Manuela Capano

Wood 14C Dating with AixMICADAS: Methods and Application to Tree-Ring Sequences from the Younger Dryas Event in the Southern French Alps

The AixMICADAS facility is in part dedicated to research on radiocarbon ( 14 C) calibration by means of various archives. For this purpose, we are improving upon the capacity to accurately date subfossil wood. In the current study, nine chemical pretreatment protocols are tested on six wood samples of known ages. The optimization based on 14 C ages, 13 C/ 12 C ratios, carbon % and overall mass yield % leads us to favor the acid-base-acid-bleaching pretreatment (ABA-B). This efficient method is shown to provide a residue of holocellulose with optimal blanks equivalent to an age of 51,300 14 C BP with a standard deviation of 1500 yr based on 25 analyses. The seven wood samples from the Sixth International Radiocarbon Intercomparison (SIRI) are then analyzed as a further verification of the accuracy of our method. As a first scientific contribution, we studied two tree-ring sequences from subfossil pines (Barb12 and Barb17) collected in the southern French Alps. New 14 C analyses were performed at high resolution (every third year) and are shown to agree well with results obtained previously by high precision β-counting on CO 2 from large samples at lower resolution for Barb17 and accelerator mass spectrometry (AMS) data for Barb12. The new 14 C series are then matched to the Kauri and YDB chronologies: the new sequence of Barb12-17 tentatively corresponds to the interval between 12,836 and 12,594 cal BP within the Younger Dryas cold period. The 14 C comparison between the Barb12-17 sequence from France and the Kauri sequence from New Zealand allows calculating the 14 C Inter-Hemispheric Gradient (IHG), with an average value of ca. 57 yr. The IHG stayed relatively high throughout the studied period. Interestingly, the IHG exhibits a transient maximum value (ca. 100 yr) during the period of rapid Δ 14 C rise (12,750–12,720 cal BP), a behavior that could be due to a delayed response of the Southern Hemisphere.

Mortar Dating Methodology: Assessing Recurrent Issues and Needs for Further Research

Absolute dating of mortars is crucial when trying to pin down construction phases of archaeological sites and historic stone buildings to a certain point in time or to confirm, but possibly also challenge, existing chronologies. To evaluate various sample preparation methods for radiocarbon (14C) dating of mortars as well as to compare different dating methods, i.e. 14C and optically stimulated luminescence (OSL), a mortar dating intercomparison study (MODIS) was set up, exploring existing limits and needs for further research. Four mortar samples were selected and distributed among the participating laboratories: one of which was expected not to present any problem related to the sample preparation methodologies for anthropogenic lime extraction, whereas all others addressed specific known sample preparation issues. Data obtained from the various mortar dating approaches are evaluated relative to the historical framework of the mortar samples and any deviation observed is contextualized to the composition and specific mineralogy of the sampled material.

Radiocarbon Dating of Mortars with a Pozzolana Aggregate Using the Cryo2Sonic Protocol to Isolate the Binder

To date, finding a technique able to effectively isolate the carbon signal from the binder of a mortar is still an open challenge. In this paper, the radiocarbon (14C) dating of one of the most challenging and diffuse types of mortar, the one with pozzolana aggregate, is investigated. Eight mortar samples from three archaeological sites near Rome (Italy) underwent a selection process called Cryo2SoniC. The selected fractions were analyzed by the accelerator mass spectrometry (AMS) 14C technique and compared to known historical references. Additional scanning electron microscopy analysis and petrographic investigations were done, respectively, to check the grain size of the fractions selected by Cryo2SoniC, and further, to characterize the original mortar samples. The masses of carbon yielded from the dated fractions were almost half of those released from some aerial mortars. The 14C dating results were accurate for pozzolana mortars, from buried and unburied structures, with calcination relics and small contamination of secondary calcite. A limitation in the purification protocol was observed on samples with a massive contamination of secondary calcite deposition of ground water origin, occluding porosity and substituting up to the 80% of the original binder matrix

Preparation and Dating of Mortar Samples-Mortar Dating Inter-Comparison Study (MODIS)

Seven radiocarbon laboratories: Abo/Aarhus, CIRCE, CIRCe, ETHZ, Poznan, RICH, and Milano-Bicocca performed separation of carbonaceous fractions suitable for 14C dating of four mortar samples selected for the MOrtar Dating Inter-comparison Study (MODIS). In addition, optically stimulated luminescence (OSL) analyses were completed by Milano-Bicocca and IRAMAT-CRP2A Bordeaux. Each laboratory performed separation according to laboratory protocol. Results of this first intercomparison show that even though consistent 14C ages were obtained by different laboratories, two mortars yielded ages different than expected from the archaeological context.

AMS Radiocarbon Dating of an Ancient Pottery Workshop in Hepu County, China

An ancient pottery workshop belonging to the Han Dynasty was excavated in Caoxie village, Hepu County. Caoxie village is an important archaeological site in Hepu County, Beihai City, in south Chinas Guangxi Zhuang Autonomous Region. It is believed that Hepu County was the oldest departure point on the ancient maritime trading route during the Han Dynasty (206 BC to AD 220) due to the ideal natural geographical conditions and the existence of a large number of Han tombs. Radiocarbon measurements on wood and charcoal samples from the Caoxie village site were performed at the Peking University AMS facility (PKU-AMS), Beijing, and the Centre for Isotopic Research for Cultural and Environmental Heritage (CIRCE) at Naples Second University, Italy. Calibrated ages were obtained with code CALIB 5 (Stuiver and Reimer 1993). The results of these measurements are presented and the related chronology is discussed.