Using Paleogeographic Maps to Portray Phanerozoic Geologic and Paleotectonic History of Western North America

Ronald C. Blakey
Professor Emeritus Northern Arizona University, Flagstaff, Arizona
([email protected].)

Paleogeographic maps provide clear, concise pictures of the evolving complex geologic events of Western North America. Time slices are selected to show critical stages in the geologic history thereby providing a continuous view of the evolution of the region and clearly showing sequences of paleogeography and paleotectonics. The maps are particularly effective in demonstrating the geometry and history of terrane accretion and the affects of accretionary events on the growth of Western North America from Devonian to Present. The maps are also powerful tools for comparing varying or contrasting models of various terrane-accretion events and for showing cause and effect across broad geologic provinces. Other maps (isopach, paleogeology, facies, paleocurrent, etc.) can be used in conjunction with paleogeographic maps to further explain the geologic history.

The models presented here are derived and modified from the geologic literature. Data is plotted on basemaps and paleogeography is cloned from digital elevation maps to match the inferred distribution of landforms at given times and places. The paleogeography is shown in palinspastic restoration with reference to present political boundaries. The maps are finished in a fashion to show how paleogeography might have appeared as if seen from space. Colors suggest paleovegetation and inferred paleoclimate. Water depths are shown in shades of blue from evidence presented in the literature and presumed modern analogs. Although maps are assigned a specific geologic age, ranges are given to suggest the interval for which the maps are valid. The resulting series of paleogeographic maps provides a coherent picture of the geologic and tectonic history of Western North America that respects known and inferred geologic rates and geodynamic models.

AAPG Search and Discovery Article #90159©2012 AAPG Foundation Distinguished Lecturer Series 2012-2013.