LIME MORTAR AND PLASTER: A RADIOCARBON DATING TOOL FOR DATING NABATEAN STRUCTURES IN PETRA, JORDAN Khaled Al-Bashaireh Department of Archaeology, Yarmouk University, Postal code 211-63, Irbid, Jordan. Corresponding author. Email: khaledsm@email.arizona.edu. Gregory W Hodgins NSF Arizona Accelerator Mass Spectrometry Laboratory, Physics Building, 1118 East Fourth Street, PO Box 210081, Uni- versity of Arizona, Tucson, Arizona 85721-0081, USA. ABSTRACT. This research aims at radiocarbon dating 2 structures of archaeological interest from Petra, south Jordan, using lime plaster and mortar. Initially, the samples' content of calcareous contamination was examined by petrography and cathod- oluminescence. In order to date clean lime binders, the samples were gently crushed and 63-45 powders were collected by dry sieving, then the C0 2 gases, collected by a hydrochloric acid hydrolysis of the powders, were dated. The interpreted 14 C dates clarify the chronology of the studied structures, show an agreement with the archaeological and historical data, and may indicate the efficiency of the cleaning and hydrolysis procedures. INTRODUCTION Archaeologists usually depend on archaeological materials, mainly pottery and written inscriptions, to date and build the chronology of the archaeological sites they are excavating. However, it is often difficult to find a suitable material whose age can reliably be assumed to represent the time of the construction of archaeological structures. In Petra, south Jordan (Figure 1), the date of the construc- tion of several structures of historic interest cannot be confirmed by written sources and datable arti- facts in primary contexts and/or a dendrochronological dating method. Nevertheless, these struc- tures have sufficient quantities of the original lime mortar and lime plaster from the early stage of their construction. Gypsum- and lime-based mortar, plaster, and stucco were widely used in Petra (Zayadine 1987). They were used for constructing its free-standing structures, decorations, and cov- ering the fa ades of its monuments and tombs carved in the cliffs of the mountains. Since there is a strong need to clarify the chronology of these structures, we are at present left with mortars and plas- ters as the only possibility for 14 C dating them. This material offers a potential dating key to the Nabateans' structures in Petra. Plasters and mortars can be dated by optically stimulated luminescence (OSL) or thermolumines- cence (TL) dating sand and pottery inclusions within them and radiocarbon dating of organic inclu- sions they contain and/or the lime binder itself after it has absorbed atmospheric carbon dioxide to form the plaster or mortar matrix. Several studies of dating mortars and plasters have focused on dat- ing charcoal or organic inclusions. This approach has been used for dating structures at Petra (Al- Bashaireh and Hodgins 2011a). Most of these dates, derived from charcoals, woods, and straws teased out of plaster and mortar samples, were in concordance with the samples' historic data. How- ever, 14 C dating organic inclusions does not always work. Tubbs and Kinder (1990) and Heinemeier et al. (2010) have warned about the unreliability of dating mortar based on organic inclusions because of the old-wood problem. The samples in their research produced dates older than expected. Moreover, many mortars and plasters do not contain organic inclusions, and alternative approaches are thus required. TL and OSL dating of sand aggregates from mortars and plasters, although theo- retically possible, has not been reported in the literature. 2012 by the Arizona Board of Regents on behalf of the University of Arizona Proceedings of the 6th International Radiocarbon and Archaeology Symposium, edited by Boaretto and R Rebollo Franco RADIOCARBON, Vol 54, Nr 3-4, 2012, 905-914 905 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S003382220004755X Downloaded from https://www.cambridge.org/core. IP address: 3.92.57.205, on 23 May 2020 at 16:51:29, subject to the Cambridge Core terms of use, available at