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The study of paleo shorelines, particularly of those formed during the late Quaternary, provides robust insights into past climate variability. Advances in surveying techniques and chronological methodologies have dramatically improved the inter-comparability of regional and basin-wide paleo shoreline surveys. However, these advances have been applied unevenly across the globe. This is especially true in southwestern Madagascar, where, in the 1960s and 1970s, emerged Pleistocene beach and reef facies were first described in detail and dated to Marine Isotope Stage (MIS) 5a using U–Th alpha activity counting by french geologist René Battistini. Now, 50 years on, no further analysis of the coastal sequence has been made. In this study, we present an updated late Pleistocene coastal evolution model for the southwestern Madagascar coast. Utilizing a combination of Structure-from-Motion/Multi-View Stereo techniques and differential Global Navigation Satellite System surveys, we have created five high-resolution 3D outcrop reconstructions that have, in turn, been chronologically constrained using 10 U-series ages from both in situ and reworked coral samples. Our data suggest that the emerged reef was deposited during MIS 5e (∼125 ka), then was covered by intertidal and beach sediment (including redeposited coral clasts of MIS 5e age), and finally capped off by thick eolianites. This sequence would suggest that the local sea level must have remained stable throughout MIS 5e in order to allow for the progradation of both the beach and reef environments.

Meaningful analysis of uranium‐series isotopic disequilibria in basaltic lavas relies on the use of complex forward numerical models like dynamic melting (McKenzie, 1985, https://doi.org/10.1016/0012-821x(85)90001-9) and equilibrium porous flow (Spiegelman & Elliott, 1993, https://doi.org/10.1016/0012-821x(93)90155-3). Historically, such models have either been solved analytically for simplified scenarios, such as constant melting rate or constant solid/melt trace element partitioning throughout the melting process, or have relied on incremental or numerical calculators with limited power to solve problems and/or restricted availability. The most public numerical solution to reactive porous flow, UserCalc (Spiegelman, 2000, https://doi.org/10.1029/1999gc000030) was maintained on a private institutional server for nearly two decades, but that approach has been unsustainable in light of modern security concerns. Here, we present a more long‐lasting solution to the problems of availability, model sophistication and flexibility, and long‐term access in the form of a cloud‐hosted, publicly available Jupyter notebook. Similar to UserCalc, the new notebook calculates U‐series disequilibria during time‐dependent, equilibrium partial melting in a one‐dimensional porous flow regime where mass is conserved. In addition, we also provide a new disequilibrium transport model which has the same melt transport model as UserCalc, but approximates rate‐limited diffusive exchange of nuclides between solid and melt using linear kinetics. The degree of disequilibrium during transport is controlled by a Damköhler number, allowing the full spectrum of equilibration models from complete fractional melting (Da=0) to equilibrium transport (Da=∞). Access the full executable Jupyter notebook version of this manuscript here .

Sarıhıdır travertines and associated manganese mineralization are located in an area known as the Central Anatolian Volcanic Province (CAVP). The topic of the study, the Sarıhıdır manganese mineralization, was deposited in association with fault zones in this tectonically-active region. Paragenesis of the mineralization includes pyrolusite, rhodochrosite and goethite with gangue minerals of calcite and quartz observed. Diagrams drawn using major oxide and trace elements like Fe–Mn–(Ni+Co+Cu)×10, Fe-Si×2-Mn, Co/Ni vs Cu+Co+Ni, Si/Al, Na/Mg, Fe/Ti vs. Al/(Al+Fe+Mn), Co+Ni/As+Cu+Mo+Pb+V+ Zn and FeO–MnO2–10× MgO show the mineralization found in the region is sourced in the hydrothermal field. The low total REE values and LREE>HREE ratio indicate the effect of hydrothermal solutions. Additionally, Ce, Eu and Ceanom anomalies indicate the source of the mineralization was hydrothermal with oxic-anoxic formation environment. The Y/Ho ratio is mean 30.1 which is lower compared to hydrothermal fluids. Mean values are δ13CPDB 12.24‰ and δ18OPDB 10.87‰ indicating deposition from fluids with a deep CO2 component. In conclusion, the Sarıhıdır mineralization and travertine were determined to have formed about 50–53 ka (Upper Pleistocene) based on U-series age data, as fault-controlled, hydrothermal-sourced mineralization.

