Evolution of thrust system deformation in an intracratonic chain: Study of the Southern-Central Tunisian Atlas

The development of belt structures in intracratonic chains is guided by the convergence system. In the Southern-Central Tunisian Atlas, several parameters control the evolution of thrust folds during different tectonic phases. One of these phases is tectonic inheritance, which leads to the reactivation of pre-existing normal faults during compressive phases. The angle between the direction of these faults and the shortening axis (NNW-SSE) is the most important parameter for interpreting the mode of the evolution of thrust folds. Jebel Elkebar is an example of a structure developed on NW-SE-oriented faults that is perpendicular to the shortening axis. Based on the geometry of its folds, Jebel Elkebar is interpreted as a 'Fault Related Fold'. The E-W-oriented Orbata structure is oblique to the direction of the shortening axis and is interpreted through the model 'Fault Propagation Fold' with 'Breakthrough'. The Gafsa Fault, which is parallel to the shortening axis, is a transpressional fault interpreted through the 'Strain Partitioning' mode, which is associated with the oblique ramp fold. The development of various thrust folds requires the presence of a basal decollement level during the Triassic succession. In the Southern-Central Tunisian Atlas, the deformation is variable (geometry of fold closure) and is correlated with the depth of the decollement level; indeed, the intensity of deformation is proportional to the depth of the decollement level. Consequently, the most important deformation is in the higher successions and is a vertical migration of the decollement level associated with thin-skinned deformation.     

The ore genesis of the Jebel Mecella and Sidi Taya FBa (ZnPb) Mississippi Valley-type deposits,Fluorite Zaghouan Province,NE Tunisia,in relation to Alpine orogeny: Constraints from geological,sulfur, and lead isotope studies

Jebel Mecella and Sidi Taya F–(BaPbZn) deposits are located within the Fluorite Zaghouan Province (NE Tunisia). The mineralization occurs along the unconformity surface between the Jurassic limestones and Upper Cretaceous rocks. The mineralization consists mainly of fluorite, barite, sphalerite, and galena. The δ³⁴S values of barite at Jebel Mecella (14.8–15.4‰) and at Sidi Taya (21.6–22.2‰) closely match those of the Triassic evaporites and Messinian seawater, respectively. The range of δ³⁴S values of galena and sphalerite in both deposits (?6.9 to +2.4‰) suggests the involvement of thermochemical sulfate reduction and possibly organically-bound sulfur in the generation of sulfur. Lead isotope data with ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios of 18.893–18.903, 15.684–15.699, and 38.850–38.880, respectively suggests a single homogeneous source reservoir of Paleozoic age and/or the homogenization of the Paleozoic–Cretaceous multireservoir-derived fluids along their long migration paths to the loci of deposition during the Alpine orogeny.     

Sources and genesis of the Pleistocene gravelly deposits in Northern Kuwait

The Dibdibba Formation is of Pleistocene age and consists of a fluviatile sequence of ungraded, often cross-bedded sand and gravels intercalated with minor sandy clay layers. It occurs in the northern desert of Kuwait as subparallel elongated ridges trending NE-SW. Structures and mineralogy of the Dibdibba deposits suggest that they have been derived from the basement complex of the northeastern area of Saudi Arabia as sheet floods and deposited in the alluvial fan of the Wadi Ar-Rimmah-Al Batin valley system. Floods transporting these deposits were intermittent; the gravelly bands were deposited during severe floods and the sandy beds during relatively quiet floods.     

Beryllium-10 in continental sediments

The concentration of¹⁰Be has been measured in 10 samples taken from a transect of surface sediments beginning in the Atchafalaya River and extending across the Bay 136 km into the Gulf of Mexico. If corrected for a lower retentivity of sand for Be, they have a concentration that is constant within 13%. This concentration is about an order of magnitude smaller than that of deep ocean sediments. For comparison, measurements of¹⁰Be in rainwater, in a sample of soil and in a deep ocean core were made.     

Répartition des minéraux argileux et contrôle tectono-eustatique dans les bassins de la marge tunisienne

We have studied the clay assemblages found in the different palaeogeographic domains located at the several Tunisian margin basins, ranging in age from Palaeozoic to Neogene. This study has allowed us to characterize and highlight the relationship between the clay distribution in time and space and the geodynamic and eustatic events. Marine regressions, with the intensification of erosion, seem to be responsible for illite increases, whereas transgressions, in concordance with a warm and dry climate, coincide with the smectite dominance. The minimum marine level coincides with the abundance of palygorskite. Mineralogic changes in the clay assemblages as well as in the proportion of the different clay minerals will tentatively be related to erosive tectonic events and/or to subsiding and rifting events, marked by the inheritance or the neoformation of the several clays.     

A reassessment of the human dimension of desertification

So far, the human dimension of desertification has been confined to some peripheral aspects of desertification. Man is either set at the beginning of the process as a triggerer or at the end as a victim. This paper tries to show the high degree of involvement of human communities in the process of desertification itself and that they undergo degradation just like the vegetation associations and the wildlife communities. A new, more human-orientated definition of desertification is discussed here.     

Sea-level rise impact on the evolution of a microtidal Mediterranean coastline without human-made structures——a case of the Port aux Princes-Sidi Daoued coastline,Gulf of Tunis,NE-Tunisia

The evolution of the natural and pristine Mediterranean coastline Port aux Princes-Sidi Daoued(Gulf of Tunis,NE-Tunisia) is studied during the period of 1887–2010 on the basis of an ancient minute of bathymetry(1887) and aerial photographs treated by numerical photogrammetric methods. Morphological changes of the coastline shows a general retreat despite the absence of the various anthropogenic actions. Adding to the drift currents and the currents of high energy that are generated by the N-W dominant waves along steeply sub-marine funds, the erosion is mainly due to the sea level rise which increased since the beginning of the 2000 s. The Port aux PrincesSidi Daoued coastline works as a single littoral cell limited by Jbel Korbous to the SW and the fishing harbor of Sidi Daoued to the N-E.     

Assessing Metal Content in Halophila stipulacea Seagrass as an Indicator of Metal Pollution in the Northern Gulf of Aqaba,Red Sea

Ocean Science Journal - To assess the utility of the seagrass (Halophila stipulacea) for biomonitoring of metal pollution, seagrass samples were collected from four sites along the Jordanian coast...