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 as we understood it in the closing years of the 20th century. It was compiled by Jack Reed (USGS), John Wheeler (GSC), and Brian Tucholke (Woods Hole Oceanographic Institution. 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 tectonic, before radiometric dates were widely available, and when the geology of the sea floors was largely unknown. The old map distinguished about 100 rock 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 previous map, including volcanoes, calderas, impact structures, axes of submarine canyons, spreading centers, transform faults, magnetic isochrons, 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. The map was compiled over an interval of almost 25 years and its assembly spanned the technological change from tradition 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 raises new questions and encourages new work in critical areas. We hope that this new map will play a role in the training of a new generation of earth scientists and in planning new research. We also hope that it will provide the basis for a variety of derivative maps that address geologic hazards, wise development of mineral and energy resources, and environmental concerns including water quality, waste disposal, and land-use planning.