Sedimentary and structural setting of the Aptian reservoir deposits in the Kasserine area, west-central Tunisia (original) (raw)
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During the whole Cretaceous, Southern Tunisia corresponds to a very shallow carbonate platform slightly deeper toward the Chotts and Jeffara areas. The lower Cretaceous series, in southern Tunisia, are characterized by lateral and vertical changes of facies, the sequences are more restricted and associated with siliciclastics and evaporites southward. The sedimentary deposits include four major transgressive-regressive sedimentary sequences with distinctive sabkha, tidal to shallow carbonate marine platform, and mixed siliciclastic ramp environments. Sedimentation rates, as well as thickness and facies changes were controlled by tectonic, climatic and eustatic factors. Transgression pulses encompassing the whole Late Hauterivian-Barremian, Early Aptian and Upper Albian have controlled the basin infill. Evaporites and siliciclastic systems pass gradually to carbonate deposits in the Chotts area. The lateral evolution helps to highlight the roles of tectonics and, to a lesser extent, climate and paleogeographic changes as the key factors of evaporites, carbonate and siliciclastic deposit sequences. Furthermore, sea level changes exert additional control on the environmental differentiations of the sedimentary basin. Analysis of the lower Cretaceous deposit sequences between the Chotts and Jeffara areas indicate a progressive thickening towards the southeast. The Chotts and the Jeffara deposition, separated by the Tebaga Medenine high area, were developed and characterized by irregular subsidence. The Cretaceous subsidence of platform might be considered as a good model to explain the major lateral variation of thicknesses and facies of the lower Cretaceous deposits along Southern Tunisia showing the relationship between tectonic movements and the uplifting of the Tebaga Medenine area. This study regarding the regional structural context may explain both sequential and sedimentological evolution of the area. At least, these interpretations are integrated in the more general context (sea level changes…..) of both tethyan realm and Atlantic area.
Sequence Stratigraphy, Basin Dynamics, and Petroleum Geology of the Miocene from Eastern Tunisia
AAPG Bulletin, 1996
On the eastern margin of Tunisia, Miocene limestones, marl, and siliciclastic deposits crop out poorly and are lacking in age-diagnostic faunal content. The biostratigraphic and lithostratigraphic subdivisions of these series are not clearly defined. A regional study of subsurface sequences of this margin (Cap Bon, Gulf of Hammamet, and Sahel) by means of sequence stratigraphy and subsurface structural analyses permits the identification of seven third-order sedimentar y sequences of inferred Langhian to Messinian age, the boundaries of which are characterized by downlap and onlap/toplap relationships. These sequences include turbidites, sands, and sandstones deposited in connection with eustatic sea level changes and tectonic movements of east-west and southnorth deep-seated faults due to the Alpine and Atlassic paroxysm. Stratal sequences are organized around Miocene syndepositional grabens, halfgrabens, platforms, and folds occurring inside and outside of regional tectonic corridors. The geodynamic evolution of Miocene basins has led to the deposition of turbiditic black argillaceous source rocks, and sandstone and carbonate reservoirs that present new Miocene petroleum targets. The basin subsidence in response to the Alpine/Atlassic orogeny has permitted the maturation of Miocene source rocks, oil generation, and the formation of oil traps, stratigraphic pinch-outs, and structural enclosures on the flanks of folds and on the borders of grabens.
Aptian-Albian boundary in Central Southern Atlas of Tunisia: New tectono-sedimentary facts
Journal of African Earth Sciences, 2017
The Aptian-Albian boundary preserves one of the most important events in Central-Southern Atlas of Tunisia, which belongs to the Southern Tethyan margin. A major sedimentary break was recorded between Early Aptian and Albian series in Bouhedma-Boudouaou Mountains. This major hiatus probably linked to the ''Austrian phase'' and to the Aptian and Albian ''Crisis'' testify a period of major tectonic events. In this paper, field observations on the Mid-Cretaceous stratigraphy combined with seismic profile interpretation were used for the first time to characterize the Aptian-Albian boundary in Central-Southern Atlas of Tunisia. Our new results reveal that Aptian-Albian boundary marks a critical interval not only in Maknassy-Mezzouna orogenic system but also in the Tunisian Atlas. Furthermore, Aptian-Albian series outcrop is marked by the important sedimentary gaps as well as a dramatic thickness change from West to East and predominately from North to South. This is linked to the extensional tectonic features which characterize all the Central-Southern Atlas of Tunisia.
