Layered carbonates in Roman aqueducts: a new archive for environmental studies and archaeology

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Terrestrial carbonate deposits such as speleothems, tufa and travertine are important archives for palaeoclimate and palaeohydrology. Recently, carbonate deposits formed in historical aqueducts have been recognised as a new high-resolution archive of this type, with the additional possibility to obtain archaeological information. Aqueduct channels are well-defined geometric structures, and carbonate deposition therein is easier to understand and model than in natural freshwater carbonate deposits. A better understanding of the layering in carbonate deposits from historical aqueducts is essential to explore their worldwide potential for high-resolution palaeo-environmental and archaeology studies. In a previous study on Roman aqueducts in Turkey our group has shown that stable isotopes can be used to identify annual layering in the deposits even when the typical petrographic alternation of dense, coarse-crystalline winter and fine-crystalline, porous summer calcite is not clearly visible or complex. We propose to expand this method and to make this new high-resolution archive more widely applicable to other climate zones and for all types of water sources. This will be achieved by investigating two Roman aqueducts in a new climatic area, in southern France (Fréjus and Cahors). The precise nature of summer and winter deposits and other layering will be investigated by a combined analysis of a series of carbonate samples along each of the two aqueducts, by monitoring of the springs feeding these aqueducts and by monitoring carbonate growth in a still functioning ancient channel. The study is multi- and transdisciplinary involving research on freshwater carbonate depositional mechanisms, palaeoclimate, rock microstructures, freshwater microbiology, water resources, historical engineering and archaeology. Natural freshwater terrestrial carbonates are also important reservoir rocks for oil and gas with increasing economic significance.Terrestrial carbonate deposits, such as speleothems, tufa and travertine, are important archives for palaeoclimate and palaeohydrology. In recent years, carbonate deposits formed in historical aqueducts have been recognised as a new high-resolution archive of this type, with the additional possibility to obtain archaeological information. Aqueduct channels are well-defined geometric structures, and carbonate deposition therein is easier to understand and model than in the majority of natural freshwater carbonate deposits. A better understanding of the layering in carbonate deposits from historical aqueducts is essential to explore their worldwide potential for high-resolution palaeoenvironmental and archaeological studies. In a previous study on Roman aqueducts in Turkey, our group has shown that stable oxygen and carbon isotopes can be used to identify annual layering even if the typical petrographic alternation of dense, coarse-crystalline winter and fine-crystalline, porous summer calcite is not clearly visible macro- and microscopically. We propose to expand this method in order to make this new high-resolution archive more widely applicable to other climate zones and for other types of water sources. This will be achieved by investigating three Roman aqueducts in another climate zone in southern France (Béziers, Fréjus, and Cahors). The precise nature of summer and winter deposits will be investigated by a combined analysis of a series of samples along each of the two aqueducts, by monitoring the springs feeding these aqueducts and by monitoring carbonate growth in a still functioning channel. The study is multi- and transdisciplinary involving research on freshwater carbonate depositional mechanisms, palaeoclimate, carbonate microstructures, freshwater microbiology, water resources, historical engineering and archaeology.