New Mexico Geological Society Annual Spring Meeting — Abstracts

Single-rupture fault scarps reflect erosional, depositional and pedogenic processes that have acted, through time to modify slopes produced in a single, nearly instantaneous event. These features offer the opportunity to study catenary soil development in the absence
of the complex sequence of events that comprise the genesis of other slopes. This study uses soil morphologic and stratigraphic data to assess catena development and slope degradation on three late Quaternary fault scarps in New Mexico. The study areas include the Hubbell Springs Bench east of Los Lunas and piedmonts of the Sacramento and San Andres Mountains (east of Alamogordo and near the Very Large Array, respectively). Diffusion modeling and trends in relative soil development indicate that the Hubbell Springs scarp is the youngest feature examined (mid to late Holocene). The Sacramento scarp and San Andres scarps are of late to latest Pleistocene age. Diffusion results are complicated, however, by winnowing of fine material down slope and mantling of slopes by coarser clasts. These
phenomena produce erroneously low diffusion age values. Soil pits (n = 13) were hand-excavated transects. Profile development indices, carbonate morphology, profile thickness and thickness and development of Bt horizons indicate that mid-slope positions on fault scarps are most weakly developed. The weak development of these soils can be explained by fluvial and colluvial processes acting on scarp surfaces. Truncation or thinning of pedons near crests and production of thick cummulic soils near toes of the scarps were recognized and are related to soil development prior to faulting, increased scarp age, and slow rates of erosion and deposition relative to pedogenesis.