Dates and rates of arid region geomorphic processes

Abstract

Analysis of in situ-produced cosmogenic nuclides, including 10 Be, 26 Al, and 36 Cl, has changed how geologists understand desert surface processes. Here, we provide a series of examples from arid mountain-piedmont systems that illustrate both the power and limitations of this geochronometer. Analyses of samples collected from bare bedrock surfaces at the Alabama Hills, California, demonstrate slow but variable (1.4-20 m m.y. −1) rates of erosion, whereas cosmogenic dating of the Blackhawk landslide debris (~6.5-31 k.y.) and the Castle Dome piedmont allows linkages between landscape-scale processes and climate change. However, data show that nuclides inherited from prior periods of exposure, as well as the effect of post-depositional surface change, limit the accuracy and precision of exposure dating in some settings. On the broad Castle Dome piedmont, detailed isotopic stratigraphies, coupled with analysis of desert soils, indicate depositional histories over the past ~70 k.y. in the absence of radiocarbon-datable organic material. Transect-based amalgamated sampling techniques allow for estimation of sediment velocity down mountain-fringing piedmonts. In drainage basins, the concentration of 10 Be in fluvial sediment demonstrates the efficacy of fluvial mixing even in areas where surface flow is intermittent. Considered together, these applications of the cosmogenic technique allow the delineation of sediment budgets in areas where no other technique has been useful. Such data are important for the arid Southwest, where population is increasing rapidly, as is the interaction of society and surface processes.

Large rockslides in the Southern Central Andes of Chile (32–34.5°S): Tectonic control and significance for Quaternary landscape evolution

“…Only a few of the replicate TCN ages are within their 2σ analytical precisions, impeding precise determination of the age of most events, and confirming that even in large landslides a large number of samples is needed to constrain accurately the events involved (e.g., Ivy-Ochs et al, 2008). In samples MAC001 and POT008 (both ∼ 80 ka), and PAN003 (∼ 24 ka), we interpret them as representing inheritance, a feature that is far more common in landslide boulders (e.g., Nichols et al, 2006;Ivy-Ochs et al, 2008) than in moraine boulders.…”

Study of RADARSAT-2 synthetic aperture radar data for observing sensitive factors of global environmental change

“…6 Alluvial fans in arid and semiarid regions provide an important record of neotectonics and paleoclimate change, revealing the evolutionary characteristics of the regional paleoenvironment. [7][8][9][10][11] For example, by studying the surfaces of alluvial fan units, information about weathering, age, and past climatic conditions, all of which affect surface morphology, can be determined 12 and are an indicator of paleoclimate and paleoenvironment change. SAR can play an important role in mapping alluvial fan surfaces.…”

The Temporal-Spatial Distribution of Shule River Alluvial Fan Units in China Based on SAR Data and OSL Dating

“…Alluvial fans in arid and semi-arid areas are important recorders of both tectonic and climatic signals [1][2][3][4][5][6][7][8]. Fan units of varying ages, with different geomorphic features, can contain vast amounts of information for the study of paleoclimatic and paleoenvironmental changes [2,[8][9][10].…”

“…Fan units of varying ages, with different geomorphic features, can contain vast amounts of information for the study of paleoclimatic and paleoenvironmental changes [2,[8][9][10]. Some of the most important pieces of such information are the temporal-spatial distribution characteristics of alluvial fan geological units.…”

“…Based on this geological information, we try to better understand the following questions: (1) Which parameters extracted from SAR data are associated with the geomorphic features of alluvial fan units and can be used to map them? (2) What is the characteristic of the SRAF units' temporal-spatial distribution, and what is the correlation of that distribution to tectonic activities and paleoenvironmental changes?…”