BUILDING PALEOGEOGRAPHIC MAPS TO UNDERSTAND THE GEOLOGIC HISTORY OF AN AREA: HOW WE MAP AND VISUALIZE DEEP TIME

Plate tectonics is a theory that describes how thin, crustal “tectonic plates” form, move, deform, and are destroyed on the Earth. These movements are confirmed and measured today using GPS monitoring. We can estimate the magnitude and direction(s) of plate movement in the geologic past using several lines of evidence, including (but not limited to) oceanic crust ages, hot spot tracks, and estimated offset on geologic structures. By integrating these lines of data geoscientists can build paleogeographic maps which show the estimated position of land masses through geologic time. In addition, by using interpretations form rock units of the same age as the reconstructed map we can add information about what the Earth’s surface looked like at that time: positions of mountains, rivers, coastlines, etc.

In this talk, I will present an example of a set of paleogeographic maps that show Nevada reconstructed to ~360-305 million years ago. Building the base map involved restoring deformation from several events, including periods of crustal stretching, contraction, and lateral sliding. Eight paleoenvironment maps were generated using that paleogeographic map as a base, which show how the distribution of different sedimentary rock types changed through time. The changes in rock types through time are a function of changes in sedimentary depositional environment related to a combination of local deformation and sea-level change. Building maps like these is important because it gives us a picture of how the sedimentary systems in the area responded to these deformation events which we can then use for resource and geothermal exploration.