A03_P11

¹⁴C dating for MODIS 2 carbonate mortars – do time and size matter?

Pawełczyk F¹, Gu Y^2,3, Piotrowska N¹, Ustrzycka A¹, Hajdas I²

¹Institute of Physics - CSE, Silesian University of Technology, Gliwice, Poland, ²Laboratory of Ion Beam Physics, ETHZ, Zurich, Switzerland, ³Laboratory of AMS Dating and the Environment, School of Geography and Ocean Science, Nanjing University, Nanjing, China

In our work we present a procedure applied for the ¹⁴C dating of three samples of mortars from the project MODIS 2, which is an international laboratory intercomparison. The samples selected for the exercise comprise three different mortars:

1) MODIS2.1: mortar from Finnish medieval church

2) MODIS2.2: mortar from Swedish medieval church

3) MODIS2.3: mortar from Spanish early Christian basilica

The material was sieved and three different size fractions were separated: <45 micrometers, 45-63 micrometers, and >63 micrometers. The composition of each fraction was analyzed under the binocular microscope.

The mortar carbonates were dissolved under vacuum conditions, using H₃PO₄ and the CO₂ coming from following time intervals was collected: 1-3sec, 4-6sec, 7-9sec, 10-12sec, and remaining CO₂. Also, the bulk carbonate from each size fraction was dated. In general, a growing age trend was observed with older age for samples from later time intervals, and the oldest for remaining CO₂ fraction.

The CO₂ was graphitized using AGE system at the ETH or Gliwice, or introduced to gas ion source of the MICADAS at the ETH. Moreover, the charcoal fragments were discovered in a sample MODIS2.2. The age of this charcoal was measured in ETH and Gliwice laboratories to 1090±30 BP and 950±30 BP, respectively.  For comparison, the age of carbonate fractions for this mortar ranged from 600 to over 2000 BP.

In addition, the stable isotope IRMS measurements were performed for carbonates from different size fractions and bulk material using the CF-IRMS IsoPrime coupled to Multiflow device.