The Building Stone of the Roman City of Dougga (Tunisia): Provenance
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Geoscience xxx (2017) xxx–xxx Contents lists available at ScienceDirect Comptes Rendus Geoscience ww w.sciencedirect.com Hydrology, Environment The building stone of the Roman city of Dougga (Tunisia): Provenance, petrophysical characterisation and durability a,b, c d Karima Zoghlami *, Juan Diego Martı´n-Martı´n , David Go´ mez-Gras , e f e Antonia Navarro , David Parcerisa , Joan Ramon Rosell a De´partement de Ge´ologie, Faculte´ des Sciences de Bizerte, Universite´ de Carthage, 7021 Bizerte, Tunisia b Laboratoire des ressources mine´rales et environnement (LRME), Universite´ El Manar, 1068 Tunis, Tunisia c Departament de Mineralogia, Petrologia i Geologia Aplicada, Universitat de Barcelona, 08028 Barcelona, Spain d Departament de Geologia, Universitat Auto`noma de Barcelona, 08193 Bellaterra (Cerdanyola del Valle`s), Spain e Departament de Construccions Arquitecto`niques II, Escola Polite`cnica Superior d’Edificacio´ de Barcelona, UPC, 08028 Barcelona, Spain f Departament d’Enginyeria Minera, Industrial i TIC, Escola Polite`cnica Superior d’Enginyeria de Manresa, Universitat Polite`cnica de Catalunya, Av. Bases de Manresa 63-71, 08242 Manresa, Spain A R T I C L E I N F O A B S T R A C T Article history: Preservation of the architectural integrity of archaeological sites requires detailed Received 8 August 2017 information about the properties of the building materials and their decay processes. This Accepted after revision 21 September 2017 study investigates the petrophysical properties of the Eocene nummulitic limestone rock Available online xxx used in the construction of the Roman City of Dougga (Tunisia) and its resistance to various factors of decay. The petrographical study is carried out using standard microscope Handled by Franc¸ois Chabaux techniques and the petrophysical behaviour by a combination of techniques focusing on hydric and mechanical properties. The pore network is studied by fluorescence Keywords: microscopy and mercury intrusion porosimetry. Durability was assessed by ice Nummilitic limestone crystallization and SO2 attack ageing tests. The results allowed the identification of four Building stone Dougga main building lithotypes and their exact stratigraphic point of mining in the ancient Petrophysics quarries. The petrographic variations between lithotypes correlate well with their physical Durability properties. In addition, the four lithotypes show high resistance to ageing tests, confirming the excellent characteristics of the studied nummulitic limestones as a building rock. C 2017 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved. 1. Introduction others. The use of these limestones was, and still it is, facilitated by (i) the abundant exposures located in the Nummilitic limestones have been extensively used as circum-Mediterranean countries, and (ii) the common easy building rocks in the Mediterranean basin since the first extraction and shaping process of limestones compared to constructions made by humans. This is the case of harder rock types. important archaeological sites like the ancient Corinth Nummulitic limestones, Eocene (Ypresian–Lutetian) in (Greece), several monuments in Cairo (Egypt) such as age, belonging to the El Garia Fm (Metlaoui Group) temples and pyramids (Fitzner et al., 2002), and the (Fournie´, 1978; Moody and Grant, 1989; Perthuisot, cathedral of Girona in Spain (Esbert et al., 1989), among 1974, 1979; Tlig et al., 2010) (Fig. 1 and Fig. S1), are the most common building rock used in the Roman City of Dougga (Thugga). Dougga is located in the north-central part of Tunisia, in the Be´ja Governorate, at around 100 km * Corresponding author. De´partement de Ge´ologie, Faculte´ des Sciences southwest of Tunis. Dougga has a warm-temperature de Bizerte, Universite´ de Carthage, 7021 Bizerte, Tunisia. E-mail address: [email protected] (K. Zoghlami). Mediterranean climate, with a hot and dry summer, which https://doi.org/10.1016/j.crte.2017.09.017 C 1631-0713/ 2017 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved. Please cite this article in press as: Zoghlami K, et al. The building stone of the Roman city of Dougga (Tunisia): Provenance, petrophysical characterisation and durability. C. R. Geoscience (2017), https://doi.org/10.1016/ j.crte.2017.09.017 G Model CRAS2A-3379; No. of Pages 10 2 K. Zoghlami et al. / C. R. Geoscience xxx (2017) xxx–xxx Fig. 1. A. Location of Dougga in Diapir Zone of the north-central part of Tunisia. B. Simplified geological map of the Teboursouk region, showing the age of the rocks cropping out in the area of Dougga (based on Perthuisot, 1979). is classified as Csa according to the Ko¨ ppen–Geiger representing the synthesis