Influence of the halokinesis on the clay mineral repartition of upper Maastrichtian–Ypresian in the Meknassy-Mezzouna basin,centerwestern Tunisia

The Meknassy-Mezzouna basin is affected by a fault system, assembling two main directions, northsouth and eastwest. The Triassic outcrops are widely noticeable at Jebel Jebbes El Meheri and the Mezzouna link. During the late Maastrichtian–Ypresian, the sedimentation in the basin is influenced by halokinetic events, which are clearly manifested either by the thickness of El Haria formation along the Triassic outcrops (rim syncline) or by an alteration surface at the top of the Abiod formation. Such events also confirm the emersion of the basin from the late Maastrichtian to the early Lutetian. However, the present work tries to highlight the effects of halokinetic uplift on the clay mineralogical variations at that area. In harmony with this halokinetic activity, the clay minerals of this time interval (during the late Maastrichtian–Ypresian) show a trend of variation which corresponds to the evolution from illite and kaolinite, indicating a strongly hydrolytic marine environment, to smectite, sepiolite, and palygorskite, reflecting a very rapid evolution from this marine environment to a lagoon environment, then to a more confined continental environment. In fact, the appearance of sepiolite and palygorskite on the top of El Haria formation and the Paleocene–Eocene transition can be explained by a transformation or neoformation mechanism in an alkaline environment, rich in silica and magnesium, under arid to semi-arid climatic conditions. Moreover, the palygorskite can be formed in continental deposits as well as in close marine environment, which displays a limited communication with the open sea. Under these conditions, the evaporation leads to high ionic concentration of alkaline pH, which is favorable to the formation and stability of this mineral.     

Study of geoid–quasigeoid separation obtained from terrestrial gravity data and two geopotential models

In this article, separation between the geoid and the quasigeoid was calculated using ground gravity data and the data extracted from two Global Geopotential Models (GGMs). The calculated results were compared together. To do so, the authors used the terrestrial gravity data in a vast region of Iran, comprising 8,245 stations which are kindly put in our disposal by the National Cartographic Center of Iran, as well as two GGMs, namely EGM96 and EGM2008 for comparison. The calculation of the separation for GGMs was performed by iteration method. The results showed that the geoid–quasigeoid separations obtained from the terrestrial data versus the orthometric heights are nonlinear in mountainous areas, whereas they are almost linear in flat regions due to decreasing the values of the topographic potential of the masses between the earth surface and the geoid. On the other hand, in case of GGMs, a positive correlation was observed between the separations and the orthometric heights in both mountainous and flat areas. As the difference between the separations extracted by two methods in mountainous areas—especially in the regions with ragged topography—differs strongly, it is recommended to use the dense gravity and height networks for accurate determination of the geoid–quasigeoid separation in these regions. Finally, we can conclude that the mean values of separation by two global geopotential models (EGM96 and EGM2008) are 21.87 and 21.23 cm, respectively, values which did not differ strongly, whereas this mean value obtained from ground gravity data is 16.10 cm, which differs from the GGMs’ results with approximately 5 cm.     

Integration of the MODIS Snow Cover Produced Into Snowmelt Runoff Modeling

Because of the difficulty of monitoring and measuring snow cover in mountainous watersheds, satellite images are used as an alternative to mapping snow cover to replace the ground operations in the watershed. Snow cover is one of the most important data in simulation snowmelt runoff. The daily snow cover maps are received from Moderate Resolution Imaging Spectroradiometer (MODIS), and are used in deriving the snow depletion curve, which is one of the input parameters of the snowmelt runoff model (SRM). Simulating Snowmelt runoff is presented using SRM model as one of the major applications of satellite images processing and extracting snow cover in the Ghara - Chay watershed. The first results of modeling process show that MODIS snow covered area product can be used for simulation and forecast of snowmelt runoff in Ghara - Chay watershed. The studies found that the SCA results were more reliable in the study area.     

Effect of nonthermality of ions on the nature of dust acoustic waves in two temperatures charged dusty grains

Effect of nonthermality of ions on the propagation of dust-acoustic waves (DAWs) in unmagnetized plasma having electrons, singly charged ions, hot and cold dust grains have been investigated. The reductive perturbation method is employed to reduce the basic set of fluid equations to the Korteweg-de Vries (KdV) equation. Moreover, the energy of two temperatures charged dusty grains were computed. The present investigation can be of relevance to the electrostatic solitary structures observed in various space plasma environments.     

Evidence of Quaternary active folding near Utique (Northeast Tunisia) from tectonic observations and a seismic profile

The present-day seismicity in northeastern Tunisia reported from permanent networks is of low to moderate magnitude. However, earthquakes are mentioned in the literature, specially a destructive one in the antique city of Utique. Geologic, seismic, and neotectonic investigations in this area show that the Utique fold is closely related to the recent tectonic activity in this region. Data show that the Utique fold is built on an east-west fault, and we found evidence of activity of this fault in the past 20 kyr. A seismic section and balanced cross-section show that the slip rate is of the order of 0.38 mm.yr⁻¹. Our data show definitively the Late Pleistocene–Holocene activity of the Utique Fault; and we can predict the earthquake recurrence interval which should be of ∼10³–10⁴ yr. This high seismic risk zone deserves to be taken into account during the establishment of important regional development programs and in the application of seismic building codes.