Papers by Elia D'Acremont
Marine Geology, 2016
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Tectonophysics
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<p&amp... more <p>Over the last 23 Myr, the roughly east-directed subduction of the Nazca Plate beneath South America led to the formation of several mountain ranges associated with the overall northern Andes evolution. Along the active southwestern Ecuadorian margin, the compressional setting involves the Cretaceous-Miocene Chongón-Colonche / Santa Elena terranes, overlain by recent sedimentary basins. This geological setting, generally interpreted as an onshore-offshore forearc system, evolves in close relation with the active tectonic escape of the North Andean Sliver and the opening of the Gulf of Guayaquil. This region is characterised by a widespread extensional deformation in the upper plate that overprints moderate subduction and crustal earthquakes.</p><p>To better document such extensional processes, we specifically explore the offshore shelf and the littoral area of the Santa Elena Peninsula using academic and industrial 2D seismic profiles calibrated with local wells and field observations. We document a trench-parallel fault network, composed of >20km-long normal faults that take place on top of the former Chongón-Colonche accretionary wedge. These faults are linearly-steep along the trench, and are listric toward the continent where they clearly control fault-block rotation. They separate flexural basins developing on the platform ahead the Chongón-Colonche Cordillera, and are associated with immerged terraces most likely formed during the Last Glacial Maximum. They also may link to further onshore marine terraces developing since the Pleistocene across the coastline.</p><p>These observations suggest a peculiar dismantlement of the margin, mainly affected by tectonic erosion involving reactivation of former compressional features. Normal faults are specifically interpreted as a regional syn-orogenic collapse of the Chongón-Colonche Cordillera, which may result from transecting subducting ridges, fracture zones and seamounts controlling, at least partially, the geometry and the nature of the deformation along the southwestern Ecuadorian margin. This deformation pattern is likely linked to a weak interseismic coupling along the subduction interface to which the active opening of the Gulf of Guayaquil overlaps. This project is funded by the project ANR MARACAS ANR-18-CE31-0022 (<em>MARine terraces along the northern Andean Coast as a proxy for seismic hazard ASsessment</em>).</p>
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<p class="Body">Mediterranean Outflow Water (MOW) acts as a net source of... more <p class="Body">Mediterranean Outflow Water (MOW) acts as a net source of salt and heat into North Atlantic intermediate depths that ultimately contributes to the Atlantic Meridional Overturning Circulation. On this basis, it has been hypothesised that MOW variability might influence global climate. Although several studies have documented major glacial-interglacial changes in deep- and intermediate Mediterranean circulation patterns, little is known about associated impacts on MOW properties, in particular its residence time and geochemical signature. Using a set of cold-water coral samples from along the ‘pre-MOW’ and MOW path, i.e. from the Alboran Sea to the northern Galician Bank including the Strait of Gibraltar and the Gulf of Cadiz, we aim to identify changes in both the ventilation state of the water masses flowing out of the Mediterranean and the distribution of coral growth.With this purpose, paired Uranium-series and AMS radiocarbon ages have been obtained in the same coral samples allowing any potential change in the reservoir age to be inferred accurately, as well as allowing a spatio-temporal ‘coral map’ to be created. Furthermore, these results have been complemented by trace element measurements in benthic foraminifera from the Alboran coral mound sediment core.</p> <p class="Body">Our results show a particular spatio-temporal coral distribution with glacial presence only at the deepest sites of the Gulf of Cadiz (~1000m), followed by ~300m Western Mediterranean (WMed) coral appearance across the deglaciation/mid Holocene (14-4 kyr), to end with a proliferation at the Strait of Gibraltar and Galicia Bank from ~6 kyr towards the present. We hypothesise 1) that ~300m WMed area might have been bathed in Atlantic waters inflow during the glacial due to sea-level drop, returning to LIW (Levantine Intermediate Water) influence over the deglaciation, and 2) that MOW reached deeper areas outside of the Mediterranean Sea in the Gulf of Cadiz during the glacial period. Regarding the reservoir age, little change at the WMed is observed at 150-450m across the deglaciation as compared to the large ventilation excursion detected in the Iberian Margin at ~1000m. However, a ventilation age gradient of ~300 yr related to water depth is observed within WMed corals when appearing at the Bølling-Allerød, in synchrony with significant changes in hydrographical parameters inferred from foraminiferal trace element from the same area. Overall, our results suggest a water mass reorganization at the surface-intermediate layer of the WMed during the deglaciation and early Holocene, but the ultimate nature of these changes needs yet to be explored by further analysis of Nd isotopes as well as of trace elements beyond the deglaciation.</p>
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Marine Geology
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Nature Communications
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Terra Nova
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Geophysical Journal International, 2017
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Tectonophysics, 2016
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Basin Research, 2016
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Marine Geology, 2016
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Earth and Planetary Science Letters, 2016
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La zona central de la Cuenca de Alborán se caracteriza por presentar los elementos fisiográficos ... more La zona central de la Cuenca de Alborán se caracteriza por presentar los elementos fisiográficos más importantes de Alborán, como son las dorsales de Alborán y Adra que limitan la depresión del Canal de Alborán. Estos elementos morfoestructurales son el resultado de la convergencia de las placas Africana y Euroasiática. El análisis de datos batimétricos y de perfiles de sÃsmica con diferentes grados de resolución, ha permitido establecer dos fases de deformación recientes: una de carácter transcurrente de salto normal y otra posterior compresiva que produce una inversión tectónica. Esta última fase serÃa el resultado de la colisión del Bloque tectónico de la Dorsal de Alborán con el de Adra al consumirse el espacio del curso medio del Canal de Alborán.
