RECONSTRUCTING THE GREAT AMERICAN BANK: AN EXERCISE IN DEVELOPING BETTER PALEOGEOGRAPHIC INTERPRETATIONS FOR STUDENT CONSIDERATION

Orbital and aerial images of Earth effectively enable students to connect tectonic and surficial processes with Earth surface features. In contrast, imagery available for historical geology instruction commonly consists of: 1) bland, generalized paleogeographic maps and onshore-offshore models that give the impression of a much simpler ancient world; and 2) images of analogous modern environments that show the complexity of today’s Earth surface. To an introductory-level student, this information seems incongruous (different yet similar, simple yet complex).

Text treatments of the Cambro-Ordovician carbonate deposits of North America provide a prime example. These strata were part of a vast and highly varied carbonate complex known as the Great American Bank, yet it appears quite uniform and unrealistic in most text reconstructions. In order to present a more accurate representation of ancient North America during the Early Paleozoic, a series of synthetic orbital/aerial images of the Great American Bank were created from the compilation of regional sedimentary and paleomagnetic interpretations. Digital images of modern carbonate environments (i.e. Bahamian platforms) were cropped, altered and blended to reflect the regional interpretations, and then applied to base maps of North America. Multiple images were made to reflect evolution of the bank with time and sea-level changes.

These images present a more dynamic and interesting ancient world, and stimulate discussion of important topics such as: 1) carbonate production; 2) the effects of sea-level/climate change; 3) the effects of land plant evolution on sedimentary environments; and 4) tectonic overprinting. Through related class lectures and lab exercises, students consider the many steps in the development of these images. In doing so, they gain more respect for the interpretive process and pitfalls involved, as well as a better appreciation for the scope of Earth surface environments and events of the distant past.