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International audience; The numerous processes (superficial and deep) occurring on margins, their origins, consequences, interactions and quantifications are only very partially described and understood. The identification of the relative role of factors is sometimes completely contradictory between authors. Here, we showed the results of a long-term multidecadal and multidisciplinary study (using geophysical, geological, stratigraphic, paleontological, geomorphologic, geochemical, microbiological and numerical models) in the Western Mediterranean Sea that acts as a natural laboratory at many different scales. We showed how sediments efficiently recorded at the same time: variations of glacio-eustatic sea-level changes, variations of sediments yield and sources, and also enabled quantifying vertical movements and geodynamic worldwide events but also detailed regional mass transport, turbidites and contourites deposits. They are also an archive of paleoclimatic, palaeoceanographic and diagenetic processes.

The Essaouira-Agadir Basin (EAB, Morocco) presents numerous and well-exposed outcrops of the Lower Cretaceous series. Here we present an integrated stratigraphic framework for the latest Barremian-early Albian, and for the western Tethys based on i) the identification of sedimentary discontinuities, ii) the establishment of a high-resolution ammonite and calcareous nannofossil biozonation, and iii) a carbon isotope record. Various sedimentary discontinuities corresponding to erosive surfaces were recognized within these deposits. Most of these surfaces are correlated within the EAB, and correspond to drops in sea level. The distribution of ammonite assemblages was calibrated with the standard Mediterranean zonation. Several ammonite index-species have been identified, in particular for the early Aptian and earliest late Aptian. This was crucial because the lower series are dominated by condensed sedimentation and temporal hiatuses. Most of the uppermost Barremian to lower Albian ammonite standard zones have been recognized. Four new and reliable calcareous nannofossil bioevents have been identified in the late Aptian allowing to revise the NC7 Zone. The taxonomic criteria used to define species markers of both NC8A and NC8B subzones have been specified, thereby improving the calibration of these subzones with ammonite biozones. The delta C-13(carb) values from whole rock samples decrease from the late Aptian to the early Albian. The new biostratigraphic and chemostratigraphic scheme for the EAB allowed rather good correlations between sections from southern and northern Tethyan margins.

International audience; Aptian to early Albian times are marked by various geodynamic and paleoenvironmental events such as large igneous province volcanism , perturbations of climate and the carbon cycle, and sea-level changes. The Essaouira-Agadir basin (EAB), located on the Atlantic passive margin of Morocco, offers good and fossiliferous exposures of the Aptian-Albian sedimentary series. A detailed analysis of this succession made it possible to establish a biostratigraphic framework. The identification of discontinuities allowed to define eight depositional sequences. As most of them are correlatable with depositional sequences of other Tethyan areas, they suggest that eustacy was the main parameter controlling sedimentation. The analysis of sedimentary facies and nannofossil assemblages provides information on paleoenvironmental changes. Sedimentation in the EAB evolved from a very low energy, carbonate ramp in the early Aptian to a low energy, slightly deeper, mixed carbonate-clastic ramp in the early Albian. This change occurred along with an increase of clastic input, a change from oligotrophic to mesotrophic faunal assemblages, and a decrease of sea-surface temperatures. The occurrence of current sedimentary features, sporadic dysaerobic deposits and local phosphatic and glauconitic crusts suggests that upwelling currents weresignificant during this period. Paleogeographic and isopach maps support a transgressive trend in the late Aptian and early Albian, and unravel subsidence anomalies suggesting mild halokinetic movements during Aptian-early Albian times.

In diapir flanks, unconformity-bounded sedimentary packages associated with gravity-driven deposits, controlled by the ratio between the rates of sediment accumulation and diapir growth can be interpreted in the context of halokinetic sequences. The Bakio Breccias Formation (Basque Country, Spain) corresponds to redeposited carbonate deposit that developed in response to the Bakio diapir growth during the Middle Albian. These deposits provide on of the rare documented example of carbonate-dominated halokinetic sequences. The Bakio Breccias Formation consists of an alternation of clast- and matrix-supported breccias, calcirudite, calcarenite and marl, deposited along the flanks of the diapir. The description and the analysis of the Bakio Breccias Formation lead to a new model for carbonate-dominated halokinetic sequences. These sequences differ from their siliciclastic counterpart because sediment accumulation rate is controlled by carbonate platform growth on the topographic relief top of the diapirs, while sediments are preferentially deposited in the mini-basins adjacent of the diapirs, in siliciclastic settings. During transgressive system tract, carbonate platform are able to keep up with the sea level rise and to aggrade on top of the diapirs, forming thick and resistant roof, which is assumed to limit the diapir growth and thus to favour the development of halokinetic sequences with low angle unconformities (wedge halokinetic sequences). During late highstand system tract deposition (and lowstand system tract if present), platform progradation results in high sediment accumulation in the adjacent depocenters, loading the autochthonous salt layer and promote diapir growth and creation of topographic relief. In addition, if the diapir roof reaches emersion, karstification of the carbonate platform top may also favour roof destruction and diapir growth. Depending on the thickness of the roof developed previously and the amplitude of the sea level fall, the halokinetic sequences with the emersion and the karstification of the carbonate platform may display high angle unconformities (hook halokinetic sequences). Furthermore, gravity-driven deposits are assumed to be more common in carbonate-dominated halokinetic sequences, compared to their siliciclastic counterparts, since carbonate platform aggradation creates steep slopes on the diapir margins, leading to the partial collapse of the margin, even when limited diapir growth occurs. The carbonate-dominated halokinetic sequence model proposed here is an important tool for the prediction of potential reservoir distribution, seal and hydrocarbon migration in flanks of salt diapirs where carbonate platform developed., The authors would like to thank the ARNT-CIFRE and Geolink (382/2008), for the funding of the Ph.D. work of Y. Poprawski.

Study of carbonate facies from Cretaceous lithostratigraphic units of Peru has led to the identification of calcareous algae, mainly Dasycladales (Apinella hispanica, Salpingoporella ? hasi, Korkyrella sp., Neomeris spp., Trinocladus divnae, and Terquemella spp.), mostly from Cenomanian strata. These algae represent the first records of these taxa on the Pacific margin of South America, in a back-arc setting.