The sedimentological features of the Holocene deposits outcropping along southeastern Tunisia sho... more The sedimentological features of the Holocene deposits outcropping along southeastern Tunisia show a littoral para-sequence including red silt, conglomerates, bioclastic, and siliciclastic deposits. At Sebkha Boujmel, they are represented by a buried lagoon characterized by a transgressive-regressive para-sequence. The latter displays seven facies integrated within a transgressive biodedritic complex followed by bioclastic and oolitic sands, laminated silty carbonate sand, and eolian silts rich in gypsum, crowned by microbial mats. Lateral correlations have identified the spatiotemporal distribution of facies. The neighboring Sebkha el Melah (10 km further north) displays a Holocene para-sequence consisting of a transgressive biodetritic complex overtopped by thick evaporitic series. The sedimentation in this region, which has remained tectonically stable since the last 125 ka BP, was driven by coastal thresholds, climate and recent sea level changes that formed three different para-sequences in three nearby sites. Our observations with those available from previous studies provide new insights on the evolution on the landscape of southeastern Tunisia before and during the Holocene that driven the formation of an inland shoaled homoclinal ramp with a lagoon system.
Pollen and clay mineralogical analyses of a Holocene sequence from Sebkha Boujmel (southern Tunis... more Pollen and clay mineralogical analyses of a Holocene sequence from Sebkha Boujmel (southern Tunisia) trace the climatic and environmental dynamics in the lower arid bioclimatic zone over the last 8000 years. During the mid-to late Holocene transition, between ca. 8 and 3 ka BP, a succession of five wet-dry oscillations is recorded. An intense arid event occurs between ca. 5.7 and 4.6 ka BP. This episode marks the onset of a long-term aridification trend with a progressive retreat of Mediterranean woody xerophytic vegetation and of grass steppes. It ends with the establishment of pre-desert ecosystems around 3 ka BP. The millennial-scale climate change recorded in the data from Sebkha Boujmel is consistent with records from the south and east Mediterranean, as well as with climatic records from the desert region for the end of the African Humid Period (AHP). Eight centennial climatic events are recorded at Sebkha Boujmel and these are contemporary with those recorded in the Mediterranean and in the Sahara. They indicate a clear coupling between the southern Mediterranean and the Sahara before 3 ka BP. The event at 4.2 ka BP is not evidenced and the link between events recorded in Sebkha Boujmel and the North Atlantic cooling events is clearer from ca. 3 ka BP onwards. These variations indicate the importance of climatic determinism in the structuring of landscapes, with the establishment of the arid climatic conditions of the late Holocene. It is only from ca. 3 ka BP onwards that the dynamic of plant associations is modified by both human activity and climatic variability. The climatic episodes identified during the historic period indicate strong regionalisation related to the differential impact of the North Atlantic Oscillation (NAO) and the Mediterranean Oscillation (MO) on the Mediterranean Basin. The local human impact on regional ecosystems is recorded in the form of episodes of intensification of pastoral and/or agricultural activities. The development of olive production and of several taxa associated with agriculture attest to increasing sedentism among human populations during classical antiquity. The significant increase in Artemisia (wormwood) between ca. 1.1 and 0.8 ka BP (850-1150 AD) is linked to intensive pastoral activity, associated with heightened interannual and/or seasonal climatic instability. A complete reshaping of the landscape is recorded during the 20th century. The remarkable expansion of the olive tree, and the deterioration of regional ecosystems with the spread of desert Published by Copernicus Publications on behalf of the European Geosciences Union. 1340 S. Jaouadi et al.: Environmental changes, climate and anthropogenic impact species, is linked to recent local socioeconomic changes in Tunisia.
On the southeastern Tunisian coastline, very diverse living microbial mats colonize the lower sup... more On the southeastern Tunisian coastline, very diverse living microbial mats colonize the lower supratidal and intertidal zones, and locally may extend into the upper infratidal zone. The interaction between the benthic cyanobacteria and their siliciclastic substratum leads to the development of several types of microbially induced sedimentary structures (MISS). The mapping of the microbial mats has allowed the identification of the types of MISS that characterize the different segments of the coastal environment. The modern microbial mats have been compared with those recorded at the top of the Holocene deposits, which are composed of biodegraded microbial black mats alternating with white laminae made of clastic and evaporitic sediments, indicative of very high frequency cycles of flood and drought. A hypothetic profile showing their occurrences along the different areas bordering the coastline is proposed as a guide for the reconstruction of the ancient depositional environment. Th...
Journal of Petroleum Exploration and Production Technology
The Bir M'Cherga basin (North-east Tunisia), with about 600 km 2 area, had recorded four Middle C... more The Bir M'Cherga basin (North-east Tunisia), with about 600 km 2 area, had recorded four Middle Cretaceous source rocks well stratigraphically correlated with the four known oceanic anoxic sub-events: OAE1a, OAE1b, OAE1c, and OAE1d. Variety of lithology, thickness and organic richness had characterized these source rocks. The sedimentary tectonic analysis, the petrology and geochemistry study established the petroleum system of these source rocks. Basin formation began early in the Barremian-Aptian interval by synsedimentary tectonics reactivating old basement faults. During the Aptian-Albian, the formed basin had a depocenter that recorded thicker black shales while its NW and SE edges remained raised under the Triassic halokinetic activities. The evolution of the sedimentary filling during this period generated two sedimentary cycles corresponding to two filling second-order fining and thickening upwards sequences. The black shales that constitute these source rocks are formed between subtidal and external platform environment and are interbedded with juxtaposed high organic rich layers and poor ones. The rich organic facies consists of dark shale that constitutes the source rock. The poor organic beds formed by light grey and nodular limestones constitute an intra host reservoir. Thereby, petroleum system consists in an "unconventional oil shale hybrid systems with a combination of juxtaposed organic-rich and organic-lean intervals associated to open fractures". The kerogen is essentially amorphous, with marine planktonic origin and low ligneous organic matter contribution. This organic material of dark facies had been well preserved in an anoxic environment with little or no energy. Light grey limestones were of oxic-to-sub-oxic environment. The stage of the thermal evolution for these source rocks provided by IH/T max diagram is of the "oil window". The average transformation ratio (TR) is estimated as 45% suggesting thus black shales are oil shale resources which still close about untransformed 55% of its hydrocarbon generating potential. The expulsion and release of oil into these source rocks are proven by the observation of hydrocarbons filling micro-cracks and by the variable values of the oil saturation index OSI ranging from 0 to 138%. The latter exceeds 100% near the paleo-high reliefs indicating two "oil crossover" areas attributed to the high degree of oil source rock saturation and accumulation of hydrocarbons considered ideal for hydraulic fracturing. This oil crossover is a consequence of secondary migration into black shale source rock, achieved by various faults created during the distensive phase that were reactivated again several times.
L'étude sédimentologique concerne des dépôts holocènes enfouis dans l'actuelle sebkha Boujmel com... more L'étude sédimentologique concerne des dépôts holocènes enfouis dans l'actuelle sebkha Boujmel comprenant des sables détritiques et/ou carbonatés gypsifères, des vases riches en matière organique et des boues blanchâtres riches en carbonates hypermagnésiens, des sables carbonatés bioclastiques et à oolithes de faible énergie et enfin des sables carbonatés silteux laminés et tapis microbiens associés. Ces faciès s'organisent en une séquence typiquement lagunaire. Les faciès holocènes situés plus au Nord, en affleurement sur les bordures de la bahira el Bougrara et l'Ile de Djerba, englobent des faciès qui sont plus ouverts aux influences marines énergétiques (faciès de shoal). Ils sont représentés par dépôts essentiellement oolithiques et bioclastiques parfois à quartz. Ainsi, une séquence sédimentaire holocène a pu être identifiée au Sud-Est de la Tunisie. Cette séquence est lagunaire dans les dépressions et littorale sur les bordures. Les corrélations des faciès, appuyées par des datations au 14 C, ont permis d'établir l'extension de la transgression holocène au niveau du Sud-Est de la Tunisie.
Interactive comment on "Environmental changes, climate and anthropogenic impact in southern-easte... more Interactive comment on "Environmental changes, climate and anthropogenic impact in southern-eastern Tunisia during the last 8 kyr" by Sahbi Jaouadi et al. Sahbi Jaouadi et al.
The sedimentological features of the Holocene deposits outcropping along southeastern Tunisia sho... more The sedimentological features of the Holocene deposits outcropping along southeastern Tunisia show a littoral para-sequence including red silt, conglomerates, bioclastic, and siliciclastic deposits. At Sebkha Boujmel, they are represented by a buried lagoon characterized by a transgressive-regressive para-sequence. The latter displays seven facies integrated within a transgressive biodedritic complex followed by bioclastic and oolitic sands, laminated silty carbonate sand, and eolian silts rich in gypsum, crowned by microbial mats. Lateral correlations have identified the spatiotemporal distribution of facies. The neighboring Sebkha el Melah (10 km further north) displays a Holocene para-sequence consisting of a transgressive biodetritic complex overtopped by thick evaporitic series. The sedimentation in this region, which has remained tectonically stable since the last 125 ka BP, was driven by coastal thresholds, climate and recent sea level changes that formed three different para-sequences in three nearby sites. Our observations with those available from previous studies provide new insights on the evolution on the landscape of southeastern Tunisia before and during the Holocene that driven the formation of an inland shoaled homoclinal ramp with a lagoon system.
Pollen and clay mineralogical analyses of a Holocene sequence from Sebkha Boujmel (southern Tunis... more Pollen and clay mineralogical analyses of a Holocene sequence from Sebkha Boujmel (southern Tunisia) trace the climatic and environmental dynamics in the lower arid bioclimatic zone over the last 8000 years. During the mid-to late Holocene transition, between ca. 8 and 3 ka BP, a succession of five wet-dry oscillations is recorded. An intense arid event occurs between ca. 5.7 and 4.6 ka BP. This episode marks the onset of a long-term aridification trend with a progressive retreat of Mediterranean woody xerophytic vegetation and of grass steppes. It ends with the establishment of pre-desert ecosystems around 3 ka BP. The millennial-scale climate change recorded in the data from Sebkha Boujmel is consistent with records from the south and east Mediterranean, as well as with climatic records from the desert region for the end of the African Humid Period (AHP). Eight centennial climatic events are recorded at Sebkha Boujmel and these are contemporary with those recorded in the Mediterranean and in the Sahara. They indicate a clear coupling between the southern Mediterranean and the Sahara before 3 ka BP. The event at 4.2 ka BP is not evidenced and the link between events recorded in Sebkha Boujmel and the North Atlantic cooling events is clearer from ca. 3 ka BP onwards. These variations indicate the importance of climatic determinism in the structuring of landscapes, with the establishment of the arid climatic conditions of the late Holocene. It is only from ca. 3 ka BP onwards that the dynamic of plant associations is modified by both human activity and climatic variability. The climatic episodes identified during the historic period indicate strong regionalisation related to the differential impact of the North Atlantic Oscillation (NAO) and the Mediterranean Oscillation (MO) on the Mediterranean Basin. The local human impact on regional ecosystems is recorded in the form of episodes of intensification of pastoral and/or agricultural activities. The development of olive production and of several taxa associated with agriculture attest to increasing sedentism among human populations during classical antiquity. The significant increase in Artemisia (wormwood) between ca. 1.1 and 0.8 ka BP (850-1150 AD) is linked to intensive pastoral activity, associated with heightened interannual and/or seasonal climatic instability. A complete reshaping of the landscape is recorded during the 20th century. The remarkable expansion of the olive tree, and the deterioration of regional ecosystems with the spread of desert Published by Copernicus Publications on behalf of the European Geosciences Union. 1340 S. Jaouadi et al.: Environmental changes, climate and anthropogenic impact species, is linked to recent local socioeconomic changes in Tunisia.
On the southeastern Tunisian coastline, very diverse living microbial mats colonize the lower sup... more On the southeastern Tunisian coastline, very diverse living microbial mats colonize the lower supratidal and intertidal zones, and locally may extend into the upper infratidal zone. The interaction between the benthic cyanobacteria and their siliciclastic substratum leads to the development of several types of microbially induced sedimentary structures (MISS). The mapping of the microbial mats has allowed the identification of the types of MISS that characterize the different segments of the coastal environment. The modern microbial mats have been compared with those recorded at the top of the Holocene deposits, which are composed of biodegraded microbial black mats alternating with white laminae made of clastic and evaporitic sediments, indicative of very high frequency cycles of flood and drought. A hypothetic profile showing their occurrences along the different areas bordering the coastline is proposed as a guide for the reconstruction of the ancient depositional environment. Th...
