LOESSFEST'09 | Aug. 31st – Sept. 3rd, 2009 |Novi Sad-Serbia
Potential of Quartz and Feldspar in OSL to Date Middle Pleistocene Loess From the Eifel Area – A Comparison with Independent Age Control
Schmidt, E.D.1,2, Murray, A.S.2, Tsukamoto, S.1, Frechen, M.1
1Leibniz Institute for Applied Geophysics (LIAG), Geochronology and Isotope Hydrology, Stilleweg 2, D-30655 Hannover, Germany
2Nordic Laboratory for Luminescence Dating, Department of Earth Sciences, Aarhus Universitiy, Risø DTU, DK- 4000 Roskilde, Denmark
Recently, new methods to extend the age range of luminescence dating applied to sediments using both quartz and feldspar have been proposed. The aim of our study is to evaluate the applicability of the new methods for quartz and feldspar from the loess of the Middle Pleistocene from the Middle Rhine area.
The Luminescence signals from feldspars grow to much higher doses than these from quartz, which offers the possibility of extending the age range. However, luminescence dating of feldspars has a tendency to underestimate the age, because of anomalous fading (Wintle, 1973). Buylaert et al. (in press) proposed SAR protocol, with detection in the blue (320-460 nm), this involves a stimulation with IR for 100s at 50°C prior to an elevated temperature stimulation with IR for 100s at 225°C, a so called post IR IR measurement sequence. They have shown that the observed fading rates for the post IR IR signal are significantly lower than from the conventional IRSL at 50°C and that the signal is bleachable in nature. In our study we included pulsing the IR LEDs in this protocol to test if we can reduce the fading rates even more (Tsukamoto et al., 2006).
The optically stimulated luminescence (OSL) of quartz has been widely used to estimate the age of sediments and is usually regarded as accurate and precise (Murray and Wintle, 2000, 2006). However, the fast component of quartz (that is normally used for dating) saturates around doses of 200-400 Gy (Wintle and Murray, 2006). Thermally transferred OSL (TTOSL; Wang, et al. 2006, 2007; Tsukamoto et al., 2008) overcomes this problem by using a signal that saturates at doses more than 10 times higher than the OSL signal. This dose dependent part of the thermally transferred OSL signal from quartz, which can be measured after depleting the OSL and giving a preheat. These studies show that the TT-OSL and can therefore be used to date sediments of the Middle Pleistocene.
To find the most suitable protocol for dating loess from the Middle Rhine area, these methods were tested on fine-grained loess extracts from the Kärlich clay pit in the Eifel area, Germany. This section provides an excellent archive of climate and environmental change and it is one of the most important Quaternary sites in the Middle Rhine area. At Kärlich Pleistocene fluvial deposits as well as loess and loess derivatives are exposed in an about 30 m section. Independent age control is provided by 40Ar/39Ar dating on the intercalated tephra layers. Preliminary results using both minerals as dosimeters are presented and the ages compared with independent estimates for these Middle Pleistocene loess deposits.
References:
- Buylaert, J.P., Murray, A.S., Thomson, K.J., Jain, M. (in press): Testing the potential of an elevated temperature IRSL signal from K-feldspar, Rad. Meas., doi: 10.1016/j.readmeas.2009.02.007.
- Murray, A.S. & Wintle, A.G. (2000) Luminescence dating of quartz using an improved single-aliquot regenerative- dose protocol. Radiation Measurements 32, 57-73.
- Porat, N, Duller, G.A.T., Roberts, H.M. & Wintle, A.G. (in press): A simplified SAR protocol for TTOSL. Tsukamoto, S., Denby, P. M., Murray, A, S., and Bøtter- Jensen, L. (2006). Time-resolved pulsed luminescence from feldspars: new insight into fading. Radiation Measurements, 41: 790-795.
- Tsukamoto, S., Duller, G.A.T. and Wintle, A.G. (2008). Characteristics of thermally transferred optically stimulated luminescence (TT-OSL) in quartz and its potential for dating sediments. Radiation Measurements, 43: 1204-1218.
- Wang, X.L., Wintle, A.G., Lu, Y.C. (2006): Thermally transferred luminescence in finegrained quartz from Chinese loess: Basic observations. Radiation Measurement, 41: 649-658.
- Wang, X.L., Wintle, A.G., Lu, Y.C. (2007): Testing a single-aliquot protocol for recuperated OSL dating. Radiation measurements, 42, 380–391.
- Wintle, A.G. (1973): Anomalous fading of thermoluminescence in mineral samples. Nature, 245(5421): 143- 144.
- Wintle, A.G. & Murray A.S. (2006): A review of quartz optically stimulated luminescence characteristics and their relevance in single-aliquot regeneration dating protocols. Radiation Measurements, 41: 369- 391.