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Tectonophysics, 2014
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ABSTRACT The discovery of hyper-thinned continental crust and exhumed mantle on continental margi... more ABSTRACT The discovery of hyper-thinned continental crust and exhumed mantle on continental margins has raised several key questions, such as how the crust thins until the breakup or what controls the locus of extreme crustal thinning, exhumation and final oceanic spreading. Reflection seismic lines (ENCENS-Sheba, Encens, Marges-Aden cruises) and seismological investigations (YOCMAL ANR project) across conjugate margins of the Oman/Socotra margins allow a detailed study of the crustal and sedimentary structure and a discussion on the structures and the age of the deformation. Structural analysis of new dataset enables mapping the area where the continental extension seems to be coupled to the mantle illustrating the exhumation phase. The crustal thinning is abrupt occurring mostly at the shoreline on both margins and shows along-margin variations.The thinning progressively migrates towards the locus of final breakup, which is interpreted by a progressive weakening of the mantle by lithospheric thinning and serpentinization. Then, a stage of uplift and erosion is observed in the proximal margins after the thinning phase. Uplift is usually higher where crustal thinning is more important in the deep basin, which could be interpreted by the onset of small-scale convection driven by the lateral temperature gradients at the necking zone.
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ABSTRACT The Gulf of Aden is a young and narrow oceanic basin formed in Oligo-Miocene time betwee... more ABSTRACT The Gulf of Aden is a young and narrow oceanic basin formed in Oligo-Miocene time between the rifted margins of the Arabian and Somalian plates. The distal margin and particularly the Ocean-Continent Transition (OCT) domain were previously studied considering a large set of data (Leroy et al., 2004; d'Acremont et al., 2005; d'Acremont et al., 2006; Autin, et al accepted). This study focus on the sedimentary cover identified on seismic reflection profiles collected during Encens-Sheba (2000) and Encens (2006) cruises. Sedimentary stratal pattern and seismic facies succession permit us to highlight a late tectonic event affecting the Dhofar margin. The understanding of facies and depositional sequences is a major challenge for the knowledge of the post-rift tectono-sedimentological evolution of the Gulf of Aden during the spreading. This study let us to distinguish three domains, which match to the structural segmentation inherited from the rifting episode of this margin. The sedimentary record is strongly controlled by a recent (quaternary to now) tectonic phase. Vertical movements lead to the formation of numerous instabilities on the continental slope and Mass-transport deposits (MTDs) on the lower slope and deep basin. The quaternary uplift rate increases eastward, toward the Socotra Hadbeen transform fault zone. The recurrence of the gravitational events shows that the margin history can be divided into active and passive periods since the beginning of the post-rifting evolution of North Aden (17-6 Ma). There is a main sedimentological switch in the studied zone around 7- 10 Ma. This major changes of sedimentation rate and facies types (slope-wash detritus, Mass-transport deposits MTDs, first occurrence of deep sea fans) is probably due to the uplift of the margin and climatic change (first occurrence of the Monsoon in this region). All the incision/erosion stages of continental slope (from slope instabilities set up to the formation of mature canyon) observed on the eastern part of the margin lead to an incision shaping model on a steep continental slope. Elevated topography observed along many passive margins suggests permanent uplift of rift flank. This configuration should be due to flexural isostatic rebound in response to mechanical unloading of the lithosphere during extension.
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Papers by Elia D'Acremont