44 research outputs found
Contourite distribution and bottom currents in the NW Mediterranean Sea: Coupling seafloor geomorphology and hydrodynamic modelling
Contourites are common morphological features along continental margins where currents encounter the seafloor. They can provide long-term archives of palaeoceanography, may be prone to sediment instability, and can have a great potential for hydrocarbon exploration. Despite their importance and increasingly recognised ubiquitous occurrence worldwide, the link between oceanographic processes and contourite features is poorly constrained. In particular, it is unclear under which specific conditions sediments are mobilised, modified and deposited by bottom currents. Here, we aim to determine key bottom current characteristics (velocity and bottom shear stress) affecting contourite deposition, by assuming that recent oceanographic regimes may be extended back in time over the past glacial-interglacial cycles, with strong winter circulation assumed similar to glacial conditions and weak summer circulation to interglacials. We present an integrated study from the NW Mediterranean Sea that couples results of the MARS3D hydrodynamic model with high-resolution sedimentological and geophysical data (piston cores, multibeam bathymetry and high resolution seismic data). Near bottom circulation was modelled during winter and summer 2013 as representative of past periods of high and low current intensity, respectively. Model results match well with the extent of contourite depositional systems and their different localised morphologic elements. We deduce that higher intensity events control the formation of erosional features such as moats and abraded surfaces. The heterogeneous distribution of bottom-current intensity on slopes explains the development of different types of contourite drifts. Plastered drifts form in zones of low bottom-current velocities constrained upslope and downslope by higher current velocities. Separated elongated mounded drifts develop where fast bottom-currents decelerate at foot of the slope. In contrast, no mounded contourite morphologies develop when the current velocity is homogeneous across the slope, especially in margins prone to downslope sediment transport processes. In confined basins, gyres may transport sediment in suspension from a margin with a high sediment supply to an adjacent starved margin, favouring the development of fine-grained contourites in the latter. Our results provide new insights into how detailed bottom-circulation modelling and seafloor geomorphological analyses can improve the understanding of palaeoflow-regimes, at least over time spans when the overall paleogeography and the distribution of contourite drifts is comparable to present-day conditions. The approach of coupled hydrodynamic models and geomorphological interpretations proposed here for depositional, erosional and mixed contourite features may be used to understand other areas affected by bottom currents, and for a better conceptual understanding of bottom-current processes and their interactions with the seafloor
Perched basins of Mediterranean Sea : geodynamic, and impact of the Messinian salinity crisis on the sedimentary fluxes (Valencia and Adriatic basins)
LâĂ©volution gĂ©odynamique et physiographique de lâespace MĂ©diterranĂ©en, en particulier au sein des bassins bordiers de Valence et Adriatique, sont intimement liĂ©es Ă lâhĂ©ritage antĂ©-NĂ©ogĂšne. Lâidentification de la segmentation des bassins et leur implication dans lâhistoire tectonique et environnementale au NĂ©ogĂšne, en particulier lors de la crise dâĂ©rosion et de salinitĂ© Messinienne (MESC - 5.96-5.32 Ma), reste cependant mĂ©connus et font lâobjet de ce travail de recherche. Afin de les mettre en lumiĂšre, nous proposons une vision complĂšte du remplissage sĂ©dimentaire NĂ©ogĂšne des deux bassins, sur la base dâune compilation de profils sismiques et de forages industriels. Nos rĂ©sultats illustrent une segmentation du domaine Valence-Provençal en trois sousbassins dâĂąges, de subsidences et de nature crustales diffĂ©rentes. Un nouveau scĂ©nario cinĂ©matique est proposĂ© Ă lâĂ©chelle des bassins Valencien et AlgĂ©rien. Cette segmentation met