HIERARCHICAL CLASSIFICATION OF MAP UNITS USING THE SEAMLESS INTEGRATED GEOLOGIC MAPPING (SIGMA) EXTENSION TO THE GEOLOGIC MAP SCHEMA (GEMS) TO SUPPORT DYNAMIC ASSEMBLY AND REVISION OF LARGE GEOLOGIC MAP DATABASES (PART 1)

The process of managing the stratigraphic framework for a national geologic map database is more complex than for a traditional quadrangle-based geologic map. To provide timely release of map data, the database needs to be assembled and published incrementally. The number of map units is constantly changing in this dynamic environment, in stark contrast to typical workflows where a map and its stratigraphic framework consist of a fixed number of map units and are published as a single, stand-alone product. Simplified stratigraphies, like generic age-lithology classification, for example, have been used for small-scale (national) maps. This simplified stratigraphy would likely require fewer modifications throughout construction of a national geologic map; however, application of the geologic data is limited because map units are disassociated from previous mapping and research that largely utilize formation-level nomenclature. To ensure usability of a national map database, formation-level stratigraphy is necessary. These factors result in an extremely large and constantly changing stratigraphy. The Geologic Map Schema (GeMS) provides some schematic tools for representing a stratigraphic framework but supporting a constantly changing stratigraphy is beyond its intended purpose. The Seamless Integrated Geologic Mapping (SIGMa) extension to GeMS supports a dynamic database stratigraphy through a structured hierarchical map unit organization. The hierarchy is based on time-restricted geologic provinces that represent depositional, tectonic, and magmatic settings and processes related to the genesis of map units. Mapped features are the spatial component, and stratigraphic relationships and geochronology define the temporal components of the geologic provinces. Advantages to this hierarchical structure include: (1) expandability; (2) geologically meaningful organization incorporates the hierarchical nature of crustal-scale geologic processes; (3) the ability to maintain stratigraphy independent of a single project thereby supporting multiple map scales; (4) map units are placed in a regional- to continental-scale geologic context; and (5) local, real-world stratigraphies are represented as consecutive table records improving end-user comprehension.