Mabrouk Montacer

A high relative sea-level stand in the middle Holocene of southeastern Tunisia

Abstract Study of the marine Holocene deposits in southeastern Tunisia shows bioclastic beaches at elevations ranging between 0 and 100 cm above high tide level (a.h.t.l.). Depending on the elevation of these fossilized shorelines, the ages obtained are different. The age of the older deposits ranges between 5900 and 4000 14CC yr B.P. (6400-4300 calendar yr B.P.), there deposits consist of bioclastic beaches attaining an elevation of about +40 to +100 cm a.h.t.l. The younger deposit is dated at around 2100 14C years ago (1850 calendar yr B.P.), and is found today at the same elevation as the present sea level. This deposit also consists of bioclastic beach material, and contains pottery fragments. Postglacial melting should not be responsible for this observed higher relative sea level stand, because deglaciation ended about 7000-6000 14C years ago (Fairbanks, 1989). Furthermore, the regularity of the paleobeach deposit elevation over a broad area in southeastern Tunisia suggests that tectonics cannot explain the emergence. The emergence of up to 1 m of marine deposits dating back to between 5900 and 4000 14C yr B.P. should rather be interpreted as the result in the region of a postglacial hydro-isostatic rebound, as predicted in the Theological models of continental margins by, for example, Clark et al. (1978) and Lambeck (1993). The present situation was reached 2100 14C years ago.

Variabilité climatique rapide lors du dernier Interglaciaire (stade isotopique marin 5e), enregistrée dans les sédiments littoraux du Sud-Est tunisien

We have compared the sedimentological record of the Pleistocene coastal deposits in southeastern Tunisia with the climatic data obtained on two deep-sea cores recovered in the Mediterranean Sea. Coastal marine deposits are composed of two distinct lithostratigraphic units separated by an erosion surface. The radiochemical dating shows that these two units were developed during the unique marine isotopic substage 5e (the Last Interglacial). The lower unit mainly consists of quartz-rich sands whereas the upper one consists of carbonate deposits. This petrographic contrast indicates that the palaeoclimatic evolution in the southeastern coast of Tunisia was identical to that observed in the western Mediterranean Sea and the surrounding continents. In particular, the establishment of humid conditions at the beginning of the Last Interglacial was responsible for a supply of terrigenous material and siliciclastic sedimentation along the coastal area of southeastern Tunisia, whereas the regression of these wet conditions during the second half of the Last Interglacial favoured carbonate sedimentation.

Natural hydrocarbon accumulation related to formation overpressured interval; study case is the Saharan platform (Southern Tunisia)

Organic geochemistry analysis and formation fluid overpressure study have been performed on several oil well data located to the northern part of the Ghadames Basin (southern Tunisia Saharan platform). The main results of this work highlight the important role of overpressured interval in hydrocarbon accumulation. In fact, the analysis of the Paleozoic–Mesozoic petroleum systems in Southern Tunisia shows that the hydrocarbons generated by Ordovician and Silurian source rocks migrate upward following fault systems or through the major Hercynian unconformity to finally accumulates in structural or stratigraphic traps. These migration pathways provide favorable conditions to fill up the Silurian, Devonian, or Triassic reservoirs. The overpressured zone located above Triassic reservoir constitutes a continuous and efficient seal to hydrocarbon trap structures. So the overpressure plays the role of hydraulic seal advantaging oil and gas accumulation in the Ghadames Basin associated with the impermeable (evaporites) and then stopping any upward migration of natural hydrocarbon.

Microstructural and Mechanical Properties in Traditional Ceramics as a Function of Quartzofeldspathic Sand Incorporation

We intend to study the influence of addition of quartzo-feldspathic sand on the mechanical properties and the microstructure of Tunisian illite-kaolinite clay ceramics. The fired characteristics of the clay and quartzo-feldspathic sand mixtures have been studied separately at soaking temperatures reaching respectively 850°, 950° and 1050°C during a firing profile of ∼7–8 h. Investigation of phase transformations of the mixed samples shows that albeit the proportion of the quartz has been increased, its peak intensity remains constant. Such stability may be explained by quartz dissolution in the glassy phase. The mechanical strength of the mixed samples has been examined in terms of flexural strength. In the studied case, the latter increases from 13.5 to 23.3 N.mm−2 as the sample becomes denser in the mixture M2. It may also be noticed that an overdose of quartz reduces the mechanical strength. Hence, a moderate addition of well-sorted fine quartzofeldspathic sand ameliorates the mechanical properties and the microstructure. The latter is analysed by scanning electron microscope (SEM).

Organic geochemical study of Ypresian sediments at Jebel Ousselat, Tunisia

This new study was carried out in order to accurately characterize the geochemical pattern of Ousselat organic-rich facies from the Ypresian basin in central-northern Tunisia. It has been found that the organic matter is located towards the end of diagenesis/beginning of catagenesis. This assumption is supported by the relative low Tmax values (429–439°C) and by steranes maturity parameters such as C29 αα 20S/(20S + 20R), and C29 ββ/(ββ + αα). High HI values and the abundance of saturates (1–83%) compared to aromatics (2–27%) are unequivocal evidence of type-II organic matter as indicated by a high abundance of cholestane and the predominance of short-chain n-alkanes centred at n-C18 and at n-C20. Total organic carbon (TOC) content and petroleum potential values suggest that the Ypresian period corresponds to an anoxic event which led to the accumulation and preservation of large quantities of organic matter with high primary production. Due to their geochemical characteristics, the Lower Eocene facies represent a new potential source rocks in central-northern Tunisia.

New potential hydrocarbon source-rocks in the Lower Eocene Metlaoui Formation (Central-Northern Tunisia, Northern Africa)

Significant quantities of organic matter accumulated and were preserved in central-northern Tunisia during the Ypresian (Early Eocene). The organic geochemical characterization of the organic-rich facies of the Ypresian Metlaoui Formation (Ousselat and Es-Sfeia sections) shows their significant potential as source rocks and increases interest in the Central-Northern Tunisia oil play. The TOC content in these rocks ranges from 0.09 to 3.71% suggesting their petroleum potential, whereas their T max fluctuates from 429 to 439°C. These values and the predominance of the hetero compounds (NSO; 2-95%) point to low organic matter maturation. The diverse maturity levels reported for these organic-rich rocks never reached the conventional oil window peak stage and resulted from their different locations within the basin. The HI values and the high saturate concentrations (1-91%) compared to aromatics (1-33%), as well as the predominance of short-chain n-alkanes centered atn-C18 and n-C20 are indicative of unequivocal type-II kerogen. The fluctuation of the pristane/phytane ratio (0.97-2.53) records changes of the basin redox conditions, which mainly evolved around the sub-oxic range.