Morphological controls on the dynamics of carbonate landscapes under a mediterranean climate          下载免费PDF全文

Franck Thomas  Vincent Godard  Olivier Bellier  Esmaeil Shabanian  Vincent Ollivier  Lucilla Benedetti  Magali Rizza  Nicolas Espurt  Valéry Guillou  Fabrice Hollender  Stéphane Molliex  ASTER Team 《地学学报》2017,29(3):173-182

The influence of the morphological setting on the denudation of carbonate landscapes and the respective contributions of mechanical and chemical weathering processes are still debated. We have addressed these questions by measuring ³⁶Cl concentrations in 40 samples from the Luberon mountain, SE France, to constrain the denudation of various landscape elements. We observe a clear contrast between the local denudation rates from the flat summit surface, clustered around 30 mm/ka, and the basin‐average denudation rates across the flanks, ranging from 100 to 200 mm/ka. This difference highlights the transient evolution of the range, whose topography is still adjusting to previous uplift events. Such a pattern also suggests that carbonate dissolution is not the only driver of denudation in this setting, which appears to be significantly controlled by slope‐dependent processes.  相似文献   

A complete hydro-climate model chain to investigate the influence of sea surface temperature on recent hydroclimatic variability in subtropical South America (Laguna Mar Chiquita,Argentina)     

Magali Troin  Mathieu Vrac  Myriam Khodri  Daniel Caya  Christine Vallet-Coulomb  Eduardo Piovano  Florence Sylvestre 《Climate Dynamics》2016,46(5-6):1783-1798

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Macrobenthic community response to copper in Shelter Island Yacht Basin, San Diego Bay, California     

Neira C  Mendoza G  Levin LA  Zirino A  Delgadillo-Hinojosa F  Porrachia M  Deheyn DD 《Marine pollution bulletin》2011,62(4):701-717

We examined Cu contamination effects on macrobenthic communities and Cu concentration in invertebrates within Shelter Island Yacht Basin, San Diego Bay, California. Results indicate that at some sites, Cu in sediment has exceeded a threshold for “self defense” mechanisms and highlight the potential negative impacts on benthic faunal communities where Cu accumulates and persists in sediments. At sites with elevated Cu levels in sediment, macrobenthic communities were not only less diverse but also their total biomass and body size (individual biomass) were reduced compared to sites with lower Cu. Cu concentration in tissue varied between species and within the same species, reflecting differing abilities to “regulate” their body load. The spatial complexity of Cu effects in a small marina such as SIYB emphasizes that sediment-quality criteria based solely on laboratory experiments should be used with caution, as they do not necessarily reflect the condition at the community and ecosystem levels.  相似文献   

Disappearance of a crater lake: implications for potential explosivity at Soufrière volcano,St Vincent,Lesser Antilles     

Nicolas Fournier  Magali Moreau  Richard Robertson 《Bulletin of Volcanology》2011,73(5):543-555

Soufrière volcano in St Vincent, West Indies, is one of the most active volcanoes in the Eastern Caribbean with at least six eruptions since 1718 AD, the latest of which occurred in 1979. Prior to the 1979 eruption, the active crater hosted deep-water lakes during periods of repose, which were always replenished within a few years after the eruptions. In 1979, the crater was filled with 10⁸ m³ of fragmental material and, despite constant precipitation, has remained virtually dry ever since, with the exception of a small shallow pond. A resistivity survey was conducted in July 2006 to investigate groundwater occurrence in the crater. Results from the resistivity data inversion on several 2-D profiles show a shallow horizontal conductor across the crater floor, consistent with a water-saturated aquifer. They also show that the post-1979 pond, currently present in the crater lake is in fact an outcropping part of the groundwater water reservoir. The reservoir water table is ∼28 m above the pre-1979 lake level and reflects mass equilibrium in the system where constant seepage underground balances the meteoric recharge. We suggest that the groundwater body extends at depth to the bottom of the pre-1979 crater lake, either due to a significant structural discontinuity or because of a reduction of permeability at depth. The estimated maximum volume of water stored underground is 10–30 × 10⁶ m³ and energy considerations indicate that 2.4–7.3 × 10¹⁰ kg of magma would potentially be sufficient to vaporise the whole groundwater body. This amount of magma represents only 13–41% of the mass erupted during the last eruption in 1979 which was the smallest of the past 3 eruptions (1902, 1971–72, 1979). Since explosive phreatic or phreatomagmatic eruptions at Soufrière seem to be linked to magma-water interaction within confined space, the results from this survey suggests that phreatic or phreatomagmatic activity is a distinct possibility during future magma intrusion in the summit area, despite the apparent disappearance of water in the summit crater.  相似文献   

Two successive phases of ultrahigh temperature metamorphism in Rogaland,S. Norway: Evidence from Y‐in‐monazite thermometry          下载免费PDF全文

Antonin T. Laurent  Stephanie Duchene  Bernard Bingen  Valerie Bosse  Anne‐Magali Seydoux‐Guillaume 《Journal of Metamorphic Geology》2018,36(8):1009-1037

