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Time series analysis has been performed for the first time on the Cenomanian-Turonian sequence in Central Tunisia in order to shed light on its Milankovitch-like cyclicity. This analysis was applied to two foraminiferal genera: the biserial Heterohelix, an oxygen-minimum zone (OMZ) dweller, and the triserial Guembelitria, a eutrophic surface dweller. Average sedimentary rates and the duration of the oceanic anoxic event (OAE2) in each studied section were estimated. The fluctuations in abundance of these two opportunistic species can be related mainly to both precessional (ca. 20 kyr) and eccentricity (100 and 400 kyr) cyclicity suggesting that changes in surface water fertility were linked to climate changes in the Milankovitch frequency band. Source


The late Cenomanian-early Turonian deposits in Tunisia recording the OAE2 event are commonly attributed to the Bahloul Formation. These deposits are composed of dark clayey limestone and organic-rich black shales with abundant planktic foraminifera. At the Bargou area, Oued Kharroub section, these organic-rich deposits include siliceous beds with abundant radiolarians recalling the "Livello Bonarelli". A total of 25 radiolarian species are identified with a maximum of 18 species per sample. Moreover, the species skeleton preservation is usually poor to moderate in the most studied samples [estimated preservation index (PI) values ranging between 4 and 6]. Two successive assemblages are distinguished. The oldest one (RI) is dominated by nassellarians, which includes mainly Stichomitra, Pseudodictyomitra and Rhopalosyringium genera. It is included within the upper part of foraminiferal Rotalipora cushmani Zone and lower part of Whiteinella archaeocretacea zone. In contrast, the youngest assemblage (RII), which belongs to the upper part of the W. archaeocretacea zone and the earliest Turonian Watinoceras ammonite assemblage, is dominated by spumellarians and includes mainly Archaeocenosphaera, Cavaspongia, Pseudoeucyrtis and Pyramispongia genera. In addition, major and trace elements are analysed to test whether the geochemical record was synchronous to the biotic event or not. Thus, selected crossplots, Al2O3 vs. SiO2 and Al2O3 vs. TiO2, are used to evaluate the detrital input, and V/Cr vs. V/(V + Ni) and U/Th vs. V/(V + Ni) are used to evaluate the bottom redox conditions and the primary productivity within the Bahloul Formation. A strong Si/Al increase is marked in the lower part of the siliceous and organic-rich Bahloul Formation that could be explained by a local increase in upwelling-related biogenic SiO2 (silica-secreting organisms). Relative low abundance of terrigenous-related Ti/Al and K/Al ratios and enrichment of some productivity proxies such as Ba (organic matter related trace elements) suggests that the Bahloul was of relatively elevated primary productivity and minimal detrital input. Enrichments in redox-sensitive trace metals U and V in the Bahloul Formation deposits and redox indices, such as V/(V + Ni), U/Th and V/Cr, indicate that oxygen-restricted conditions prevailed during the late Cenomanian-earliest Turonian times and correlate well with relative abundances of some radiolarian and foraminiferal paleo-environmental indicators. In addition, indicators of detrital flux variations are used. Al2O3 shows a slight positive correlation with TiO2 and a less distinct correlation with SiO2. © 2011 Saudi Society for Geosciences. Source


Sous M.,Entreprise Tunisienne dActivites Petrolieres
SPE Middle East Oil and Gas Show and Conference, MEOS, Proceedings | Year: 2013

Through this last decade numerous wells have been drilled to the Ordovician in southern Tunisian Ghadames basin. They have met mudlog gas as well as mudlog oil shows in one or several sandstone levels. Some producing wells from the Silurian section display log pay in the Ordovician but seem to be off to the mapped Ordovician depth structural closure. Alternatively, large 3D seismic survey has been undertaken in southern Tunisia in order to map the Ordovician. Isochore, isopachs and isobaths maps have been generated on four (04) main reservoir intervals all of which have produced from several fields in the Ghadames Basin (including Algeria and Libya). These reservoirs are (1) Jeffara, (2) Bir Ben Tartar, (3) Kasba Leguine and (4) Sanghar Formations (Tunisian nomenclature). In Southern Tunisia the Upper Jeffara sandstones, the Jeffara sandstones and the Bir Ben Tartar are classified as the primary reservoir intervals. Generated isochore map of the upper Jeffara sandstones, has been used as evidence of a "geant" Tunnel valley shape in relationship with other valley structures pertaining to the Libyan side. As the Ordovician sandstone reservoirs in Tunisia have poor reservoir quality but locally some intervals have tested condensate, some fields have proved that syn-glacial deposits form a gas reservoir (e.g. Tiguentourine field in south-eastern Algeria). Within such facies, the Ordovician has tested gas and/or condensate from a number of wells in the Ghadames basin. This proposal will involve the existence of valley-fill sandstones pertaining to the Jeffara formation in southern Tunisia giving evidence of sub-glacial environment of deposition where iceproximal glaciofluvial deposits form the highest quality reservoirs using (1) isochore and isopachs maps of the Ordovician, (2) core analyses, (3) cyclostratigraaphy and (4) chemostratigraphy (major and trace elements). This will enhance the exploration activity for the Ordovician in southern Tunisia. Copyright 2013, Society of Petroleum Engineers. Source


Zaghbib-Turki D.,Tunis el Manar University | Soua M.,Entreprise Tunisienne dActivites Petrolieres
Journal of African Earth Sciences | Year: 2013

High-resolution foraminiferal biostratigraphic analysis has been undertaken on the Bahloul Formation, in Bargou, Jerisa, Guern Halfaya (Central Tunisia), Kherij (North-eastern Tunisia) and Gafsa (southern Tunisia) sections, which prove the preservation of the worldwide expression of the Cenomanian-Turonian transition (C-T) Oceanic Anoxic Event (OAE2). This study confirms that the OAE2 was rather a long-term global event. The high resolution biostratigraphical analysis has allowed subdividing the Whiteinella archaeocretacea zone of the standard biostratigraphic scheme. The ability to apply same subzones in both Tethyan and transitional/Boreal provinces during the C/T boundary has important palaeobiogeographical and palaeoecological implications. The palaeoecological framework shows that the OAE2 development is composed of several successive phases. In addition, a faunal turnover during the W. archaeocretacea zone interval is recorded. However, we confirm that the faunal turnover in the W. archeocretacea zone did not result in a loss of biodiversity, but rather in replacement through originations. © 2012 Elsevier Ltd. Source


Soua M.,Entreprise Tunisienne dActivites Petrolieres | Smaoui J.,Entreprise Tunisienne dActivites Petrolieres | Zaghbib-Turki D.,Tunis el Manar University
North Africa Technical Conference and Exhibition 2010, NATC 2010 - Energy Management in a Challenging Economy | Year: 2010

Time series analysis has been performed for the first time on the Cenomanian-Turonian sequence in Central Tunisia in order to shed light on its Milankovitch-like cyclicity. This analysis was tested and applied on two foraminiferal species: the biserial Heterohelix, an oxygen minimum zone (OMZ) dweller, and the triserial Guembelitria, a eutrophic surface dweller. Average sedimentary rates and the duration of the second Oceanic Anoxic Event OAE-2 in each studied section were estimated. Alternatively, the fluctuations of these two opportunistic species can be related mainly to both precessional (23-19 ka) and eccentricity (414-106 ka) cyclicity suggesting that changes in surface water fertility were linked to the Milankovitch parameters. Copyright 2010. Society of Petroleum Engineers. Source

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