Combined uranium series and 10Be cosmogenic exposure dating of surface abandonment: A case study from the Ölgiy strike-slip fault in western Mongolia

L. C. Gregory*, A. L. Thomas, R. T. Walker, R. Garland, C. Mac Niocaill, C. R. Fenton, A. Bayasgalan, T. Amgaa, B. Gantulga, S. Xu, C. Schnabel, A. J. West

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Time-averaged fault slip-rates can be established by reliably dating the abandonment of an alluvial deposit that has been displaced by Quaternary movement along a cross-cutting fault. Unfortunately, many Quaternary dating techniques are hindered by uncertainties inherent to individual geochronometers. Such uncertainties can be minimised by combining multiple independent techniques. In this study, we combine <sup>10</sup>Be exposure dating of boulder tops and U-series dating of layered pedogenic carbonate cements accumulated on the underside of clasts from two separate alluvial surfaces. These surfaces are both displaced by the active Ölgiy strike-slip fault in the Mongolian Altay Mountains. We date individual layers of pedogenic carbonate, and for the first time apply a Bayesian statistical analysis to the results to develop a history of carbonate accumulation. Our approach to the U-series dating provides an age of initiation of carbonate cement formation and avoids the problem of averaging contributions from younger layers within the carbonate. The U-series ages make it possible to distinguish <sup>10</sup>Be samples that have anomalously young exposure ages and have hence been subject to the effects of post-depositional erosion or exhumation. The combination of <sup>10</sup>Be and U-series dating methods provides better constrained age estimates than using either method in isolation and allows us to bracket the abandonment ages of the two surfaces as 18.0-28.1kyr and 38.4-76.4kyr. Our ages, combined with measurements of the displacement of the surfaces, yield a right-lateral slip-rate for the Ölgiy fault of 0.3-1.3mmyr<sup>-1</sup>, showing that it is a relatively important structure within the active tectonics of Mongolia and that it constitutes a substantial hazard to local populations.
Original languageEnglish
Pages (from-to)27-43
Number of pages17
JournalQuaternary Geochronology
Volume24
DOIs
Publication statusPublished - 1 Jan 2014

Keywords

  • Active faulting
  • Altay
  • Cosmogenic isotopes
  • Quaternary dating
  • Uranium series

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