Showing papers by "Anders Meibom published in 2009"

The grinding tip of the sea urchin tooth exhibits exquisite control over calcite crystal orientation and Mg distribution

Abstract: The sea urchin tooth is a remarkable grinding tool. Even though the tooth is composed almost entirely of calcite, it is used to grind holes into a rocky substrate itself often composed of calcite. Here, we use 3 complementary high-resolution tools to probe aspects of the structure of the grinding tip: X-ray photoelectron emission spectromicroscopy (X-PEEM), X-ray microdiffraction, and NanoSIMS. We confirm that the needles and plates are aligned and show here that even the high Mg polycrystalline matrix constituents are aligned with the other 2 structural elements when imaged at 20-nm resolution. Furthermore, we show that the entire tooth is composed of 2 cooriented polycrystalline blocks that differ in their orientations by only a few degrees. A unique feature of the grinding tip is that the structural elements from each coaligned block interdigitate. This interdigitation may influence the fracture process by creating a corrugated grinding surface. We also show that the overall Mg content of the tooth structural elements increases toward the grinding tip. This probably contributes to the increasing hardness of the tooth from the periphery to the tip. Clearly the formation of the tooth, and the tooth tip in particular, is amazingly well controlled. The improved understanding of these structural features could lead to the design of better mechanical grinding and cutting tools.

Proto-Planetary Disk Chemistry Recorded By D-Rich Organic Radicals In Carbonaceous Chondrites

Abstract: Insoluble organic matter (IOM) in primitive carbonaceous meteorites has preserved its chemical composition and isotopic heterogeneity since the solar system formed ∼4.567 billion years ago. We have identified the carrier moieties of isotopically anomalous hydrogen in IOM isolated from the Orgueil carbonaceous chondrite. Data from high spatial resolution, quantitative isotopic NanoSIMS mapping of Orgueil IOM combined with data from electron paramagnetic resonance spectroscopy reveals that organic radicals hold all the deuterium excess (relative to the bulk IOM) in distinct, micrometer-sized, D-rich hotspots. Taken together with previous work, the results indicate that an isotopic exchange reaction took place between pre-existing organic compounds characterized by low D/H ratios and D-rich gaseous molecules, such as H2D + or HD2 + . This exchange reaction most likely took place in the diffuse outer regions of the proto-planetary disk around the young Sun, offering a model that reconciles meteoritic and cometary isotopic compositions of organic molecules.

Pristine extraterrestrial material with unprecedented nitrogen isotopic variation

Abstract: Pristine meteoritic materials carry light element isotopic fractionations that constrain physiochemical conditions during solar system formation. Here we report the discovery of a unique xenolith in the metal-rich chondrite Isheyevo. Its fine-grained, highly pristine mineralogy has similarity with interplanetary dust particles (IDPs), but the volume of the xenolith is more than 30,000 times that of a typical IDP. Furthermore, an extreme continuum of N isotopic variation is present in this xenolith: from very light N isotopic composition (δ15NAIR = −310 ± 20‰), similar to that inferred for the solar nebula, to the heaviest ratios measured in any solar system material (δ15NAIR = 4,900 ± 300‰). At the same time, its hydrogen and carbon isotopic compositions exhibit very little variation. This object poses serious challenges for existing models for the origin of light element isotopic anomalies.

Supernova Propagation and Cloud Enrichment: A new model for the origin of 60Fe in the early solar system

Abstract: The radioactive isotope Fe-60 (T-1/2 = 1.5 Myr) was present in the early solar system. It is unlikely that it was injected directly into the nascent solar system by a single, nearby supernova (SN). It is proposed instead that it was inherited during the molecular cloud (MC) stage from several SNe belonging to previous episodes of star formation. The expected abundance of Fe-60 in star-forming regions is estimated taking into account the stochasticity of the star-forming process, and it is showed that many MCs are expected to contain Fe-60 ( and possibly Al-26 [T-1/2 = 0.74 Myr]) at a level compatible with that of the nascent solar system. Therefore, no special explanation is needed to account for our solar system's formation.

