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

Abstract

Authigenic Be-10/Be-9 dating and Be-10 inventory methods have been used as a robust chronological tool to date oce-anic sediments as old as similar to 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 Be-10/Be-9 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 Be-10 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 Be-10 inventory may be due to surface erosion, insufficient Be-10 retention or inaccurate estimation of Be-10 inheritance.