The accretion of the Levant continental shelf alongside the Nile Delta by immense margin-parallel sediment transport

Following the termination of the Messinian salinity crisis ~5.3 million years ago, massive sedimentation in the Eastern Mediterranean Sea formed the huge Nile Delta. Alongside delta propagation, a continental shelf was accreted along the Levant margin. For several decades it was assumed that these two sedimentary structures were closely connected. Levant shelf deposits are composed of Nile-derived sediments and present-day measurements show that sand is currently being transported alongshore from the Nile Delta to offshore Israel. This study reexamines the existing paradigm about sediment transport and shelf-delta connection. We show that longshore sand transport is just a small part of a much larger process termed here margin-parallel sediment transport (MPST). Sand is transported in a nearshore shallow-water belt where marine currents are highly energetic. At the same time, shale is transported at greater depths over the deeper shelf and the continental slope where marine currents are weaker. To model the accretion of the Levant shelf alongside the Nile Delta we use a 3D, diffusion-based, stratigraphic modeling tool (DionisosFlow) with a new module representing MPST. Our results show that margin-parallel transport of silt and clay in the deeper waters accounts for the bulk of deposition offshore Israel and is responsible for the development of the Levant shelf. Moreover, though MPST has begun coevally with delta formation, massive accretion of the Levant shelf was delayed by 2–3 My. Initially, a continental shelf formed offshore Sinai, then offshore Israel, and most recently along the Lebanon coast. Our model also demonstrates the significant lithological differences observed between sedimentation in front of the Nile River mouth and along adjacent continental margin. High energy down-slope sediment transport carries sand, silt, and clay, whereas margin-parallel currents are relatively weak and carry mainly silt and clay. One exception within the margin-parallel system is the highly energetic nearshore current that transports sand. Thus, we point out, MPST is an efficient separator between shale and sand. © 2020 Elsevier LtdThis study was supported by the Israeli Ministry of Energy and by the Mediterranean Research Center of Israel (MERCI). The article is further based upon work of COST Action “Uncovering the Mediterranean salt giant” (MEDSALT) supported by the European Cooperation in Science and TechnologyPeer reviewe

Gravitational collapse and Neogene sediment transfer across the western margin of the Gulf of Mexico: Insights from numerical models

International audienceThe western margin of the Gulf of Mexico (Veracruz State, Mexico) displays an extensive Neogene gravitational system, whereby the Neogene siliciclastic sediments are detached from underlying Mesozoic carbonates along decollement surface in Oligocene underpressured clays. Rapidly subsiding half-grabens develop above the footwall associated with major listric faults, whereas mini-basins develop in the deepest parts of the slope, in conjunction with the growth of west-verging compressional features. Between the high-angle normal faults in the west and the thrust anticlines in the east, a wide roll-over structure has grown progressively, resulting in a major topographic break in the morphology of the slope profile. Coupled forward kinematic modelling (Thrustpack) and stratigraphic modelling (Dionisos), calibrated against seismic profiles and two key nearshore wells, have been applied to representative regional transects across the margin, in order to quantify the vertical (subsidence) and horizontal (gravitational) deformations, and to discuss the impact of various key parameters on the distribution of debris flow depositions. These simulations are compared with data from distant ODP wells and discussed in the scope of current exploration strategies in both the US and Mexican portions of the Gulf of Mexico basin

AvP: A software package for automatic phylogenetic detection of candidate horizontal gene transfers.

Horizontal gene transfer (HGT) is the transfer of genes between species outside the transmission from parent to offspring. Due to their impact on the genome and biology of various species, HGTs have gained broader attention, but high-throughput methods to robustly identify them are lacking. One rapid method to identify HGT candidates is to calculate the difference in similarity between the most similar gene in closely related species and the most similar gene in distantly related species. Although metrics on similarity associated with taxonomic information can rapidly detect putative HGTs, these methods are hampered by false positives that are difficult to track. Furthermore, they do not inform on the evolutionary trajectory and events such as duplications. Hence, phylogenetic analysis is necessary to confirm HGT candidates and provide a more comprehensive view of their origin and evolutionary history. However, phylogenetic reconstruction requires several time-consuming manual steps to retrieve the homologous sequences, produce a multiple alignment, construct the phylogeny and analyze the topology to assess whether it supports the HGT hypothesis. Here, we present AvP which automatically performs all these steps and detects candidate HGTs within a phylogenetic framework