Strontium-86 labeling experiments show spatially heterogeneous skeletal formation in the scleractinian coral Porites porites

Abstract: This paper presents the results of an effort to label calcium carbonates formed by marine organisms with stable isotopes to obtain information about the biomineralization processes. The growing skeleton of the scleractinian coral Porites porites was labeled three times with enhanced abundances of Sr-86. The distribution of Sr-86 in the skeleton was imaged with the NanoSIMS ion microprobe with a spatial resolution of similar to 200 nm and combined with images of the skeletal ultra-structure. Importantly, the distribution of the Sr-86 label in the P. porites skeleton was found to be strongly heterogeneous. This constrains the physical dimensions of the hypothetical Extracellular Calcifying Fluid (ECF) reservoir at the surface of the growing skeleton, which is implicit in most geochemical models for coral biomineralization. These new experimental capabilities allow for a much more detailed view of the growth dynamics for a wide range of marine organisms that biomineralize carbonate structures. Citation: Houlbreque, F., A. Meibom, J.-P. Cuif, J. Stolarski, Y. Marrocchi, C. Ferrier-Pages, I. Domart-Coulon, and R. B. Dunbar ( 2009), Strontium-86 labeling experiments show spatially heterogeneous skeletal formation in the scleractinian coral Porites porites, Geophys. Res. Lett., 36, L04604, doi: 10.1029/2008GL036782.

Nanostructural and Geochemical Features of the Jurassic Isocrinid Columnal Ossicles

Abstract: Calcite isocrinid ossicles from the Middle Jurassic (Bathonian) clays in Gnaszyn (central Poland) show perfectly pre− served micro− and nanostructural details typical of diagenetically unaltered echinoderm skeleton. Stereom pores are filled with ferroan calcite cements that sealed off the skeleton from diagenetic fluids and prevented structural and geochemical alteration. In contrast with high−Mg calcite skeleton of modern, tropical echinoderms, the fossil crinoid ossicles from Gnaszyn contain only 5.0–5.3 mole% of MgCO3. This low Mg content can be a result of either a low temperature environ− ment (ca. 10C) and/or low Mg/Ca seawater ratio. Both conditions have been proposed for the Middle Jurassic marine en− vironment. Occurrence of Mg−enriched central region of stereom bars of Jurassic columnal ossicle of Chariocrinus an− dreae is consistent with the concept of magnesium ions involvement in earliest growth phases of calcium carbonate biominerals. Key wor ds: Echinodermata, Crinoidea, calcite, nanostructure, geochemistry, AFM, NanoSIMS, Jurassic.

Speciation of Mg in biogenic calcium carbonates

Abstract: A selection of marine biominerals, mostly aragonitic coral skeletons were probed at the Mg K-edge by XANES spectroscopy coupled to μXRF methods and compared to an extensive set of relevant model compounds (silicates, carbonates, oxides and organic). Extensive methodologies are required to better describe the speciation of Mg in those minerals. A combination of ab-initio XANES calculations for defective clusters around Mg in aragonite together with wavelets analyzes of the XANES region are required to robustly interpret the spectra. When using those methodologies, the speciation of Mg ranges from a magnesite-type environment in some scleractinian corals to an organic-type environment. In all environments, the Mg-domains probed appear to be less than 1 nm in size.

