New Mexico Geological Society Annual Spring Meeting — Abstracts

Morphologic characteristics of drainage basins, alluvial fans and stream terraces along a tectonically active mountain front may be
influenced by both the tectonic history of the seglnented range front fault as well as by Quaternary climatic fluctuations.

The soils and sedimentologic characteristics of alluvial fan units are consistent along tectonically dissimilar mountain front segments. However, morphometric analyses suggests that the geometry and linear spacing of fans and their drainage basins changes systematically with the segmentation pattern. Larger and more elongate fans and drainage basins tend to be located at segment boundaries while smaller fans and basins with steeper slopes tend to be located between boundaries and in areas characterized by higher uplift rates.

A soilchronosequence has been developed for fluvial terraces of the Red River. Relative soil development coupled with several ¹⁴C dates indicates that at least two depositional terraces are temporally correlative with Bull Lake and Pinedale age glacial outwash deposits and spatially correlative with major alluvial fan depositional units. Carbon-14 dates obtained from younger debris-flow type deposits throughout the study are reveal that they are mid-Holocene in age, suggesting a possible relationship to neoglaciation.

These data suggest that the segmentation pattern of the tectonically active range-front -fault strongly influences the geometry of mountain front landforms. However, climate is the driving force that governs their production and stratigraphy. These results will help define the relative contribution of Quaternary climatic fluctuations and neotectonic activity onI landform evolution in the northern rift. Understanding the
sensitivities of landform morphology to neotectonic activity may also have strong implications for assessing the possible seismic hazards of tectonically active areas.