en lumiĂšre lors de la MESC un systĂšme complet de vallĂ©es incisĂ©es fluviatiles long de plus de 270 km. AssociĂ© aux diffĂ©rents cortĂšges sĂ©dimentaires, un nouveau regard est jetĂ© sur lâĂ©vĂ©nement Messinien et le paradoxe dâouverture du bassin de lâEbre. Au sein du domaine Adria, lâhĂ©ritage MĂ©sozoĂŻque contrĂŽle en premier lieu les environnements nĂ©ogĂšnes, oĂč deux dĂ©pocentres majeurs se distinguent de part et autre du seuil composite Apulien-Gargano-Pelagosa. La propagation des fronts de dĂ©formations Albanide et Apennin se surimpose Ă cet hĂ©ritage et contrĂŽle la sĂ©dimentation et les mouvements verticaux de ces dĂ©pocentres La pĂ©riode Messinienne est alors perçue comme une phase de rĂ©organisation tectonique majeure, cette derniĂšre se surimposant Ă la MESC.The geodynamic evolution of the Mediterranean area, especially in the Valencia and Adriatic basins, is strongly influenced by its ante-Neogene history. The localization of existing thresholds at that time, and their impact on the following tectono- sedimentary evolutions still remain largely unknown. In this work, we will try to reconstruct this evolution and better understand the part of these thresholds, in particular during the Messinian Erosional and Salinity Crisis (MESC, 5.96-5.32 Ma). We provide here a complete view of the Neogene sedimentary infilling for the both Valencia and Adriatic basins thanks to a compilation of seismic profiles correlated to industrial boreholes.Our results allow us to individualize the Valence-Provençal domain into three subbasins whose ages, subsidence and crustal nature differ. A new kinematic and geodynamic scenario for the Valencia and Neogene Algerian basins is proposed here. This segmentation provides also information about MESC. We highlight a fully incised-valley system whose length reaches more than 270 km, the latter associated with the development of several system tracts. Overall, these interpretations lets us look the Ebro basin connection paradox from a different angle.The Mesozoic Apulian-Gargano-Pelagosa composite threshold mainly control the Neogene sedimentation in the Adria domain and distinguishes two main depocenters. The propagating of the Albanid and Apennine deformation fronts control also the evolution of vertical movements and the sedimentation. Our results imply that the Messinian period corresponds to a major tectonic and/or kinematic reorganization phase within which the MSC is a superimposed event
Géodynamique et impact de la crise d'érosion et de salinité Messinienne sur les transferts sédimentaires (bassin de Valence, bassin Adriatique)
The geodynamic evolution of the Mediterranean area, especially in the Valencia and Adriatic basins, is strongly influenced by its ante-Neogene history. The localization of existing thresholds at that time, and their impact on the following tectono- sedimentary evolutions still remain largely unknown. In this work, we will try to reconstruct this evolution and better understand the part of these thresholds, in particular during the Messinian Erosional and Salinity Crisis (MESC, 5.96-5.32 Ma). We provide here a complete view of the Neogene sedimentary infilling for the both Valencia and Adriatic basins thanks to a compilation of seismic profiles correlated to industrial boreholes.Our results allow us to individualize the Valence-Provençal domain into three subbasins whose ages, subsidence and crustal nature differ. A new kinematic and geodynamic scenario for the Valencia and Neogene Algerian basins is proposed here. This segmentation provides also information about MESC. We highlight a fully incised-valley system whose length reaches more than 270 km, the latter associated with the development of several system tracts. Overall, these interpretations lets us look the Ebro basin connection paradox from a different angle.The Mesozoic Apulian-Gargano-Pelagosa composite threshold mainly control the Neogene sedimentation in the Adria domain and distinguishes two main depocenters. The propagating of the Albanid and Apennine deformation fronts control also the evolution of vertical movements and the sedimentation. Our results imply that the Messinian period corresponds to a major tectonic and/or kinematic reorganization