ONE OUTCROP, TWO POSSIBLE INTERPRETATIONS: USING FIELD WORK TO TEACH GEOLOGICAL REASONING

We offer several field excursions in our senior-level sedimentary petrology class that provide practical experiences in sedimentology to our geology majors. The first excursions are usually to local sand pits that contain Holocene and Tertiary “outcrop”. These trips introduce simple field techniques (e.g., how to measure sedimentary sections and paleocurrents, identification of structures etc.) Later excursions to Mesozoic and Paleozoic outcrops permit introduction of more complex concepts such as vertical and horizontal facies changes, correlation techniques and biostratigraphy. The final trip that we offer is to Moscow Landing, an exposure of shallow marine Cretaceous-Tertiary chalk and associated facies located along the cutback side of the Tombigbee River in west central Alabama. This popular site (it is regularly visited by the general public and university students from all parts of Alabama) contains an exceptional exposure of the K-T boundary which some researchers feel preserves a record of the terminal Cretaceous asteroid impact that happened approximately 1200 km to the south. Others interpret the K-T boundary at this site as a disconformity. Paleontological and sedimentological evidence has been used to support both hypotheses. The two opposing interpretations have proven to be a useful exercise in scientific reasoning for our students. Using data they collected during field work, as well as information obtained from other sources, geology students are required to draw their own conclusions about the K-T boundary at the Moscow Landing. By challenging each other to prove their interpretations, students learn the proper scientific practices that they will need later in their geological careers.