U th dating on calcite

26-Jul-2016 08:34 by 2 Comments

U th dating on calcite - Sex chat free portal

Figure 1 shows the basis of U-series dating via the activity ratio of Th-230/U-234: The trace element uranium is easily dissolved and transported by karstic, carbonate-rich waters seeping through the limestone rock.

The a-decay of U-234 now slowly generates Th-230 a-activity again, so that the a-activity ratio of Th-23O/U-234 will constantly increase for about 4x 1O5 years.

In figure 5 a pair of such a-spectra is presented giving all the data needed for the Th-23o/U-234 age calculation.

Both the U- and Th-a-spectrum are from an inner section of a stalagmite found in a small cave near Letmathe in the Sau- erland5area in Germany.

The Th-23o/U-234 activity ratio of 0.64 corresponds to an age of 1.1x10 years, the average formation age of the whole growth ■ layer .

This would imply that times of ice-sheet collapse should correspond to peaks in Northern Hemisphere June insolation.

We are developing U-Th measurements and ages of vein calcite from geothermal systems using a Neptune Plus MC-ICP-MS (with 5 CDDs and 3 SEMs) coupled to an excimer 193nm Photon Machines laser.

We will be comparing our results with an 189ka in-house flowstone calcite standard previously dated by TIMS, as well as developing a geothermal calcite standard.

Age determination via Th-23O/U-234 is usually started by cutting a layered speieothem into several sections along visible growth layers.

Each single growth zone is then dissolved in HC1 or HNO3, and the trace amounts of uranium and thorium are separately isolated by means of a specially developed chemical procedure (fig. Artificially produced isotopes U-232 and Th-228 are added as tracers for the different uranium and thorium yields.

Uranium-thorium dating, also called thorium-230 dating, uranium-series disequilibrium dating or uranium-series dating, is a radiometric dating technique commonly used to determine the age of calcium carbonate materials such as speleothem or coral.

Unlike other commonly used radiometric dating techniques such as rubidium-strontium or uranium-lead dating, the uranium-thorium technique does not measure accumulation of a stable end-member decay product.

Such "speleothems" are usually regarded to be a most suitable material for dating purposes, and they are not altered as is bone material after long times of storage.

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