Research Paper Testing the use of range-finder OSL dating to inform field sampling and laboratory processing strategies J.A. Durcan a, * , H.M. Roberts a , G.A.T. Duller a , A.H. Alizai b a Institute of Geography & Earth Sciences, Aberystwyth University, Aberystwyth SY23 3DB, UK b Department of Geology and Petroleum Geology, University of Aberdeen, Aberdeen AB24 3UE, UK article info Article history: Received 20 October 2008 Received in revised form 10 February 2009 Accepted 11 February 2009 Available online 21 February 2009 Keywords: Harappan Pakistan Luminescence abstract A newly developed range-finder luminescence dating method is applied to samples from the eastern Punjab region of Pakistan. Overbank sediments from this area are the subject of an ongoing project into the demise of the Harappan civilization about 4.2 ka and the range-finder technique was used to ascertain whether samples from three pits are from this part of the Holocene. Luminescence measure- ments of raw sample gave a signal dominated by feldspars, even when using a [post-IR] optically stimulated luminescence (OSL) signal. Following etching in hydrofluoric acid samples gave OSL signals characteristic of quartz and these were used to calculate the equivalent dose. The total dose rate was estimated from beta counting. Eight range-finder OSL ages extend from 4000 to 6600 years ago and are consistent with two radiocarbon ages from the same pits demonstrating that these sediments do straddle the period of interest for this project. The range-finder approach provides a rapid means of informing future field sampling campaigns. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction The sample preparation and measurements required to deter- mine a quartz optically stimulated luminescence (OSL) age are time consuming and labour intensive. Recently, Roberts et al. (in press) investigated ways of providing rapid age estimates, albeit with lower levels of precision and accuracy than would be expected from fully prepared samples. The ‘range-finder’ protocol proposed was not intended to be a replacement for comprehensive laboratory preparation and measurement, however, it does allow the rough yet rapid approximation of an OSL age in situations where this is all that is initially required e.g. a pilot field campaign or to plan a field or laboratory sampling strategy (Roberts et al., in press). This paper seeks to apply the range-finder technique to samples taken during a pilot field campaign in Pakistan, to investigate the viability of this technique as an estimator of age for a series of sediment sections which may subsequently be sampled during the main field campaign. The pilot study sites were selected as part of an investigation into the cause and timing of the demise of the Harappan civilization which appears to have occurred suddenly around 1900 BC (Possehl, 1997). Archaeological remains of Harappan sites are found widely in Pakistan and western India, but are densely clustered east of the Indus River (Fig. 1). Collapse of this developed society may be due to a sharp decline in intensity of the summer monsoon at 4.2 ka (e.g. Staubwasser et al., 2003), or due to a loss of water from rivers flowing close to the major centres, for example through drainage basin reorganisation triggered by tectonic activity; alternatively, the demise may be due to de-urbanisation, caused by as yet unknown factors (Possehl, 1997). The range-finder technique was adopted to assess whether the critical time period required for this study had been captured in the pilot sample sites. Independent age control for two of the study sites is provided by radiocarbon dates from molluscs. If successful, the results of these range-finder investigations will be used to guide further field campaigns and to inform appropriate sampling resolution in the field, in addition to aiding the selection of samples for further full analysis in the laboratory. 2. Study area The Cholistan desert lies in the eastern Punjab region of Pakistan, adjoining the Thar Desert. At present, mean annual precipitation is approximately 150–200 mm and mean minimum and maximum temperatures are 9  C and 42  C respectively (Mukhtar et al., 2003). From satellite imagery, a number of palae- ochannels are visible, indicating that in the past the region has been wetter than present. Three sites in palaeochannels in this region * Corresponding author. E-mail address: jjd08@aber.ac.uk (J.A. Durcan). Contents lists available at ScienceDirect Quaternary Geochronology journal homepage: www.elsevier.com/locate/quageo 1871-1014/$ – see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.quageo.2009.02.014 Quaternary Geochronology 5 (2010) 86–90