COMPILED STRUCTURAL DATA FOR CHATHAM COUNTY, NC - UTILIZING GIS TO UNRAVEL STRUCTURAL GEOLOGY PROBLEMS

The NC Geological Survey (NCGS) is conducting detailed geologic mapping in Chatham County, NC with partial support from STATEMAP. We have collected structural data from parts of 14 quadrangles by 8 geologists over a 25-year period. This data was compiled into one GIS database consisting of 18,757 attributes. This dataset includes over 750 primary features, 3,500 foliation and cleavage measurements, and 4,300 joints. This data, used in conjunction with the detailed geology polygons, appears to have great potential for various structural analyses over larger areas and provides the ability to easily share the dataset with collaborators.

Geologically, the majority of Chatham County is underlain by the Neoproterozoic to Cambrian Carolina terrane and its two lithotectonic assemblages, the older Hyco and younger Aaron Formations, that consists of various metamorphosed intrusive, extrusive, and volcanogenic sedimentary rocks. The eastern portion of the county is underlain by Triassic sediments of the Deep River basin. Abundant evidence of brittle faulting at the outcrop scale and large-scale lineaments are present in the map area. The brittle faulting and lineaments are interpreted to be associated with Mesozoic extension. Diabase dikes of Jurassic age intrude the crystalline rocks of the map area.

We have identified anomalous low-lying bedding and foliations (< 30 degree dips) in Carolina terrane lithologies with reoriented trends from a typical steeply dipping regional orientation, and the occurrence of a composite foliation. The nature of these features is problematic. Preliminary observations utilizing this dataset in GIS include: 1) primary bedding within the Carolina terrane rocks are concentrated along the flanks of volcanic centers probably representing distal sedimentation. 2) local foliation trends show significant variation from the regional trend. This may be due to overprinting relationships of multiple deformation events and/or rotation of foliation by brittle faulting. 3) symbolization of dip inclinations with varying color schemes and sizes highlight areas of structural complexity that could use further investigation.