Academic literature on the topic 'Bassin aquitain offshore'

Abstract In the western Mediterranean Sea, the Liguro-Provençal Basin (LPB) is a key area for studying passive margins because of its recent formation and abundance of onshore and offshore data. The Nerthe area located in the northern margin of LPB provides the unique continuous Oligo-Miocene deposits contemporaneous of the transition rifting to drifting. However, the age of the deposits remains debated and the link between outcrops and offshore seismic data is poorly constrained. The purpose of this paper is double. First, we intend to propose a new chronostratigraphic frame based on bio- (planktonic foraminifera, calcareous nannofossils) and magneto-stratigraphy. Second, we aim to make, through the integration of new highly time-resolved seismic data and field works, a coherent onshore-offshore link concretized by a 3D geological model. The new temporal and spatial data presented in this paper allow correlating the Oligo-Miocene sequences, defining their geometry and specifying precisely the timing of syn- and post-rift stages. The first marine transgression is now precisely dated latest Chattian within the syn-rift deposits and appears to be synchronous with the first marine deposits in the offshore wells and other marginal basins. The transition from syn-rift to post-rift appears to last 3.3 Ma at maximum, between 21.8 and 18.5 Ma (late Aquitanian to early Burdigalian). It is underlined by two major erosional unconformities bearing a hiatus of around 1 Ma. The post-rift started with a major marine transgression that is now dated from middle Burdigalian, at around 18.5 Ma, as elsewhere in the LPB. Contrarily to recent proposals, the post-rift deposits are widely represented on the northeastern margin of the “Golfe du Lion”. There, the subsidence of the margin was low during the syn-rift and the transitional periods and high during the post-rift. The onset of this high post-rift subsidence appears to be synchronous with the slowdown of the Corsica-Sardinia block (CSb) motion.

Abstract The Pelotas Basin, located on the SE Brazilian shelf, has evolved since the Aptian. Stratigraphical data from the basin can be used for delineation of the unconformity-bounded units (synthems) on the shelf, which is a first step towards a full understanding of its stratigraphic architecture, evolution, and hydrocarbon potential. Hiatuses in the Cenozoic succession of the Pelotas Basin are established with both biostratigraphic (planktonic foraminifers and calcareous nannofossils) and isotopic (87Sr/86Sr) data. The seven recognised hiatuses are dated respectively as (1) Palaeocene (Danian- Thanetian), (2) Palaeocene/Eocene boundary (Thanetian-Ypresian), (3) Eocene (Ypresian-Lutetian), (4) Eocene-Oligocene (Lutetian-Rupelian), (5) early-late Oligocene (Rupelian-Chattian), (6) early Miocene (Aquitanian-Burdigalian), and (7) middle-late Miocene (Serravallian-Tortonian). These intervals between the hiatuses are correlated with those of the Santos and Campos Basins north from the Pelotas Basin. The breaks in sedimentation that these basins have in common occurred (1) at the Palaeocene-Eocene and (2) Eocene-Oligocene transitions, (3) in the early Miocene, and (4) in the middle-late Miocene. These main unconformities outline five synthems on the SE Brazilian shelf, viz. the SEBS-1 (Palaeocene), SEBS-2 (Eocene), SEBS-3 (Oligocene), SEBS-4 (early-middle Miocene) and SEBS-5 (late Miocene-Holocene). The above unconformities are correlated with those established in the Cenozoic sedimentary successions of different regions such as Western Siberia, Arabia, NW and NE Africa, peninsular India, S Australia, the Gulf of Mexico, NW Europe, and South Africa. The only regional unconformity, near the Oligocene/Miocene boundary, coincides with the nearly-global sedimentation break. The latter was resulted from a climatic event, i.e., the ‘Mi-1 glaciation’. Thus, a eustatic origin is supposed for this regional unconformity. The other regional unconformities also correspond to global sea-level falls (probably with an exception for the Palaeocene/Eocene surface), which suggests that global eustatic movements controlled the development of the regional synthem architecture.

