IF YOU FLEW OVER THIS AREA BACK THEN: VISUALIZING EARLY PALEOZOIC MOUNTAIN BUILDING EVENTS IN HISTORICAL GEOLOGY COURSES

It is difficult for many introductory historical geology students to visualize the phenomena associated with ancient orogenic events. As instructors, we strive to tie the salient features in stratigraphic cross-sections and bedrock maps to the interpreted settings depicted in generalized paleogeographic map reconstructions. Many introductory geology students lack the skills for interpreting maps and cross-sections, as well as the “3-D geologic imagination” necessary to make such connections. After discussing the general origin of rocks in a region, we commonly resort to the question, “If you flew over this region back then, what would you see?” to stimulate visual interpretation by students. However, visualizing the past is difficult in regions where the interpreted geologic events have few modern analogs, and are complicated by tectonic overprinting.

Synthetic orbital images are useful tools for introducing students to the geologic history of a tectonically complex region, such as the southern Appalachians. Current research suggests that the southern Appalachian portion of Laurentia experienced two collisions with exotic terranes during Ordovician time. In order to enhance visualization of these events in historical geology lectures, a sequence of synthetic orbital images were developed that depict southern Appalachian paleogeography during several times in the Ordovician Period. These images were built from the assembly and digital blending of hundreds of fragments of real, scaled orbital photographs and real-color satellite images. Instructors can draw attention to as much detail as is appropriate for their class, due to the photographic quality of the images. Similar images reconstructing the Great American Bank interpret the sedimentary response to Cambrian Period sea-level changes in the southern Appalachians (Griffing, 2002). Combined with the Cambrian images, the Ordovician images aid in visualizing the transition from passive margin to active margin paleogeography. Images portray the development of key orogenic events, including: the spread of ash from volcanic eruptions, the formation and migration of foreland basins, the building of clastic wedges, and the character and timing of deformation.