Reconstruction of the formation history of the Darwin Mounds, N Rockall Trough: How the dynamics of a sandy contourite affected cold-water coral growth

Cold-water coral mounds, formed through a feed-back process of cold-water coral growth and sediment baffling, have been studied all along the NE Atlantic continental margin. However, major questions remain concerning their formation history, especially their initiation and early development in relation to the surrounding sediment dynamics. For the first time, two small mounds located in a sandy contourite have been cored from the top to mound base: here, the formation history of the Darwin Mounds, located in the Northern Rockall Trough was investigated and reconstructed from two piston cores using a multidisciplinary approach. This consisted of CT-scanning for quantifying coral density changes with depth, grain-size analysis to obtain the hydrodynamic trends and radiocarbon and U-series dating to place the results into a wider paleoceanographic context. The results show that the Darwin Mounds formed during the early Holocene (~ 10 ka BP) through sediment baffling, mainly by Lophelia pertusa. The initiation of both mounds shows a similar pattern of increased current velocities resulting in coarser sediment deposition and a relatively high coral density with a peak of 23 vol%. The mound growth was rapid between ~ 10–9.7 ka BP (up to 277 cm ka− 1 in one of the mounds), with further vibrant growth periods around ~ 8.8 ka BP, 6.5 ka BP and 3.4 ka BP. The demise of the mounds ca. ~ 3 ka BP was likely caused by an intensification in bottom current velocities causing a hostile environment for coral growth in the contourite setting. In a wider context, the development of the Darwin Mounds appears to have responded to the relative strength and position of the Subpolar Gyre, which affected food supply to the corals, sedimentation rates, current speeds and other water mass properties in the area

Bathymetry and uplift rate of the Gulf of Aqaba, Dead Sea Fault.

peer reviewedInitially described in the late 50"s, the Dead Sea Fault system connects at its southern end to the Red Sea extensive system, through a succession of left-stepping faults. In this region, the left-lateral differential displacement of the Arabian plate with respect to the Sinai micro-plate along the Dead Sea fault results in the formation of a depression corresponding to the Gulf Aqaba. We acquired new bathymetric data in the areas of the Gulf of Aqaba and Strait of Tiran during two marine campaigns (June 2018, September 2019) in order to investigate the location of the active faults, which structure and control the morphology of the area. The high-resolution datasets (10-m posting) allow us to present a new fault map of the gulf and to discuss the seismic potential of the main active faults.We also investigated the eastern margin of the Gulf of Aqaba and Tiran island to assess the vertical uplift rate. To do so, we computed high-resolution topographic data and we processed new series of U-Th analyses on corals from the uplifted marine terraces.Combining our results with previous studies, we determined the local and the regional uplift in the area of the Gulf of Aqaba and Strait of Tiran.Eventually, we discussed the tectonic evolution of the gulf since the last major change of the tectonic regime and we propose a revised tectonic evolution model of the area

De vuelta al punto de partida: Nuevas dataciones del arte de la Cueva de la Peña de Candamo (Asturias)

La Peña de Candamo was discovered by the scientific community in 1914, being one of the first known caves in the Cantabrian region, and declared a UNESCO World Heritage site in 2008. The only monographic study of its parietal art was led and published by E. Hernández Pacheco in 1919, showing exceptional complexity and graphic density. In 2007, a new research project was launched to update all the information related to the cave's parietal art from a multidisciplinary perspective. Within this context, and starting from the radiocarbon tests made by J. Fortea in the late 20th century, tests have been conducted at the Gif-sur-Yvette to date a series of black dots located on the "Engraving's Wall". The fact that the results are di - fferent to those published to date leads to the discussion as to which to accept based on the followed metho - dologies and protocols. Likewise, the implications of these results in the decorating of the cave and their place within the artistic production of the region during the Upper Palaeolithic period are also analyse

Apport des datations U/Th de spéléothèmes à la connaissance de l’incision du réseau hydrographique de l’Est du Bassin parisien

