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Luminescence dating of P leistocene alluvial sediments affected by the A lhama de M urcia fault (eastern B etics, S pain) – a comparison between OSL , IRSL and post‐ IR IRSL ages

Year: 2011

Type: article

Abstract: The ages of nine alluvial units, identified by the integration of data obtained from five trenches at the southern termination of theAlhama deMurciaFault (AMF) (easternBetics,Spain), are constrained using luminescence dating based on theOpticallyStimulatedLuminescence (OSL) from quartz,InfraredStimulatedLuminescence (IRSL) at 50°C, and post‐IRelevated temperature (225°C)IRSLsignals fromK‐feldspar. All signals pass the routine tests associated with the Single Aliquot Regenerative (SAR) protocol, including the recycling ratio, recuperation, and dose recovery tests. The equivalent doses (De), residual doses and anomalous fading rates (‘g’‐values) of theIRSLat 50°C (IR50) and post‐IRIRSLat 225°C (pIRIR225) fromK‐feldspar are compared for 16 samples. The residual doses in laboratory‐bleached samples suggest that there is no significant unbleachable residual dose using these signals; the residual doses are 0.17±0.15 Gyand 0.93±0.80 Gy, respectively. For both signals, the residual doses appear to depend on the corresponding natural doses; that is, the larger the natural doses, the larger the residuals, an observation made for the first time forIRSLsignals. The average fading rate for thepIRIR225(0.94±0.07%/decade,n= 48) is markedly lower than that forIR50(2.08±0.16%/decade,n= 48), indicating that the age correction for thepIRIR225is much smaller than that forIR50. The agreement between the quartzOSL, correctedIR50, and correctedpIRIR225for the two youngest samples suggests that thepIRIR225is an accurate dating signal in this age range (<25 ka). The oldest age obtained using the correctedpIRIR225signal is 320±20 ka for sample 098807; the correctedIR50age is only 154±15 ka. Although this suggests that thepIRIR225signal circumvents the effect of anomalous fading to a great extent, the resulting age cannot be regarded as necessarily accurate because of the limitations of the fading correction model used, and the absence of independent age control for the old samples. Nevertheless, our luminescence ages provide the first age constraints on the seismic activity of the southern termination of theAMF.

Source: Boreas

DOI: 10.1111/j.1502-3885.2011.00230.x

Authors: Reza Sohbati, Andrew S. Murray, Jan‐Pieter Buylaert, Maria Ortuño, Pedro P. Cunha, Eulàlia Masana