The following HTML text is provided to enhance online
readability. Many aspects of typography translate only awkwardly to HTML.
Please use the page image
as the authoritative form to ensure accuracy.
Active Tectonics: Studies in Geophysics
are assumed not to have been added to or leached from the sample. Wintle and Huntley (1982) listed criteria for evaluating TL dates of sediment and discussed problems that merit further research.
TL dating of loesses has yielded reasonable results. Late Pleistocene loess in Germany yielded TL ages that are stratigraphically consistent and concordant with carbon-14 ages of an associated ash (Wintle and Brunnacker, 1982; Figure 13.7).
Electron spin resonance (ESR) dating is similar to TL dating in that a mineral acts as a dosimeter for local ra
FIGURE 13.7 Thermoluminescence (TL) dating of loess deposits in West Germany showing that the TL ages are both stratigraphically consistent and concordant with existing carbon-14 ages on the volcanic ash that was dated elsewhere (redrawn from Wintle and Brunnacker, 1982).
diation, but differs in the feature measured and the method of measurement. ESR dating of corals from marine terraces of Japan yielded results in good agreement with carbon-14 (2–4 ka) and 230Th/234U (40–>200 ka) dating (Ikeya and Ohmura, 1983).
Uranium-trend dating is an isochron-type method for dating Quaternary sediments and soils (Rosholt, 1980; Szabo and Rosholt, 1982). Rather than requiring a closed system as do most uranium-series methods, this method depends on a flux of uranium (mostly 238U) through sediments and the consequent embedding of recoil products 234U and 230Th in the sediments. The method can be used on almost all sedimentary materials and has produced generally reasonable ages (Rosholt, 1980). The calibration of the method initially depended on ages determined by other methods, but ages can now be calculated using the established calibration. The method is expensive, requiring determination of 238U, 234U, 230Th, and 232Th for five or more samples from a given deposit. Although widely applicable, the method has so far experienced limited use because of its newness, complexity, and cost.
Cosmogenic Isotopes Other Than Carbon-14
Similar to carbon-14, several other radiogenic isotopes are generated by cosmic-ray bombardment and may be useful in tectonic studies. Dating rationales exist for 32Si, 41Ca, 36Cl, 26Al, 10Be, 129I, and 53Mn, which are analyzed by accelerator mass spectrometry (half-lives given in Table 13.2).
Beryllium-10 is produced by cosmic-ray bombardment and is carried to the Earth’s surface by rain and dust. Pavich et al. (1984) showed that 10Be is adsorbed onto clays in soils and systematically increases in abundance with soil age for at least the first 100 ka of soil development. More research is needed to evaluate this method for dating surface and buried soils.
RELATIVE-DATING METHODS, SIMPLE PROCESS
These methods (Table 13.1, column 4) do not depend on radiogenic processes but are based on relatively simple chemical or biological processes whose rates are related to controlling variables such as temperature and chemical composition or species effects.