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International audience; We present a study to estimate the large-scale landscape history of a continental margin, by establishing a source-to-sink volume balance between the eroding onshore areas and the offshore basins. Assuming erosion as the primary process for sediment production, we strive to constrain a numerical model of landscape evolution that balances the volumes of eroded materials from the continent and that deposited in the corresponding basins, with a ratio imposed for loss of erosion products. We use this approach to investigate the landscape history of Madagascar since the Late Cretaceous. The uplift history prescribed in the model is inferred from elevations of planation surfaces formed at various ages. By fitting the volumes of terrigenous sediments in the Morondava Basin along the west coast and the current elevation of the island, the landscape evolution model is optimized by constraining the erosion law parameters and ratios of sediment loss. The results include a best-fit landscape evolution model, which features two major periods of uplift and erosion during the Late Cretaceous and the middle to late Cenozoic. The model supports suggestions from previous studies that most of the high topography of the island was constructed since the middle to late Miocene, and on the central plateau the erosion has not reached an equilibrium with the high uplift rates in the late Cenozoic. Our models also indicate that over the geological time scale, a significant portion of materials eroded from Madagascar was not archived in the offshore basin, possibly consumed by chemical weathering, the intensity of which might have varied with climate.

Fossil carbonate reefs are common along rifts and rifted passive margins. They provide valuable paleoecological and paleogeographical information. Moreover, porous reef buildups are targeted as potential oil and gas reservoirs and sites for gas storage.The Red Sea and Gulf of Suez contain several generations of reef deposits: (1) syn-rift Early and Middle Miocene reefs that formed along the eroded footwalls of normal faults, and (2) post-rift Pliocene-Holocene coastal reefs that split apart, subsided, and aggraded to form carbonate platforms by salt-driven raft tectonics. The Late Miocene lacks reefs due to evaporitic conditions. This study focuses on the uplifted Early-Middle Miocene reef deposits, which outcrop sporadically along the Arabian and African margins of the Red Sea, particularly the northern half, over a distance of ~1000 km. They are exhumed along the coastal plain at elevations of 50-150 meters. We studied several reefs on the Arabian side and carried out age determination implementing a revised planktonic foraminifera zonation and paleoenvironmental interpretation. We also used satellite images to identify and map similar exhumed reefs on the African side.The Miocene reefs are located along the eroded footwalls of normal fault scarps that form the first or second marginal half grabens, usually sitting unconformably over the basement. The flat reef and back-reef lagoonal facies are often removed by erosion, but the dipping thick fore-reef talus breccias are preserved. The breccias are an unsorted mix of coral reef and back reef debris and also contain basement clasts. The linear fore-reef talus deposits follow along the fault scarps, revealing paleo-valleys incised into the hanging wall. Placing the reef on the basin-scale helps us distinguish the tectonic influence, accompanied by climate and eustatic sea-level variation, on shallow marine carbonates during rifting.Mapping all published, newly discovered, and inferred outcrops along the African and Arabian coast of the Red Sea allow us to develop a new tectono-sedimentary model for reef evolution in the syn-rift setting. The proposed model explains the absence of the reef outcrops in the southern areas of the Arabian Red Sea and predicts subsurface zones where reef growth possibly took place. Nature of the contact between reef carbonates and the underlying Precambrian basement in conjunction with the consistently preserved fore-reef zone disclose the uplift history and erosion events prior and post reef growth. In addition, following the reef distribution, we developed a syn-rift paleogeographic model of the Red Sea.

This presentation describes the structure and morphologies associated with seafloor spreading in the Red Sea inferred from bathymetric, gravity, magnetic and seismic data. We show that the orientation of the structures is consistent with an Arabia-Nubia Euler pole located within the 95% confidence of Ar-Rajehi et al, (2010) Euler pole and with the tectonic model initially proposed by Girdler (1984). At the Red Sea scale, our model shows that a spreading axis extends along its entire length, even though it is mostly covered by allochthonous Middle Miocene salt and Late Miocene minibasins flowing inward from the margins. In the northern Red Sea, oceanic basement is only exposed through small windows within the salt, forming a series of deeps. The seafloor segments symmetrically bisect the new ocean in the south. Right-stepping transform faults that cluster near Jeddah, Zabargad and Ikhwan Islands offset the ridge axis as spreading is getting more oblique towards the Euler Pole. The northern, central and southern Red Sea segments display a well-developed mid-ocean ridge flanked by landward-dipping volcanic basement, typical of slow spreading ridges. In the northern magma poor spreading segment, mantle exhumation is likely at the transition between continental and oceanic crust. Transpression and transtension along transform faults accounts for the exhumation of the mantle on Zabargad Island as well as the collapse of a pull-apart basin in the Conrad deep.We propose a new structural model for the Red Sea constrained by the geodetic rules of tectonic plates movements on a sphere. Finally, we discuss the effect of the Danakil microplate on the ridge morphology and show that the Arabia-Nubia-Danakil triple junction is likely located further north than previously described, around 18±0.5°N, where we observe a shift in the ridge axis orientation as well as in the spreading orientation.

