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Selection of suitable data sets improves 230Th/U dates of dirty material

Geyh M. A.

Geochronometria

2008

Vol. 30

69-77

230Th/U dating of dirty material such as fen peat and secondary carbonates depends on the ability to select suitable and to discard unsuitable data sets before the calculation of 230Th/U ages. This means that open system conditions with respect to uranium during ageing are excluded and solely one source of detrital contamination was present in the samples. Three kinds of selection approaches of suitable data sets were applied: (1) isotope ratio plots, (2) the isotope-ratio evolution plot and the iterative determination of the decay-corrected initial detrital 230Th/232Th activity ratio (AR) as well as (3) depth profiles of the uranium concentration and the 234U/238U AR and the ash content. For reliable 230Th/U age dating of dirty material all selection procedures have to be commonly applied because none of them works perfectly.

Symbiosis between geochronologists and quaternary geoscientists

Geyh M. A.

Geochronometria

2001

Vol. 20

1-8

There is an apparent conflict between the high output of absolute dates of automated devises installed in geochronological laboratories and the growing need of an individual and thorough interpretation of absolute physical dates determined for geoscientists and archaeologists. This conflict can only be solved by a symbiotic co-operation with universal geochronologists. The benefit will be an increase of the reliability and precision of the geochronological time marks, an improvement of the dating methods and an extension of the fields of application for the many absolute dating methods based on cosmogenic isotopes, radiation damage or uranium-series disequilibrium.

Reflections on the 230Th/U dating of dirty material

Geyh M. A.

Geochronometria

2001

Vol. 20

9-14

High correlation coefficients between the activity ratios of the uranium and thorium isotopes common for the "isochron" approach of 230Th/U dating of dirty material mask the requirement to check for closed-system conditions of uranium in addition to the detrital correction of 230Th/U ages. The difficulty to calculate standard deviations of 230Th/U dates derived by the "isochron" approach complicates the problem. The methodical reasons are discussed. Closed-system conditions are checked by the 234U/ 238U - 230Th/ 238U AR plot which can also be used to carry out least-squares fitted detrital correction of 230Th/U ages of dirty material.