Impact on environmental conditions and skeletal ultra-structure on the Li isotopic composition of scleractinian corals

Abstract: The lithium isotope compositions (Li-7/Li-6) and Li/Ca ratios of shallow-water and deep-sea corals (Porites lutea, Cladocora caespitosa, Lophelia pertusa and Desmophyllum cristagalli) were measured using a Cameca ims 1270 ion microprobe. The two C. caespitosa samples were grown under controlled conditions at CO2 partial pressures (pCO(2)) of 416 +/- 29 mu atm and 729 +/- 30 mu atm, respectively. In situ analyses show that all samples are isotopically homogeneous (within analytical precision, +/- 1.1 parts per thousand, 1 sigma) and display significantly lower delta Li-7 values relative to seawater. indicating a significant isotope fractionation during aragonite formation. In contrast to all other elements analysed so far, there is no relationship between the Li isotopic compositions and the skeletal ultrastructure. However, Li/Ca does show variation correlated with ultrastructure, albeit with significant differences between species. This implies that the bio mineralization mechanisms, which are supposed to be different for the different skeletal components, do not influence the Li isotopic composition in corals. In particular, the model of Rayleigh fractionation in a semi-enclosed calcifying fluid is incompatible with the homogeneity of the Li isotope compositions at the micrometer scale We also. show that changes in pCO(2) (and pH) do not significantly affect the Li isotope signature. Nevertheless, a small but significant and systematic difference in Li isotopic composition is observed between deep-sea azooxanthellate and shallow-water zooxanthellate corals. The lack of dependence on pH and pCO(2) and on skeletal ultrastructure indicates that the U isotopic signature of corals could be used as a proxy for reconstructing the paleo-delta Li-7 of seawater and, potentially, for deconvolving past continental weathering rates. (C) 2009 Elsevier B.V. All rights reserved.

Biodata of Dorothy Z. Oehler, author (with François Robert, Smail Mostefaoui, Anders Meibom, Madeleine Selo, David S. McKay, and Everett K. Gibson) of "NanoSIMS Opens a New Window for Deciphering Organic Matter in Terrestrial and Extraterrestrial Samples"

Abstract: Recognition of the earliest morphological or chemical evidence of terrestrial life has proved to be challenging, as organic matter in ancient rocks is commonly fragmentary and difficult to distinguish from abiotically-produced materials (Schopf, 1993; Van Zuilen et al., 2002; Altermann & Kazmierczak, 2003; Cady et al., 2003; Brasier et al., 2002, 2004, 2005; Hofmann, 2004; Skrzypczak et al., 2004, 2005). Yet, the ability to identify remnants of earliest life is critical to our understanding of the timing of life's origin on earth, the nature of earliest terrestrial life, and recognition of potential remnants of microbial life that might occur in extraterrestrial materials. The search for earliest life on Earth now extends to early Archean organic remains; these tend to be very poorly preserved and considerably more difficult to interpret than the delicately permineralized microfossils known from many Proterozoic deposits. Thus, recent efforts have been directed toward finding biosignatures that can help distinguish fragmentary remnants of ancient microbes from either pseudofossils or abiotic organic materials that may have formed hydrothermally or in extraterrestrial processes (House et al., 2000; Boyce et al., 2001; Kudryavtsev et al., 2001; Schopf, 2002; Schopf et al., 2002, 2005a,b; Cady et al., 2003; Garc a-Ruiz et al., 2003; Hofmann, 2004; Brasier et al., 2005; Rushdi and Simoneit, 2005; Skrzypczak et al., 2005). An exciting area of biosignature research involves the developing technology of NanoSIMS. NanoSIMS is secondary ion mass spectrometry (SIMS) for ultrafine feature, elemental and isotopic analysis. Its resolution approaches 0.05 micrometers for element mapping, which is 10-50 times finer than that attainable with conventional SIMS or electron microprobes. Consequently, NanoSIMS has the potential to reveal previously unknown, chemical and structural characteristics of organic matter preserved in geologic materials. Robert et al. (2005) were the first to combine NanoSIMS element maps with optical microscopic imagery in an effort to develop a new method for assessing biogenicity. They showed that the ability to simultaneously map the distribution of organic elements [such as carbon (C), nitrogen (N), and sulfur (S)] and compare those element distributions with optically recognizable, cellularly preserved fossils could provide significant new insights into the origin of organic materials in ancient sediments. This chapter details a recent NanoSIMS study which was designed to acquire new data relevant to establishing critical biosignatures (Oehler et al., 2006a-c). In this study, NanoSIMS was used to characterize element distributions of spheroidal and filamentous microfossils and associated organic laminae in chert from the approx. 0.85 billion year old (Ga) Bitter Springs Formation of Australia. Previous work established preservation of a diverse microbiota in the Bitter Springs Formation (Schopf, 1968; Schopf and Blacic, 1971), and there is no dispute within the scientific community regarding the biogenicity of any of the Bitter Springs structures evaluated in this new study. Thus, the NanoSIMS results described below provide new insight into - and can be used as a guide for assessing - the origin of less well understood organic materials that may occur in early Archean samples and in meteorites or other extraterrestrial samples.