In Rogaland, South Norway, a polycyclic granulite facies metamorphic domain surrounds the late‐Sveconorwegian anorthosite–mangerite–charnockite (AMC) plutonic complex. Integrated petrology, phase equilibria modelling, monazite microchemistry, Y‐in‐monazite thermometry, and monazite U–Th–Pb geochronology in eight samples, distributed across the apparent metamorphic field gradient, imply a sequence of two successive phases of ultrahigh temperature (UHT) metamorphism in the time window between 1,050 and 910 Ma. A first long‐lived metamorphic cycle (M1) between 1,045 ± 8 and 992 ± 11 Ma is recorded by monazite in all samples. This cycle is interpreted to represent prograde clockwise P–T path involving melt production in fertile protoliths and culminating in UHT conditions of ~6 kbar and 920°C. Y‐in‐monazite thermometry, in a residual garnet‐absent sapphirine–orthopyroxene granulite, provides critical evidence for average temperature of 931 and 917°C between 1,029 ± 9 and 1,006 ± 8 Ma. Metamorphism peaked after c. 20 Ma of crustal melting and melt extraction, probably supported by a protracted asthenospheric heat source following lithospheric mantle delamination. Between 990 and 940 Ma, slow conductive cooling to 750–800°C is characterized by monazite reactivity as opposed to silicate metastability. A second incursion (M2) to UHT conditions of ~3.5–5 kbar and 900–950°C, is recorded by Y‐rich monazite at 930 ± 6 Ma in an orthopyroxene–cordierite–hercynite gneiss and by an osumilite gneiss. This M2 metamorphism, typified by osumilite paragenesis, is related to the intrusion of the AMC plutonic complex at 931 ± 2 Ma. Thermal preconditioning of the crust during the first UHT metamorphism may explain the width of the aureole of contact metamorphism c. 75 Ma later, and also the rarity of osumilite‐bearing assemblages in general.  相似文献   

Tree water deficit and dynamic source water partitioning     

Magali F. Nehemy  Paolo Benettin  Mitra Asadollahi  Dyan Pratt  Andrea Rinaldo  Jeffrey J. McDonnell 《水文研究》2021,35(1):e14004

The stable isotopes of hydrogen and oxygen (δ²H and δ¹⁸O, respectively) have been widely used to investigate tree water source partitioning. These tracers have shed new light on patterns of tree water use in time and space. However, there are several limiting factors to this methodology (e.g., the difficult assessment of isotope fractionation in trees, and the labor-intensity associated with the collection of significant sample sizes) and the use of isotopes alone has not been enough to provide a mechanistic understanding of source water partitioning. Here, we combine isotope data in xylem and soil water with measurements of tree's physiological information including tree water deficit (TWD), fine root distribution, and soil matric potential, to investigate the mechanism driving tree water source partitioning. We used a 2 m³ lysimeter with willow trees (Salix viminalis) planted within, to conduct a high spatial–temporal resolution experiment. TWD provided an integrated response of plant water status to water supply and demand. The combined isotopic and TWD measurement showed that short-term variation (within days) in source water partitioning is determined mainly by plant hydraulic response to changes in soil matric potential. We observed changes in the relationship between soil matric potential and TWD that are matched by shifts in source water partitioning. Our results show that tree water use is a dynamic process on the time scale of days. These findings demonstrate tree's plasticity to water supply over days can be identified with high-resolution measurements of plant water status. Our results further support that root distribution alone is not an indicator of water uptake dynamics. Overall, we show that combining physiological measurements with traditional isotope tracing can reveal mechanistic insights into plant responses to changing environmental conditions.  相似文献   

Xenon in Archean barite: Weak decay of Ba, mass-dependent isotopic fractionation and implication for barite formation     

Magali Pujol  Bernard Marty  Pascal Philippot 《Geochimica et cosmochimica acta》2009,73(22):6834-306

In order to investigate radioactive decay of ¹³⁰Ba and ¹³²Ba which have half-lives on the order 10²⁰-10²¹ a, the isotopic composition of xenon has been measured in 3.5 Ga barite of the Dresser Formation, Pilbara, Western Australia. The analyzed samples were collected at about 86 m depth from a diamond drill core (Pilbara Drilling Project). The fact that the sample has been shielded from modern cosmic ray exposure reduces the number of potentially interfering production pathways, simplifying interpretation of the Xe isotope spectrum. This spectrum is clearly distinct from that of either modern or ancient atmospheric Xe. A strong excess of ¹³⁰Xe is identified, as well as other isotopic excursions which are attributed to mass-dependent isotopic fractionation and contributions from products of uranium fission. The mass-dependent fractionation, estimated at 2.1 ± 0.3% amu⁻¹, can be accounted for by mutual diffusion and Rayleigh distillation during barite formation that is consistent with geological constraints. After correction for mass-dependent fractionation, the concentrations of fissiogenic Xe isotopes demonstrate that the U-Xe isotope system has remained closed over 3.5 Ga. From the excess of ¹³⁰Xe, the two successive electron capture half life of this isotope is estimated at 6.0 ± 1.1 × 10²⁰ a, which is 3.4 times faster than previously estimated (Meshik et al., 2001). We could not find evidence of ¹³²Ba decay within our Xe isotope spectra.  相似文献   

