Orientation Analysis of Geologic Map Data Within ArcView

Author: Nicole V. Bolay
Organization: Colorado State University

Fort Collins, CO 80523
USA

Phone: (970) 491-1961
nvbolay@cnr.colostate.edu

The utility of current geological maps is limited by the lack of tools to quantitatively summarize and analyze map data. This research created Avenue scripts for ArcView that allow the objective analysis of arcuate geologic map features. The scripts break arcs representing fault traces, fold axes, and geological contacts into line segments whose orientations can be summarized by vector mean calculations and represented as rose diagrams of line trends. This information can then be used to determine the angular relationships between different types of geological data and to test geological hypotheses. These methods were used to test whether the Rocky Mountains in Wyoming, Colorado and New Mexico formed due to multiple stages and directions of compression during the Laramide Orogeny (70-40 Ma). Fault and fold orientations systematically change with latitude from New Mexico to Wyoming, indicating that observations from one location may not be valid elsewhere in the Rocky Mountains. The general lack of consistent multi-modal fold axis trends indicates that multi-stage, multi-directional deformation did not occur over the entire area. This example shows how these spatial analysis methods can expand the capabilities of GIS-based geologic maps.