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Detrital quartz grains extracted from sebkha sediments in southeastern Tunisia underwent scanning electron microscopy analysis to identify sediment sources and assess the influence of the saline environment on the grains. Core sediments collected from Sebkha el Melah and Sebkha Mhabeul cover the last 5000 and 2000 BP, respectively. The uppermost Unit III, present in both cores, exhibits two distinct facies based on the mechanical microtextures of its quartz grains. The aeolian facies sediments are characterized by quartz grains with rounded outlines, upturned plates, and crescentic percussion marks. In contrast, the fluvial facies sediments are associated with quartz grains featuring subangular outlines, v-shaped percussion cracks, conchoidal fractures. Observations on the quartz grains of the sebkhas suggest multiple transportation and processing events, indicating long-distance transport and rapid deposition rates. The majority of quartz grains appear to originate from the surrounding terrain, reflecting the dynamic geological history of the region. This study delves into the connection between microtexture variations on quartz grain surfaces and specific historical climatic conditions in the sebkhas. By examining geochemical variations along the cores, facies with elevated salt concentrations corresponding to warmer periods reveal extensively weathered quartz grains. This substantial chemical alteration is evident through microtextures such as oriented etch pits, anastomosed dissolution networks and solution crevasses. The profound dissolution has significantly impacted the quartz lattice, resulting in the decomposition of the grains and the formation of "cauliflower" or "spongy" shapes, erasing prior microtextures. Conversely, during less warm periods, quartz dissolution was less severe, thereby preserving microtextures. Sand grain surfaces are notably sensitive to both transport processes and variations in the physicochemical environment. In the hypersaline and confined environments of sebkhas in southeastern Tunisia, potent post-sedimentary processes can obliterate and obscure the original microtextures recorded on grains from previous environments due to highly fluctuating physicochemical conditions. • Quartz grain microtextures have been analyzed to identify sediment sources in Tunisian sebkhas. • Fluvial deposits show angular grains with v-shaped cracks, indicating water transport. • Aeolian deposits show rounded grains with crescentic percussion marks, indicating wind transport. • High salt concentrations recorded during warm periods enhance chemical weathering on quartz grains. • Hypersaline conditions can obscure previous textures on quartz grain surfaces. [ABSTRACT FROM AUTHOR]

In our research work, the central focus is upon the multi-proxy analysis of sediment core recovered in sebkha Mhabeul (southeastern Tunisia), provides the first high-resolution, continuous sedimentary record in the region, extending back to mid Holocene. The integration of sedimentary facies, elemental geochemistry and magnetic susceptibility, together with an age model based on tephrochronology, enable reconstruction of the main hydrological and climate changes in the region. Arid conditions, represented by thick gypsum interval at the bottom of Mh2 core occurred during Bronze Age. However, the period extending from Iron Age to the Present time is characterized by alternating episodes of higher effective moisture and severely arid climatic conditions. Magnetic and geochemical compositions provide information concerning changes of elemental and mineralogical compositions from flood events materials interrupted by thin deposits of aeolian origin. Indeed, six binary data consist of dominant silty fractions rich in heavy minerals and increasing with wadi-derived elements like Na 2 O/K 2 O and Na 2 O/Fe 2 O 3. These wadi sediments are covered with sandy/silty Saharan aeolian input occurring commonly after rapid and short climate change towards drier conditions. These sandstorm events are known for increasing redox-sensitive elements Na 2 O/K 2 O. [ABSTRACT FROM AUTHOR]

Quaternary formations occupy all the lower levels of large sedimentary basins, forming thus ephemeral lakes in closed salt depressions, called commonly "sebkhas." They are continental aquatic ecosystems, classified as wetlands of inland backwaters. They provide several functions; such as aquatic life, geochemical and hydrological cycles. The aim of this paper is to characterize the surface states of salty soils of sebkha Sefioune and its surroundings in the north of Ouargla (South-eastern Algeria), by linking the remote sensing data acquired by satellite, observation and exploration of land surface in order to differentiate the surface states of the study area (sebkha Sefioune and nearby). The realization of spectral signatures from the satellite image (Landsat 7 ETM +), allowed us to individualize the soil surface states of sebkha Sefioune and its surroundings (North of Ouargla-Algeria) according to the spectral responses of each surface states. This approach allows us to say that the land surface states have different spectral behaviour according to their colour, water content (humidity), structure (roughness,) mineralogical and geochemical nature. [ABSTRACT FROM AUTHOR]

Integrated sedimentological studies, diagenesis, sequential analysis and clay mineralogy on the Upper Paleocene rocks in Tamerza area provide important information on the reconstruction of the depositional basin, cyclicity, and paleoclimatic contexts. Facies analysis and petrographic studies have led to the recognition of nine facies that were deposited in three facies belts: Sebkha, inner ramp and outer ramp summarized in a carbonate ramp model: Homoclinal ramp under an arid climate. The upward and lateral changes in thickness and composition show a general regressive trend that records a transition from an outer ramp to Sebkha, creating different types of confinement. The facies stacking patterns constitute several kinds of meter-scale, shallowing-upward cycles. Nine different types of depositional cycles and several models of Sebkha sequences were defined. These different types of facies, characterized within the Thelja Formation, compose seven depositional sequences, mainly made of carbonates, marls and evaporates. Detailed multi approach analysis provides important information on evaporitic sequence stratigraphy. In carbonates beds, the diagenetic analysis provides an overview and chronology of diagenetic processes. A particular attention was paid to early stage cementation which enables us to characterize better the depositional environments. In addition to cementation, other features define the diagenetic history. X-ray diffraction reveals the presence of smectite suggesting an arid climate. Moreover, the clinoptilolite and the frequency of primary dolomite indicate different degrees of confinement. The seven depositional sequences showing a hierarchical organization of many cycles, as described above, suggested that eustatic sea level oscillations caused by cyclic perturbations of the Earth's orbit play a fundamental role in determining the formation of hierarchical cyclic rhythmicity. [ABSTRACT FROM AUTHOR]