CAN GEOLOGIC MAPS BENEFIT FROM SOILS DATA? AN EXPLORATIVE INVESTIGATION OF BEDROCK AND SURFICIAL GEOLOGIC MAPS IN NASH COUNTY, NORTH CAROLINA

Abstract

Soils are complex natural bodies that express the varying effects of five (5) soil-forming factors: parent material (geology), length of time of soil formation, climatic history, landscape position (geomorphology), and biological activity. Soil map units reflect the complex relationships between the soil forming factors and are mapped based on the inter-relationships of soil physical, chemical, and biologic properties in the top 2 meters of the land surface. Soil maps are produced to guide land use and management for all land areas. Once soil relationships are developed, intensive field mapping is conducted to confirm and further refine soil associations and distributions. Soil map units can be sorted based on the geologic material from which they formed. While geologic data embedded in soil maps are typically broadly categorized (i.e. basic rock types), soil maps have potential to provide refinement of geologic map units in certain applications. We selected two USGS 1:24,000 quadrangles in Nash County, North Carolina based on recent work on Tertiary sedimentary deposits and associated soil relationships in this region (Stadelman SEGSA 2017). Nash County is located in the Fall Line Zone between the eastern piedmont and inner coastal plain of North Carolina about 40 miles east of Raleigh. Bedrock geology consists of Paleozoic metavolcanics and igneous intrusive rocks overlain by Tertiary sediments. GIS analysis of geologic and soil survey maps indicated good potential to improve delineation of bedrock map units in Nash County and especially boundaries between metavolcanics and intrusive igneous map units. This analysis also indicated high potential for improvement in delineation of sedimentary deposits. Field investigations were done in selected areas, and results with preliminary geologic map revisions will be presented.