Geodynamic Framework of Saline Systems in Eastern Tunisia: Saline Depressions Inherited from the Triassic Intrusions and/or the Messinian Salinity Crisis

Based on the geodynamic context, two hypotheses of origin of salt in the subsurface of the Sahel area are worth being defended. The first suggests that the halokinesis activities, namely, of the Triassic evaporitic sedimentation, may still be until now influencing the functioning of the saline systems in the Sahel. The second integrates the Sahel area geodynamic evolution in the framework of the convergence between African and Eurasian plates. It suggests a link between the blockage of the subduction between African and Eurasian plates in North Tunisia, the Messinian Salinity Crisis, and eventually the concrete opening and evolution of the playa during the Quaternary. Such a suggestion is materialized by a geodynamic model relating successively these events. This scenario suggests that the Messinian Salinity Crisis constituted huge quantities of salt and/or salty water. This saline subsurface reserve is until now influencing the Sahel behavior as a whole. Through groundwater convergence, huge quantities of salt are accumulated within depressions of the Sahel area. Currently, the convergence of the plate between African and Eurasian plates results in a tectonic activity within these saline systems materialized by the formation of fault spring mounds along preferential orientation ensuring the surface-subsurface connectivity.

Fluid Evolution of the Magmatic Hydrothermal Porphyry Copper Deposit Based on Fluid Inclusion and Stable Isotope Studies at Darrehzar, Iran

The Darrehzar porphyry Cu-Mo deposit is located in southwestern Iran (~70 km southwest of Kerman City). The porphyries occur as Tertiary quartz-monzonite stocks and dikes, ranging in composition from microdiorite to diorite and granodiorite. Hydrothermal alteration and mineralization at Darrehzar are centered on the stock and were broadly synchronous with its emplacement. Early hydrothermal alteration was dominantly potassic and propylitic and was followed by later phyllic and argillic alteration. The hydrothermal system involved both magmatic and meteoric water which were boiled extensively. Copper mineralization was accompanied by both potassic and phyllic alterations. Based on number, nature, and phases number which are available in room temperature, three types of fluid inclusions are typically observed in these veins: (1) vapor rich, (2) liquid rich and (3) multi phase. The primary multiphase inclusions within the quartz crystals were chosen for microthermometric analyses. Early hydrothermal alteration was caused by high-temperature, high-salinity orthomagmatic fluid and produced a potassic assemblage. Phyllic alteration was caused by high-salinity and lower-temperature orthomagmatic fluid. Magmatic and meteoric water mixtures were developed in the peripheral part of the stock and caused propylitic alteration which is attributed to a liquid-rich, lower temperature.

Facies Analysis and Depositional Environments of the Late Palaeozoic Coal-Bearing Madzaringwe Formation in the Tshipise-Pafuri Basin, South Africa

The late Palaeozoic coal-bearing Madzaringwe Formation of the Karoo Supergroup in the Tshipise-Pafuri Basin in the Limpopo Province, South Africa, records part of the infill of a passive continental margin terrain. Lithofacies analysis was performed with a view to deduce the nature of depositional environments of the Formation. Sedimentological and sequence stratigraphic evidence indicates that this unit represents a complex siliciclastic facies that reflects a fluvial paleodepositional environment. Eleven facies, which were grouped into five facies associations, were recognised. The base of the Madzaringwe Formation (Lower Member) represents a sequence deposited by braided channels. The coal deposits represent flood plain and swamp deposits, which is characterised by shale, thick coal seams, siltstone, and sandstone. The Middle Member is characterised by both clast and matrix supported conglomerates, major tubular and lenticular sandstones, and finely calcareous, micaceous siltstone. The deposition represents a sequence being formed from fluvial and particularly braided channels. The crudely stratified, coarse to pebbly sandstone indicates channel lag deposits within a heavy loaded fluvial system. The fine-grained sandstone represents deposition by shift channel and side bar deposits during lower flow conditions. The Upper Member is characterised by facies associations similar to the Lower Member, representing a new depositional cyclothem.

