Utilización de los depósitos de la Fm areniscas de Salamanca (Cretácico terminal-paleoceno) en la calzada y sillares del Puente Romano de Salamanca: análisis geoarqueológico

Abstract

The geoarchaeological study of the building materials used in the pavement and ashlar of the Roman Bridge over the Tormes River in the city of Salamanca allows them to be assigned to the Salamanca Sandstone Fm (Latest Cretaceous-Palaeocene). The identification of this lithostratigraphic unit as the main building material resulted in a further search and identification of possible extraction sites, that is, quarries which could have been the source of both 20th century and older dressed stones. The stratigraphical and sedimentological analyses of the sedimentary deposits carried out in the hills of Peña Celestina, San Vicente, Peñuelas de San Blas, the slopes of Calvarrasa de Arriba, both Arapiles («Chico» and «Grande»), and Aldeatejada, together with many others, revealed the presence of lenticular-tabular shaped outcrops of coarse grained, white coloured with reddish patches sandstones and microconglomerates, cemented with silica. These sandstones are similar to those used in the Roman Bridge, especially the samples taken from the pavement during the 1999 restoration work. Stratigraphic studies did not only make it possible to establish the sequencing of the geological events associated to the Salamanca Sandstone Fm but also the stratigraphic position of deposits similar to those used in the construction of the Roman Road. Sedimentological and petrographic analyses allowed defining the sin and postsedimentary processes that conferred the present textural features of Salamanca Sandstones that differentiated them from other lithostratigraphic units of the study area. On the other hand, an X-ray diffraction study was carried out trying to find specific minerals that might allow us to differentiate between outcrops of the same Fm, which instead resulted in a homogeneous picture on the diffractograms. As a consequence, even if well-defined areas associated to the ashlar used in the construction of the Roman Bridge could be drawn, so far it has not been possible to pinpoint their exact location within them with greater precision. Concerning the building phases of the Roman Bridge, the morphological characteristics, historic records and the archaeological context of the pavement provide evidence to date it back to the late Flavio period, between 81 and 98 AD under the rule of Domitian or Nerva, whereas the ashlar of the upper structure of the bridge can be seen as pertaining to a much later work in the 18th Century.