Radiocarbon Dating of Lime Mortar to Determine the Age of Three Visigothic and Early Medieval Buildings of Controversial Age in the Northern Iberian Peninsula

The age of the first construction of the churches of Nuestra Señora de las Viñas (Quintanilla de las Viñas, Burgos), Santa María de Rute (Ventas Blancas, La Rioja), and San Juan Bautista (Barbadillo del Mercado, Burgos) of the northern Iberian Peninsula has been subject to debate for decades. Some scholars date the construction of the churches to the Visigothic period (6th and 7th centuries), while others attribute them to the early Middle Ages (9th and 10th centuries). To shed light on this controversy, the 14C dating of the binder fraction of mortars of the earliest construction phases was carried out. To determine the suitability of the mortars for 14C dating, the mineral composition of the binder was determined by X-ray diffraction (XRD) and thermogravimetric analysis (TGA). Samples were dated using 14C Accelerator Mass Spectrometry (AMS). Binder mineralogy precludes some samples from radiocarbon dating. Radiocarbon dating of the Nuestra Señora de las Viñas mortars yielded ages of 534–640 cal AD and 584–658 cal AD. Santa María de Rute yielded ages of 564–650 cal AD, corresponding to Visigothic ages. The San Juan Bautista sample yielded an age of 876–995 AD, although a mortar stratigraphically below results was not suitable for dating.