NanoSIMS opens a New Window for Deciphering Organic Matter in Terrestrial and Extraterrestrial Samples

Abstract: Recognition of the earliest morphological or chemical evidence of terrestrial life has proved to be challenging, as organic matter in ancient rocks is commonly fragmentary and difficult to distinguish from abiotically-produced materials (Schopf, 1993; Van Zuilen et al., 2002; Altermann & Kazmierczak, 2003; Cady et al., 2003; Brasier et al., 2002, 2004, 2005; Hofmann, 2004; Skrzypczak et al., 2004, 2005). Yet, the ability to identify remnants of earliest life is critical to our understanding of the timing of life's origin on earth, the nature of earliest terrestrial life, and recognition of potential remnants of microbial life that might occur in extraterrestrial materials. The search for earliest life on Earth now extends to early Archean organic remains; these tend to be very poorly preserved and considerably more difficult to interpret than the delicately permineralized microfossils known from many Proterozoic deposits. Thus, recent efforts have been directed toward finding biosignatures that can help distinguish fragmentary remnants of ancient microbes from either pseudofossils or abiotic organic materials that may have formed hydrothermally or in extraterrestrial processes (House et al., 2000; Boyce et al., 2001; Kudryavtsev et al., 2001; Schopf, 2002; Schopf et al., 2002, 2005a,b; Cady et al., 2003; Garc a-Ruiz et al., 2003; Hofmann, 2004; Brasier et al., 2005; Rushdi and Simoneit, 2005; Skrzypczak et al., 2005). An exciting area of biosignature research involves the developing technology of NanoSIMS. NanoSIMS is secondary ion mass spectrometry (SIMS) for ultrafine feature, elemental and isotopic analysis. Its resolution approaches 0.05 micrometers for element mapping, which is 10-50 times finer than that attainable with conventional SIMS or electron microprobes. Consequently, NanoSIMS has the potential to reveal previously unknown, chemical and structural characteristics of organic matter preserved in geologic materials. Robert et al. (2005) were the first to combine NanoSIMS element maps with optical microscopic imagery in an effort to develop a new method for assessing biogenicity. They showed that the ability to simultaneously map the distribution of organic elements [such as carbon (C), nitrogen (N), and sulfur (S)] and compare those element distributions with optically recognizable, cellularly preserved fossils could provide significant new insights into the origin of organic materials in ancient sediments. This chapter details a recent NanoSIMS study which was designed to acquire new data relevant to establishing critical biosignatures (Oehler et al., 2006a-c). In this study, NanoSIMS was used to characterize element distributions of spheroidal and filamentous microfossils and associated organic laminae in chert from the approx. 0.85 billion year old (Ga) Bitter Springs Formation of Australia. Previous work established preservation of a diverse microbiota in the Bitter Springs Formation (Schopf, 1968; Schopf and Blacic, 1971), and there is no dispute within the scientific community regarding the biogenicity of any of the Bitter Springs structures evaluated in this new study. Thus, the NanoSIMS results described below provide new insight into - and can be used as a guide for assessing - the origin of less well understood organic materials that may occur in early Archean samples and in meteorites or other extraterrestrial samples.

