Allan Asked:

"The only one of these methods I am familiar with is TL.
Do the other 2 somehow require an impact shock to be applicable,..."

No.

"...ie. could they be used to date a site like Topper?"

However, in case of both methods, the answer is "no".

Cosmogenic dating can only be "applied to the dating of any
surface that is composed of material that was not exposed
to cosmic rays prior to formation of the surface, and has
been exposed more-or-less continuously since". Since the
surfaces and sediments of interest at the Topper site have
been buried, this method cannot be used to date them.

Go look at "Cosmogenic dating of young basaltic lava flows" web
page by Nelia W. Dunbar, New Mexico Bureau of Geology and
Mineral Resources at [geoinfo.nmt.edu]

and "Geochronology of the Carrizozo Malpais" by the same
author at [geoinfo.nmt.edu] . It provides a brief discussion
of this technique.

A couple of the references the former gives are:

Dunbar, N., 1999, Cosmogenic 36-Cl-determined age of the
Carrizozo lava flows, south-central New Mexico. New Mexico
Geology, vol. 21, pp. 25-29. ABSTRACT

Phillips, F. M., N. W. Dunbar, and M. G. Zreda, 1997, A
Test of Chlorine-36 for Dating of Late Quaternary Basaltic
Volcanoes [abs]: Eos, Transactions, American Geophysical
Union, vol. 78, p. 760.

Some more references can be found in "Carrizozo Malpais
Reference List" at [geoinfo.nmt.edu] .

Zreda, M. G., Phillips, F. M., Elmore, D., Kubik, P. W.,
Sharma, P., and Dorn, R. I., 1991, Cosmogenic chlorine-36
production rates in terrestrial rocks. Earth and Planetary
Science Letters, vol. 105, pp. 94-109.

Zreda, M. G., Phillips, F. M., Kubik, P. W., Sharma, P.,
and Elmore, D., 1993, Cosmogenic 36Cl dating of a young
basaltic eruption complex, Lathrop Wells, Nevada.
Geology, vol. 21, pp. 57-60.

The above references should provide an explanation of this
technique, which can be used to date Holocene and Quaternary
age rock and sometimes other surfaces.

Beryllium-10 and Aluminium-26 dating are two other cosmogenic
dating methodss. They can be used to date a surface composed
of quartz-bearing "material that was not exposed to cosmic
rays prior to formation of the surface, and has been exposed
more-or-less continuously since"

Some web pages:

Cosmogenic exposure ages by Carrie Patterson, MGS
[www.fettes.com]

Terrestrial In Situ Cosmogenic Nuclides...
[www.dal.ca]
[www.dal.ca]

New way to date old stone By Kristan Hutchison in the
January 5, 2003 "Antarctic Sun" at [www.polar.org]

Although not applicable to dating the Topper Site, Quaternary
geologists find them quite helpful for determining the age of
stone surfaces. The wide range of ages of stone surfaces, which
can be dated is seen when Hutchinson stated in the above article;

"Indeed, a Swiss study five years ago found a
boulder on Mt. Feather in the Dry Valleys that
had been exposed to the surface for at least
10 million years, based on their measurements
of helium-3. Much of the Transantarctic range
has been exposed from 1 million to 5 million
years. In other areas of the world, it’s more
typical to find rocks that have been exposed
for 1,000 to 100,000 years."

Best Regards,

Paul
Baton Rouge, LA






Edited 3 time(s). Last edit at 03/13/2005 12:38AM by Paul H..