The Dating Process
Cosmogenic (Burial) Dating
Over the last decade in-situ-produced cosmogenic nuclides such as 26Al, 10Be and 36Cl have been increasingly used to date glacial landforms. This method has been checked by other dating techniques (Grainger 1997 and 2001) and has been proven to be effective. As uses diversify for this technique applications were soon taken to the cave environment primarily because the only requirements is the presents of quartz and depth of burial but also because the range of accurate dates is extends from ~ 100,000 years to ~ 5 million years. There are two main requirements for this technique to be useful. First there must be quartz present in the sediment for the nuclides to be created by the neutron spallation of quartz and second the quartz must be buried deep enough for neutron spallation to stop. Normally sediment above 5 meters in depth encounters is not acceptable for this type of technique. By measuring the different decay rates of 10 Be with a half life of 1.5 million years to 26Al with a half life of 700,000 years a date of burial (nuclide production ends) an approximate age of burial can be identified. This constant decay rate is also matched by a constant production ratio. The 26Al nuclide produces six times faster than 10Be nuclide which makes calculating decay rates less tenuous. The results of the cosmogenic testing resulted in a sequential set of dates. Starting from the bottom of the type section sediment column (L-8) which is a grey clay layer dated at 800,000 years + or - 50,000 years. The overlying channel gravel (Mammoth Horizon)(L-6 and L-7) that is the same deposition feature dated at 660,000 years + or 50,000 years. The field and laboratory preparation was performed by David Gaunt in association with Dr. Rovey at Southwest Missouri State University. The isotope dating was conducted by Dr. Balco at the University of Washington.

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