THE NEW GEOLOGIC MAP OF NORTH AMERICA---A NEW LOOK AT AN OLD CONTINENT

The new Geologic Map of North America, the final product of the DNAG project, portrays the grand architecture of the continent and the surrounding sea floor as we understood them in the closing years of the 20th century. The map is at a scale of 1:5M and covers about 15 % of the Earth's surface. The previous geologic map of North America was published in 1965, before general acceptance of plate tectonics, before radiometric dates were widely available, and when the geology of the sea floors was poorly known. The previous map distinguished about 100 units, all of them onshore. The new map distinguishes 939 units, of which 142 are offshore. It also depicts many geologic features not shown on the 1965 map, including volcanoes, calderas, impact structures, submarine canyons, spreading centers, transform faults, seafloor crustal ages, and subduction zones. For the first time it portrays the relationships between the geology of the continent and the geology of the ocean basins that flank it. This essential component adds the large-scale perspective of major plate tectonic components not expressed in the continental geology alone and thus provides a more global context within which to interpret geologic patterns.

The map was compiled over an interval of almost 25 years and its assembly spanned the technological change from traditional cartography to digital cartography. Although the map is not yet available in digital form, plans are underway for construction of a digital database and ultimately for the release of GIS-compatible files.

No map of this kind is ever really “finished”; the best the compilers can hope for is to produce a map that raises new questions and encourages new work in critical areas. We hope that the map will play a role in the training of a new generation of earth scientists and in planning future research. We also hope that it will provide the basis for a variety of derivative maps that address geologic hazards, wise development of land, mineral and energy resources, and environmental concerns.

To quote Bert Bally, one of the early supporters of the map: “Today mankind finds itself as a significant geologic agent, modifying the evolution not only of North America but of the Earth as a whole. An understanding of the evolution of our continent will put our own activities in a proper and responsible perspective.”