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| Titel |
Age calibration of weathering fractures in desert clasts: A new approach to dating geomorphic surfaces in arid landscapes |
| VerfasserIn |
Mitch D'Arcy, Duna Roda Boluda, Alex Whittaker |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250091622
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| Publikation (Nr.) |
 EGU/EGU2014-5923.pdf |
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| Zusammenfassung |
| Advances in geomorphological and sedimentological research depend on the availability of
reliable exposure age constraints. Establishing robust age models at a high spatial and
temporal resolution is crucial for measuring rates of geomorphological change and decoding
complex landscapes shaped by time-dependent forces, e.g. climate fluctuations. A number of
isotopic and luminescence techniques are now available for dating geomorphic surfaces,
however they remain expensive and time-consuming to deploy with detailed coverage over
space and time in many study areas. For this reason, quick and accessible methods for
correlating and extrapolating these chronologies are needed. In arid landscapes, among
others, a variety of weathering-induced changes occur to geomorphic and sedimentary
surfaces, and many of these processes occur at predictable rates and can be quantified
using objective, field based measurements. One example is the gradual widening of
fractures that exist within boulders on desert surfaces, by a combination of processes
including salt weathering and freeze-thaw cycles. The recent emergence of very
detailed exposure age models in a number of locations means it is now possible to
measure the rates of desert weathering processes, and use them as fully calibrated age
indicators themselves. With the potential to significantly extend the coverage of
existing age constraints, this kind of quantitative age correlation would enable a
broad range of geomorphological and sedimentological research that depends on
detailed absolute age models. We have measured the mean widths of hundreds of
vertical fractures that dissect granitic boulders, on a variety of alluvial surfaces
in Owens Valley, California, which have themselves been independently dated in
detail using cosmogenic nuclides. Our data demonstrates for the first time that these
fractures widen at a predictable, steady rate of approximately 1 mm ka-1 for at
least the last 150 ka, in this arid study area in the south-western United States.
This finding, which is repeatable at a number of test sites, allows clast fracture
widths to be exploited as a simple and powerful technique for the inexpensive dating
of geomorphic surfaces in the field. We introduce a robust statistical method for
this new approach to exposure dating, perform a full uncertainty analysis on its
results, and discuss the potential usefulness of this technique in other arid landscapes. |
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