AbstractThe seaward extension of onshore formations and structures were previously almost unknown in Provence. The interpretation of 2D high-resolution marine seismic profiles together with the integration of sea-bottom rock samples provides new insights into the stratigraphic, structural and paleogeographic framework of pre-Messinian Salinity Crisis (MSC) deposits of the Provence continental shelf. Seven post-Jurassic seismic units have been identified on seismic profiles, mapped throughout the offshore Provence area and correlated with the onshore series. The studied marine surface and sub-surface database provided new insights into the mid and late Cretaceous paleogeography and structural framework as well as into the syn- and post-rift deformation in Provence. Thick (up to 2000 m) Aptian-Albian series whose deposition is controlled by E-W-trending faults are evidenced offshore. The occurrence and location of the Upper Cretaceous South-Provence basin is confirmed by the thick (up to 1500 m) basinal series downlaping the Aptian-Albian unit. This basin was fed in terrigenous sediments by a southern massif (“Massif Méridional”) whose present-day relict is the Paleozoic basement and its sedimentary cover from the Sicié imbricate. In the bay of Marseille, thick syn-rift (Rupelian to Aquitanian) deposition occurred (>1000 m). During the rifting phase, syn-sedimentary deformations consist of dominant N040 to N060 sub-vertical faults with a normal component and N050 drag-synclines and anticlines. The syn-rift and early post-rift units (Rupelian to early Burdigalian) are deformed and form a set of E-W-trending en echelon folds that may result from sinistral strike-slip reactivation of N040 to N060 normal faults during a N-S compressive phase of early-to-mid Burdigalian age (18–20 Ma). Finally, minor fault reactivation and local folding affect post-rift deposits within a N160-trending corridor localized south of La Couronne, and could result from a later, post-Burdigalian and pre-Pliocene compressive phase.

Three extensional phases can be recognized in the northern, Anglona area of the Oligo-Miocene Sardinian Rift during a fifteen million year period which spanned Corsica–Sardinia continental microplate separation and Western Mediterranean back-arc basin opening. In response to this multiphase rifting, a complex facies architecture involving clastic, carbonate and volcanic rocks developed. Integrated onshore facies and structural analysis, dating and offshore seismic data are here used to reconstruct the tectono-stratigraphic history of the Anglona area. Initial late Oligocene extension created a half-graben geometry with syn-rift clastic deposits shed locally from fault-bounded highs, passing laterally to lacustrine marlstones. Calc-alkaline volcanic activity subsequently predominated as volcanic centres developed along one half-graben bounding fault. Voluminous pyroclastic and epiclastic material was supplied to the adjacent half-graben accommodation space and was deposited in marginal to marine conditions. Second-phase mid-Aquitanian–early Burdigalian extensional faulting, recognized from localized clastic syn-rift stratal wedges, truncated and subdivided the half-graben. The syn-rift sediments were sealed by a regionally correlated ignimbrite that in turn was offset by late second-phase faulting. Third-phase extensional fault movement which reactivated the original fault trend then occurred. A perched lake developed in the resultant topography coeval with the progressive marine transgression of lower areas. As sea-level rose during mid-Burdigalian times, reefal carbonates and grainstones developed on fault-block highs whilst calcarenites and marlstones were deposited in hangingwall locations. Initial extension was coeval with the formation of the Sardinian proto-rift and the initiation of the Western Mediterranean basin. Second-phase faulting occurred as the Corsica–Sardinia microplate rotated to its present position during Western Mediterranean back-arc basin spreading. Final extension can be correlated to a second major extension phase along the Oligo-Miocene Sardinian Rift following back-arc basin opening, as extension was transferred towards the fore-arc. In Anglona, the main influence of multiphase tectonism was on rift topography, providing accommodation space and localized uplifted source areas. Varying relative sea-level mainly controlled the broad types of facies belts that developed. Contemporaneous calc-alkaline volcanism played a major role in the supply of basin filling material and in changing the topography locally.

The Miocene rocks of the Marádah Formation have been stratigraphically investigated from four stratigraphical sections around the Marádah Oasis in the Central Sirt Basin of Libya. The field investigations led to the identification of two members, the lower Qarat Jahannam Member and the upper Ar Ráhlah Member. Fourteen sedimentary facies at the outcrop-scale representing a gradual development of sedimentation from a continental clastic witness in the southwestern outcrops to transitional estuarine, lagoonal, and beaches to the proximal offshore in the northern outcrops, were recognized. The results indicates that the accumulation of the Marádah Formation is transgressive in nature and corresponding to two phases of deposition which have been mentioned in the earlier studies. The first phase is continental-dominated facies in which cross-bedded sandstones and calcareous sands comprise most of the depositional sequence of the lower Qarat Jahannam Member at the southwestern outcrops. This phase, however, is characterized by extremely bioturbated laminated-shale conquered by Skolithos ichnofacies in the lower part of the upper Ar Ráhlah Member at the northern outcrops. This phase is providing further evidence that the contact between the two members is diachronous everywhere in the study area. The clastic-phase has thought to be deposited in the Lower Miocene (Aquitanian-Burdigalian) since the lower Qarat Jahannam Member rests on an erosional surface of submarine origin in the southwestern outcrops above a 0.5 m. thick of a nummulitic unit of the Oligocene Bu Hashish Formation. The second phase is marine-dominated facies in which a bioclastic limestone unit rich in thick and disarticulated oysters, including Crassostrea gryphoides (Schlottheim), characterizes the sediments of the Ar Ráhlah Member at the southwestern outcrops. This phase also includes the upper part of the latter member at the northern outcrops in which a detrital limestone unit rich in turritelline gastropods is overlying by thick-bedded calcarenites rich in disarticulated oysters, gastropods, irregular echinoids (notably, Clypeaster and Echinolampas), bryozoans, and celestite corals. The upper part of the Ar Ráhlah Member at the northern outcrops, nevertheless, is terminated by a quite hard dolomitic limestone and by a pretty soft dolomitic marly limestone. Both lithologies, however, are combined with medium-sized oysters, including Ostrea digitalina Fuchs, and pectinid bivalves. The second phase, however, is interpreted to be deposited in the Middle Miocene (Langhian and Serravallian) based on the total-stratigraphic range of the larger benthic foraminifera Borelis melo melo (Fichtel & Moll), which recovered from the studied washed residues, and the associated microfacies.

