Groundwater influence on the aeolian sequence stratigraphy of the Mechertate-Chrita-Sidi El Hani system, Tunisian Sahel: Analogies to the wet-dry aeolian sequence stratigraphy at Meridiani Planum, Terby crater, and Gale crater, Mars

A multidisciplinary study of the watershed and depressions of the Mechertate–Chrita–Sidi El Hani
(MCSH) system in eastern Tunisia 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 is downward enriched with evaporitic minerals. These minerals
precipitate as cement and protect the sediment outcrops from aeolian erosion. The water table is the
limiting control on erosion and deposition, and also influences the succession of sediment along the
system. The water table further determines the local base level, which controls the deposition within
depressions. With increasing humidity at the limit of the capillary fringe, the landscape of the
evaporative system is organized according to three sedimentary types: (1) unconsolidated sediment of
aqueous and/or aeolian origin that is eroded and transported toward depressions (away from groundwater interactions), (2) consolidated sediment that is also aqueous and/or aeolian in origin and is
protected from aeolian erosion by groundwater influence, and (3) sedimentary filling of depressions
located within accumulation zones. These sediments are organized along a lateral, basinward profile.
Here we show that during periods of relative water table fall, sediments from the watershed prograde to
cover the sabkha basin fill. The rise and fall of the water table and the connected base level result in the
deposition of genetically-related progradational and retrogradational sequences. We propose that these
genetic sequences can be useful to interpret the sequence stratigraphy at three locations on Mars where
sedimentary formations were probably controlled by direct groundwater influence: Meridiani Planum,
Terby crater, and Gale crater. At Meridiani Planum, the exposed stratigraphic sequence of the Burns
formation starts with deposition of dry aeolian sediment derived from a former watershed. Then, due to
the rise of the water table, wet sediments of a sabkha rest 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 analog
scenarios for diverse depositional sequences on Mars, in all cases involving groundwater activity