DELIMITING THE URBAN GROWTH OF SANTIAGO DE COMPOSTELA (NW SPAIN) BY OSL DATING OF MEDIEVAL ANTHROPOGENIC SEDIMENTS

Abstract

A group of 22 hollows filled with sediment were found excavated in the ground during the construction of an auditorium in the city centre of Santiago de Compostela (NW Spain). This city is part of the UNESCO World Heritage. The hollows were from 3.30 m to 0.8 m depth and from 1.5 to 1 m diameter. Fourteen of them were excavated and some materials recovered (sediment, charcoal and fragments of vessels) to date the infill. The hollows were used to move and store water (as most of them are connected by channels), and their characteristics and arrangement are similar to leather tanning workshops found in the same city. Samples of the sediment infill recovered from two hollows and a pottery fragment taken from another one, were dated by OSL and TL, respectively. Recovered charcoals were also dated by AMS 14C for independent age comparison. OSL signals were suitable for dating and evidences of partial bleaching of quartz grains extracted from the sediment were observed from small multi-grain aliquots. The Minimum Age Model was used to calculate the equivalent dose and OSL results provided ages in agreement with independent ages, providing crucial information on the city growth in medieval times.