Approaching Cave Level Identification with GIS: A Case Study of Carter Caves

Cave passages that are found at similar elevations are grouped together and called levels. The current understanding is that passages within a level are speleogenetically linked to a common static baselevel or stratigraphic control. Cave levels have provided an interpretive framework for deciphering cave development, landscape evolution, and climatic changes. Cosmogenic dating has been successfully used to interpret levels in Mammoth Cave and the Cumberland Plateau; however, this technique is expensive and there are limited funding resources available. Geographic information systems may be used as preliminary procedures to identify cave levels and constrain the timing of level development. A GIS method is applied to the Carter Cave system in northeastern Kentucky. Cave entrance elevations along stream valleys were found by extracting elevation values from a m digital elevation model. Using a histogram generated from the frequency of cave elevations and a natural breaks classifier, four cave levels were identified in the Carter Cave system. This work improves the understanding of the Carter Cave system evolution and contributes toa methodology that can be used to ascertain an erosion history of karst systems.

Record of the Climatic Variability and the Sedimentary Dynamics during the Last Two Millennia at Sebkha Dkhila, Eastern Tunisia

This paper aimed to study the record of the climatic variability during the last two millennia within the sebkha of Dkhila. Six climatic stages were recognized along the 104 cm core: the Warming Present (WP), the Late Little Ice Age (Late LIA), the Early Little Ice Age (ELIA), the Medieval Climatic Anomaly (MCA), the Dark Age (DA), and the Roman Warm Period (RWP). The WP stretches along the uppermost 1 cm with a high grey scale as sign of a dry climate. The Late LIA is located between 1 cm and 6 cm. The ELIA is located between 6 cm and 40 cm. The MCA spanning from 40 cm to 72 cm is marked by a sharp increase of the GS revealing a wet period. The DA appears along the part between 72 cm and 84 cm; a shift from light to dark sediments is recorded. The RWP appears between 84 cm and 104 cm. Based on the grain size distribution, two low frequency cycles were identified indicating radical global changes of climatic conditions, the differential tectonics, and the groundwater fluctuations. On the other hand, high frequency cycles indicate local modifications of the climatic conditions.

Comparison of Tidalites in Siliciclastic, Carbonate, and Mixed Siliciclastic-Carbonate Systems: Examples from Cambrian and Devonian Deposits of East-Central Iran

For the comparison of lithofacies in siliciclastic, carbonate, and mixed siliciclastic-carbonate tidal systems, three successions including Top Quartzite (Lower-Middle Cambrian), Deranjal Formation (Upper Cambrian), and Padeha Formation (Lower-Middle Devonian) in the north of Kerman and Tabas regions (SE and E central Iran) were selected and described, respectively. Lithofacies analysis led to identification of 14 lithofacies (Gcm, Gms, Gt, Sp, St, Sh, Sl, Sr, Sm, Se, Sr(Fl), Sr/Fl, Fl(Sr), and Fl) and 4 architectural elements (CH, LA, SB, and FF) in the Top Quartzite, 7 lithofacies (Dim, Dp, Dr, Ds, Dl, Dr/Dl, and Fcl) and 2 architectural elements (CH, CB) in the Deranjal Formation, and 17 lithofacies (Sp, St, Sh, Sl, Sr, Se, Sr(Fl), Sr/Fl, Fl(Sr), Fl, Dr, Ds, Sr/Dl, El, Efm, Efl, and Edl) and 5 architectural elements (CH, LA, SB, FF, and EF) in the Padeha Formation that have been deposited under the influence of tides. The most diagnostic features for comparison of the three tidalite systems are sedimentary structures, textures, and fabrics as well as architectural elements (lithofacies association). The CH element in siliciclastics has the highest vertical thickness and the least lateral extension, while in the carbonate tidalites, it has the least vertical thickness and the most lateral extension compared to in other systems.