Paper No. 4
Presentation Time: 2:00 PM


BLAKEY, Ron, Colorado Plateau Geosystems, 1133 Flowing Springs Trail, Flagstaff, AZ 86004,

A newly generated detailed paleogeographic map series of North America and vicinity presents the last 550 million years of geologic, tectonic, and paleogeographic history. The large size of the maps (~5400 X 6000 pixels) permits the presentation of moderate detail across the mapped area. The detail and clarity shown on the maps raises several questions: 1) What are the sources of data? 2) How much artistic license is employed? 3) What is the reliability for each given time slice across the area of the map? 4) How are controversies with interpretation addressed?

Data are shown as a comprehensive list of references. The reliability and artistic license issues are explained in an accompanying document that discusses these issues relative to different types and quality of data and interpretation. Areas with robust data (eg. sedimentary basins) are obviously more reliable than areas with little data; however, areas such as shields that have little stratigraphic information over much of their history can be portrayed using geologic inference. For example, widespread Middle Ordovician quartz sandstone sequences imply uplift and erosion of the Canadian Shield during the Early Ordovician. The geometry of orogenic belts is based on structural-tectonic data and the resulting paleogeography is cloned from modern mountain ranges believed to be modern analogues. Controversies in geologic interpretation are decided by the paleogeographer. A final test of map accuracy follows the principle that each successive time slice must follow logical geologic order and obey modern geodynamic principles and rates.