Neogene evolution and demise of the Amapá carbonate platform, Amazon continental margin, Brazil

International audienceThe Amazon continental shelf hosted one of the world's largest mixed carbonate-siliciclastic platforms from the late Paleocene onwards - the Amapá carbonates. The platform architecture, however, remains poorly understood and causes and timing of the cessation of carbonate deposition are still controversial. Here we present a stratigraphic analysis of the Neogene succession of the Amapá carbonates, based on a grid of 2D/3D seismic data correlated to revised micropaleontological data from exploration wells. The results provide improved constraints on the age of the transition from predominantly carbonate to siliciclastic sedimentation, which is shown to have varied through time across three different sectors of the shelf (NW, Central and SE). Four Neogene evolutionary stages of carbonate deposition could be defined and dated with reference to the new age model: (1) between ca. 24 and 8 Ma a predominantly aggrading mixed carbonate-siliciclastic shelf prevailed across the entire region carbonate production gave way to siliciclastic sedimentation across the Central and SE shelves; (2) between 8 and 5.5 Ma carbonate production continued to dominate the NW shelf, as deposition was able to keep up with base level oscillations; (3) between 5.5 and 3.7 Ma (early Pliocene), sediment supply from the paleo-Amazon River promoted the progressive burial of carbonates on the inner NW shelf, while carbonates production continued on the outer shelf (until 3.7 Ma). Longer-lasting carbonate sedimentation on the NW shelf can be explained by a lesser influx of siliciclastic sediments due to the paleo-geography of the Central shelf, characterized by a 150-km-wide embayment, which directed most terrigenous sediments sourced from the paleo-Amazon River to the continental slope and deep ocean; (4) from 3.7 Ma onwards, when the Central shelf embayment became completely filled, continuous sediment supply to the NW shelf resulted in the final transition from carbonate to siliciclastic-dominated environments on the entire Offshore Amazon Basin

Sedimentary sequences in the Gulf of Lion: A record of 100,000 years climatic cycles

The wide continental shelf of the Gulf of Lion (up to 70 km) has been the object of numerous investigations since the early days of oceanography. Yet, the question of sequences duration, the mechanisms of deposition and factors implied remained unanswered. A study of a very dense grid of Very High Resolution (VHR) seismic reflection (Sparker) data associated with surficial cores both, collected by IFREMER between 1992 and 2001 on the outer shelf and upper slope offshore of Sète in the Languedoc region gives a new insight into these issues. Analysis of the 3D geometry of the sedimentary record reveals a basic depositional pattern consisting of a pair of horizontally juxtaposed and downlapping prisms. Prism PI with low angle clinoforms (<1°) lies on the upper part of the shelf and is interpreted to be prodeltaic-offshore deposits. Prism PII with steeply dipping clinoforms (4°) lies on the outer shelf between 40 and 70 km from the present day coastline and is interpreted to be littoral deposits. Results obtained from integrating lithology, palynology, micropaleontology, seismic stratigraphy, stratigraphic simulation, support the hypothesis that the basic depositional pattern records a 100 000-years glacioeustatic (interglacial/glacial) cycle. As previously suggested by Aloïsi [Aloïsi, J.C., 1986. Sur un modèle de sédimentation deltaïque: contribution à la connaissance des marges passive, Thèse de Doctorat d'Etat. Université de Perpignan, 162 pp], prisms PI corresponds to deposition at high sea level and prisms PII to deposition during low sea level at glacial maxima. Five sequences of paired prisms capped by five major erosion surfaces have been identified and modelled showing that the corresponding glacioeustatic cycles (the last five cycles at least) are recorded on the shelf of the western part of the Gulf of Lio

Long lasting interactions between tectonic loading, unroofing, post-rift thermal subsidence and sedimentary transfers along the western margin of the Gulf of Mexico: Some insights from integrated quantitative studies

