Roman aqueduct maintenance in the water supply system of Divona, France

Carbonate deposits formed in Roman aqueducts provide a window onto the environment and water management in antiquity. These laminated archives precipitated over a period of decades to centuries and are a potential high-resolution source of unwritten history. However, their use as environmental archives is hampered by local and partial removal during maintenance work in some aqueducts. This apparent problem, however, creates a unique opportunity to study Roman water management. We present the discovery of traces of regular maintenance in carbonate deposits of the Roman aqueduct of Divona (Cahors, France). The main objective of this study is to determine the periodicity of local carbonate removal and repairs in this aqueduct. Traces such as tool marks, calcite deformation twins, debris from cleaning and repairs are attested in the deposits as proof of periodic manual carbonate removal by Roman maintenance teams. The δ 18 O profile, recording at least 88 years of deposition, shows that maintenance work was done at intervals of 1–5 years. The undisturbed periodicity of the δ 18 O profile indicates that work was carried out rapidly and never in summer, consonant with the advice of the Roman author Frontinus about maintenance of the aqueducts of the city of Rome. Maintenance intervals lengthened and cleaning became less frequent close to the final years of the aqueduct. This change in maintenance policy gives insight into changing local population and socioeconomic dynamics in late antiquity

Reconstructing the hydraulics of the world’s first industrial complex, the second century CE Barbegal watermills, France

The Barbegal watermill complex, a unique cluster of 16 waterwheels in southern France, was the first known attempt in Europe to set up an industrial-scale complex of machines during the culmination of Roman Civilization in the second century CE. Little is known about the state of technological advance in this period, especially in hydraulics and the contemporary diffusion of knowledge. Since the upper part of the Barbegal mill complex has been destroyed and no traces of the wooden machinery survived, the mode of operation of these mills has long remained elusive. Carbonate incrustations that formed on the woodwork of the mills were used to reconstruct its structure and function, revealing a sophisticated hydraulic setup unique in the history of water mills. The lower mills used an elbow shaped flume to bring water onto overshot millwheels. This flume was specially adapted to the small water basins and serial arrangement of the mills on the slope. Carbonate deposits from ancient water systems are therefore a powerful tool in archaeological reconstructions and provide tantalizing insights into the skills of Roman engineers during a period of history that is the direct predecessor of our modern civilization

Fluid inclusions associated with the generation of pseudotachylyte and ultramylonite in the French Pyrénées

In the Saint-Barthélemy Massif, French Pyrenees, narrow ultramylonite and pseudotachylyte bands were generated in a major ductile shear zone at the end of a retrogressive mylonitic event. Ultramylonite bands formed partly by grain size reduction and recrystallization mechanisms and partly by ductile deformation of pseudotachylyte. Microthermometry shows that fluid inclusions in the major shear zone contain pure CO2, and are never aqueous. The low water content of the rock probably hampered hydrolitic weakening during mylonitic deformation. As a result, ultramylonite and pseudotachylyte bands were formed at 2-3.5 kbar an 450-550 °C The relatively high temperature of the host rock is probably the main cause for ductile deformation of pseudotachylyte. Fluid inclusion study can be an important method to detect depth of pseudotachylyte generation.Dans le Massif du Saint-Barthélémy, des rubans d'ultramylonite et de pseudotachylite se sont développés dans une zone de cisaillement importante à la fin d'une phase de mylonitisation à caractère rétromorphique. Certains rubans ultramylonitiques ont été partiellement formés par des mécanismes de recristallisation et de décroissance de la taille des grains, d'autres par une déformation ductile de la pseudotachylite. Des mesures microthermométriques indiquent que les inclusions fluides dans la zone de cisaillement contiennent du CO2 pur. Le manque d'eau dans la phase fluide a probablement entraîné le durcissement de la roche pendant la déformation mylonitique. L'ultramylonite et la pseudotachylite ont été formées à 2-3,5 kbar et 450-550 °C. La température relativement élevée de la roche-hôte est probablement la cause principale de la déformation ductile de la pseudotachylite. Des recherches sur les inclusions fluides autour des rubans de pseudotachylite peuvent être importantes pour déterminer les conditions de formation de tels rubans.Passchier Cees W. Fluid inclusions associated with the generation of pseudotachylyte and ultramylonite in the French Pyrénées. In: Bulletin de Minéralogie, volume 107, 2, 1984. Inclusions fluides