Cretaceous Research, 2009
Albian-Maastrichtian successions of the central and southern Atlas Mountains of Tunisia were investigated using seismic data, complemented by well and outcrop information. Basin-wide deformation can be related to tectonics and appears to have been the major control on variable distribution of Albian-Maastrichtian strata. The northeast-southwest Albian-Cenomanian extension was focussed on major faults and minor antithetic and synthetic faults creating structural depressions and grabens. Transtensional inversion was started during the Turonian. It was characterized by change of the field stress that changed from northeast-southwest to east-west then northwest-southeast during the Coniacian-Campanian. These transtensional events were followed by a northwest-southeast Campanian-Maastrichtian transpression as evidenced by the reactivation of preexisting faults and formation of new reverse faults and associated blind subtle anticlines. The structural rejuvenations were also influenced by holokinesis, which caused the block rotation. This diapirism coupled with sea-level fluctuations has controlled the sediment distributions. Seismic stratigraphic schemes developed for two adjacent sub-basins and two depocenters suggest coeval changes in deposition. Six second-order seismic-sequences are identified in the southern Gafsa sub-basin. These sequences are unequally distributed between depocenters. The Mè jel Bel Abbè s subbasin and Ali Ben Khalifa depocenter contain four second-order seismic-sequences, whereas only three seismic-sequences are identified in the Gamouda depocenter. Third-order sequences are defined by unconformities along the slopes and on the platforms where Upper Cretaceous sediment volume and sedimentation rates decrease. The major sequence boundaries recognized in the subsiding basins are correlated with outcrop unconformities and are considered to have regional significance, possibly controlled by eustatic sea-level changes. Each sequence constitutes the interaction and the dual signatures of the eustasy and the regional or local tectonics. The results of this integrated seismic stratigraphic and structural analysis have implications for evaluating the hydrocarbon potential. The distribution of Upper Cretaceous stratigraphic and structural traps and seals enable us to assess the petroleum potential of central Tunisia.
The Albian tectonic “crisis― in Central Tunisia: Nature
2013
The Mid-Cretaceous tectonic ''crisis'' is a classical feature of the tectono-sedimentary evolution of Tunisia. A reappraisal of synsedimentary deformation observed in the Tajerouine and Kasserine areas shows that deformation began in the earliest Albian, increased during the Early Albian, and culminated in the Middle Albian. Late Albian deposits overly, locally with a strong angular unconformity, Aptian to Early Albian sediments. In the southern part of the studied area, fault tectonics and tilted blocks dominate, whereas in the northern area, the occurrence of slumps and olistoliths suggests deformation related to incipient salt movements at depth. These new chronological constraints suggest that this tectonic event is most probably related to the final opening of the Atlantic Ocean at equatorial latitudes.
Marine and Petroleum Geology, 2018
In this paper, we present an updated biostratigraphic evaluation of the Serdj Formation of the Tunisian Atlas. Newly collected ammonites, combined with available biostratigraphic data, allowed the establishment of a new and robust stratigraphic framework for this well-known formation. For the first time the characterization of the Mellegueiceras chihaouiae Zone has permitted the specification of the Aptian-Albian transition. This study reveals an early Albian age for the top of the Serdj Formation that includes the main reservoir flow unit which is producing oil in both onshore and offshore Tunisia. Outcrop data analysis has revealed nine transgressive-regressive cycles within the Aptianearly Albian carbonates. During early Aptian the carbonate deposition occurred in deepmarine settings that gave way to shallow, open shelf carbonates deposition during the late Aptian-early Albian. These successions provide evidences enabling their correlation with the third-order global depositional sequences detected in the sedimentary basins of the Tethyan domains. Regional surface to subsurface stratigraphic correlation, based on seismic and wire-line logs, enabled: (1) a reliable correlation between the stratigraphic elements of the buried successions with those of the Serdj Formation, (2) the characterization of the platform-basin transition domain and (3) the verification of the hypothesis that the Serdj Formation carbonates constitute the surface analogue of the subsurface oil field reservoirs. The detailed conceptual stratigraphic model suggests that the Serdj platform developed diachronous. Its demise occurred in the early Albian and not during the Aptian-Albian transition as previously believed. The hydrocarbon-productive reservoirs developed during the regressive phases especially in the up-dip settings of the platform where dolomitization greatly enhanced the reservoir quality.
