The oxygen isotopic composition of water extracted from carbonaceous chondrites

The oxygen isotopic composition of water from carbonaceous chondrites suggests that close to isotopic equilibrium was attained on CI and CM parent bodies. This is more consistent with a closed system than one with fluid flow. Tagish Lake does not display such equilibrium

Noble gases in Tagish Lake

From the introduction: Tagish Lake has been classified as a CI2 chondrite [1] with an interstellar grain abundance enhanced over that of CI1 and CM2 chondrites [2]. Noble gases have been used as markers for the presence of exotic, presolar grains in chondritic meteorites: Xe-HL (nanodiamonds) and Xe-s/Ne-E (SiC). We have measured 4He, Ne, Ar and Xe in whole-rock Tagish Lake, and an orthophosphoric acid-resistant residue, in an effort to define more precisely the relative abundances of the different presolar components present, and to verify whether or not the meteorite has an enhanced complement of presolar diamonds. For comparison, whole-rock samples of Orgueil and Murchison have also been analysed using the same experimental procedure

Nitrogen Isotopic Variation in Irons and Other Fe-Ni Metal Rich Meteorites

An investigation of the nitrogen concentration, its distribution, location and isotopic composition in iron meteorites and the anomalous metal-rich mesosiderite Bencubbin has been undertaken with the use of a high sensitivity mass spectrometer. Existing stepped heating extraction systems were modified for the types of material analysed in this study and a laser microprobe technique was developed for the purpose of analysing well characterised sample areas of the Bencubbin meteorite with high spatial resolution. The irons display a range in values which is to too large to be the result of fractionation processes in the nebula. An explanation involving primordial heterogeneity is favoured, with the iron meteorite parent bodies having sampled at least four isotopically distinct nitrogen reservoirs. One of the factors controlling the variation may be an input of 1%-rich nitrogen, together with 26Al, from a nova event prior to solar nebula collapse. The behaviour of nitrogen during core formation processes is also considered and compared with the observed nitrogen variation in the non-magmatic group lAB. Other secondary processes affecting nitrogen in the iron meteorites are also identified. The isotopic composition of nitrogen has been used to identify genetic links between iron and stony meteorites, thereby enhancing the normal technique based on oxygen isotopic composition (prohibited by the rarity of oxygen bearing minerals). A second factor influencing the primordial nitrogen isotopic variability has been identified in the unusual polymict breccia Bencubbin. This meteorite contains two nitrogen components, Na and Np, with a value = +1000%o (twice the content of atmospheric nitrogen), present in the metal clasts and probably in the silicate clasts and matrix also. The carrier phase of Na appears to be a chromium-rich sulphide ((Cro.67» ^60,33)283) with a structure similar to pseudo-hexagonal pyrrhotite, containing sulphur slightly depleted in Np may be associated with carbon showing a small enrichment of The data gathered so far indicate that these components formed from a supernova

Insight into the evolution of the Tagish Lake carbonaceous chondrite by analysis of the oxygen isotopic composition of extracted water and Mössbauer spectroscopy

Analysis of oxygen isotopes in water from Tagish Lake together with Mössbauer Spectroscopy suggest some similarities to the CI group of meteorites but also suggest differences in the extent of parent body hydrothermal alteration

New data on carbon isotopic compositions of some ureilites

We have collected new C data from high resolution stepped combustion analyses of 5 ureilites to better constrain their relationships with O and mineralogical/petrographic groupings. This may help the future development of petrogenetic models

Tubular microfossils from ∼2.8 to 2.7Ga-old lacustrine deposits of South Africa: A sign for early origin of eukaryotes?

Unequivocal evidence for Archean eukaryotic life has been long sought for and is a matter of lively debate. In the absence of unambiguous fossils this debate has focused on biogeochemical signatures and molecular phylogenies. Most researchers agree that fossil forms comparable with modern eukaryotic cells can be credibly identified only in Proterozoic (∼1.8–1.6 Ga) and younger rocks. Herein, we report for the first time, Neoarchean mineralized tubular microfossils from ∼2.8 to 2.7 Ga lacustrine deposits of South Africa. The exceptional preservation of these microfossils allows recognition of important morphological details in petrographic thin section and in HF-macerates that links them to modern siphonous (coenocytic) green or yellow-green microalgae (Chlorophyta and Xanthophyta). The microfossil identification is supported by Raman spectroscopic analyses, EPMA, SEM/BSE and SEM/EDS microprobe analytical results, NanoSIMS elemental mapping and micro-tomographic sectioning of the thalli. All results point to indigenous, bona fide eukaryotic microfossils of algal affinity. These Neoarchean microalgae-like remains and their assumingly combined in vivo and early post-mortem precipitated mineral envelopes greatly improve our knowledge of early life and its habitats and may have far-reaching consequences for the studies of the evolution of life

An integrated mineralogical, petrographic, light stable isotope and noble gas investigation of Sahara 99201 ureilite

New ureilite Sahara 99201 has been investigated to determine mineralogy, petrography, light stable isotopes and noble gases. The sample is a typical olivine pigeonite ureilite (Fo 78, Wo 10, En 72). C, N, O and Ar are consistent with other ureilites