Dans l’Est du Bassin parisien, la karstification s’exprime selon deux modes essentiels, soit au contact d’une couverture argilo-sableuse sur les plateaux calcaires, soit au contact d’une nappe alluviale dans les fonds de vallée. Dans tous les cas, l’évolution de ces karsts suit l’incision des vallées. On présente ici trois sites karstiques majeurs (Pierre-la-Treiche, Trampot et le Barrois), inféodés à trois grandes vallées de l’Est du Bassin parisien (la Moselle, la Meuse et la Marne) recoupant trois grandes masses carbonatées (Bajocien, Oxfordien, Tithonien). Dans ces karsts, 84 datations ont été entreprises par la méthode U/Th soit en alpha, soit en TIMS. La synthèse de ces dates confirme l’apport que constitue le karst dans les reconstitutions paléoenvironnementales en particulier dans le domaine de l’incision du réseau hydrographique, du recul des couvertures non carbonatées et des reconstitutions paléoclimatiques.In the eastern part of the Paris Basin, karstification occurs, essentially in two modes, one at the contact of a sandy-clayey cover on limestone plateaus, the other beneath alluvium in the floors of valleys. In every case, evolution of the karsts follows incision of the valleys. In this paper, three major karstic systems are presented (Pierre-la-Treiche, Trampot and the Barrois), associated with three large valleys (the Moselle, the Meuse and the Marne), cutting three large limestone masses (Bajocien, Oxfordien, Tithonien). In these karsts, 84 dates were obtained using the U/Th method (alpha, TIMS). These dates confirm the contribution of the karst to palaeoenvironmental reconstruction in the fields of river system incision, retreat of the non-carbonate cover and palaeoclimatic reconstruction.Im Osten des Pariser Beckens  erscheint die Verkarstung in zwei wesentlichen Formen – in Kontakt mit einer lehmig-sandigen Decke auf den Kalkplateaus oder in Kontakt mit einer alluvialen Schicht in den Talgründen. In allen Fällen folgt die Entwicklung dieser Karste dem Einschneiden der Täler. Hier werden drei größere Karstbereiche vorgestellt (Pierre-la-Treiche, Trampot und das Barrois), die drei grossen Tälern (Mosel, Maas und Marne) zugehören und drei grosse Kalkmassive (Bajocien, Oxfordien, Tithonien) anschneiden. In diesen Karstgebieten wurden 84 Datierungen nach der Methode U/Th in alpha oder in TIMS vorgenommen. Die Synthese dieser Daten bestätigt den Beitrag, den der Karst für die paläogeographische Rekonstruierung liefert, insbesondere im Bereich des Einschneidens des hydrographischen Netzes, des Rückweichens der nichtkalkigen Deckschichten und paläoklimatischer Rekonstruktionen

Apport des datations U/Th de spéléothèmes à la connaissance de l’incision du réseau hydrographique de l’Est du Bassin parisien

