Jamel Ouali

Growth-strata geometry in fault-propagation folds: a case study from the Gafsa basin, southern Tunisian Atlas

The structural and sedimentological study of fault-propagation folds in Southern Tunisia highlights a special geometry of the growth strata (strata deposited simultaneously with the formation or growth of a fold). This distinct geometry is visible in the uppermost growth-strata beds and consists of one flank with unconformity as opposed to the other flank with perfect conformity. This geometry can be explained by the mechanism of fault-propagation folding, with asymmetrical flank dips and hinge migration kinematics. This kinematics was originally predicted by the fault-propagation fold model, which facilitates the study of this special geometry in a narrow domain of sedimentation-to-shortening ratios. A plot projection provides a generalisation of the results of all types of fault-propagation folds by revealing the expected geometry of the growth strata. This study constitutes one of the most complete examples of kinematic model validation on a field scale.

Tectonique syn-sédimentaire en Tunisie centrale (région du Jebel Mrhila) pendant l’Aptien-Albien

Abstract The important sedimentary gaps, the variations of thicknesses and fades which characterize the Aptian-Albian series in the J. Mrhila area, are linked, at least partly, to the action of two tectonic features. 1. The Mrhila-Cherichira fault, with a NNE-SSW direction, is responsible for the collapse of the area located north of this major accident; the southwards tilt of this area made the accumulation of very thick marine sediments possible, during Clansayesian toLateAlbian time, at Koudiat El Beida (KEB) and in Bled El Gouna 1 (BEG. 1) wells. These sediments do not occur in the uplifted area, south of the fault. 2. The second feature, corresponding to the Sbiba fault, with a N140 direction, had, as effect, the reduction of the Albian series within the Tiouacha 1 (Ti. 1) boring. This variation is significant, even if it is, by far, less important than that occurring on both sides of the major NNE-SSW fault. It seems that this Sbiba fault played a role in Clansaysian to Upper Albian sedimentation, which resulted in the formation of a losangic basin.

Diagenetic process as tool to diagnose paleo-environment conditions, bathymetry and oxygenation during Late Paleocene-Early Eocene in the Gafsa Basin

Abstract Late Paleocene–Early Eocene deposits cropping out in Tamerza area were settled on a carbonate homoclinal ramp. Deposits which are ranged in six main facies record a gradual transition from intertidal to upper circatidal environment. Lateral variations in terms of facies and thickness infers to the main role of synsedimentary tectonics. The characterization of paleoenvironments was established in respect to the lithology, fauna content, sedimentary structures and diagenetic features. Detailed analysis of deposits shows that the diagenetic processes are reliable tools to reconstruct each depositional environment. Moreover, they bring out precious information concerning the chemical and physical parameters and the sedimentary dynamics of the studied interval. The early stage cementation is favored under low rates of sedimentation and a calm sea floor. The arrangement and the morphology of crystals permit to appreciate the bathymetry and to better characterize the depositional environment. Phosphogenesis seems in a tight relation with silicification requiring both an acidic environment. The occurrence of upwelling currents engendered the blooming of fauna guarantying test preservation after death and allowed to establish a linkage between fauna content and diagenetic features. Silicification processes concern test replacement and the genesis of chert beds included within the enclosing deposits. Micritization processes, occurring in the inner ramp, advocate calm environments and are engendered by endolithic algae, bacteria and fungi. The X-Ray diffraction shows the frequency of smectites associated with clinoptilolites, sepiolite and palygorskite. The clay paragenesis helps to identify several diagenetic contexts occurring under xeric and confined conditions.

Application of Geochemistry to Characterize the Progressive Paleoenvironmental Changes Linked to Abrupt Warming Hyperthermal Event During the Latest Danian of Central Tunisia (Southern Tethys) and Impact on Foraminifera Fauna

The Latest Danian Event is a short warming event, documented for the early Paleogene. Similar to Paleocene-Eocene Thermal Maximum, this event is characterized by global warming, carbonate disolution and shallowing of lysocline and CCD, poor oxygenated and stratified column water.

Sedimentological, Mineralogical and Geochemical Analysis of the Hyperthermal Latest Danian Event across the Galuconitic Marker Bed (Central Tunisia)

Field prospecting of the El-Haria Formation, which is Paleocene in age, leads to the discovery of the glauconitic marker bed in inner neritic to bathyal setting from Southern Tethyan realm. The recognition of this interval is based on lithological changes and an accurate stratigraphic proxy allows to distinguish of three main facies. The use of multivariate (cluster analysis and principal component analysis) and univariate (one-way Anova test) analysis confirm dissimilarities in composition between facies as testified by the significant differences. Sedimentological, geochemical and mineralogical analysis leads to assess paleo-environmental changes and to ascertain the variation of the lysocline and CCD across the glauconitic marker bed. Facies 1, particularly, rich in cobalt, sulfides and iron oxides reflects containment conditions affecting the surface and bottom water. These conditions lead to the extinction of the majority of benthic foraminifera and the disruption in planktonic foraminifers’ assemblage. In addition, the Facies 1 displays a brief shoaling of lysocline and CCD evidenced by the low calcite content, the bad preserved benthic foraminifera associated to the maximum fragmentation shells of planktonic foraminifera. In contrary, the rapid pattern of microfossil and the calcite recovery through the Facies 2 indicate suboxic to oxic conditions and a deepen lysocline and CCD. The cobalt lightly increases within the upper Facies, suggesting slightly oxygen deficient bottom water environment. The base of the glauconitic marker bed seems to be a lateral equivalent of the Latest Danian Event recorded throughout the Tethyan Realm (Spain and Egypt) and the Pacific Ocean.