Dating techniques in glacier forelands

The resolution and reliability of any moraine chronology is only as good as the precision and accuracy of the dating technique, and the interpretation of the relationship between dated layers and geomorphological processes. The interpretation of dated chronological records obtained from landforms, and moraine sequences in particular, rarely pay attention to the inherited complexity in interpreting landform formation. The uncertainties may include availability of datable material, the sensitivity of the system to change, and the subsequent erosion or destruction of the landform (Kirk-bride and Brazier, 1998).

Dating techniques found useful for retreating glaciers are normally divided into four categories: (1) observation and measurements; (2) historical documents; (3) biological dating; and (4) physicochemical techniques. In the investigation of Holocene glacier and climate variations, where precise dates are needed for frequent and low-amplitude events, it is important to adopt a critical approach to dating (e.g. Matthews, 1985, 1997). Problems related to historical dating may be the small number of glaciers for which there are reliable historical evidence, the difficulties of dating moraines by the use of historical data, and the lack of reliable data for the period prior to the Little Ice Age maximum. Lichenometry may be limited by the relatively extensive Little Ice Age glacier advances in some areas, the sparse independent historical evidence for calibration of lichenometric dating curves in the older parts, and the reliance in some regions on radiocarbon-dated palaeosols for calibration of lichenometric growth curves. Relative dating based on weathering-based criteria (e.g. Schmidt hammer, surface roughness and weathering rinds) may be limited by the lack of quantitative data on weathering rates and reliable calibration points. With radiocarbon dating, major problems include the reliance of moraine dating of palaeosols, the existence of steep age-depth gradients in buried soils, the inherent precision of radiocarbon dates (one or two sigma), and finally, problems in interpreting various stratigraphical contexts, for example, glacial, glaciofluvial and glaciolacustrine sediments (Matthews, 1997).

0 0

Post a comment