Dans l’Est du Bassin parisien, la karstification s’exprime selon deux modes essentiels, soit au contact d’une couverture argilo-sableuse sur les plateaux calcaires, soit au contact d’une nappe alluviale dans les fonds de vallée. Dans tous les cas, l’évolution de ces karsts suit l’incision des vallées. On présente ici trois sites karstiques majeurs (Pierre-la-Treiche, Trampot et le Barrois), inféodés à trois grandes vallées de l’Est du Bassin parisien (la Moselle, la Meuse et la Marne) recoupant trois grandes masses carbonatées (Bajocien, Oxfordien, Tithonien). Dans ces karsts, 84 datations ont été entreprises par la méthode U/Th soit en alpha, soit en TIMS. La synthèse de ces dates confirme l’apport que constitue le karst dans les reconstitutions paléoenvironnementales en particulier dans le domaine de l’incision du réseau hydrographique, du recul des couvertures non carbonatées et des reconstitutions paléoclimatiques.In the eastern part of the Paris Basin, karstification occurs, essentially in two modes, one at the contact of a sandy-clayey cover on limestone plateaus, the other beneath alluvium in the floors of valleys. In every case, evolution of the karsts follows incision of the valleys. In this paper, three major karstic systems are presented (Pierre-la-Treiche, Trampot and the Barrois), associated with three large valleys (the Moselle, the Meuse and the Marne), cutting three large limestone masses (Bajocien, Oxfordien, Tithonien). In these karsts, 84 dates were obtained using the U/Th method (alpha, TIMS). These dates confirm the contribution of the karst to palaeoenvironmental reconstruction in the fields of river system incision, retreat of the non-carbonate cover and palaeoclimatic reconstruction.Im Osten des Pariser Beckens  erscheint die Verkarstung in zwei wesentlichen Formen – in Kontakt mit einer lehmig-sandigen Decke auf den Kalkplateaus oder in Kontakt mit einer alluvialen Schicht in den Talgründen. In allen Fällen folgt die Entwicklung dieser Karste dem Einschneiden der Täler. Hier werden drei größere Karstbereiche vorgestellt (Pierre-la-Treiche, Trampot und das Barrois), die drei grossen Tälern (Mosel, Maas und Marne) zugehören und drei grosse Kalkmassive (Bajocien, Oxfordien, Tithonien) anschneiden. In diesen Karstgebieten wurden 84 Datierungen nach der Methode U/Th in alpha oder in TIMS vorgenommen. Die Synthese dieser Daten bestätigt den Beitrag, den der Karst für die paläogeographische Rekonstruierung liefert, insbesondere im Bereich des Einschneidens des hydrographischen Netzes, des Rückweichens der nichtkalkigen Deckschichten und paläoklimatischer Rekonstruktionen

A multi-proxy stalagmite record indicates a shift in forcing of twentieth century drought events in Normandy

Drought events are increasingly impacting Europe. The study of past droughts helps disentangle the different factors that trigger hydrological drought, helping to forecast future drought severity. Here we identify the historical drought events of the twentieth and twenty-first centuries in geochemical records of a stalagmite from Caumont cave in Northern France and develop a mechanistic understanding of their root causes. Subannually-resolved stable carbon isotope (δ13C) and trace element data are directly compared with historical climatic records. δ13C, Mg, and Sr peaks align well with most of the historical drought events of the twentieth and twenty-first centuries. The comparison reveals a good correspondence between summer effective rainfall and δ13C, Mg, and Sr concentrations. Further comparison of geochemical records with the precipitation-evapotranspiration index (SPEI) reveals a change in the drought forcings for the past two decades. During most of the twentieth century, droughts appear driven by a pluvial regime, whereas since the late 1990s, drought was driven by higher evapotranspiration due to increased temperature

South Atlantic intermediate water advances into the North-east Atlantic with reduced Atlantic meridional overturning circulation during the last glacial period

The Nd isotopic composition (epsilon Nd) of seawater and cold-water coral (CWC) samples from the Gulf of Cadiz and the Alboran Sea, at a depth of 280-827 m were investigated in order to constrain middepth water mass dynamics within the Gulf of Cadiz over the past 40 ka. epsilon Nd of glacial and Holocene CWC from the Alboran Sea and the northern Gulf of Cadiz reveals relatively constant values (-8.6 to -9.0 and -9.5 to -10.4, respectively). Such values are similar to those of the surrounding present-day middepth waters from the Mediterranean Outflow Water (MOW; epsilon Nd approximate to -9.4) and Mediterranean Sea Water (MSW; epsilon Nd approximate to -9.9). In contrast, glacial epsilon Nd values for CWC collected at thermocline depth (550-827 m) in the southern Gulf of Cadiz display a higher average value (-8.90.4) compared to the present-day value (-11.70.3). This implies a higher relative contribution of water masses of Mediterranean (MSW) or South Atlantic origin (East Antarctic Intermediate Water, EAAIW). Our study has produced the first evidence of significant radiogenic epsilon Nd values (approximate to -8) at 19, 23-24, and 27 ka, which are coeval with increasing iceberg discharges and a weakening of Atlantic Meridional Overturning Circulation (AMOC). Since MOW epsilon Nd values remained stable during the last glacial period, it is suggested that these radiogenic epsilon Nd values most likely reflect an enhanced northward propagation of glacial EAAIW into the eastern Atlantic Basin

