18 Surficial geology and neotectonics in the West: Celebrating and advancing the legacy of Kirk Bryan through field-based geomorphology studies

This session invites and examines recent field-based geomorphology studies in the West. Contributions regarding soils geomorphology, neotectonics, pediments, fluvial terraces, and landscape development are invited.

Tuesday, 19 May 2026
8:00 AM - 12:00 PM
Alvarado A

The Influence of Late Pleistocene Climatic Variability on Landscape Evolution in the foothills of the Sandia Mountains, New Mexico

Paper number: 18-8
Program: Technical Sessions
Time: 10:10 AM – 10:30 AM

Authors

Abstract

In the foothills of the Sandia Mountains, exposures of aplite bedrock are coincident with curvilinear hillslopes in a landscape otherwise dominated by granitic corestone topography. Despite the smooth slopes with extensive soil mantles, these hillslope systems do not exhibit steady-state behavior. Instead, rates of colluvium production and slope erosion have varied during the late Pleistocene associated with climatic variability. These soil mantles are created by the periodic production of blocky aplite clasts that favors the entrapment and accumulation of dust in pores spaces between clasts. During periods of lower rates of colluvial production, dust accumulation continues, resulting in cumulic soils with thick Bk and Bt horizons. The lower B horizons are stable resulting in accretionary soil development that thickens the overall hillslope deposit. Aplite clasts on the surface and in the shallow subsurface, however, are transported downslope by creep-related processes at a faster rate. In the Holocene, 10Be-derived rates of aplite clast production are low and there has been net erosion of hillslope soils. Higher rates of aplite clast production occurred in the late Pleistocene, prior to the LGM, at ~35 ka. Temperature depressions of 4-10°C and enhanced moisture during this time likely favored enhanced frost shattering. This period of clast production far exceeded erosion rates and hillslope soils thickened. Soil morphologic features, 10Be abundances in aplite clasts, and optically stimulated luminescence dates of eolian material indicate a previous period of aplite accumulation also in the late Pleistocene, ~65 ka. This period of accumulation was followed by stabilization, incorporation of eolian material at depth, and erosion of surface soil horizons. These aplite slopes highlight how volumetrically minor occurrences of rock with different weathering properties combined with climatic variability can profoundly impact the complex geomorphic evolution of hillslope landforms. Colluvial thickness and slope form are not the result of a long-term balance between colluviation and erosion. In contrast, these slopes and their forms are the product of non-steady rates of weathering and erosion that are intimately linked to prior environmental conditions, rock type, and eolian accumulation.

Geological Society of America Abstracts with Programs. Vol. 58, No. 4

doi: 10.1130/abs/2026RM-410728

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