Supernova Propagation and Cloud Enrichment: A new model for the origin of 60Fe in the early solar system

Abstract: The radioactive isotope Fe-60 (T-1/2 = 1.5 Myr) was present in the early solar system. It is unlikely that it was injected directly into the nascent solar system by a single, nearby supernova (SN). It is proposed instead that it was inherited during the molecular cloud (MC) stage from several SNe belonging to previous episodes of star formation. The expected abundance of Fe-60 in star-forming regions is estimated taking into account the stochasticity of the star-forming process, and it is showed that many MCs are expected to contain Fe-60 ( and possibly Al-26 [T-1/2 = 0.74 Myr]) at a level compatible with that of the nascent solar system. Therefore, no special explanation is needed to account for our solar system's formation.

Spatial Relations Between D/H and N Isotopic Anomalies in Orgueil and Murchison Insoluble Organic Matter: A NanoSIMS Study

Abstract: Introduction: Most of the organic carbon in Carbonaceous Chondrites (CC) is in the form of Insoluble Organic Matter (IOM). Isotopically, the IOM in CC appears to be highly un-equilibrated: discrete H and N isotopic anomalies-the so-called hotspots-with δ values up to +19400‰ and +1770‰, respectively, are embedded in the bulk IOM, which has average compositions that are lower by a maximum one order of magnitude [1]. This isotopic heterogeneity is often interpreted as a result of interstellar-like processes occurring in the Solar Nebula or inherited from its parent molecular cloud [1]. Previous studies have observed that the D and 15 N hotspots can be either spatially correlated (i.e. at the same location in the IOM) or uncorrelated [1,2]. Here we present new Hydrogen and Nitrogen isotopic measurements with the NanoSIMS in order to shed light on these spatial correlations. Methods: IOM from Murchison and Orgueil, extracted by acid attack from the bulk meteorite [3], was pressed in pure gold foil. Two terrestrial kerogen standards (Type I and III) were analyzed in parallel. A 16 keV Cs + primary ion beam of 10pA rastered across a 20x20μm 2 surface with an ion spot of 200 nm and a counting time of 1 ms/pixel. Three magnetic fields were used to measure successively: (i) Hand D

Ultra-Pristine Extra-Terrestrial Material with Unprecedented Nitrogen Isotopic Variation

Abstract: Gounelle, Y. Marrocchi, S. Mostefaoui, F. Robert, H. Leroux and A. Meibom. Laboratoire d’Étude de la Matière Extraterrestre, Muséum National d’Histoire Naturelle, 57, rue Cuvier, 75005, Paris, France; Laboratoire de Structure et Propriétés de l’Etat Solide, Université des Sciences et Technologies de Lille, 59655 Villeneuve d’Ascq, France; Dipartimento di Astronomia e Scienza dello Spazio, Università di Firenze, Largo Fermi 2, 50125, Firenze, Italy (briani@mnhn.fr).