We discuss the drivers of the Pyrenean post-orogenic exhumation, including drainage migration, flexural rebound and tectonic reactivation.We provide new low-temperature thermochronological data and inverse thermal modeling from both the hinterland and foreland of the western Pyrenees. Our new thermochronological ages range from 6.6 to 61.4 Ma and reveal a Late Miocene exhumation phase in several massifs. The contrasting thermal histories define a domain of focused exhumation in the western Pyrenees that coincides with the present-day extensional tectonics in a region to the north of the Axial Zone. Based on the inferred cooling rates and paleogradient estimates, we highlight an exhumation phase of c. 1 mm yr–1 between 11 and 9 Ma in the Axial Zone, well above rates expected for a post-orogenic evolution. The thermal evolution inferred from three boreholes of the Aquitaine foreland basin reveals that sediments eroded from the hinterland did not accumulate in the Piedmont region but were transported offshore in the Bay of Biscay. We infer that the significant c. 10 Ma post-orogenic exhumation event must be related to the modern normal faulting regime of the western Pyrenees, associated with contrasting crustal thickness and densities, inherited from the Mesozoic rift evolution of the northern Pyrenees.Supplementary material: Laboratory analytical procedures, radial plot visualization of AFT detrital data and Age/eU relationship of AHe and ZHe samples are available at https://doi.org/10.6084/m9.figshare.c.5212581

Les sédiments marins des marges continentales sont enrichis en Matière Organique Sédimentaire (MOS) qui peut être transformée en méthane par l'activité microbienne. Les précédents résultats obtenus dans le cadre du projet de recherche PAMELA ont permis d'identifier plusieurs points d’émissions de méthane biogénique sur le plateau continental du Golfe de Gascogne et le long des marges du Mozambique et de Madagascar. Afin de mieux comprendre l'impact de la nature de la Matière Organique (MO) sur ces systèmes fluides, nous avons (1) caractérisé la MO et (2) proposé une nouvelle approche de modélisation pour estimer la présence de gaz biogénique à l'échelle du bassin. Les premiers résultats concernant l'évolution du matériel organique à grande échelle dans le Canal du Mozambique, ont montré des hétérogénéités en termes de qualité et de quantité de MO entre les marges du Mozambique et de Madagascar. Nous avons conclu que les variations des signatures isotopiques peuvent être le résultat des conditions de transport et de préservation différentes entre les deux sites. Une nouvelle approche de modélisation a été appliquée au système biogénique localisé sur le rebord du plateau aquitain (Golfe de Gascogne). Les résultats ont conduit à un scénario de référence pour la production de méthane microbien dans le Bassin Aquitain offshore qui est cohérent avec les quantités de méthane émis au fond de la mer. Le gaz biogénique est généré actuellement dans les sédiments du Plio-Pléistocène, avec une quantité moyenne de gaz émis estimée entre 0,87 et 1,48 Tcf / My
Marine sediments in continental margins are known to be enriched in Sedimentary Organic Matter (SOM) which can yield methane by microbial activity. Previous results collected in the framework of the PAMELA research project allowed to identify several seepages of microbial methane offshore Aquitaine (Bay of Biscay) and along the Mozambique and Madagascar continental margins. In order to better understand the impact of the Organic Matter (OM) on such fluid systems, we (1) characterized the OM, and (2) proposed a new modelling approach to predict methane cycle at the basin scale from its generation to migration and release. The OM in the Mozambique Channel shows heterogeneities at large scale in quality and quantity between the Mozambique and the Madagascar margins. We concluded that isotopic signature variations can be the result of different transport and preservation conditions between the two sites. A new modelling approach was applied to the Bay of Biscay biogenic fluid system. It consists of a basin modelling workflow of microbial gas generation and migration process at the basin scale and accounts for OM biodegradation processes and the main biogenic gas sink. The results allowed us to propose a reference scenario for microbial gas production in offshore Aquitaine that is compared with measured data from in situ bubbling sites and acoustic water column signatures. The biogenic system appears to be sourced by biogenic gas system found in the Plio-Pleistocene sediments that is still active, with a mean flow rate estimated between 0.87 and 1.48 Tcf/My