IMPROVING BEDROCK GEOLOGICAL MAPPING THROUGH THE USE OF DIGITAL SOIL MAPS AND SURVEYS

Most soil scientists and geologists know that the character of residual soil is closely linked to the nature of the underlying bedrock. For this reason, use of soil surveys to facilitate mapping of bedrock geology is deemed common practice. In the past era of paper maps, however, geologists became quickly overwhelmed by the reams of detailed data available from county soil surveys for incorporation into their geological mapping programs. Consequently, soil surveys have probably not been utilized to the fullest extent possible in some bedrock mapping efforts. With the advent and availability of digital data sets via GIS, however, soil surveys can now be easily incorporated in geological mapping efforts. The digital soil maps are particularly valuable in unglaciated settings where bedrock exposures are limited (areas with subtle topographic relief).

For the state of Oklahoma, we used available digital soil maps as well as soil surveys for each of the counties to create a new bedrock geology map. Using the MIADS soil data, we mapped the bedrock based on the parent material information of the soils gleaned from the soil surveys. This exercise required the consolidation of 2406 soil mapping units. One of the challenges encountered during this step of the process was that descriptions from the soils surveys and other resources were sometimes vague or incomplete. To remedy this situation, we evaluated the geographically associated soils and their bedrock descriptions providing us with a better idea of the bedrock in question. The consolidation of the mapping units produced sixteen general categories of bedrock lithologies. These bedrock lithologies were further subdivided into about ten mapping classes of geologic time as defined by the soil surveys.

The resulting map is a representation of the bedrock geology based on the soils. This approach has the potential to improve detailed bedrock geological mapping for use in resource assessment, civil engineering, agriculture, and land preservation.