Student Research Projects

Balancing Cross Sections from the Sixteen Quadrangle, Montana Using Geographical Information System (GIS)

Student James Griczin ‘15 (Earth and Environmental Science)
Faculty Mentor(s)
Department Earth and Environmental Sciences
Course Earth and Environmental Science 489: Research in Earth and Environmental Science

Abstract

Stratigraphic profiles, or geologic cross sections, are interpretations of subsurface geology given in a particular mapped area, and they are a fundamental part of geologic mapping. Balancing a cross section is the method of restoring a cross section to its undeforemed state in order to check the interpretation for plausibility. A cross section is said to be balanced if all bedding lengths between a set of reference lines are the same both before and after restoration. The purpose of this investigation was to see if GIS was a good medium to use in cross section balancing. A scanned copy of the Sixteen Quadrangle, Montana geologic map from the USGS website (projection predefined) was uploaded into GIS, and Cross Section B digitized. We then cut our newly formed polygons at the two major fault lines that went through the entire stratigraphy and restored all rock layers matching the beds on either side of the faults. Reference lines were placed on the axial planes of major folds or planes of no slip and measurements were taken between reference lines and interpretations were drawn to fill in places where the bedding planes went outside the cross section. After restoration of the cross section, it was found that the bedding planes were at proper lengths, and thicknesses were uniform throughout each bed with the exception of some variations where slip was present.