Today's GeoSeminar (1:00-2:00 p.m. in Mudd 218):Today's GeoSeminar (1:00-2:00 p.m. in Mudd 218):

Dr. Karl Kreutz

University of Maine, OronoPacific Climate Variability over the Last MillenniumPacific Climate Variability over the Last Millennium

Radiocarbon Dating:Radiocarbon Dating:

The great tool ofThe great tool ofthe Quaternarythe Quaternary

( ( Plus a few special wrinkles in dating Plus a few special wrinkles in dating techniques thrown in for fun! techniques thrown in for fun! ))

(( WHY NOT ??WHY NOT ?? ))

Aniakchak Volcano erupted ~3400 years ago to devastate the SW Alaskan coast.Aniakchak Volcano erupted ~3400 years ago to devastate the SW Alaskan coast.

Lower sediments in the section revealed Lower sediments in the section revealed that numerous volcanic ashes had buried that numerous volcanic ashes had buried the regional landscape previously.the regional landscape previously.

11,250 +/- 5011,250 +/- 50

6800 +/- 606800 +/- 60

7900 +/- 507900 +/- 508800 +/- 708800 +/- 70

3400 +/- 803400 +/- 80

On the southern coast, the volcanic debris On the southern coast, the volcanic debris thickness was thickness was onlyonly about 1 meter .... about 1 meter ....

(Museum reconstruction of bog body burial)

Costs: Conventional: $345; AMS: $595 per sampleCosts: Conventional: $345; AMS: $595 per sample

The density of the "tracks" through the grain is The density of the "tracks" through the grain is a function of its age and the uranium content. a function of its age and the uranium content.

Rubidium-strontium dating (Rubidium-strontium dating (8787Rb --> Rb --> 8787Sr) is also useful Sr) is also useful for the oldest metamorphic shield rocks, and can give for the oldest metamorphic shield rocks, and can give ages of both the parent rock and the time of ages of both the parent rock and the time of metamorphism. metamorphism. (T(T1/21/2 of of 8787Rb is ~ 50 Rb is ~ 50 BILLION BILLION yrs.)yrs.)

Uranium-Uranium-seriesseries dating (relying on dating (relying on intermediate decay intermediate decay productsproducts) can be used ) can be used sometimessometimes to determine ages of to determine ages of corals, sedimentary units or soils up to 500,000 years corals, sedimentary units or soils up to 500,000 years old.old.

Chemistry of the EarthChemistry of the Earthand anand an

Introduction to MineralsIntroduction to Minerals

Coming Monday:Coming Monday: