HR: 1340h
AN: PP33B-1288    [Abstracts]
TI: Constraints on Chlorine-36 Production Rates Using Beryllium-10 at Lake Bonneville, UT
AU: * Marrero, S M
EM: shasta@nmt.edu
AF: New Mexico Tech, E&ES, 801 Leroy Pl., Socorro, NM 87801, United States
AU: Phillips, F M
EM: phillips@nmt.edu
AF: New Mexico Tech, E&ES, 801 Leroy Pl., Socorro, NM 87801, United States
AU: Caffee, M
EM: mcaffee@physics.purdue.edu
AF: PRIME Lab Purdue University, 525 Northwestern Ave, West Lafayette, IN 47907, United States
AB: The CRONUS-Earth geological calibration at the Lake Bonneville shoreline has provided a unique opportunity to constrain the chlorine-36 production rates based on the well-known beryllium-10 production rate by comparing the inventories of both nuclides in the same samples. Lake Bonneville, an ancient glacial lake, occupied a large area surrounding the current Great Salt Lake in Utah during the last glacial period. The highest stage, called the Bonneville shoreline, was very brief and lasted from 18.9-17.2 cal ka before catastrophic flooding lowered the lake level to the Provo shoreline. The geological calibration at Lake Bonneville shoreline consists of two different sites: the Tabernacle Hill basalt and the Promontory Point quartzite. The Tabernacle Hill basalt is a radiocarbon age-constrained flow that represents the Provo shoreline. The basalt erupted after the catastrophic flood into the Provo lake based on the dating of the bounding flood and tufa deposits. The Promontory Point site is a quartzite wave-cut bench at the Bonneville shoreline level. The cutting action of the waves removed significant amounts of rock and exposed a fresh surface at the base of the current cliffs. The sampling was done close to the cliffs in order to minimize the possible effects of muon production prior to exposure by the cutting action and flood. The first chlorine-36 results from Tabernacle Hill have shown that most samples fall within the time frame indicated by the carbon-14 dating and the average (16.7 +/- 0.8 ka) is within one sigma of the lower age limit. Each sample was sent to several labs and analyzed for multiple cosmogenic nuclides. The comparison of beryllium-10 concentrations from the Promontory Point quartzite with chlorine-36 inventories in rocks of varying chemistry enables closer constraints to be placed on chlorine-36 production rates. This new information will allow tests to be performed on the current production schemes and provide insight into the chlorine-36 production rate discrepancy.
DE: 1150 Cosmogenic-nuclide exposure dating (4918)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting