Aptian–Albian shale oil unconventional system as registration of Cretaceous oceanic anoxic sub-events in the southern Tethys (Bir M’Cherga basin, Tunisia)

Abstract The Bir M’Cherga basin (North-east Tunisia), with about 600 km2 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

Correction to: Aptian–Albian shale oil unconventional system as registration of Cretaceous oceanic anoxic sub-events in the southern Tethys (Bir M’Cherga basin, Tunisia)

In the original publication, article title has been incorrectly published as “Aptian–Albian oil shale unconventional system as registration of Cretaceous oceanic anoxic sub-events in the southern Tethys (Bir M’Cherga basin, Tunisia)” instead of Aptian–Albian shale oil unconventional system as registration of Cretaceous oceanic anoxic sub-events in the southern Tethys (Bir M’Cherga basin, Tunisia). Also the part of Fig. 3 caption has been incorrectly added to Fig. 4 caption. The corrected figures captions are given here

Apport de l’analyse pollinique des sédiments de la sebkha Boujmel (Sud-Est tunisien) à la reconstitution des paléopaysages et paléoclimats holocènes en milieu aride

Une analyse palynologique a été menée sur les dépôts de l’Holocène moyen et supérieur ainsi que sur des échantillons de surface de la sebkha Boujmel. Les résultats préliminaires montrent une importante diversité végétale et enregistrent les réponses de la végétation au changement climatique et à l’impact des activités humaines. Entre 7 000 et 4 000 cal. BP, la présence d’une steppe graminéenne dans la plaine de Jeffara et d’une strate de taxons xérophytes-méditerranéens sur les reliefs proches reflètent les conditions climatiques plus humides de l’Holocène moyen. L’impact anthropique demeure très limité et les modifications de la végétation seraient plutôt d’origine climatique. L’aridification observée à partir de la transition Holocène moyen-supérieur engendre un recul des éléments méditerranéens et une progression de l’armoise et des taxons désertiques. Les échantillons de surface reflètent des changements environnementaux marqués par l’essor des écosystèmes désertiques, l’importance de l’olivier et une pression anthropique accrue sur les écosystèmes locaux. Ces enregistrements polliniques soulignent la complexité de la dynamique de l’Armoise, ainsi que l’absence d’indices d’une steppe à Acacia en Tunisie présaharienne au cours de l’Holocène.Pollen analyses are undertaken on Mid- to Late Holocene sediments and on surface samples from the sebkha Boujmel. Preliminary results highlight vegetation changes with large pollen taxonomic diversity and the vegetation response to both palaeoclimate change and human impact. From ca. 7000 to 4000 cal. BP, during the humid Mid‑Holocene episode, a grass steppe was widespread in the Jeffara coastal plain while a Mediterranean shrub covered the mountainous hinterland. At that time, human impact remains limited and major vegetation changes were triggered by climate forcing. At the Mid- to Late Holocene transition, the decrease of Mediterranean vegetation and both spreads of Artemisia and desert taxa may be related to increasing aridity. The surface samples reflect how human pressure is responsible for modern landscapes. The desert taxa develop while Olea and other pollen indicators attest to the increasing human activity on local ecosystems. Furthermore, pollen records stress the complex Artemisia dynamic and point to the lack of evidence towards an Acacia steppe in the southern pre-Saharan Tunisia during the Holocene

Environmental changes, climate and anthropogenic impact in south-east Tunisia during the last 8-kyr

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 3aEuro-kaaEuro-BP, a succession of five wet-dry oscillations is recorded. An intense arid event occurs between ca. 5.7 and 4.6aEuro-kaaEuro-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 3aEuro-kaaEuro-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 3aEuro-kaaEuro-BP. The event at 4.2aEuro-kaaEuro-BP is not evidenced and the link between events recorded in Sebkha Boujmel and the North Atlantic cooling events is clearer from ca. 3aEuro-kaaEuro-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. 3aEuro-kaaEuro-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 0.8aEuro-kaaEuro-BP (850-1150aEuro-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 species, is linked to recent local socio-economic changes in Tunisia

Dynamiques des zones humides littorales et enjeux de gestion en Méditerranée

Ce numéro de Méditerranée interroge la diversité des relations actuelles entre les sociétés méditerranéennes et les différents milieux humides qui occupent un grand nombre d’espaces littoraux. Cette réflexion apparaît comme opportune à un moment où les enjeux de gestion entourant les zones humides littorales se trouvent à la croisée de changements écologiques, hydro-climatiques et géomorphologiques rapides et inédits liés aux activités anthropiques et de bouleversements géopolitiques régionaux récents. L’importance de ces écosystèmes est écologique, économique mais également historique et scientifique. Si les lagunes ont une forte valeur économique et tiennent une place notable dans l’histoire des rivages méditerranéens, les marais maritimes ont eux un intérêt pour la reconstitution des paléo-milieux grâce aux indicateurs qu’ils peuvent offrir pour la connaissance de l’évolution récente des rivages ainsi que pour les approches prospectives dans une conjoncture d’élévation du niveau marin. Les contributions rassemblées concernent principalement les pays du Maghreb, mais également une région plus rarement étudiée telle que le littoral Albanais. Les thèmes abordés sont relatifs à l’évolution des paléopaysages côtiers ainsi qu’aux impacts anthropiques actuels que subissent les zones humides littorales mais ils mettent aussi en évidence le rôle que peuvent jouer ces milieux dans les économies locales