THE U.S. GEOLOGIC NAMES LEXICON GEOLEX IN THE AGE OF GEOLOGIC MAP DATABASES

In the late 1800's, the USGS, under the leadership of Director John Wesley Powell, began a systematic mapping program that produced the Geologic Atlas of the United States folios. Recognizing the need to provide a consistent set of geologic maps, he formed committees to develop standards for cartography, principles of rock and sediment classification and nomenclature, and a geological time scale. Essential to these standards and to the Atlas series was a catalog of geologic names of the U.S.

The catalog of geologic names remains essential to this day, both to the science and to preparation of the National Geologic Map Database (NGMDB, http://ngmdb.usgs.gov); today, the U.S. Geologic Names Lexicon (GEOLEX) is a component of the NGMDB. It contains ~16,000 geologic units, and provides original and revised definitions, type localities, geologic ages, geographic extent, variations in geologic name usage, and publication synopses. Information has been compiled mostly from formal reports and maps published since 1836, emphasizing outcrop-level descriptions, age determinations, and relationships to other geologic units.

Geologic map databases introduce new challenges to the management of GEOLEX; although these allow for comprehensive documentation of individual geologic features (e.g., an observation point, an outcrop area), it is widely recognized that preparing this documentation can be a great burden to the geologist. However, it is critical to document changes in nomenclature and usage, so they can be recorded in GEOLEX. We are developing mechanisms to encourage and facilitate a more informative and useful documentation of individual geologic features in these map databases; for example, to note the method of geologic age determination, revisions to unit boundaries, or areas where a unit was previously misidentified.