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International audience; The Main Ethiopian Rift, in (East Africa), is a classic example where to analyse the interplay between tectonics and magmatic activity during rifting. This continental rift records indeed all different stages of rift evolution and is characterised by significant volcanic activity spanning from the Oligocene to present. However, despite recent improvements in the knowledge of single volcanic centres thanks to recent scientific projects (e.g., RiftVolc), volcanic activity in many rift sectors still remains poorly documented. In this work we provide new constraints on the timing, evolution and characteristics of the poorly documented volcanic activity at the southern termination of the Main Ethiopian Rift. We present new fieldvolcanological, petrographic, geochemical and geochronological data, together with and the results of a statistical analysis of the distribution of volcanic vents from remote sensing, together with petrographic, geochemical and geochronological analyses on the collected samples, for the Mega and the Dilo-Dukana volcanic fields, near the Kenya-Ethiopia border. In line with previous works, our data delineate the occurrence of two distinct groups of rocks: 1) a group of subalkaline basalts, observed only in the Dilo-Dukana volcanic field, forming a Pliocenic lava basement during Pliocene, faulted during an important rifting phase; 2) a group of alkaline basalts, characterising the Quaternary activity in both areas and sampled from Quaternary volcanic vents or from their associated lava flows, that are associated to several, mainly monogenetic volcanic centres. The products of this activity lay in discordance above the lava platform and seal the rift-related faults. Ar/Ar dating allowed to constrain the large basal lava plateau to 3.7 Ma, whereas the youngest volcanic activity characterizing the two areas dates back to 134 ka for Dilo-Dukana and Holocene age for Mega volcanic field. Interestingly, no direct relations are observed between the Pliocene, roughly N-S major boundary faults of the Ririba Rift and the NE-SW structures feeding the Quaternary volcanic activity, indicating a non-correlation between recent volcanism and rifting in the area. Conversely, our analysis suggests a major influence exerted by deep, inherited structures on the distribution of the recent volcanic vents under a complex, local stress field resulting from a major episode of reorganization of extensional structures in the region, recording the history of related to rift propagation and abandonment.

Continental rift systems commonly form by progressive growth of isolated rift segments that interact and link, eventually evolving into continuous zones of deformation. Propagation and interaction between adjacent rift segments are important features of rifting, influencing the distribution of volcanoes, seismicity and sedimentary basins. The process also controls the morphology of the rift at breakup with possible implications for the segmentation of mid-ocean ridges. However, how the punctuated, discontinuous zones of extension propagate and interact to form a continuous rift system and how the complex zones of interaction evolve remain poorly documented and understood. The Turkana depression in East Africa is an ideal place where to analyse these processes: within this NW-SE lowland, two major sectors of the East African rift, the Kenyan and Ethiopian rifts, interact giving rise a complex, >300km-wide region of faulting and volcanic activity. In this work, we present geological-structural, geochemical and geochronological data from the poorly documented Ririba rift (South Ethiopia), which is part of the complex, wide region of volcano-tectonic activity in the Turkana depression. This rift is of special interest because it is commonly accepted to represent the southernmost, youngest and less-developed sector of the Ethiopian Rift, having formed from recent southward propagation of this rift into the Turkana depression. Our data confirm the Ririba rift formed from the southward propagation of the Ethiopian rift during the Pliocene but this propagation was short-lived and aborted close to the Pliocene-Pleistocene boundary, when rift-related deformation ceased. Integration of seismicity data with new numerical models indicates that abandonment of laterally offset and overlapping tips of the Ethiopian and Kenyan rifts resulted from progressive focusing of the tectonic and magmatic activity into an oblique, throughgoing rift zone which directly connects the rift sectors. These sectors link by near pure extension without forming the strike-slip transfer faults interpreted as precursors of oceanic transform faults

International audience; The trace-element geochemistry of speleothems is becoming increasingly used for reconstructing palaeoclimate, with a particularemphasis on elements whose concentrations vary according to hydrological conditions at the cave site (e.g. Mg, Sr, Baand U). An important step in interpreting trace-element abundances is understanding the underlying processes of their incorporation.This includes quantifying the fractionation between the solution and speleothem carbonate via partition coefficients(where the partitioning (D) of element X (DX) is the molar ratio [X/Ca] in the calcite divided by the molar ratio [X/Ca] in theparent water) and evaluating the degree of spatial variability across time-constant speleothem layers. Previous studies of howthese elements are incorporated into speleothems have focused primarily on stalagmites and their source waters in naturalcave settings, or have used synthetic solutions under cave-analogue laboratory conditions to produce similar dripstones. However,dripstones are not the only speleothem types capable of yielding useful palaeoclimate information. In this study, weinvestigate the incorporation of Mg, Sr, Ba and U into a subaqueous calcite speleothem (CD3) growing in a natural cave poolin Italy. Pool-water measurements extending back 15 years reveal a remarkably stable geochemical environment owing to thedeep cave setting, enabling the calculation of precise solution [X/Ca]. We determine the trace element variability of ‘modern’subaqueous calcite from a drill core taken through CD3 to derive DMg, DSr, DBa and DU then compare these with publishedcave, cave-analogue and seawater-analogue studies. The DMg for CD3 is anomalously high (0.042 ± 0.002) compared to previousestimates at similar temperatures (~8 °C). The DSr (0.100 ± 0.007) is similar to previously reported values, but datafrom this study as well as those from Tremaine and Froelich (2013) and Day and Henderson (2013) suggest that [Na/Sr] mightplay an important role in Sr incorporation through the potential for Na to outcompete Sr for calcite non-lattice sites. DBa inCD3 (0.086 ± 0.008) is similar to values derived by Day and Henderson (2013) under cave-analogue conditions, whilst DU (0.013 ± 0.002) is almost an order of magnitude lower, possibly due to the unusually slow speleothem growth rates(