New chronological constraints on the intrakarstic fluvio glacial fan of the cave Sous les Sangles (Bas Bugey, France)

International audienceThe age of the Last Glacial Maximum extension of the French north western Alps is still under discussion. Lateral to the ancient glacial valleys, karstic galleries functionned as glacial sinkholes during the glacial retreat phases and are thus relevant recorders of these glacial phases. In the Bas Bugey (Ain, France), the cave Sous les Sangles hosts a remarkable laminated detrital sequence associated with an ancient position of the Isère glacier in the "Cluse des Hôpitaux". Several U/Th alpha dates undertaken 20 years ago are revised here. Five new U/Th ICP MS dates on speleothems frame the detrital complex, providing a terminus post quem (TPQ) and a terminus ante quem (TAQ) to this glacial invasion. The TPQ is dated 87.3 ± 3.9 ka (MIS 5.b.c) and the TAQ is dated 11.6 ± 4.3 ka (MIS 1). The laminated detrital sequence is thus better constrained and the glacial invasion could have only been deposited during MIS 4 (locally Würm II, first max) or MIS 2 (Last Glacial Maximum or locally Würm IV) stages. The cave Sous les Sangles has a strategic position to constrain maximum glacial extension during the last cold stages of the Quaternary in the French Alps.Nouvelles contraintes chronologiques sur le cône fluvio glaciaire intrakarstique de la grotte Sous les Sangles (Bas Bugey, France). L'âge de la dernière extension maximale glaciaire des Alpes nord occidentales françaises est toujours discutée. En position latérale aux anciennes vallées glaciaires, des conduits karstiques ont fonctionné en pertes juxtaglaciaires durant les phases de retrait glaciaire et constituent des enregistreurs pertinents de ces phases glaciaires. Dans le Bas Bugey (Ain, France), la grotte Sous les Sangles abrite une remarquable séquence détritique laminées associée à une position du glacier de l'Isère dans la cluse des Hôpitaux. Des datations entreprises il y a 20 ans (U/Th alpha) sont ici révisées. Cinq nouvelles dates U/Th MC ICP MS ont été entreprises sur des spéléothèmes encadrant l'ensemble détritique offrant un terminus post quem et un terminus ante quem à cette invasion glaciaire. Le TPQ est daté à 87,3 ± 3,9 ka (MIS 5) et le TAQ est daté à 11.6 ± 4.3 ka (MIS 1). La série détritique laminée est ainsi mieux contrainte et l'invasion glaciaire ne peut se situer que dans les stades MIS 4 (localement Würm ancien) ou MIS 2 (localement Würm récent). La grotte Sous les Sangles confirme sa position stratégique pour contraindre l'extension maximale glaciaire au cours des derniers stades froids du Quaternaire

New chronological constraints on the intrakarstic fluvio glacial fan of the cave Sous les Sangles (Bas Bugey, France)