Origines, développement et preuves du nettoyage des concrétions calcaires durant le fonctionnement de l’aqueduc gallo-romain de Divona-Cahors (Lot)

International audienceThe archaeological excavations carried out on the aqueduct that supplied the Gallo-Roman city of Cahors (Divona) have discovered sections partially filled with carbonate deposits. These deposits present a laminated facies and variations in thickness along the way of the aqueduct. The recent study of a sequence of deposits 28 cm thick presented here demonstrates the ancient maintenance of the hydraulic structure by identifying anthropic traces of cleaning, sometimes followed by re-capping with hydraulic mortar, in the sedimentary sequences.Les opérations de fouilles programmées et préventives effectuées sur l’aqueduc qui alimentait la cité gallo-romaine de Cahors (Divona) ont permis de mettre au jour des tronçons partiellement colmatés par des dépôts carbonatés. Ces dépôts présentent un faciès laminé et des variations d’épaisseur le long du tracé de l’aqueduc, selon la morphologie de ce dernier. L’étude récente d’une séquence de dépôts de 28 cm d’épaisseur présentée ici démontre l’entretien antique de la structure hydraulique par l’identification de traces anthropiques de nettoyage, parfois suivis de rechapages à l’aide de mortier de tuileau, dans les séquences sédimentaires

Modelling of segment structures: Boudins, bone-boudins, mullions and related single- and multiphase deformation features

Finite element modelling has been used to simulate the development of segment structures, deformed layer segments separated by veins, such as boudins, mullions, and bone-boudins. A parameter sensitivity analysis is used to compare the influence of the nature of the flow, the relative viscosities of veins in necks and the host rock, and the initial geometry of the layer segments. Parameter fields have been determined for the relative viscosity of veins and layers, and the kinematic vorticity number of flow. Reworked segment structures can have several shapes such as bone-, bulging, shortened bone-boudins and their asymmetric equivalents such as domino- and shearband-boudin geometry. The model for asymmetric reworked segment structures is applied to such features from the Lower Ugab Metaturbidites in NW Namibia. The model suggests that these structures form where the neck veins are stronger than the boudinaged layer, with a significant simple shear component of the bulk flow. The quartz filled necks in the Lower Ugab are therefore stronger than the quartz-rich wall rock in greenschist facies where the progressive deformation occurred. Bone-boudins are usually interpreted to form in transpressional flow, but simulations of the rotation of tension gashes show that they can also form in simple shear or slightly transtensional shear flow

Origines, développement et preuves du nettoyage des concrétions calcaires durant le fonctionnement de l’aqueduc gallo-romain de Divona-Cahors (Lot)

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Dynamics of hydrofracturing and permeability evolution in layered reservoirs

International audienceA coupled hydro-mechanical model is presented to model fluid driven fracturing in layered porous rocks. In the model the solid elastic continuum is described by a discrete element approach coupled with a fluid continuum grid that is used to solve Darcy based pressure diffusion. The model assumes poro-elasto-plastic effects and yields real time dynamic aspects of the fracturing and effective stress evolution under the influence of excess fluid pressure gradients. We show that the formation and propagation of hydrofractures are sensitive to mechanical and tectonic conditions of the system. In cases where elevated fluid pressure is the sole driving agent in a stable tectonic system, sealing layers induce permutations between the principal directions of the local stress tensor, which regulate the growth of vertical fractures and may result in irregular pattern formation or sub-horizontal failure below the seal. Stiffer layers tend to concentrate differential stresses and lead to vertical fracture growth, whereas the layer-contact tends to fracture if the strength of the neighboring rock is comparably high. If the system has remained under extension for a longer time period, the developed hydrofractures propagate by linking up confined tensile fractures in competent layers. This leads to the growth of large-scale normal faults in the layered systems, so that subsequently the effective permeability is highly variable over time and the faults drain the system. The simulation results are shown to be consistent with some of the field observations carried out in the Oman Mountains, where abnormal fluid pressure is reported to be a significant factor in the development of several generations of local and regional fracture and fault sets