Extreme deuterium enrichment in organic matter from cometary antarctic

Abstract: Introduction: Hydrogen isotopes in extraterrestrial materials provide unique insights on the origin of organic matter (OM) in the solar system. Large deuterium (D) enrichments have been reported in micrometer-sized regions (“hotspots”) of interplanetary dust particles [1, 2], and insoluble organic matter (IOM) extracted from primitive meteorites (carbonaceous and ordinary chondrites) [3]. Although an heritage from cold interstellar chemistry has often been favoured to explain these isotopic anomalies, both the origin of the organic matter (OM) and the location of its deuteration remain largely undetermined [4, 5]. Samples and methods: Since the pioneering work of M. Maurette in Adelie Land [6], large collections of micrometeorites (MMs, interplanetary dust particles with sizes ranging from ~ 20 to 1000 μm) have been collected in Antarctic ice and snow [7, 8]. Since 2000, we have collected unaltered micrometeorites from central Antarctic surface snow in the vicinity of the permanent French-Italian CONCORDIA station located at Dome C [9]. MMs studied here were extracted from ultra-clean snow in a trench at depths ranging from 3.3 m to 4.3 m, corresponding to fall on Earth between 1955 and 1970. Among the recovered finegrained micrometeorites, we selected particles exhibiting a fluffy fine-grained texture with no evidence of heating during atmospheric entry (i.e. vesicles and/or magnetite rim) [10]. A scanning electron microscope survey of this subgroup revealed 6 particles with sizes between 40 x 80 μm and 110 x 275 μm that are exceptionally rich in carbon, hereafter referred as UltraCarbonaceous Antarctic MicroMeteorites (UCAMMs) [11, 12]. We characterrized the structure and mineralogy of two UCAMMs, DC06-09-19 and DC06-09-119 (hereafter quoted #19 and #119) by field emission gun scanning electron microscopy and Transmission Electron Microscopy (TEM). Using the NanoSIMS-50 National Facility at LEME-MNHN (Paris), we performed isotopic imaging of their C, H and O isotopic compositions. Results: UCAMMs # 19 and # 119 consist of fine scale assemblages of OM and submicron to micron mineral phases including Mg-rich olivines and pyroxenes, Fe-sulphides and Mg-rich carbonates [13]. Carbon is dominantly present in the form of OM and represents from 60% up to 80% of the particle's volume. The presence of both Fe-sulphides and carbonates in UCAMMs indicate that they experienced little to no modification upon atmospheric entry and during their terrestrial residence at low temperature (-75°C 10 (δD > 6400 ‰) extend over 139 μm2 and 208 μm2 in #19 and #119, respectively, accounting for 27% and 83% of the analyzed surface. It is, to our knowledge, the first time that such deuterium enrichments are observed over such large areas.

Kaidun carbonates: Re-examining the 53Mn-53Cr systematics

Abstract: Introduction: The Kaidun meteorite is a complex polymict breccia containing lithic clasts spanning a wide range of chondrite groups, including enstatite, ordinary and carbonaceous chondrites [1]. The latter is represented by the CR, CI and CM lithologies. These lithologies all contain carbonates, derived from aqueous alteration. Given that many other clasts are anhydrous, aqueous alteration probably occurred before compaction. In the first and only Mn-Cr chronological study of Kaidun carbonates, Hutcheon et al. [2] used an ims 3f to analyze several carbonate grains from 3 different lithologies finding a good correlation of δCr with Mn/Cr implying an initial Mn/Mn ratio of ~ 9×10. This value is within error of the bulk rock carbonaceous chondrite initial value (Mn/Mn = 8.5 ± 1.5) [3,4], a recent estimate of the initial ratio of the solar system. The result of [2] suggests very early, essentially simultaneous aqueous activity on several parent bodies prior to their disruption and the assembly of Kaidun. Such a chronology is surprising given that the onset of aqueous activity overlaps the period inferred for chondrule formation [5,6] and that carbonates in CI chondrites have significantly younger Mn-Cr closure ages. In this work, we used a NanoSims to characterize Mn-Cr internal isochrons on individual dolomite grains in Kaidun.

Strontium-86 labeling experiments show spatially heterogeneous skeletal formation in the scleractinian coral Porites porites

Abstract: abundances of 86 Sr. The distribution of 86 Sr in the skeleton was imaged with the NanoSIMS ion microprobe with a spatial resolution of 200 nm and combined with images of the skeletal ultra-structure. Importantly, the distribution of the 86 Sr label in the P. porites skeleton was found to be strongly heterogeneous. This constrains the physical dimensions of the hypothetical Extracellular Calcifying Fluid (ECF) reservoir at the surface of the growing skeleton, which is implicit in most geochemical models for coral biomineralization. These new experimental capabilities allow for a much more detailed view of the growth dynamics for a wide range of marine organisms that