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Geochronology Advances in geochronological science
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https://doi.org/10.5194/gchron-2019-2
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/gchron-2019-2
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 30 Apr 2019

Research article | 30 Apr 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Geochronology (GChron).

Chlorine-36/beryllium-10 burial dating of alluvial fan sediments associated with the Mission Creek strand of the San Andreas Fault system, California, USA

Greg Balco1, Kimberly Blisniuk2, and Alan Hidy3 Greg Balco et al.
  • 1Berkeley Geochronology Center, 2455 Ridge Road, Berkeley CA 94550 USA
  • 2Department of Geology, San Jose State University, San Jose, CA USA
  • 3Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, CA USA

Abstract. We apply cosmogenic-nuclide burial dating using the 36Cl-in-K-feldspar/10Be-in-quartz pair in fluvially transported granitoid clasts to determine the age of alluvial sediment displaced by the Mission Creek strand of the San Andreas Fault in southern California. Because the half-lives of 36Cl and 10Be are more different than those of the commonly used 26Al/10Be pair, 36Cl/10Be burial dating should be applicable to sediments in the range ca. 0.2–0.5 Ma that are too young to be accurately dated with the 26Al/10Be pair, and should theoretically be more precise for middle and late Pleistocene sediments in general. However, using the 36Cl/10Be pair is more complex because the 36Cl/10Be production ratio varies with the chemical composition of each sample. We use 36Cl/10Be measurements in samples of granodiorite exposed at the surface at present to validate calculations of the 36Cl/10Be production ratio in this lithology, and then apply this information to determine the burial age of alluvial clasts of the same lithology. This particular field area presents the additional obstacle to burial dating (which is not specific to the 36Cl/10Be pair, but would apply to any) that most buried alluvial clasts are derived from extremely rapidly eroding parts of the San Bernardino Mountains and have correspondingly extremely low nuclide concentrations, the majority of which most likely derives from nucleogenic (for 36Cl) and post-burial production. Although this precludes accurate burial dating of many clasts, data from surface and subsurface samples with higher nuclide concentrations, originating from lower-erosion-rate source areas, show that upper Cabezon Formation alluvium is 260 ka. This is consistent with stratigraphic age constraints as well as independent estimates of long-term fault slip rates, and highlights the potential usefulness of the 36Cl/10Be pair for dating upper and middle Pleistocene clastic sediments.

Greg Balco et al.
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Greg Balco et al.
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Latest update: 17 Jun 2019
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Short summary
This article applies a new geochemical dating method to determine the age of sedimentary deposits useful in reconstructing slip rates on a major fault system.
This article applies a new geochemical dating method to determine the age of sedimentary...
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