The building stone of the Phoenician-Roman city of Lixus (NW Morocco): provenance, petrography and petrophysical characterization

Characterization of building material is a key tool to assess deterioration processes and improve potential restoration works of archaeological sites. The aim of this paper is to identify and characterize the building stone used in the construction of the Phoenician-Roman city of Lixus (Larache, Morocco) by means of petrographic and petrophysical technics. Based on the visual analysis of the monuments, three major building stones (i.e., lithotypes) have been identified: (1) Oligocene sandstones, (2) Quaternary sandstones, and (3) Quaternary conglomerates. Based on the analysis of the regional geology and exploitation marks, these three lithotypes have been identified to crop out in the surroundings of Lixus and the quarries, presumably Roman in origin, recognized. The Oligocene sandstone is the primary building stone in Lixus as form and crop out extensively in the Tchemmis hill, at top of which the city is settled. The Quaternary sandstones and conglomerates, which represent nearshore deposits and eolianites, are less abundant as building rocks in Lixus and crop out along the Atlantic coast where form part pf the cliffs close to Larache.

Petrographic results indicate that lithotypes differ notably in grain size, ratio of detrital to allochemical components, and the configuration of their porous system. Mechanical analysis show that the Oligocene sandstones are more resistant to compression than the Quaternary sandstones and conglomerates, the latter exhibiting low compressive strength. The Oligocene sandstones, which display scarce porosity and permeability, show a hydric behaviour characterized by a very low degree of absorbing and desorbing water, likely resulting from a poor connectivity of the pore network. Contrary to later lithotype, the Quaternary sandstones and conglomerates, which exhibit very high porosity and permeability, display a hydric behaviour characterized by high degree of both absorbing and desorbing water. This behaviour is attributed to both the low degree of cementation and excellent connectivity of the porous network of the lithotype typical of coastal deposists. Finally, the accelerated artificial aging test they do not show a significant weight loss after twelve cycles of salt crystallization, indicating that the three lithotypes are not vulnerable to sodium sulphate attacks. Results of this study indicate that the good state of conservation of the building rocks of Lixus is linked to intrinsic factors as mineralogy and petrophysical characteristics together with the favourable effect of the climatic condition of the study area.