The Mediterranean region and the Levant have returned some of the clearest evidence of a climatically dry period occurring around 4200 years ago. However, some regional evidence is controversial and contradictory, and issues remain regarding timing, progression, and regional articulation of this event. In this paper, we review the evidence from selected proxies (sea-surface temperature, precipitation, and temperature reconstructed from pollen, δ18O on speleothems, and δ18O on lacustrine carbonate) over the Mediterranean Basin to infer possible regional climate patterns during the interval between 4.3 and 3.8 ka. The values and limitations of these proxies are discussed, and their potential for furnishing information on seasonality is also explored. Despite the chronological uncertainties, which are the main limitations for disentangling details of the climatic conditions, the data suggest that winter over the Mediterranean involved drier conditions, in addition to already dry summers. However, some exceptions to this prevail – where wetter conditions seem to have persisted – suggesting regional heterogeneity in climate patterns. Temperature data, even if sparse, also suggest a cooling anomaly, even if this is not uniform. The most common paradigm to interpret the precipitation regime in the Mediterranean – a North Atlantic Oscillation-like pattern – is not completely satisfactory to interpret the selected data.

A detailed geomorphological survey was undertaken in the area of Puerto Deseado (Santa Cruz Province, Argentina) to reconstruct the Relative Sea-level (RSL) position during the Last Interglacial highstand. The presence of active and well-preserved abrasive notches and inner margins of terraces related to the MIS5e and to the Holocene, measured with DGPS, allowed to accurately estimate the RSL change from the present to the MIS5e highstand at ca. 21 m. The geomorphological and geochronological analyses support the notion of the presence of a significant regional tectonic uplift in the Atlantic Patagonia, which can be locally estimated at ca. 0.12 mm/yr.

Ground wedge structures of cryogenic origin are common in the Quaternary sediments along the coast of the Patagonia, and their formation is related to climatic cold events experienced by this area in the Late Quaternary. The infilling sediments of two wedges generations were analyzed in the area of Puerto Deseado. Bulk chemistry (major elements), X-ray diffraction (XRD), morphoscopic observations with Scanning Electronic Microscope (SEM) and chemical analyses of volcanic glass shards were undertaken to provide indications about infilling sediment provenience, along with chronological constraint for wedge formation. Bulk chemistry and XRD patterns indicate a significant SiO2- enriched composition of the sediment infilling compared to the most of the loess deposits of the North Argentina and the present day dust originated in Patagonia. This was interpreted as due to the nature of the bedrock present over the Deseado Massif. SEM morphoscopic characteristics of glass shards evidence typical aeolian reworking features, with impact structures and indented edges of the volcanic fragments. Chemical analyses of the glass shards indicate that they were probably generated by the H0 eruption (17,300-17,400 cal yr BP) of the Hudson volcano. Volcanological data indicate that H0 eruption dispersed toward NE, but volcanic glasses were available for reworking due to a WNW component in the western wind direction. Over the Deseado Massif structural high the glass shards mixed with sediments enriched in SiO2, and were eventually deflated further to SE reaching the present coastal area and infilling the frost cracks. The age of the glass shards (17,300-17,400 cal yr BP) and that of the sandy layer affected by cryogenic structures (14,670±750 yr BP) well constrain to the Late Glacial both wedge generations. RESUMEN Las cuñas de hielo son estructuras comunes en sedimentos cuaternarios a lo largo de la costa patagónica, y su formación está relacionada con eventos climáticos fríos experimentados en esta área en el Cuaternario Tardío. Se analizaron sedimentos que rellenan dos generaciones de cuñas de hielo en la zona de Puerto Deseado. Análisis químicos de elementos mayores, difractometría de rayos X (DRX), observaciones con microscopio electrónico de barrido (SEM) y análisis químico de fragmentos de vidrio volcánico contenidos en el sedimento que rellena las cuñas proporcionaron información sobre la precedencia del relleno, además de inferir antecedentes cronológicos sobre su formación. La composición química del sedimento y la difracción de rayos X indican una composición enriquecida en SiO2 en comparación con la mayoría de los depósitos de loess del norte de Argentina y el polvo actual originado en la Patagonia. Esto fue interpretado como producto de la influencia de las rocas que constituyen el macizo del Deseado. Las características morfológicas de los fragmentos de vidrio evidencian rasgos típicos de retrabajo eólico, con presencia de estructuras de impacto y bordes dentados. Los análisis químicos de los fragmentos de vidrio son compatibles con un origen en la erupción H0 (17.300-17.400 cal yr BP) del volcán Hudson. Datos volcanológicos indican que la erupción H0 originó una pluma de dispersión hacia el NE. El material volcánico dispersado por esta erupción quedó disponible para ser retrabajado por una componente WNW de los vientos del W dominantes en la zona. Sobre el macizo del Deseado, los fragmentos de vidrio se mezclaron con sedimentos ricos en SiO2 y fueron adicionalmente, enriquecidos en este elemento hasta alcanzar el área de costa actual, rellenando las cuñas de hielo. La edad de los fragmentos de vidrio (17.300-17.400 cal yr BP) y de la capa arenosa afectada por las estructuras criogénicas (14.670±750 años BP) limitan al glacial tardío la formación de ambas generaciones de cuñas.