Journal of Petroleum Exploration and Production Technology
The Bir M'Cherga basin (North-east Tunisia), with about 600 km 2 area, had recorded four Middle C... more The Bir M'Cherga basin (North-east Tunisia), with about 600 km 2 area, had recorded four Middle Cretaceous source rocks well stratigraphically correlated with the four known oceanic anoxic sub-events: OAE1a, OAE1b, OAE1c, and OAE1d. Variety of lithology, thickness and organic richness had characterized these source rocks. The sedimentary tectonic analysis, the petrology and geochemistry study established the petroleum system of these source rocks. Basin formation began early in the Barremian-Aptian interval by synsedimentary tectonics reactivating old basement faults. During the Aptian-Albian, the formed basin had a depocenter that recorded thicker black shales while its NW and SE edges remained raised under the Triassic halokinetic activities. The evolution of the sedimentary filling during this period generated two sedimentary cycles corresponding to two filling second-order fining and thickening upwards sequences. The black shales that constitute these source rocks are formed between subtidal and external platform environment and are interbedded with juxtaposed high organic rich layers and poor ones. The rich organic facies consists of dark shale that constitutes the source rock. The poor organic beds formed by light grey and nodular limestones constitute an intra host reservoir. Thereby, petroleum system consists in an "unconventional oil shale hybrid systems with a combination of juxtaposed organic-rich and organic-lean intervals associated to open fractures". The kerogen is essentially amorphous, with marine planktonic origin and low ligneous organic matter contribution. This organic material of dark facies had been well preserved in an anoxic environment with little or no energy. Light grey limestones were of oxic-to-sub-oxic environment. The stage of the thermal evolution for these source rocks provided by IH/T max diagram is of the "oil window". The average transformation ratio (TR) is estimated as 45% suggesting thus black shales are oil shale resources which still close about untransformed 55% of its hydrocarbon generating potential. The expulsion and release of oil into these source rocks are proven by the observation of hydrocarbons filling micro-cracks and by the variable values of the oil saturation index OSI ranging from 0 to 138%. The latter exceeds 100% near the paleo-high reliefs indicating two "oil crossover" areas attributed to the high degree of oil source rock saturation and accumulation of hydrocarbons considered ideal for hydraulic fracturing. This oil crossover is a consequence of secondary migration into black shale source rock, achieved by various faults created during the distensive phase that were reactivated again several times.
L'étude sédimentologique concerne des dépôts holocènes enfouis dans l'actuelle sebkha Boujmel com... more L'étude sédimentologique concerne des dépôts holocènes enfouis dans l'actuelle sebkha Boujmel comprenant des sables détritiques et/ou carbonatés gypsifères, des vases riches en matière organique et des boues blanchâtres riches en carbonates hypermagnésiens, des sables carbonatés bioclastiques et à oolithes de faible énergie et enfin des sables carbonatés silteux laminés et tapis microbiens associés. Ces faciès s'organisent en une séquence typiquement lagunaire. Les faciès holocènes situés plus au Nord, en affleurement sur les bordures de la bahira el Bougrara et l'Ile de Djerba, englobent des faciès qui sont plus ouverts aux influences marines énergétiques (faciès de shoal). Ils sont représentés par dépôts essentiellement oolithiques et bioclastiques parfois à quartz. Ainsi, une séquence sédimentaire holocène a pu être identifiée au Sud-Est de la Tunisie. Cette séquence est lagunaire dans les dépressions et littorale sur les bordures. Les corrélations des faciès, appuyées par des datations au 14 C, ont permis d'établir l'extension de la transgression holocène au niveau du Sud-Est de la Tunisie.
Interactive comment on "Environmental changes, climate and anthropogenic impact in southern-easte... more Interactive comment on "Environmental changes, climate and anthropogenic impact in southern-eastern Tunisia during the last 8 kyr" by Sahbi Jaouadi et al. Sahbi Jaouadi et al.
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