between several cultures, climate system (Kottek et al., 2006). The average annual including Numidian, Roman, Punic and Byzantine ones. temperature is 18 8C, with a minimum average value of The city of Dougga possesses a remarkable group of 11.4 8C and a maximum average value of 24.7 8C, the public buildings dating back, for the most part, to the 2nd annual precipitation is 504 mm, and the mean month and 3rd centuries A.D. (Fig. 2). It conserves traces of the insulation is 211 h (National Institute of Meteorology of different periods of the Antique city with all its compo- Tunisia). nents: the monumental centre (capitol, forum, market, This archaeological site covers an area of approximately Rose of the winds square, etc.), entertainment buildings 75 ha, although only one third of them have been (theatre, circus), and public baths. Dougga is considered excavated. The building rock was extracted from local the best-preserved example of an Africo-Roman city in quarries that are still located and perfectly recognized in North Africa (Ennabli, 2000), and so was inscribed on the the vicinity of the city (Fig. S2). The ruins of Dougga World Heritage List of UNESCO in 1997. represent a complete city with all its components, Despite the overall good state of preservation of Dougga testimony of more than 15 centuries of history (Khanoussi, compared to other Roman cities of Tunisia such as 1989, 2003). They are an extraordinary illustration Carthage, some buildings have been partially destroyed, Please cite this article in press as: Zoghlami K, et al. The building stone of the Roman city of Dougga (Tunisia): Provenance, petrophysical characterisation and durability. C. R. Geoscience (2017), https://doi.org/10.1016/ j.crte.2017.09.017 G Model CRAS2A-3379; No. of Pages 10 K. Zoghlami et al. / C. R. Geoscience xxx (2017) xxx–xxx 3 Fig. 2. Field views of some of Dougga’s buildings made with nummulitic limestones. A. Panoramic view of the amphitheatre with the valley and Nouvelle Dougga (arrow) in the background (S. II AD). B. View of the market’s entrance with the Capitoline Temple (s. I AD) in the background. C. Wall made of centimetre- to decimetre-sized rock blocks. Note the meter-scale blocks used in the base of the wall. D. Detail of a column from the amphitheatre showing fractures (white arrows) and macrovugs (black arrows). and numerous original rock elements are broken or ering. To achieve these goals, the petrophysical properties disappeared (Fig. 2). Based on their work about the of these materials are determined allowing the under- geomorphological hazard in Dougga, Lazzari and Lazzari standing of decay mechanisms of the building rock and so (2012) recommended the reinforcement of the monumen- facilitate and improve its use in future restoration works. tal structures to inhibit the movements of the soils and save the city from its progressive deterioration and from 2. Results the risks caused by natural disasters. Moreover, the building rocks show some located weathering patterns 2.1. Petrography of the building rock such as fissures, desquamations, pitting, and fragmenta- tion, typically affecting columns. Surface erosion and Macroscopic observations allow determining four main biological colonization are also frequent. In this regard, rock lithotypes of the Eocene nummulitic limestones used future conservation and restoration works will need as building materials in the archaeological site of Dougga, information regarding the origin and characteristics of labelled here as 2F, 2G, L1, and L3 (Fig. S3). Lithotype L1 is the building rock. Nevertheless, no works regarding the characterised by the presence of terrigenous grains that petrophysical properties and durability of this building appear partially dissolved in the surface of the rock, likely stone have been carried out up to now and most, increasing porosity compared to other lithotypes. Litho- restoration works are realized without preliminary stud- type L3 is characterised by very coarse-sized nummulites ies. Petrographic, physical, hydric, mechanical studies and that appear aligned with each other, providing to this rock ageing tests are the standard petrophysical analyses a very distinctive aesthetics appearance compared to other frequently used for this purpose (Borrelli and Urland, lithotypes. Lithotypes 2F and 2G have very similar 1999; De Kock et al., 2015; Esbert and Marcos, 1983; Esbert characteristics but differ in the grain size of the skeletal et al., 2008; Gauri and Punuru, 1989; Lazzarini and components, mostly nummulites, being 2F characterised ´ ˜ Laurenzi Tabasso, 1986; Lopez-Arce et al., 2008; Ordonez by fine-sized specimens and 2G by coarser-sized speci- et al., 1997; Robertson, 1982; Torraca, 1999; Villegas mens. Lithotypes L1, 2F and 2G have been preferentially