International audienceThe age of the Last Glacial Maximum extension of the French north western Alps is still under discussion. Lateral to the ancient glacial valleys, karstic galleries functionned as glacial sinkholes during the glacial retreat phases and are thus relevant recorders of these glacial phases. In the Bas Bugey (Ain, France), the cave Sous les Sangles hosts a remarkable laminated detrital sequence associated with an ancient position of the Isère glacier in the "Cluse des Hôpitaux". Several U/Th alpha dates undertaken 20 years ago are revised here. Five new U/Th ICP MS dates on speleothems frame the detrital complex, providing a terminus post quem (TPQ) and a terminus ante quem (TAQ) to this glacial invasion. The TPQ is dated 87.3 ± 3.9 ka (MIS 5.b.c) and the TAQ is dated 11.6 ± 4.3 ka (MIS 1). The laminated detrital sequence is thus better constrained and the glacial invasion could have only been deposited during MIS 4 (locally Würm II, first max) or MIS 2 (Last Glacial Maximum or locally Würm IV) stages. The cave Sous les Sangles has a strategic position to constrain maximum glacial extension during the last cold stages of the Quaternary in the French Alps.Nouvelles contraintes chronologiques sur le cône fluvio glaciaire intrakarstique de la grotte Sous les Sangles (Bas Bugey, France). L'âge de la dernière extension maximale glaciaire des Alpes nord occidentales françaises est toujours discutée. En position latérale aux anciennes vallées glaciaires, des conduits karstiques ont fonctionné en pertes juxtaglaciaires durant les phases de retrait glaciaire et constituent des enregistreurs pertinents de ces phases glaciaires. Dans le Bas Bugey (Ain, France), la grotte Sous les Sangles abrite une remarquable séquence détritique laminées associée à une position du glacier de l'Isère dans la cluse des Hôpitaux. Des datations entreprises il y a 20 ans (U/Th alpha) sont ici révisées. Cinq nouvelles dates U/Th MC ICP MS ont été entreprises sur des spéléothèmes encadrant l'ensemble détritique offrant un terminus post quem et un terminus ante quem à cette invasion glaciaire. Le TPQ est daté à 87,3 ± 3,9 ka (MIS 5) et le TAQ est daté à 11.6 ± 4.3 ka (MIS 1). La série détritique laminée est ainsi mieux contrainte et l'invasion glaciaire ne peut se situer que dans les stades MIS 4 (localement Würm ancien) ou MIS 2 (localement Würm récent). La grotte Sous les Sangles confirme sa position stratégique pour contraindre l'extension maximale glaciaire au cours des derniers stades froids du Quaternaire

New chronological constraints on the intrakarstic fluvio glacial fan of the cave Sous les Sangles (Bas Bugey, France)

International audienceThe age of the Last Glacial Maximum extension of the French north western Alps is still under discussion. Lateral to the ancient glacial valleys, karstic galleries functionned as glacial sinkholes during the glacial retreat phases and are thus relevant recorders of these glacial phases. In the Bas Bugey (Ain, France), the cave Sous les Sangles hosts a remarkable laminated detrital sequence associated with an ancient position of the Isère glacier in the "Cluse des Hôpitaux". Several U/Th alpha dates undertaken 20 years ago are revised here. Five new U/Th ICP MS dates on speleothems frame the detrital complex, providing a terminus post quem (TPQ) and a terminus ante quem (TAQ) to this glacial invasion. The TPQ is dated 87.3 ± 3.9 ka (MIS 5.b.c) and the TAQ is dated 11.6 ± 4.3 ka (MIS 1). The laminated detrital sequence is thus better constrained and the glacial invasion could have only been deposited during MIS 4 (locally Würm II, first max) or MIS 2 (Last Glacial Maximum or locally Würm IV) stages. The cave Sous les Sangles has a strategic position to constrain maximum glacial extension during the last cold stages of the Quaternary in the French Alps.Nouvelles contraintes chronologiques sur le cône fluvio glaciaire intrakarstique de la grotte Sous les Sangles (Bas Bugey, France). L'âge de la dernière extension maximale glaciaire des Alpes nord occidentales françaises est toujours discutée. En position latérale aux anciennes vallées glaciaires, des conduits karstiques ont fonctionné en pertes juxtaglaciaires durant les phases de retrait glaciaire et constituent des enregistreurs pertinents de ces phases glaciaires. Dans le Bas Bugey (Ain, France), la grotte Sous les Sangles abrite une remarquable séquence détritique laminées associée à une position du glacier de l'Isère dans la cluse des Hôpitaux. Des datations entreprises il y a 20 ans (U/Th alpha) sont ici révisées. Cinq nouvelles dates U/Th MC ICP MS ont été entreprises sur des spéléothèmes encadrant l'ensemble détritique offrant un terminus post quem et un terminus ante quem à cette invasion glaciaire. Le TPQ est daté à 87,3 ± 3,9 ka (MIS 5) et le TAQ est daté à 11.6 ± 4.3 ka (MIS 1). La série détritique laminée est ainsi mieux contrainte et l'invasion glaciaire ne peut se situer que dans les stades MIS 4 (localement Würm ancien) ou MIS 2 (localement Würm récent). La grotte Sous les Sangles confirme sa position stratégique pour contraindre l'extension maximale glaciaire au cours des derniers stades froids du Quaternaire