Synthesis of In‐House Produced Calibrated Silver Phosphate with a Large Range of Oxygen Isotope Compositions     

Christophe Lcuyer  Franois Fourel  Magali Seris  Romain Amiot  Jean Goedert  Laurent Simon 《Geostandards and Geoanalytical Research》2019,43(4):681-688

The large range of stable oxygen isotope values of phosphate‐bearing minerals and dissolved phosphate of inorganic or organic origin requires the availability of in‐house produced calibrated silver phosphate of which isotopic ratios must closely bracket those of studied samples. We propose a simple protocol to synthesise Ag₃PO₄ in a wide range of oxygen isotope compositions based on the equilibrium isotopic fractionation factor and the kinetics and temperature of isotopic exchange in the phosphate–water system. Ag₃PO₄ crystals were obtained from KH₂PO₄ that was dissolved in water of known oxygen isotope composition. Isotopic exchange between dissolved phosphate and water took place at a desired and constant temperature into PYREX? tubes that were placed in a high precision oven for defined run‐times. Samples were withdrawn at desired times, quenched in cold water and precipitated as Ag₃PO₄. We provide a calculation sheet that computes the δ¹⁸O of precipitated Ag₃PO₄ as a function of time, temperature and δ¹⁸O of both reactants KH₂PO₄ and H₂O at t = 0. Predicted oxygen isotope compositions of synthesised silver phosphate range from ?7 to +31‰ VSMOW for a temperature range comprised between 110 and 130 °C and a range of water δ¹⁸O from ?20 to +15‰ VSMOW.  相似文献   

华南陡山沱期古地理环境及"雪球地球"研究新进展   总被引：4，自引：1，他引：4  

孙知明杨振宇  裴军令Jean BESSE　Melina MACOUIN　Stuart GILDER　Magali ADER 《地质通报》2004,23(8):728-731

华南地块陡山沱组的古地磁和C同位素研究揭示了其形成于赤道附近的古地理环境。对冰期后的盖帽白云岩的C同位素研究表明，δ^13C从-5‰开始有缓慢升高的趋势，与世界上Marinoan冰期其他剖面的c同位素变化相一致。陡山沱期大气中CO2含量的升高可能与kodinia超大陆的裂解及火山活动等密切相关。  相似文献   

A large epeiric methanogenic Bambuí sea in the core of Gondwana supercontinent?     

Sergio Caetano-Filho  Pierre Sansjofre  Magali Ader  Gustavo M.Paula-Santos  Cristian Guacaneme  Marly Babinski  Carolina Bedoya-Rueda  Matheus Kuchenbecker  Humberto L.S.Reis  Ricardo I.F.Trindade 《地学前缘(英文版)》2021,12(1):203-218

Carbon isotope compositions of both sedimentary carbonate and organic matter can be used as key proxies of the global carbon cycle and of its evolution through time,as long as they are acquired from waters where the dissolved inorganic carbon(DIC)is in isotope equilibrium with the atmospheric CO2.However,in shallow water platforms and epeiric settings,the influence of local to regional parameters on carbon cycling may lead to DIG isotope variations unrelated to the global carbon cycle.This may be especially true for the terminal Neoproterozoic,when Gondwana assembly isolated waters masses from the global ocean,and extreme positive and negative carbon isotope excursions are recorded,potentially decoupled from global signals.To improve our understanding on the type of information recorded by these excursions,we investigate the pairedδ^13Ccarb andδ^13Corg evolution for an increasingly restricted late Ediacaran-Cambrian foreland system in the West Gondwana interior:the basal Bambui Group.This succession represents a 1~(st)-order sedimentary sequence and records two majorδ^13Ccarb excursions in its two lowermost lower-rank sequences.The basal cap carbonate interval at the base of the first sequence,deposited when the basin was connected to the ocean,hosts antithetical negative and positive excursions forδ^13Ccarb andδ^13Corg,respectively,resulting inΔ^13C values lower than 25‰.From the top of the basal sequence upwards,an extremely positiveδ^13Ccarb excursion is coupled toδ^13Corg,reaching values of+14‰and-14‰,respectively.This positive excursion represents a remarkable basin-wide carbon isotope feature of the Bambui Group that occurs with only minor changes inΔ^13C values,suggesting change in the DIC isotope composition.We argue that this regional isotopic excursion is related to a disconnection between the intrabasinal and the global carbon cycles.This extreme carbon isotope excursion may have been a product of a disequilibria between the basin DIC and atmospheric CO2 induced by an active methanogenesis,favored by the basin restriction.The drawdown of sulfate reservoir by microbial sulfate reduction in a poorly ventilated and dominantly anoxic basin would have triggered methanogenesis and ultimately methane escape to the atmosphere,resulting in a^13C-enriched DIC influenced by methanogenic CO2.Isolated basins in the interior of the Gondwana supercontinent may have represented a significant source of methane inputs to the atmosphere,potentially affecting both the global carbon cycle and the climate.  相似文献