The Tierra Blanca (TB) eruptive suite comprises the last four major eruptions of Ilopango caldera in El Salvador (≤45 ka), including the youngest Tierra Blanca Joven eruption (TBJ; ∼106 km3): the most voluminous event during the Holocene in Central America. Despite the protracted and productive history of explosive silicic eruptions at Ilopango caldera, many aspects regarding the longevity and the prevailing physicochemical conditions of the underlying magmatic system remain unknown. Zircon 238U‐230Th geochronology of the TB suite (TBJ, TB2, TB3, and TB4) reveals a continuous and overlapping crystallization history among individual eruptions, suggesting persistent melt presence in thermally and compositionally distinct magma reservoirs over the last ca. 80 kyr. The longevity of zircon is in contrast to previously determined crystallization timescales of, Plain Language Summary: The collapse of a volcano edifice into its shallow magma chamber can produce one of the most dangerous single events in nature, known as a caldera‐forming eruption. The TBJ eruption in El Salvador is of this kind and occurred around 1,500 years ago, having a profound impact on Maya societies. Because of this, it is crucial to understand the inner workings of caldera‐forming eruptions to assess volcanic risks and their mitigation. Beneath Ilopango caldera, the micrometer‐sized radioisotopically datable mineral zircon grew within different storage levels of a silica‐rich magma reservoir suggesting continuous melt presence for up to ca. 80,000 years prior to eruption. The time information given by zircon contrasts with that extracted from other, more abundant minerals from the same rocks (, Key Points: U‐Th zircon ages for the last four explosive eruptions of Ilopango caldera reveal a long‐lived magma reservoir (>80 kyr). Contrasting residence times for major minerals and zircon suggest extraction of zircon along with evolved melt from crystal residue. Melt extraction from vertically extensive, thermally zoned magma reservoir., Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659

A precisely dated speleothem isotope record from the Sieben Hengste cave system, Switzerland, reveals a Last Interglacial (LIG) climate optimum centred at 128.1 ± 1.2 ka. The oxygen isotope signal is consistent with a temperature-dominated record and shows a strong correlation with the modelled Greenland d18O signal. The comparison with speleothems formed during the Last Glacial Maximum (LGM) in the same cave indicates a 4e5‰ difference in d18O between peak LIG and peak LGM conditions, suggesting peak LIG temperatures being up to 3 C higher than the Holocene average. Pollen extracted from the stalagmite indicates a vegetation response delayed by up to 3 ka with maximum pollen concentrations recorded at 125 ± 2.2 ka. Our results support a regional vegetation dominated by thermophile tree species including Corylus (hazel), Quercus robur-type (oak), Ulmus (elm), Tilia (lime tree) and Hedera (ivy), consistent with slightly warmer conditions than today. Despite the relatively low pollen concentration, the speleothem-based pollen spectra are consistent with regional pollen assemblage zones from paleolake sediments and provide the first direct paleovegetation evidence of thermophilization during the LIG at high altitudes in the Alps. ISSN:0277-3791

Based on previous radiocarbon and U-series (Diffusion/Adsorption) dating of bone samples, the Middle Palaeolithic has been thought to persist at Gruta da Oliveira until ∼37 thousand years (ka) ago. New U-series ages for stratigraphically constraining speleothems, coupled with new luminescence ages for sediment infill, show that the site’s ∼6 m-thick archaeological stratigraphy dates entirely within a

