Being a first notice in Tunisia, this work opens the door for forthcoming studies shedding light on potential analogies between Tunisian terrestrial analogues and extraterrestrial bodies.
In the first chapter, we investigate models of formation and activity of spring mounds occurring in the Mechertate-Chrita-Sidi El Hani (MCSH) and Boujmal systems. These terrestrial analogues are the mirror of subsurface past terrestrial analogues dating back to the Trias and Messinian. We then use these models to further understand possible spring mounds formation on Mars. In the MCSH system, the genesis of the spring mounds is a direct consequence of groundwater upwelling, triggered by tectonics and/or hydraulics. Considered as fault spring mounds, they are organized along preferential orientations, probably inherited from current or past tectonic activity. This observation supports a tectonic influence in the formation of the spring mounds. On the
one hand, the hydraulic pressure generated by the convergence of aquifers towards the surface of the system allows their consideration as artesian spring mounds. In the case of the MCSH system, our geologic investigations presented here show that both models are worth to be analyzed, and we propose a hydro-tectonic combined model as the adequate formation mechanism of artesian-fault spring mounds. During their evolution
from the embryonic to the islet stages, spring mounds behaving as obstacles are also shaped by an accumulation of a wet aeolian sedimentation, which is enhanced by the induration process. On the other hand, the tectonic model is more candidate to control the formation of spring mounds at the terrestrial analogue of Boujmal. The wet aeolian sedimentology also advocates the accumulation of tephras layers allowing the application of tephrostratigraphy. Similarly, spring mounds may be relatively common in certain provinces on the martian surface, but their mode of formation is still a matter of debate. We propose here that the tectonic, hydraulic, and hydro-tectonic models describing the spring mounds at MCSH should be considered as relevant martian
analogues because: (i) the martian subsurface may be over pressured and this overpressure would originate spring mounds on the surface, (ii) the subsurface may be fractured in such a way that explains the lining up of the spring mounds along preferential orientations, (iii) and the wet aeolian sedimentation through the induration process is a common feature on Mars.
In the second chapter, a multidisciplinary study of the watershed and depressions of the MCSH sabkha system shows that groundwater upwelling and/or seepage toward the modern surface is important in the shaping of its geomorphologic features and sediment outcrops. Along the watershed of the system, groundwater enriched sediment with evaporitic minerals. These minerals precipitate as cement to protect the outcropping sediment from aeolian erosion. The water table is the limiting control on erosion and deposition, and also influences the succession of sediment along the system. It determines the local base level, which controls the deposition within depressions. With increasing humidity at the limit of capillary fringe, the landscape of the evaporative system is organized according three sedimentary types: (1) unconsolidated sediment of aqueous or aeolian origin that is eroded and transported toward depressions (out of reach from groundwater involvement); (2) consolidated sediment is also aqueous or aeolian in origin and is consolidated due groundwater influence (protected from
aeolian erosion); and (3) sedimentary filling of depressions is located within accumulation zones. These sediments are organized along a lateral, basinward profile. Our study shows that during periods of relative water table fall, sediment from the watershed progrades to cover the sabkha basin fill. Applying key concepts of wet aeolian sequence stratigraphy, the rise and fall of the water table and the connected base level results in the deposition of genetically related progradational and retrogradational sequences. These genetic sabkha sequences are useful to interpret the sequence stratigraphy at three locations on Mars, which was controlled by direct groundwater influence. At Meridiani Planum, the deposition of Burns formation starts with a deposition of dry aeolian sediment derived from a former watershed. Then, due to the rise of the water table, wet sediment of a
sabkha rests atop the dry aeolian cycle to comprise a retrogradational sequence. At Terby and Gale craters, an opposite stratigraphic sequence starts with the wet deposition of the sabkha fill. Then, due to the fall of the water table, the dry aeolian sedimentation progrades atop to the sabkha fill to comprise a progradational sequence. We conclude that the various stratigraphic sequences at the MCSH system, described here, represent different possible analogue scenarios for diverse depositional sequences on Mars, in all cases involving groundwater activity.
In the third chapter, we discussed the chaology within the Sidi El Hani terrestrial analogue and Gale crater on Mars. Within natural systems, biologic activities and geologic conditions are linked by hierarchical
cause-effect relations gener g the organic matter within the discharge playa of Sidi El Hani, high percentages of different fractions seem abnormal in such a saline context. As it has been interpreted in previous works about Sahelarea, this maturated organic matter may be due to a human polluting activity. But this hypothesis seems less
convincing because this region is outside any polluting activity. Thus, this maturated organic matter should be
viewed in a widest context of a multidisciplinary study taking into account of the presence of petroleum
potentials in the subsurface, the converging hydrogeology and the tectonized region. For instance, the high
percentage of Aromatic Polycyclic Hydrocarbon (APH) may be hence the result of a hydrocarbons migration
rather than anthropogenic pollution. The hydrocarbon migration towards the surface of Sidi El Hani discharge
playa may be argued based on the model of fluid migration towards Mars surface. That is to say, based on what happens on Mars, we explain the case on terrestrial analogues.
Key Words: Terrestrial analogue, Mechertate-Chrita-Sidi El Hani and Boujmal systems, groundwater upwelling, spring mounds, wet aeolian sedimentation, tephrostratigraphy, wet aeolian sequence stratigraphy, Meridiani Planum, Terby crater, Gale crater, chaology, cyclostratigraphy, hydrocarbon migration, fluid migration on Mars.