The Jizan region of southwest Saudi Arabia contains large industrial point sources of CO2 and potentially the capacity to dispose substantial quantities of this gas by the subsurface mineralization of local basaltic rocks. Monte Carlo estimates suggest that the total CO2 mineralization capacity of the mafic igneous rocks in the Jizan area is ~4.2 Gt CO2, which is sufficient to store all of the carbon emissions from the local industrial facilities for four hundred years. Significant volumes of basalt were erupted in the region during the late Oligocene in a continental rift before the opening of the Red Sea. These rocks consist of lava flows and volcaniclastics intruded by dikes and shallow plutons. They are densely fractured and variably altered to chlorite-epidote-calcite assemblages. Dissolution rate measurements performed at 25 oC of four variably altered basaltic rocks from the region demonstrate their ability to increase fluid pH and liberate substantial Ca and Mg to the fluid phase. Reaction path calculations suggest that water charged CO2 will readily carbonate when interacting with the basaltic rocks at both 25 and 100 oC. Reactive transport calculations, however, suggest that while such carbonation reactions will be slow at 25 oC, these would fix more than 95% of injected water-dissolved CO2 within five years at 100 oC. Taken together, the results of this study indicate the likely success of large-scale subsurface carbon storage efforts through the subsurface carbonation of basaltic rocks in the Jizan region.

The geological evolution of the Mozambique Channel sensu largowas controlled by three major transfer zones (Davie, Mozambique and Agulhas/Falklands), (1) related to the migration of four continents (Africa, Madagascar, Antarctica, South America), (2) recording five major volcanic episodes from 186 Ma to today and (3) contemporaneous of the uplift of several plateaus (e.g. Southern African Plateau), affecting a quite heterogeneous lithosphere of Archean to Neoproterozoic ages. This is therefore a unique area for a better understanding of (1) the evolution of transform margins in a volcanic setting and (2) the relationships between deformation, relief growth and sediment routing evolution. We established in the frame of the PAMELA (Passive Margin Experiment LAboratory) project (TOTAL, IFREMER, CNRS) a chart and nine paleogeographic maps (with tectonic structures, magmatism, catchments and sediment routing system) to better constrain the timing of evolution of this domain. The main results are as follows:(1) 255-240 Ma: a first E-W extension (Karoo “Rifts”) with no ocean opening;(2) 185-160 Ma: a second NW-SE extension between Antarctica/Madagascar and Africa coeval of the Karoo Large Igneous Province and initiation of volcanic margins along the future Somali Ocean;(3) 160-145 Ma: major change of the plate migration toward a N-S extensional initiation of very oblique margins along the Mozambique Fracture Zone (FZ), indicating an Antarctica motion toward SSE;(4) 134 Ma: onset of the migration of the Falkland continental domain along the Agulhas FZ;(5) 115 Ma: major deformation of the four plates with (i) end of the southward migration of Madagascar and (ii) major inversion along the Davie FZ (initiated around 135 Ma) and uplift of Madagascar;(6) 92-70 Ma: uplift of the Southern Africa Plateau first eastward (92 Ma) and second westward (81-70 Ma);(7) 40 Ma: onset of the uplift of the Zimbabwe/Zambia/Malawi Plateaus, East African Dome and Madagascar Plateau – last uplift of the Southern African Plateau;(6) 11-5 Ma: acceleration of the uplift of the Zimbabwe/Zambia/Malawi Plateaus and East African Dome – growth of a dome crossing the Mozambique Channel from Madagascar to southern offshore of the Limpopo Plain.

Reduction in the induction period of hydrate formation and enhancement of the gas hydrate growth are vital parameters in the application of gas hydrates technique for methane storage. In this work,...

A transparent polymer film with embedded micro mirrors is developed, and it can be attached to a window glass pane for daylighting, improving visual comfort and reducing cooling load in buildings by redirecting sunlight. Despite existing cutting-edge techniques, the fabrication of large-area, linear micro structured surfaces combining high aspect ratio, curve sidewalls and a controlled shape remains challenging. In order to solve the problem, a novel mechanical scanning engraving method using blades with micro-teeth of desired patterns on soft substrates is developed. The usage of a blade enables the combination of high aspect ratio with almost any closed profile. Such blades can be obtained in a large variety of shapes using UV-LIGA technology which combines photolithography and electroforming. Master molds were prepared and the following steps of micro UV-imprinting from the master molds are also introduced. The present work confirms the feasibility of the fabrication for parabolic sidewall microstructures of aspect ratio of 3.8 and 6.7 with good controlled shapes. With a scanning speed of 0.15 m/min, the method is proven to be efficient and appropriate for large-area microstructured fabrication.