EASPEBIOmEAGROSUP; Pedogenic carbonates (calcretes) have often been proposed as possible markers of the pedogenetic processes in soils under semi-arid climate. However, precise chronological constraints on, their formation are required in order to investigate the climatic and paleo-environmental conditions that prevailed during and after their formation, and to improve our understanding of the, physical and chemical conditions that promoted their development and preservation. Moreover, these authigenic calcium carbonate precipitates provide us with an interesting test of the U-Th radioactive disequilibrium dating method, the reliability of which has been demonstrated extensively in aragonitic corals and calcitic continental speleothems, but which remains much more questionable in highly porous, chemically and mineralogically complex media such as soil profiles. We report here U-238-U-234-Th-230 radioactive disequilibrium analyses measured by Thermo-Ionization Mass Spectrometry in calcretes from two sites in southwest India. Since calcretes are impure carbonates mixed with various amounts of parent rock and weathered minerals, all ages must be computed using the isochron technique, involving the extraction of several coeval subsamples from the same soil horizon and U-Th analyses after total dissolution (TSD) method, in order to correct for the detrital component. Th-232 is usually used as index of the detrital contamination, and the isochron age is derived from the isotopic composition (Th-230/U-238; U-234/U-238) of the pure authigenic carbonate end-member of the mixing line. Our results show that each set of samples taken from decimetric blocks is characterized by a well-defined isochron line in a 3-D Osmond diagram (Th-232/U-238; Th-230/U-238; U-234/U-238). The regression lines obtained for most of the samples show probabilities of fit satisfying the mathematical assumptions of the isochron model (in most cases 0.05), and mean square weighted deviations (MSWD) values around 1. The compositions of the end-members are highly variable between the different isochrons, both for the carbonate phase, indicating various ages of cristallisation, and for the detrital phase, indicating various origins and compositions. Notably, our data demonstrate that the detrital component is in all cases out of secular equilibrium, by contrast with the standard paradigm of "dirty carbonate" dating, which is based on the assumption of average continental crust Th/U elemental ratio, and secular equilibrium values of the ((Th-230/U-238) and (U-234/U-238) ratios. At the first site (Coimbatore), we obtain U-Th ages between 304 +/- 38 ka and 44 +/- 2.9 ka (2 sigma) from the base to the top of the profile. These suggest discontinuous precipitation of the different fades in good agreement with micro morphological observations. At the second study site (Gundlupet), the carbonate nodules sampled from two different profiles, yield consistent ages of 200 ka, which suggests that precipitation of nodular carbonate occurred across the entire pediment toposequence during a single event. Surprisingly, in mere contradiction with the standard model of impure carbonate dating, two puzzling samples display "vertical isochrons", i.e., variable Th-232/U-238 without any variation of the Th-230/U-238 and U-234/U-238 ratios. Such patterns require extremely high Th-232/U-238 ratios, in an as yet unidentified detrital phase. Taken at face value, these results suggest that no clear correlation can be inferred between the precipitation of these pedogenic carbonates and major orbitally-driven climate variations recorded in other archives during the last glacial/interglacial cycles.

International audience; The present study reports data on CO2-rich geothermal waters and their associated carbonate deposits from the SW part of the Permian Lodève Basin (South of France). Both waters and carbonates are enriched in 226Ra, with activities up to 2.2 Bq/L and 3.5 Bq/g respectively. A series of carbonate samples precipitated around the studied wells since 1990 were dated through the 226Ra-210Pb and 228Ra-228Th methods, and the results are discussed in a new Concordia diagram. While both methods give comparable dates for many samples, Ra-Pb ages are sometimes much older than Ra-Th ages. We propose that these discrepancies result from the adsorption of 222Rn daughter nuclides in such a Rn-rich environment. The (228Ra/226Ra)0 activity ratios calculated at the time of deposition are remarkably constant for about 12 years, suggesting the presence of a steady-state aquifer. The low (228Ra/226Ra)0 ratios (0.348 ± 0.008) are best explained if most of the Ra derives from the Cambrian carbonate series (mainly dolostone) underlying the Permian Basin, which have low Th/U and similar (228Ra/226Ra) ratios. This study suggests that Ra and other alkaline-earth elements do not necessarily originate from the rocks surrounding the deep geothermal reservoir, but rather may be introduced into the CO2-rich water during its transfer towards the surface and interaction with carbonate rocks.

Long-term leaching experiments were done using aquifer rocks of the Aquitaine Basin, ranging in age from Santonian to upper Eocene. Leachates were sampled after one hour, one day, one week, and one month, and were analyzed for U concentrations and activity ratios. Overall, U contents in the leachate decreased with increasing time. U activity ratios were characteristic of each aquifer rock. Only slight variations, when present, were found between the one-week and the one-month leachates. In most cases, the short-lived leachates (one hour, one day) displayed U activity ratios closer to the equilibrium value.

