomes apparent to them - even to the point of predicting where an economical coal seam may be located within the section. We conclude the exercise by discussing parasequences and challenge them to predict where parasequence boundaries would exist in the outcrop.

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Undergraduate required course in sedimentary geology.

Skills and concepts that students must have mastered

Students should have an understanding of bedforms, facies, grain size, trace fossils and depositional environments. Students should also be able to speak about what they are observing using terminology such as hummocky cross-stratification, bioturbation and planar lamination.

How the activity is situated in the course

This is one of a series of field exercises taking place during a two-day field trip.


Content/concepts goals for this activity

This activity provides an opportunity for students to apply the concepts and terms learned in class and from their textbook to an actual outcrop. Students discover the importance of Walther's law for making predictions about parasequence boundaries.

Higher order thinking skills goals for this activity

Apply knowledge of bedforms in the field; interpret facies within a formation; generate a stratigraphic column; interpret observations; defend interpretations; make predictions using observations and Walther's Law.

Other skills goals for this activity

Students work in groups of two to make observations. They also record their observations in their field notebooks.

Description of the activity/assignment

Students are given the task of predicting where parasequence boundaries would exist within a vertical section of the Blackhawk Formation, Utah. This activity challenges students to apply their knowledge of bedforms in order to interpret the facies they observe. The students work in groups of two as they make their observations. The vertical section consists of four main outcrops to be observed by the students. After making their observations and interpretations of these four outcrops, the students then make predictions of what should be found up section. Students begin down section by observing the lowest section of the four outcrops. The students make observations about lithology, grain size, sedimentary structures and trace fossils. After recording their observations in their field notebook the class gathers for a discussion. Students are called on randomly to discuss what they observed. The class creates a group stratigraphic column on a white board and includes their observations to the right of the drawn profile. They are then asked to interpret what facies these observations represent. The students defend their interpretations and, as a group, agree upon an interpretation. The facies interpretation is then added to the white board and the group moves to the next outcrop up section. After observing, describing and interpreting each of the four outcrops the students are challenged to use all of the information gathered thus far to predict what facies should be observed further up section. This exercise provides an opportunity for the students to make and defend observations and interpretations. They also get a sense for the importance of Walther's Law and how it relates to sequence stratigraphy.

Determining whether students have met the goals

Throughout the exercise students are asked questions to check for understanding as well as to have them defend their observations, interpretations and predictions.

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