phase within which the MSC is a superimposed event.LâĂ©volution gĂ©odynamique et physiographique de lâespace MĂ©diterranĂ©en, en particulier au sein des bassins bordiers de Valence et Adriatique, sont intimement liĂ©es Ă lâhĂ©ritage antĂ©-NĂ©ogĂšne. Lâidentification de la segmentation des bassins et leur implication dans lâhistoire tectonique et environnementale au NĂ©ogĂšne, en particulier lors de la crise dâĂ©rosion et de salinitĂ© Messinienne (MESC - 5.96-5.32 Ma), reste cependant mĂ©connus et font lâobjet de ce travail de recherche. Afin de les mettre en lumiĂšre, nous proposons une vision complĂšte du remplissage sĂ©dimentaire NĂ©ogĂšne des deux bassins, sur la base dâune compilation de profils sismiques et de forages industriels. Nos rĂ©sultats illustrent une segmentation du domaine Valence-Provençal en trois sousbassins dâĂąges, de subsidences et de nature crustales diffĂ©rentes. Un nouveau scĂ©nario cinĂ©matique est proposĂ© Ă lâĂ©chelle des bassins Valencien et AlgĂ©rien. Cette segmentation met en lumiĂšre lors de la MESC un systĂšme complet de vallĂ©es incisĂ©es fluviatiles long de plus de 270 km. AssociĂ© aux diffĂ©rents cortĂšges sĂ©dimentaires, un nouveau regard est jetĂ© sur lâĂ©vĂ©nement Messinien et le paradoxe dâouverture du bassin de lâEbre. Au sein du domaine Adria, lâhĂ©ritage MĂ©sozoĂŻque contrĂŽle en premier lieu les environnements nĂ©ogĂšnes, oĂč deux dĂ©pocentres majeurs se distinguent de part et autre du seuil composite Apulien-Gargano-Pelagosa. La propagation des fronts de dĂ©formations Albanide et Apennin se surimpose Ă cet hĂ©ritage et contrĂŽle la sĂ©dimentation et les mouvements verticaux de ces dĂ©pocentres La pĂ©riode Messinienne est alors perçue comme une phase de rĂ©organisation tectonique majeure, cette derniĂšre se surimposant Ă la MESC
A comprehensive compilation of the seismic stratigraphy markers along the Adriatic Sea
Data base compilation, Adriatic sea (Seanoe document)The Mediterranean Sea is a natural laboratory for addressing questions on the formation and evolution of continental margins and the relationship between surface and deep processes. The evaporites deposited during the Messinian Salinity Crisis strongly impact its sedimentary and geomorphology evolution. We present here a compilation of the main regional seismic stratigraphic markers throughout the Central and South Adriatic Sea (CAB and SAB). The following original (uninterpolated) interpretations are provided in xyz format (z in second twt): i) Top of the Mesozoic formation, ii) Base and Top of the Gessoso Solfifera along the CAB, iii) Base and Top of the MSC detrital formation along the SAB, iv) Top of the Upper Unit, v) Base and Top of the middle Pliocene unit, vi) Seafloor. The available reflection seismic dataset the data set is compiled of processed vintage seismic profiles from the Videpi database
The late Messinian event: a worldwide tectonic revolution
A review of geological and geophysical observations points towards a worldwide kinematic change at around 6 Ma. The synchronicity of many manifestations (tectonics, magmatism, kinematics, ecological events, among others) at ~6 Ma, similar to those recognized from time to time on the geological timescale, argues for a global geodynamic event that has led to many regional consequences on Earth's surface. In particular, we propose that this global event was the main trigger for the three fold increase in sediment deposits in the world ocean over the last ~5 Ma, but also for the onset of the Messinian Salinity Crisis in the Mediterranean area, one of the most severe ecological crises in the Earth's history. We suggest this Messinian revolution to be the last occurrence of cyclic successions of global events
Co-evolution assists geographic dispersal: the case of Madagascar
