Magnetic Study of the Heated and Unheated Sedimentary Fillings of Sebkha Mhabeul, Southeast Tunisia: A Geophysical Method for Paleoclimatic Investigation and Tephrochronological Dating

This paper is meant to investigate the climatic and volcanic signals within the sedimentary filling of sebkha Mhabeul through a thermomagnetic study of a 37 cm length core. Values of the magnetic susceptibility at ambient temperature show that the core encompasses four climatic stages: the Warming Present (WP), the Little Ice Age (Late LIA), Early Little Ice Age (ELIA), and the Medieval Climate Anomalies (MCA). Added to the subcycles, the spectral analysis shows the individualization of an 888 yr cycle probably related to solar activity. The heating at 250°C is good-for-nothing since it was useful neither for climatic investigation nor for tephras layers detection. Heating at 700°C generated the complete loss of the climatic signal. On the other hand, it allowed the detection of the previously identified tephras layers. Further, it highlighted the presence of other tephras layers. The extraction by the bromoform confirms the presence of these tephras. The use of the same methodology may allow the detection of tephras layers within other sebkhas

Spatial distribution and ecological risk assessment of potentially toxic elements in agricultural soils, stream sediments, and plants around Lakhouat mine (northwestern Tunisia)

International audienc

Middle to late Holocene sedimentary filling history of the Sebkha el Melah in south-eastern Tunisia

peer reviewedThe sedimentological and geochemical properties of a 146 cm long sediment core collected from Sebkha el Melah (Ml core) in south-eastern Tunisia have been used to infer the genesis and evolution of the Sebkha el Melah over the last 5000 years. Two main sedimentary units have been defined: a huntite [Mg3Ca(CO3)4] unit at the bottom of core Ml is covered by a second unit made up of siliciclastic and evaporitic materials. The huntite level is synchronous with Holocene marine transgression, which was followed by a regression of about 5300 years bp. Geochemical data (major and trace element), magnetic analyses, grain-size distribution and microtexture of quartz grains were performed to assess the sediment provenance. The upper unit of Ml core is characterized by alternations between fluvial, aeolian and evaporite deposits. Redox proxies displaying marked Fe/Ca and Rb/S peaks, in addition to high magnetic susceptibility (MS) values, polymodal grain-size frequency curves, as well as sub-angular grains with V-shaped percussion cracks, are suggestive of palaeohydrological events. In contrast, a decreasing trend in the low MS values, bi-modal grain-size frequency curves as well as well-rounded quartz grains with crescent percussion marks would indicate enhanced aeolian sand input in the sebkah el Melah sequence. Moreover, geochemical proxies suggest formation of evaporite facies under a strongly warm climate contemporary with marine intrusion

Preparation of Silica Gel Obtained From Early Cretaceous Sidi Aich Sands (Central Tunisia) and its potential to remove pollutant dye anionic from wastewaters

The present study concerns the elimination by retention of the anionic dye orange II (OII) from aqueous solutions was studied using a silica gel prepared from Tunisian silica sands (Barremian age). These Sidi Aich sands were collected in central Tunisia. The collected raw silica sand from the Jebel Meloussi (central Tunisia) was characterised by different techniques, such as X-ray diffraction (XRD), X-ray fluorescence (XRF) and scanning electron microscopy (SEM). X-ray diffraction showed a predominance of quartz and potassic feldspars and lower amounts of kaolinite and calcite. The N-2 adsorption isotherms show that these are mesoporous materials with high chemi-physical adsorption capabilities, and indicated a multilayer process for N-2 absorption. They had pore diameters between 60 and 118 angstrom (mesoporous) and specific surface areas up to 183 m(2)/g, close to those reported for commercial silica gel materials. Maximum retention rates of the anionic dye orange II (OII, up to 89.73 % after 180 min contact time) were achieved with products prepared in acidic medium (pH 3). The adsorption is mechanism was well described with both Langmuir and Freundlich models, allowing for a multilayer coverage process of OII molecules on the gel surface, and the pseudo-second-order model is the most reliable for determining the order of absorption kinetics of OII by silica gel. The values of the adsorption capacities at equilibrium calculated (Qe = 242 mg / g) by the pseudo-second-order model are very close to the Qe determined experimentally (224 mg / g), and to those of an industrial silica gel (234 mg / g)

From the Characterization, Geochemical Behavior and Health Risk Assessments of Tunisian Phosphogypsum to a Potential Way of Inerting and Valorization

International audienc

Post-traumatic pulmonary embolism in the intensive care unit

Objective: To determine the predictive factors, clinical manifestations, and the outcome of patients with post-traumatic pulmonary embolism (PE) admitted in the intensive care unit (ICU). Methods: During a four-year prospective study, a medical committee of six ICU physicians prospectively examined all available data for each trauma patient in order to classify patients according to the level of clinical suspicion of pulmonary thromboembolism. During the study period, all trauma patients admitted to our ICU were classified into two groups. The first group included all patients with confirmed PE; the second group included patients without clinical manifestations of PE. The diagnosis of PE was confirmed either by a high-probability ventilation/perfusion (V/Q) scan or by a spiral computed tomography (CT) scan showing one or more filling defects in the pulmonary artery or its branches. Results: During the study period, 1067 trauma patients were admitted in our ICU. The diagnosis of PE was confirmed in 34 patients (3.2%). The mean delay of development of PE was 11.3 ± 9.3 days. Eight patients (24%) developed this complication within five days of ICU admission. On the day of PE diagnosis, the clinical examination showed that 13 patients (38.2%) were hypotensive, 23 (67.7%) had systemic inflammatory response syndrome (SIRS), three (8.8%) had clinical manifestations of deep venous thrombosis (DVT), and 32 (94%) had respiratory distress requiring mechanical ventilation. In our study, intravenous unfractionated heparin was used in 32 cases (94%) and low molecular weight heparin was used in two cases (4%). The mean ICU stay was 31.6 ± 35.7 days and the mean hospital stay was 32.7 ± 35.3 days. The mortality rate in the ICU was 38.2% and the in-hospital mortality rate was 41%. The multivariate analysis showed that factors associated with poor prognosis in the ICU were the presence of circulatory failure (Shock) (Odds ratio (OR) = 9.96) and thrombocytopenia (OR = 32.5).Moreover, comparison between patients with and without PE showed that the predictive factors of PE were: Age > 40 years, a SAPS II score > 25, hypoxemia with PaO2 /FiO 2 < 200 mmHg, the presence of spine fracture, and the presence of meningeal hemorrhage. Conclusion: Despite the high frequency of DVT in post-traumatic critically ill patients, symptomatic PE remains, although not frequently observed, because systematic screening is not performed. Factors associated with poor prognosis in the ICU are the presence of circulatory failure (shock) and thrombocytopenia. Predictive factors of PE are: Age > 40 years, a SAPS II score > 25, hypoxemia with PaO2 /FiO 2 < 200, the presence of a spine fracture, and the presence of meningeal hemorrhage. Prevention is highly warranted

Multidisciplinary approaches for the study of sediment discharges to the Mediterranean Sea to mitigate the impact of climate and anthropogenic activities on coastal environments

International audienc