Modeling equilibrium and bedrock controlled geomorphology using terrain analysis

The research described in this thesis combines field mapping with geographic information system (GIS) analysis of digital elevation models to better understand the timing of events and ages that led to the development of the tectonic geomorphology preserved in the North Boulder Basin of southwestern Montana. Particular attention was given to the mapping and correlation of remnant pediment surfaces and stream valley knickpoints in an 8 km by 15 km portion of the study area. The bedrock geology consists primarily of uplands containing Mississippian Madison Group to Cretaceous Kootenai Formations and Cenozoic Bozeman basin fill sediments. The boundary between the uplands and basin fill is a recently active normal fault. The field mapping revealed three remnant geomorphic surfaces (pediments) that the GIS analysis showed were consistent with the North Boulder River base-level changes of +25 m, +135 m, and +155 m. The ages of pediment surfaces were estimated through a terrain analysis of the amount of material removed by subsequent erosion and division of the volume removed per unit area by the denudation rates of 43 mm/1000 yr, 50 mm/1000 yr, and 100 mm/1000 yr. Estimates for the ages and development times of the lowest pediment remnant indicate a minimum age of 33.1K years and a maximum age of 2.8M years. The maximum age applicable for the highest pediment surface is 6.2M years based on the timing of the Bozeman Group and minimum age is 2.1 M years.;Major knickpoint locations and characteristics were analyzed in relation to the normal fault and exposed bedrock. Knickpoints have larger relief in the Madison Group, Phosphoria, and Quadrant Formations as compared to the Six Mile Member of the Bozeman Group basin fill. The knickpoints with the largest offset are formed proximal to the normal fault. The overall patterns of landscape evolution are consistent with a long period of basin fill excavation that has persisted throughout the late Cenozoic with progressively less vertical displacement along the normal fault that separates the Main Basin from the Inner Basin of North Boulder Basin, Montana.