On continental margins, oxidation of methane-rich fluids from the sediment often leads to formation of authigenic carbonate pavements on the seafloor. The biogeochemical processes involved during this carbonate precipitation are increasingly understood, but little is known about the duration or mode of carbonate crust formation. Here, we report uranium and thorium concentrations and isotope compositions for a set of 14 samples drilled across an authigenic carbonate pavement, which provide the first stratigraphy for a cold-seep carbonate crust. The 5.5-cm thick crust (NL7-CC2) was collected by submersible on the Nile deep-sea fan in an area of active fluid venting. U-Th analyses must be corrected for initial Th and measurement of co-existing sediments indicates the presence of both scavenged and detrital initial 230Th, which must be considered during this correction. The calculated 230Th/U age-depth profile for NL7-CC2 provides evidence for continuous downward carbonate precipitation at the studied location over the last ~ 5000 years. Three distinct phases can be distinguished from top to bottom with average growth rates of ~ 0.4, 5 and 0.8 cm/kyr, respectively, corresponding to carbonate precipitation rates ranging from ~ 7 to 92 μmol m2 h- 1 (rates consistent with previous estimates). High-resolution δ13C profiles [Gontharet, S., Pierre, C., Blanc-Valleron, M.-M., Rouchy, J.M., Fouquet, Y., Bayon, G., Foucher, J.P., Woodside, J., Mascle, J., The Nautinil Scientific Party, 2007. Nature and origin of diagenetic carbonate crusts and concretions from mud volcanoes and pockmarks of the Nile deep-sea fan (eastern Mediterranean Sea). Deep Sea Res. II 54, 1292-1311] and major elements across NL7-CC2 show that the variations in carbonate precipitation rates were also accompanied by changes in carbonate mineralogy and fluid composition. We suggest that these changes primarily reflect modification of the diagenetic environment, i.e. a progressive depletion of dissolved sulphate through anaerobic oxidation of methane, caused by the initial carbonate crust formation and the resulting reduction in bioirrigation. Overall, U-Th dating of cold seep carbonates offers a promising tool to bring new insights into biogeochemical processes at cold seeps and to assess the timing and duration of fluid venting on continental margins. © 2008 Elsevier B.V. All rights reserved.

International audience; We report here U-series and trace element data for an olivine-melilitite lava flow, erupted in 1957 in the Virunga volcanic field and known as the Mugogo eruption. Petrological and geochemical data show that the Mugogo magma represents a primary mantle melt, derived from a low degree of melting of a metasomatised mantle source. It is highly enriched in very incompatible trace elements (e.g. more than 300-fold compared to primitive mantle for Th), with a distinctly lower enrichment in Rb, Ba and Sr. The high Th/U and low (230Th/232Th) ratios (4.4 and 0.750, respectively, with a (230Th/238U) ratio of 1.09) are close to the values found for the Nyamuragira basanites. But the most striking feature is the very low (226Ra/230Th) ratio of 0.48, the lowest ever measured in a mafic volcanic rock. The most probable origin of this Ra deficit is the presence of phlogopite (having a high Ra partition coefficient) in the lithospheric mantle, either as a residual phase during low-degree isobaric melting (in batch-melting or a diffusion-controlled melting models), or in a phlogopite-bearing upper mantle through which the melt migrates and equilibrates (in an equilibrium porous flow model commonly used to describe adiabatic melting). The disequilibrium pattern (230Th) > (238U) > (210Pb) ≫ (226Ra), reversed compared to the pattern observed in the Oldoinyo Lengai natrocarbonatite, suggests that a carbonatite melt might have been involved to explain the Ra deficit. We thus discuss the possibility of an early separation of a Ra-enriched carbonate melt either from the olivine-melilitite melt or from a carbonated mantle source, followed by the production of a low-degree melt of olivine-melilitite composition, but the lack of available experimental, petrological and geochemical evidences makes this process somewhat speculative at present. Further studies of recent (

