Application and limitations of the authigenic 10Be/9Be dating and meteoric 10Be inventory in Bouse Formation along the lower Colorado River corridor, southwestern USA

초록

Authigenic 10Be/9Be dating and 10Be inventory methods have been used as a robust chronological tool to date oceanic sediments as old as ~12 Ma. However, their application was limited to continental sediments deposited in relatively closed lakes. We tested the two methods to examine their applicability to early-Pliocene Bouse Formation in the lower Colorado River corridor, as its stratigraphy and age are well-constrained. The calculated authigenic 10Be/ 9Be ages for the Bouse Formation range from 2.51 to 3.85 Ma, with a mean age of 3.15 Ma, which is considerably younger than the published ages of 5.4 to 4.7 Ma. The measured 10Be inventory was three orders of magnitude lower than the predicted inventory. We examined the factors that may constrain the behavior of beryllium isotopes and suggest that the offset of age could be derived from an estimated initial ratio that may not be the real one or the incomplete retentivity of the beryllium isotopes. The discrepancy between predicted and measured 10Be inventory may be due to surface erosion, insufficient 10Be retention or inaccurate estimation of 10Be inheritance. © 2023 International Union of Geological Sciences. All rights reserved.

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