International audienceInterspecific associations may limit the dispersal of individual species, but may also facilitate it when entire co-evolved systems expand their geographic ranges. We tested the recent proposal that episodic land bridges linked Africa and Madagascar at three stages during the Cenozoic by comparing divergence estimates of Madagascar's angiosperm taxa with their dispersal mechanisms. Plants that rely on gravity for seed dispersal indicate at least two episodes of land connection between Africa and Madagascar, in the Early Palaeocene and Early Oligocene. Seed dispersal by strepsirrhine primates possibly evolved in the Palaeocene, with the divergence of at least one endemic Malagasy angiosperm genus, Burasaia (Menispermaceae). This genus may have facilitated the lemur colonization of Madagascar. Frugivory, nectarivory and gummivory probably generalized in the Oligocene, with the co-evolution of modern lemurs and at least 10 new Malagasy angiosperm families. In the Late Miocene, more angiosperms were probably brought from Africa by birds via a discontinuous land connection, and radiated on Madagascar in diffuse association with birds (asities) and dwarf nocturnal lemurs (cheirogaleids). During the same connective episode, Madagascar was probably colonized by hippopotamuses, which both followed and re-seeded a variety of plants, forming the grassy Uapaca 'tapia' forest and ericoid 'savoka' thicket
Des crises récentes Causes globales de la Crise messinienne
International audienceLa crise Messinienne, point de vue gĂ©odynamique La Mer MĂ©diterranĂ©e s'est-elle ou non assĂ©chĂ©e ? Tel est le dĂ©bat qui a enflammĂ© et enflamme toujours la communautĂ© gĂ©ologique mĂ©diterranĂ©enneentendons par lĂ la communautĂ© qui s'intĂ©resse Ă la MĂ©diterranĂ©e (cf. le chapitre « La Crise de salinitĂ© messinienne »). Changeons de point de vue et posons le problĂšme diffĂ©remment : quelle que soit sa cause, il y a bel et bien un dĂ©pĂŽt important d'Ă©vaporites en un temps restreint Ă la fin du MiocĂšne, bien aprĂšs la formation des bassins et l'arrĂȘt des mouvements des morceaux de plaques qui les ont formĂ©s. L'Ă©cart est de plus de 15 Ma pour ce qui concerne le bassin Liguro-Provençal. Il est encore plus considĂ©rable en MĂ©diterranĂ©e Orientale puisque les bassins Ionien et Levantin datent du MĂ©sozoĂŻque (voir l'article de Julie Tugend et al. dans ce numĂ©ro). Ce point n'amĂšne aucune controverse. Cette simple observation rend ce phĂ©nomĂšne Ă©trange et mĂȘme unique : les dĂ©pĂŽts de sel dans les bassins ocĂ©aniques mondiaux sont situĂ©s Ă la fin de la genĂšse des marges, avant la crĂ©ation de la croĂ»te ocĂ©anique. En MĂ©diterranĂ©e, ce n'est pas le cas : le sel se dĂ©pose dans un bassin formĂ©, aprĂšs l'arrĂȘt des mouvements pour la majeure partie de la MĂ©diterranĂ©e. Il se dĂ©pose sur une sĂ©quence sĂ©dimentaire miocĂšne Ă©paisse, dont la topographie est plate. Mieux ! prenons le point de vue de Sirius, cher Ă Voltaire, et Ă©loignons-nous de cette rĂ©gion fort intĂ©ressante : dĂ©focalisons notre regard. Que nous raconte cet Ă©vĂ©nement unique et mĂ©diterranĂ©en sur notre planĂšte Terre ? Comment s'inscrit-il dans son histoire ? Les mouvements globaux, les phase
Co-evolution assists geographic dispersal: the case of Madagascar
Interspecific associations may limit the dispersal of individual species, but may also facilitate it when entire co-evolved systems expand their geographic ranges. We tested the recent proposal that episodic land bridges linked Africa and Madagascar at three stages during the Cenozoic by comparing divergence estimates of Madagascarâs angiosperm taxa with their dispersal mechanisms. Plants that rely on gravity for seed dispersal indicate at least two episodes of land connection between Africa and Madagascar, in the Early Palaeocene and Early Oligocene. Seed dispersal by strepsirrhine primates possibly evolved in the Palaeocene, with the divergence of at least one endemic Malagasy angiosperm genus, Burasaia (Menispermaceae). This genus may have facilitated the lemur colonization of Madagascar. Frugivory, nectarivory and gummivory probably generalized in the Oligocene, with the co-evolution of modern lemurs and at least 10 new Malagasy angiosperm families. In the Late Miocene, more angiosperms were probably brought from Africa by birds via a discontinuous land connection, and radiated on Madagascar in diffuse association with birds (asities) and dwarf nocturnal lemurs (cheirogaleids). During the same connective episode, Madagascar was probably colonized by hippopotamuses, which both followed and re-seeded a variety of plants, forming the grassy Uapaca âtapiaâ forest and ericoid âsavokaâ thicket