Artificial Outcrops Give Real Experience in Interpreting a Geologic History: The CMUland Group Project for Historical Geology Courses

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ABSTRACT

A basic goal of historical geology courses is for students to gain an understanding of the methods, theories, and logic used in interpreting geologic histories. This is traditionally taught as a series of individual, isolated lessons in identification of rocks, fossils, and sedimentary structures and interpretations of radiometric dating, sequences of events, past depositional environments, and past tectonic events. A supplemental project incorporating these lessons teaches students to evaluate different types of data and use critical thinking to reconstruct a geologic history. Here, a semester-long, group project has been developed that allows students to use their lab- and classroom-honed skills on real rocks in a field setting. Our "field area" includes 11 artificial outcrops, representing six rock types. Students must: (1) identify rock types and fossils; (2) calculate radiometric ages; (3) recognize stratigraphic contacts, geologic structures, and cross-cutting relationships; and (4) critically evaluate this data to give a chronological history of past environments, tectonic events, and even climate. Assessment shows that student learning was enhanced greatly as a result. Not only did students acquire more experience and a deeper understanding in the mechanics of historical geology, they also gained an appreciation for the work required to interpret a geologic history.

INTRODUCTION

The Importance of Geologic Histories in Historical Geology Courses - 200-level historical geology courses, fundamental as a prerequisite to most other geology courses, are charged with introducing students to the concept of geologic histories, both as case studies and the methods and theories that are used to interpret them. Traditionally, historical geology courses contain lab assignments that focus only on specific, individual parts of the process of interpreting a geologic history. For example, students learn to identify fossils in a hand sample and make interpretations about the age and depositional environment of that rock. Students calculate radiometric ages of imaginary rocks based on isotope ratios. However, historical geology students do not usually get a chance to work with these methods as part of a larger problem and, as a result, do not gain experience incorporating various types of geologic data into one "big picture".

During twelve semesters teaching historical geology classes, I have noted with dismay that my students often miss the "big picture". Even when they have mastered the individual lessons about rock and fossil identification, radiometric dating, etc., some students still struggle to understand how these methods can be used together to define a geologic history. As a response to this problem, I have been adding supplemental exercises to my traditional labs. These supplemental exercises have evolved into what I call the CMUland project, a semester-long, group project focused on artificial outcrops on the CMU campus. This project culminates in a 1-2 page geologic summary, a basic geologic map, a stratigraphic column, and recommendations for future study.

Why Artificial Outcrops? - The benefits of incorporating field projects into a variety of different geology courses, especially for introductory geology and structural geology, have been recognized (i.e., Granshaw, 2004; Pound et al, 2003). These projects are relatively easy to plan and execute at campuses with nearby bedrock outcrops. However, incorporating field experiences into geology courses at campuses in "outcrop-challengecr regions is much more difficult. Other attempts to do so have resulted in using rock gardens, plywood, and even books to simulate outcrops (Dillon et al, 2000; Greenberg, 2002; Kastens and Ishikawa, 2004).

Central Michigan University is located in the middle of the Lower Peninsula of Michigan. This area is covered by thick glacial sediments (Dorr and Eschman, 1970), so outcrops are not abundant. …