AN UNDERGRADUATE GEOLOGY FIELD EXCURSION TO A CRETACEOUS-TERTIARY BOUNDARY SITE IN CENTRAL ALABAMA

For the past eight years, we have conducted a 3 day undergraduate geology field trip to a Cretaceous-Tertiary exposure located at Moscow Landing in central Alabama. The field trip is intended to teach students basic sedimentological field techniques, but also presents them with a critical thinking opportunity. The 25 m high outcrop is exposed for several hundred meters along the cutbank side of the Tombigbee River, some 90 km southwest of Tuscaloosa, AL. Here, Tertiary limestone and marl sharply overlies Cretaceous chalk. Both are interpreted to have been deposited in shallow marine settings. A discontinuous layer of coarse shelly sandstone and breccia characterized by soft sediment faulting and deformation in places separates the two units. The sedimentological character of this bed has led to two opposing interpretations as to its origin; 1) a “tsunamiite” generated by the impact of the terminal Cretaceous asteroid some 1200 km south of the Moscow Landing outcrop, or 2) a Tertiary channel fill atop a disconformable K-T boundary. Paleontological evidence (primarily microfossils) has been cited to support both interpretations. Using data collected during the field trip, as well as information obtained from published sources, geology students are encouraged to draw their own conclusions about the K-T boundary at the Moscow Landing study site. Without instructor interference, students align themselves into their own camps and actively challenge each other to “prove their interpretations”. As they are self-motivated to prove their interpretation correct (or, alternatively, to demonstrate that the other guys are wrong), students study the outcrop in a meticulous fashion. As a result, students learn proper scientific practices that will hopefully be retained or developed throughout their geological careers making this one of their best field experiences… ever.