International audienceAfter Jurassic rifting, numerous carbonate platforms (i.e., the Orizaba, Cordoba and Golden Lane-Tuxpan platforms) developed during the Lower and Middle Cretaceous episode of thermal subsidence along the western passive margin of the Gulf of Mexico, with intervening basinal domains (i.e., the Tampico-Misantla, Zongolica, Veracruz and Deep Gulf of Mexico - DGM - basins).;During the Late Cretaceous-Paleocene, the east-verging Sierra Madre Oriental thrust belt developed, resulting in tectonic uplift and unroofing of the allochthonous units (i.e. tectonic units made up of former Orizaba and Cordoba platforms and Zongolica Basin series). This new topography provided also an important source of clastics to feed the adjacent foredeep, where coeval tectonic loading accounted for the bending of the foreland lithosphere. However, shallow water facies or even emersion persisted until the Eocene in the forebulge area (at the present location of the Golden Lane), preventing locally the clastics to reach the DGM. This topographic barrier was ultimately bypassed by the clastics only during the Oligocene and Neogene, once (1) the prograding clastic wedge had exceeded accommodation, and (2) the long lasting thermal subsidence of the passive margin could overpass the effect of the bending and force the former bulge to sink.;Numerous paleo-thermo-meters (Tmax, Ro), paleo-thermo-barometers (fluid inclusions), PVT and coupled forward kinematic and thermal modeling have been used to calibrate and date the progressive unroofing of the thrust belt. Coupled tectonic and sedimentologic modeling was applied in the foreland to predict the distribution of sand versus shale ratios in the Oligocene to Plio-Quaternary clastic sedimentary wedge of the passive margin, where gravitational gliding of post-Eocene series occurred during the Neogene along major listric faults.;Mantle dynamics are advocated as the main process accounting for post-orogenic uplift and regional tilting of the basement, which initiated a massive transfer of sediments from the Cordillera towards the Gulf of Mexico, from Oligocene onward, resulting in a destabilization and gravitational collapse of the western slope of the Gulf of Mexico in Neogene times

Tectonics and sedimentation interactions in the east Caribbean subduction zone: An overview from the Orinoco delta and the Barbados accretionary prism

Several marine geophysical data and piston-coring surveys acquired during the last decade allow one to better understand the close dynamic interactions between the sand-rich Orinoco turbidite system and the compressional structures of the Barbados prism. These interactions have been active since Eocene time as illustrated by the study of outcrops onshore Barbados Island. Because of strong morphologic and tectonic control in the east-Caribbean active margin, the present-day Orinoco turbiditic pattern system does not exhibit a classic fan geometry. The sea-floor geometry between the slope of the front of the Barbados prism and the slope of the South-American margin induces the convergence of the turbidite channels toward the abyssal plain, at the front of the accretionary prism. Also, whereas in most passive margins the turbidite systems are organized upstream to downstream as canyon, channel-levee and lobes, here, due to the tectonic control, the sedimentary system is organized upstream to downstream as channel-levee, canyons and channelized lobes. Indeed, at the edge of the Orinoco platform, the system has multiple sources with several distributaries and downstream the channel courses are complex with frequent convergences or divergences that are emphasized by the effects of the undulating seafloor tectonic morphologies associated with active thrust tectonics and mud volcanism. On top of the accretionary prism, turbidite sediments are filling transported piggy-back basins whose timing of sedimentation vs. deformation is complex. While erosion processes are almost absent on the highly subsiding Orinoco platform and in the upper part of the turbidite system, they develop mostly between 2000 and 4000 m of water depth, above the compressional structures of the Barbados prism (canyons up to 3 km wide and 300 m deep). In the abyssal plain, the main turbiditic channel develops toward the east and connects with the Vidal mid-Atlantic channel. The sediments transported in this channel are filling several elongated basins linked with fracture zones (notably the Barracuda Basin), and finally end their course in the Puerto-Rico trench, the deepest morphologic depression of the region. Piston-cores have demonstrated that turbidite sediments above the accretionary prism and in the abyssal plain are mostly coarse sandy deposits covered by recent pelagic planktonic-rich sediments, which corresponds to slower sand deposition during the post-glacial sea level rise. Numerical stratigraphic modelling suggests that during the last glacial event, the main depocentres were located above the tectonic prism and in the abyssal plain, at the front of the prism and that, during the Holocene eustatic rise, a large accommodation space formed on the shelf confining sedimentation mostly on the Orinoco deltaic platform and producing a starvation downstream in the turbidite system