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We report on the detection of primordial organic matter within the carbonaceous chondrite Maribo that is distinct from the majority of organics found in extraterrestrial samples. We have applied high-spatial resolution techniques to obtain C-N isotopic compositions, chemical, and structural information of this material. The organic matter is depleted in ^15N relative to the terrestrial value at around δ^15N ~ -200‰, close to compositions in the local interstellar medium. Morphological investigations by electron microscopy revealed that the material consists of µm- to sub-µm-sized diffuse particles dispersed within the meteorite matrix. Electron energy loss and synchrotron X-ray absorption near-edge structure spectroscopies show that the carbon functional chemistry is dominated by aromatic and C=O bonding environments similar to primordial organics from other carbonaceous chondrites. The nitrogen functional chemistry is characterized by C-N double and triple bonding environments distinct from what is usually found in ^15N-enriched organics from aqueously altered carbonaceous chondrites. Our investigations demonstrate that Maribo represents one of the least altered CM chondrite breccias found to date and contains primordial organic matter, probably originating in the interstellar medium., Finanziert über die DEAL-Vereinbarung mit Wiley 2019-2022.

The isotopic and chemical properties of organic matter (OM) in extraterrestrial samples record a combination of presolar, nebular, parent-body, and terrestrial processes, which can be disentangled by high-spatial resolution studies [e.g., 1]. These studies have the advantage that they also allow for analysis of the petrographic relationship to the matrix and require only minimal chemical treatment. Here we have investigated OM properties within two recent observed falls, Tarda and Winchcombe, by combined “in-situ” techniques. Carbon and nitrogen isotopic compositions were studied by NanoSIMS. OM was sectioned by the focused ion beam (FIB) technique (Hitachi Ethos NX5000). Scanning Transmission X-Ray Microscopy (STXM) was performed at the I08 beamline of Diamond Light Source. Low-kV electron energy loss spectroscopy (EELS) in the vibrational and core loss regimes was performed with a monochromated, aberration-corrected Nion UltraSTEM 100MC. Nitrogen and carbon isotopic compositions of OM aggregates and nanoglobules in Tarda show a range of δ15N values from close-to-terrestrial to ~600‰ with close-to-terrestrial or slightly heavy δ13C values. Single hotspots reach >1000‰ in δ15N and ~80‰ in δ13C, but no negative δ15N values similar to Maribo OM have been detected [2]. STXM analyses at the C K-edge show that OM in Winchcombe is typical for OM in primitive meteorites, with strong absorption at the aromatic C=C (~285 eV) and the ketone/aldehyde (~286.6 eV) bands. The presence of reactive double and triple C-N bonding is a strong indicator that some OM is still pristine. [1] Van Kooten et al. GCA 2018, [2] Vollmer et al. SciRep 2020.

Isotopically anomalous dust grains that formed in the outflows of evolved stars and in the ejecta of stellar explosions are a minor, but important component of primitive Solar System materials. These grains carry records of stellar nucleosynthesis and evolution, circumstellar grain formation, and stars contributing material to the nascent Solar System. Silicates are the most abundant type of presolar dust available for single grain analyses [1]. Presolar SiC and graphite contain various amounts of trace elements [e.g., 2], while for O-rich grains, only one study reported Sr in an O-rich grain [3]. Here, we report on a search for trace elements in a large presolar silicate by NanoSIMS. Measurements were performed with the Hyperion RF plasma O-source using three different mass sequences. Strontium, Zirconium, and Cerium were identified, with Sr/Si in compliance with astrophysical models. Zr/Si and Ce/Si ratios exceed model predictions, indicating additional effects governing their incorporation. The 90Zr- and 140Ce-distributions are correlated with 48Ti. For a gas of solar composition, Sr and Ce would condense into titanate, while Zr forms ZrO2 at higher temperatures. Due to chemical similarities between Zr and Ti, ZrO2 might have been incorporated into Sr- and Ce-bearing Ti-oxides, serving as condensation nuclei for the silicate [4]. References: [1] Floss C. & Haenecour P. (2016) Geochemical Journal 50: 3–25. [2] Amari S. et al. (1995) Meteoritics 30:679–693. [3] Leitner J. et al. (2018) Geochimica et Cosmochimica Acta 221:255–274. [4] Gail H.-P. & Sedlmayr E. (1998) Faraday Discussions 109:303–319.

We investigated the inventory of presolar silicate, oxide, and silicon carbide (SiC) grains of fine-grained chondrule rims in six Mighei-type (CM) carbonaceous chondrites (Banten, Jbilet Winselwan, Maribo, Murchison, Murray and Yamato 791198), and the CM-related carbonaceous chondrite Sutter's Mill. Sixteen O-anomalous grains (nine silicates, six oxides) were detected, corresponding to a combined matrix-normalized abundance of ~18 ppm, together with 21 presolar SiC grains (~42 ppm). Twelve of the O-rich grains are enriched in 17O, and could originate from low-mass asymptotic giant branch stars. One grain is enriched in 17O and significantly depleted in 18O, indicative of additional cool bottom processing or hot bottom burning in its stellar parent, and three grains are of likely core-collapse supernova origin showing enhanced 18O/16O ratios relative to the solar system ratio. We find a presolar silicate/oxide ratio of 1.5, significantly lower than the ratios typically observed for chondritic meteorites. This may indicate a higher degree of aqueous alteration in the studied meteorites, or hint at a heterogeneous distribution of presolar silicates and oxides in the solar nebula. Nevertheless, the low O-anomalous grain abundance is consistent with aqueous alteration occurring in the protosolar nebula and/or on the respective parent bodies. Six O-rich presolar grains were studied by Auger Electron Spectroscopy, revealing two Fe-rich silicates, one forsterite-like Mg-rich silicate, two Al-oxides with spinel-like compositions, and one Fe-(Mg-)oxide. Scanning electron and transmission electron microscopic investigation of a relatively large silicate grain (490 nm �� 735 nm) revealed that it was crystalline ��kermanite (Ca2Mg[Si2O7]) or a an ��kermanite-diopside (MgCaSi2O6) intergrowth.

The spatial distribution of transition metal valence states is of broad interest in the microanalysis of geological and environmental samples. An example is rock varnish, a natural manganese (Mn)-rich rock coating, whose genesis mechanism remains a subject of scientific debate. We conducted scanning transmission X-ray microscopy with near-edge X-ray absorption fine-structure spectroscopy (STXM-NEXAFS) measurements of the abundance and spatial distribution of different Mn oxidation states within the nano- to micrometer thick varnish crusts. Such microanalytical measurements of thin and hard rock crusts require sample preparation with minimal contamination risk. Focused ion beam (FIB) slicing was used to obtain ∼100–1000 nm thin wedge-shaped slices of the samples for STXM, using standard parameters. However, while this preparation is suitable for investigating element distributions and structures in rock samples, we observed artifactual modifications of the Mn oxidation states at the surfaces of the FIB slices. Our results suggest that the preparation causes a reduction of Mn4+ to Mn2+. We draw attention to this issue, since FIB slicing, scanning electron microscopy (SEM) imaging, and other preparation and visualization techniques operating in the kilo-electron-volt range are well-established in geosciences, but researchers are often unaware of the potential for the reduction of Mn and possibly other elements in the samples. Version of record

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