T301 CRevolution 2.5: Origin and Evolution of the Colorado River System and Cenozoic Landscape Evolution of the Colorado Plateau-Rocky Mountain Region II

Wednesday, 28 September 2016
1:30 PM - 5:30 PM
Mile High Ballroom 2A/3A

AGE OF BOUSE FORMATION ESTIMATED BY AUTHIGENIC 10BE/9BE DATING

Paper number: T301-4
Program: Technical Sessions
Time: 2:15 PM – 2:30 PM

Authors

Abstract

Bouse Formation is one of the key elements for reconstructing the evolution of the Colorado River. We applied authigenic 10Be and 10Be/9Be dating to estimate the age of deposition of Bouse Formation at Cibola, AZ. Authigenic 10Be and 10Be/9Be dating are based on the assumption that the initial ratio of 10Be/9Be as well as 10Be decayed with time which passed since deposition, with a completely closed system. Due to the variance of 10Be production manipulated by changing magnetic field intensity, the ratio of authigenic 10Be/9Be is reported to be the better proxy than pure atoms of authigenic 10Be for dating of marine pelagic sediments. The total 25 samples collected from a 2.3-m-thick section near the base of Bouse mudstsone were analyzed for this study. The 10Be abundances range from 6.28X106 – 1.44X107 and the ratio of 10Be/9Be are bracketed by 1.57X10-10 and 3.06X10-10. The corresponding values for the surface samples are 1.4X107 and 2.39X10-9. The ages based on the two proxies center around 2.3-3.9 Ma and 4.1-5.4 Ma with slight increase with depth but the authigenic 10Be/9Be shows better correlation with depth. The age range yielded from authigenic 10Be/9Be dating is generally consistent with independent age constraints for the Bouse Formation, suggesting that the 10Be/9Be ratio is a better indicator of depositional age. The difference in age between bottom and top suggests that the Bouse Formation was deposited in relatively fast (less than 1.5 Ma) fashion and the low variation in authigenic 9Be (0.63 ± 0.06 ppm) through the section documents that the provenance was relatively constant. Thus this study demonstrates that the ratio of authigenic 10Be/9Be would be the promising proxy for dating of fine-grained terrestrial sediments as well as marine ones.

Geological Society of America Abstracts with Programs. Vol. 48, No. 7

doi: 10.1130/abs/2016AM-284185

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