| Abstract: | U-series dating of pedogenic carbonate-clast coatings provides a reliable, precise minimum age of 45.1 ± 0.6 ka (2σ) for the T2 geomorphic surface of the Biskra Palms alluvial fan, Coachella Valley, California. Concordant ages for multiple subsamples from individual carbonate coatings provide evidence that the 238U-234U-230Th system has remained closed since carbonate formation. The U-series minimum age is used to assess previously published 10Be exposure ages of cobbles and boulders. All but one cobble age and some boulder 10Be ages are younger than the U-series minimum age, indicating that surface cobbles and some boulders were partially shielded after deposition of the fan and have been subsequently exhumed by erosion of fine-grained matrix to expose them on the present fan surface. A comparison of U-series and 10Be ages indicates that the interval between final alluvial deposition on the T2 fan surface and accumulation of dateable carbonate is not well resolved at Biskra Palms; however, the “time lag” inherent to dating via U-series on pedogenic carbonate can be no larger than ∼10 k.y., the uncertainty of the 10Be-derived age of the T2 fan surface. Dating of the T2 fan surface via U-series on pedogenic carbonate (minimum age, 45.1 ± 0.6 ka) and 10Be on boulder-top samples using forward modeling (preferred age, 50 ± 5 ka) provides broadly consistent constraints on the age of the fan surface and helps to elucidate its postdepositional development. |
| Genre: | Article |
| ProdID: | 70042314 |
| Citation Author: | Fletcher, Kathryn E. K.; Sharp, Warren D.; Kendrick, Katherine J.; Behr, Whitney M.; Hudnut, Kenneth W.; Hanks, Thomas C. |
| Citation Contributing Office: | Earthquake Science Center |
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| Citation End Page: | 1359 |
| Citation Issue: | 9-10 |
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| Citation Language: | English |
| Citation Larger Work Title: | GSA Bulletin |
| Citation LatN: | 42.0 |
| Citation LatS: | 32.5 |
| Citation LonE: | -114.1 |
| Citation LonW: | -124.4 |
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| Citation Phsyical Description: | 13 p. |
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| Citation Publisher: | Geological Society of America |
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| Citation Search Results Text: | 230Th/U dating of a late Pleistocene alluvial fan along the southern San Andreas fault; 2010; Article; Journal; GSA Bulletin; Fletcher, Kathryn E. K.; Sharp, Warren D.; Kendrick, Katherine J.; Behr, Whitney M.; Hudnut, Kenneth W.; Hanks, Thomas C. |
| Citation Start Page: | 1347 |
| Citation Volume: | 122 |
| Citation Year: | 2010 |
| Type: | citation/reference |
| Text: | 230Th/U dating of a late Pleistocene alluvial fan along the southern San Andreas fault; 2010; Article; Journal; GSA Bulletin; Fletcher, Kathryn E. K.; Sharp, Warren D.; Kendrick, Katherine J.; Behr, Whitney M.; Hudnut, Kenneth W.; Hanks, Thomas C. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| URL (DIGITAL OBJECT IDENTIFIER): | http://dx.doi.org/10.1130/B30018.1 |
| Date Other: | Tue, 1 Jan 2013 00:00 -0600 |
| Publisher: | Geological Society of America |
