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Bernard Marty

Publications and source records attributed to Bernard Marty.

7 recordsLinked to original sources
PubMed2006

Isotopic compositions of cometary matter returned by Stardust.

Hydrogen, carbon, nitrogen, and oxygen isotopic compositions are heterogeneous among comet 81P/Wild 2 particle fragments; however, extreme isotopic anomalies are rare, indicating that the comet is not a pristine aggregate of presolar materials. Nonterrestrial nitrogen and neon isotope ratios suggest that indigenous organic matter and highly volatile materials were successfully collected. Except for a single (17)O-enriched circumstellar stardust grain, silicate and oxide minerals have oxygen isotopic compositions consistent with solar system origin. One refractory grain is (16)O-enriched, like refractory inclusions in meteorites, suggesting that Wild 2 contains material formed at high temperature in the inner solar system and transported to the Kuiper belt before comet accretion.

Carbon Isotopes↗
PubMed2005

Neon isotopes constrain convection and volatile origin in the Earth's mantle.

Identifying the origin of primordial volatiles in the Earth's mantle provides a critical test between models that advocate magma-ocean equilibration with an early massive solar-nebula atmosphere and those that require subduction of volatiles implanted in late accreting material. Here we show that neon isotopes in the convecting mantle, resolved in magmatic CO2 well gases, are consistent with a volatile source related to solar corpuscular irradiation of accreting material. This contrasts with recent results that indicated a solar-nebula origin for neon in mantle plume material, which is thought to be sampling the deep mantle. Neon isotope heterogeneity in different mantle sources suggests that models in which the plume source supplies the convecting mantle with its volatile inventory require revision. Although higher than accepted noble gas concentrations in the convecting mantle may reduce the need for a deep mantle volatile flux, any such flux must be dominated by the neon (and helium) isotopic signature of late accreting material.

Journal Article↗
PubMed2004

Clues from Fe isotope variations on the origin of early Archean BIFs from Greenland.

Archean rocks may provide a record of early Earth environments. However, such rocks have often been metamorphosed by high pressure and temperature, which can overprint the signatures of their original formation. Here, we show that the early Archean banded rocks from Isua, Akilia, and Innersuartuut, Greenland, are enriched in heavy iron isotopes by 0.1 to 0.5 per mil per atomic mass unit relative to igneous rocks worldwide. The observed enrichments are compatible with the transport, oxidation, and subsequent precipitation of ferrous iron emanating from hydrothermal vents and thus suggest that the original rocks were banded iron formations (BIFs). These variations therefore support a sedimentary origin for the Akilia banded rocks, which represent one of the oldest known occurrences of water-laid deposits on Earth.

Journal Article↗
PubMed2003

Geochemical evidence for efficient aquifer isolation over geological timeframes.

Aquitards-layers of rock having low permeability-have been suggested as potential long-term reservoirs for toxic materials such as nuclear or chemical waste. But information about the isolation properties of aquitard layers is essential to evaluate whether they can indeed be used safely as reservoirs. Here we investigate the long-term mobility of groundwaters between two aquifers surrounding an aquitard layer in the eastern recharge area of the Paris basin, France, using helium isotopes as a geochemical tracer. The deeper Trias sandstone aquifer, which lies above the crystalline basement, accumulates radiogenic (4)He and primordial (3)He from large regions of the crust and mantle at rates comparable to the degassing of the whole crust and of mid-ocean ridges. We show that the overlying carbonate Dogger aquifer, which is separated from the Trias aquifer by an aquitard layer consisting of a approximately 600 m succession of shales and clays, is stagnant and has been extremely well isolated from the Trias over the past several million years. This finding, together with previous studies at the centre of the Paris basin, shows that diffusive mass transfer across aquitards is negligible and that cross-formational flow in basins takes place preferentially in faulted areas.

Journal Article↗
PubMed2002

Study of release kinetics of small and high molecular weight substances dispersed into spray-dried ethylcellulose microspheres.

Spray-dried ethylcellulose microspheres were used as matrices for the encapsulation of a fungal lactase and/or small paramagnetic probes (Tempol or Tempo). Their dissolution in water was studied. Kinetics fitted with the model Q = kt(n) of Korsemeyer et al. [Int. J. Pharm. 15 (1983) 25] exhibited a non-Fickian diffusion. The calculated diffusional exponent (n) values were near 0.26 whatever the encapsulated probes. The release rates (k) were only slightly different for paramagnetic probes and lactase. This result indicated that the probes' release mechanisms are not diffusion controlled. Other factors such as matrix porosity and probe solubility in the matrix and in water could influence the probes' release rate.

Cellulose↗