International audience; U-series studies in oceanic basalts are critical for understanding melting and melt extraction in the Earth's mantle. The combined results of a detailed geochemical study of melting and melt extraction at Theistareykir, northern Iceland, provide a strong case for melt extraction via channeled melt flow at an active spreading ridge. It has often been argued, however, that widely used melting and melt extraction models, which simulate channeled melt extraction (i.e. fractional and/or dynamic melting), can only partially explain the global U-series systematics in oceanic basalts. As a consequence, more complicated models have been invoked, which suggest different styles of melt extraction at different depths/pressures in the mantle, so-called “two-porosity models”. Alternatively, diffusion-controlled mechanisms have been proposed. Here we show that U–Th–Pa–Ra systematics in oceanic basalts can indeed be explained by models where melt transport occurs without chemical equilibrium between melt and solid when variations in all three critical melting parameters (residual porosity, upwelling rate of the solid mantle and melt velocity) are taken into account. Melting at ridges requires systematic variation of at least two critical melting parameters, most likely upwelling and melt extraction rate. Melts generated with increasing lateral distance to the ridge axis are generated with slower upwelling rates and are extracted with lower velocities than melts created closer to the ridge axis. Melting at ocean islands, on the other hand, can successfully be explained by variations in upwelling rate only. Global U-series systematics in OIB originate from superimposed global variations in upwelling velocity due to different buoyancy fluxes and from local variation in upwelling velocity as a function of radial distance to the plume center. The model proposed here is consistent with other geochemical data for oceanic basalts and strongly supports melt extraction via high-porosity channels as a general means of melt extraction from the Earth's upper mantle.

Une première chronologie des occupations moustériennes de la grotte des Teixoneres (province de Barcelone, Espagne) a été établie grâce à la datation uranium-thorium de deux planchers stalagmitiques encadrant les niveaux moustériens. Des âges compris entre 13 et 17 ka, après correction du 230Th détritique, ont été déterminés sur le plancher supérieur, indiquant que le dépôt de ces spéléothèmes pourrait alors correspondre à l'oscillation climatique Bølling-Allerød. Le plancher inférieur a pour sa part été attribué au stade isotopique 5.3. A first chronology of the Mousterian levels of the Teixoneres cave (province of Barcelona, Spain) was established using U-series dating method on two stalagmitic flowstones located respectively above and under the mousterian levels. For the upper one, ages range from 13 to 17 ka, after correction of the detritic 230Th, indicating that the deposit of these speleothems could then correspond to the Bølling-Allerød oscillation. The lower flowstone was deposited during the oxygen isotopic stage 5.3.

Travertines overlying and impregnating Allier terraces have been dated and confirm previous research that they register past spring activity for the last 250 kyr New U-senes ages demonstrate that surface travertines were not only mainly deposited under Interglacial but also under Interstadial conditions Detailed reconstruction of the Holocene fluvial incision suggests that the position of surface travertine precipitation at terrace scarps bear a relationship with floodplain incision (terrace formation) Unfortunately the temporal resolution of current U-senes dates is too coarse to allow a detailed reconstruction for older cycles. Travertine dating with 14C has proved to be unreliable as a result of the contamination with fossil carbonates, Les travertins qui recouvrent et imprègnent les terrasses fluviatiles de l'Allier ont été dates par U/Th. Ces résultats confirment les travaux antérieurs et montrent que ces dépôts ont enregistré l'activité des sources hydrothermales depuis environ 250 ka BP. Les nouvelles datations U/Th montrent que les travertins ne se sont pas formés uniquement pendant les interglaciaires mais aussi au cours des épisodes interstadiaires. Une reconstruction détaillée de l'incision de la vallée de l'Allier au cours de l'Holocène suggère que la précipitation de dépôts travertineux sur le talus de la terrasse de 10 m est en rapport avec l'incision de la vallée actuelle de l'Allier. Malheureusement, la precision des âges détermines par la méthode U/Th est trop faible pour permettre une reconstitution détaillée pour les cycles plus anciens. La datation des travertins par le I4C a montré que cette technique n'était pas fiable en raison de leur contamination par des carbonates fossiles., Veldkamp Antonie, Kroonenberg Salomon, Heijnis Henk, Van Den Berg Van Saparoea Rob. The suitability of dated travertines as a record of fluvial incision: Allier (France) floodplain dynamics during the Late quaternary [ Validité des travertins datés pour la reconstitution de l'histoire de l'incision fluviatile. La dynamique de la nappe alluviale de l'Allier pendant le Quaternaire récent.]. In: Quaternaire, vol. 15, n°1-2, 2004. Fluvial Archives Group. Clermond-Ferrant 2002. pp. 159-165.