Structural context of meso-scale and cartographical duplex structure genesis in thrusting tectonics: role of tear faults. Zaghouan thrust belt. Case of Bir M'Cherga-Ain Asker area     

Sabri Aridhi  Kais Aridhi  Mohamed Ghanmi  Fouad Zargouni  Eric Mercier 《Arabian Journal of Geosciences》2014,7(6):2499-2514

Bir M'Cherga-Ain Asker area, situated in the hinterland of Zaghouan thrust (Tunisian dorsal), was the land example treated with metric and cartographic scale in order to identify duplex genesis criteria and to include thrusting tectonics associated with tear faults, which are in fact the directory response generating duplex structures identified in outcrop for the first time through Tunisia in this case. Given its geological location between the "dôme" and the "dorsal" zone of Tunisia, this area was the most exposed to a highly paleostress history expressed by a huge fault system remobilization and reactivation through several tectonic events from NE–SW middle Cretaceous distension to a NW–SE and NNW–SSE Paleogene compression. Regarding fault planes generated analysis, they show numerous streak generation of normal, strike-slip, and reverse faults that go with geodynamic and paleostress evolution of the studied area; we note that each streak generation is perfectly matching with one of the tectonic event (mentioned before) affecting the area. In this paper, we analyze duplex structure elaboration scenarios to assess the involved kinematics and their geometrical recognition criterious. We propose to discuss the causes of duplex structures installation in a thrust belt system and the predictable geometrical styles after its installation on foreland or backland. Using the geometrical criteria acquired through this analysis, we will show that such, however, exceptionable structures exist on the land, and that they record the mechanisms of their genesis linked to the tear faults acting in this case. We describe "tear faults" as the sliding breaks which disunite two compartments during deformation, allowing them to undergo different independent deformations in their drawing and their width (for example more or less stretched folds). These types of faults differ from that of the true stick-slip faults, which slice and shift preformed structures (it's even this shift which makes it possible to highlight them); here, there are no shift but dissimilarity of the structures on both sides of the fault; therefore, deformations are the direct results of displacements; they are expressed in thrust belts by ramp folds, intense internal deformations, and even by complex duplex structures. A duplex feature that is not mainly studied is made up by tilted imbricate sedimentary sequences (or horses), separated by link thrusts and underlined respectively at their tops and bottoms by roof and floor thrusts. Imbrications cause a shortening, a thickening, or a thinning of stratigraphic columns and even its crushing and inverting. In thrust belts, duplexes are usually set up following two or even more deformational events; those structures start typically with decollement and imbricate sedimentary unit ones which are made cover by a roof thrust sometimes visible at outcrop. Through this paper, we suggest to discuss geometrical duplex criteria, and we will try a zooming through different scales, from regional to local one in order to show how the shape (expression) of the deformation differs.  相似文献   

Interplay between detrital and diagenetic processes since the last glacial maximum on the northwest Iberian continental shelf     

Kais Jacob Mohamed  Daniel Rey  Belen Rubio  Federico Vilas  Thomas Frederichs 《Quaternary Research》2010,73(3):507-520

Integrated analyses of magnetic, geochemical and textural data on six cores from the northwestern Iberian continental shelf allowed the reconstruction of the paleoenvironmental evolution of this area since the last glacial maximum (LGM). Four sedimentary units were identified, representing a succession from fluvial and subaerial settings to high and finally low-energy marine deposits subsequent to the post-LGM sea-level rise. The uppermost unit was deposited during the Holocene and its magnetic properties were controlled by the interplay between detrital input and early diagenetic reductive dissolution of magnetic minerals. Identification of a primary steady-state early diagenetic signal allowed the recognition of periods of increased detrital input, bounded by intervals of lower detrital input and intensified reductive diagenesis related to intensified upwelling in the area. These paleoenvironmental alternations are consistent with the climatic evolution of the late Holocene. During the Roman Warm Period and Medieval Warm Period, the combined effect of greater humidity and intense agricultural and mining activities led to a greater erosion and transport of detrital sediments to the shelf. In contrast, enhanced diagenetic reduction intervals, caused by upwelling intensification, were roughly coincident with the colder Dark Ages and the Little Ice Age.  相似文献   

Modeling and Optimization of Fluoride and Cadmium Trapping in Phosphogypsum Using Design Methodology     

Besma Hajem  Kais Djebali  Adel M'nif 《洁净——土壤、空气、水》2010,38(9):859-864

The manufacturing of phosphoric acid from natural calcium phosphate generates a solid residue containing 25–30% humidity. This solid residue (phosphogypsum) generates acidic solution (pH ≈ 2.5) containing several toxic ionic species, that coat its grains. Fluorides and heavy metals such as cadmium are considered the most harmful species contained in the released solution from phosphogypsum. The purpose of this work is to study the trapping of fluorides and cadmium in phosphogypsum as well as effluent neutralization before its discharge into natural recipient. Therefore, calcium carbonate finely ground was added and fully mixed with wet phosphogypsum. A four factors central composite design was used to model and to optimize the operating parameters that govern the process. The studied factors were temperature, reaction time, mass, and grains size of CaCO₃. Considered responses were pH, F⁻, and Cd²⁺ concentrations in the released solution after reaction with CaCO₃. The optimum operating conditions were quite efficient to trap, respectively, 99% Cd²⁺ and 97% of F⁻ with a final pH of 6.66. So an original, easy, simple, and cost effective method to trap some toxic species on phosphogypsum through CaCO₃ addition would likely to be integrated in phosphoric acid manufacturing plant.  相似文献