Geologica Carpathica, 2017
The objective and the main contribution of this issue are dedicated to using subsurface data to delineate a basin beneath the Gulf of Tunis and its neighbouring areas, and to investigate the potential of this area in terms of hydrocarbon resources. Available well data provided information about the subsurface geology beneath the Gulf of Tunis. 2D seismic data allowed delineation of the basin shape, strata geometries, and some potential promising subsurface structures in terms of hydrocarbon accumulation. Together with lithostratigraphic data obtained from drilled wells, seismic data permitted the construction of isochron and isobath maps of Upper Cretaceous-Neogene strata. Structural and litho stratigraphic interpretations indicate that the area is tectonically complex, and they highlight the tectonic control of strata deposition during the Cretaceous and Neogene. Tectonic activity related to the geodynamic evolution of the northern African margin appears to have been responsible for several thickness and facies variations, and to have played a significant role in the establishment and evolution of petroleum systems in northeastern Tunisia. As for petroleum systems in the basin, the Cretaceous series of the Bahloul, Mouelha and Fahdene formations are acknowledged to be the main source rocks. In addition, potential reservoirs (Fractured Abiod and Bou Dabbous carbonated formations) sealed by shaly and marly formations (Haria and Souar formations respectively) show favourable geometries of trap structures (anticlines, tilted blocks, unconformities, etc.) which make this area adequate for hydrocarbon accumulations.
In central Tunisia, Lower Cretaceous deposits represent carbonate and sandstone reservoir series that correspond to proven oil fields. The main problems for hydrocarbon exploration of these levels are their basin tectonic configuration and their sequence distribution in addition to the source rock availability. The Central Atlas of Tunisia is characterized by deep seated faults directed northeast-southwest, northwest-southeast and north-south. These faults limit inherited tectonic blocks and show intruded Triassic salt domes. Lower Cretaceous series outcropping in the region along the anticline flanks present platform deposits. The seismic interpretation has followed the Exxon methodologies in the 26th A.A.P.G. Memoir. The defined Lower Cretaceous seismic units were calibrated with petroleum well data and tied to stratigraphic sequences established by outcrop studies. This allows the subsurface identification of subsiding zones and thus sequence deposit distribution. Seismic mapping of these units boundary shows a structuring from a platform to basin blocks zones and helps to understand the hydrocarbon reservoir systems-tract and horizon distribution around these domains.
Arabian Journal of Geosciences, 2011
The Neogene stratigraphic series is characterized by predominant clayey facies alternated by other sand layers. The outcrop and subsurface studies show varied and complex styles of deformations and lead to relate the structures to paleoseismic events. The seismicity of eastern onshore and offshore Tunisian margin follows the master fault corridors oriented globally N-S, E-W, and NW-SE that correspond to the bordering faults of grabens and syncline corridors and associated faulted drag fold structures oriented NE-SW. Epicenters of magnitudes between 3 and 5 are located along these border fault corridors. The Neogene strata record brittle structures, including numerous and deep faults and fractures with straight and high-angle dipping planes. The structuring of NE-SW en echelon folds and synclines inside and outside NW-SE and E-W right lateral and N-S and NE-SW left lateral tectonic corridors indicates the strike-slip type of bordering faults and their seismogenic nature. Wrench fault movements that induce mud and salt diapirs, mud volcanoes, and intrusive ascensions are related to seismic shocks. Seismic waves caused by activity along one, or most likely, several tectonic structures would have propagated throughout the Quaternary cover producing seismites. The similarity of deposits, structuring, and seismites between the Tunis-Bizerte to the North and Hammamet-Mahdia to the South accredits the hypothesis that the seismic episodes might have affected sedimentation patterns along the Sahalian large geographic area. The paleoseismic events in northeastern Tunisia might be related to tectonic fault reactivations through time. This hypothesis is consistent with the geomorphologic context of the study area, characterized by several morphostructural lineaments with strong control on the sediment distribution, as well as uplifted and subsiding terrains. The estimated magnitude of the seismic events and the great regional tectonically affected areas demonstrate that the northeastern Tunisia experienced stress through the last geological episodes of its evolution. This Neogene kinematic reconstruction highlights the neotectonic system inducing the actual seismicity on this margin. Therefore, there is a straight relationship between deepseated faults and seismicity.