Claus Ditlefsen

Combined OSL (infrared) and TL studies of feldspars

An infrared (i.r.) diode array unit for optically stimulated luminescence (OSL) was developed which can be fitted directly onto the automated Riso TL dating apparatus, thus permitting combined TL and OSL measurements using the same PM tube. Thirty-two diodes with an i.r. emission of 880 Δ 80 nm are used in the array and the power delivered at the sample is about 40 mW cm-2. A specially designed feed-back system serves as control for the light output from the diodes. The i.r. unit and preliminary OSL studies of feldspar samples are described.

Bleaching of K-feldspars in turbid water suspensions: A comparison of photo- and thermoluminescence signals

Abstract In order to investigate at what levels of turbidity the luminescence signals of waterlaid sediments can be reset for dating, bleaching experiments have been performed in a test tube containing different suspensions of glacial origin. Light comparable to the solar spectrum was introduced at the surface, and grains (100–200 μm) of K-feldspars were exposed to subdued light through the suspensions for different periods of time. Thermoluminescence (TL) and photoluminescence (PL) signals from exposed and unexposed samples recorded on an automated Riso Reader were compared. For dilute suspensions ( In the more dense suspensions (>0.05 g/l) light levels were very low ( 2 ), and the light reduction was mainly caused by the suspended particles rather than by the turbulence. Only little bleaching of any of the luminescence signals was observed here. These results illustrate the potential but also some limitations of the optical technique for dating waterlaid sediments.

Compilation of a Resistivity Atlas of Danish lithologies based on direct resistivity measurements and wireline logging data

Electrical conductivity, or its inverse, the resistivity, is an important geophysical property within groundwater mapping. It is known to correlate empirically to lithology, primarily through clay minerals and pore water ions. Although, in Denmark, geoelectric and electromagnetic surveys have been carried out for decades, no systematic, nationwide study on the relationship between resistivity and lithology has been carried out. We present a procedure for generating a resistivity atlas based on resistivity measurements, which can be related directly to specific and well described soil samples. Data are obtained from archives, literature and the Danish national databases. The procedure implies a restricted use of wireline logging data in combination with direct measurements on samples, resulting in resistivity distributions for specific lithologies or geological formations. The use of documented high-quality data ensures reliable results, reflecting actual resistivity of a specific lithology. This procedure is illustrated on clay till. The resistivity variations obtained for this lithology seems to be related to real compositional variations, which reflect the process of forming the clay till. Our procedure is likely to provide equally reliable results for other main lithologies. Future detailed studies, in particular on sediments with low clay content, should consider resistivity differences related to the degree of saturation and variations in the formation water resistivity.