¹Anthony J. Carrasquillo, ²Changqun Cao, ³Douglas H. Erwin, ¹Roger E. Summons
¹Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
²State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology & Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
³Department of Paleobiology, National Museum of Natural History, PO BOX 37012, Washington, Washington DC 20013-7012, USA

Fullerene (C60) have been reported in a number of geologic samples and, in some cases, attributed to carbonaceous materials delivered during bolide impact events. The extraction and detection of C60 poses significant analytical challenges, and some studies have been called into question due to the possibility of C60 forming in situ. Here, we extracted samples taken from the Permian-Triassic Boundary section in Meishan, South China and the Cretaceous-Paleogene Boundary exposed at Stevns Klint, Denmark, and analyzed the residues using a fast and reliable method for quantifying C60. Extraction of both whole rock and completely demineralized samples were completed under conditions that previously yielded C60 as well as using an optimized approach based on recent literature reports. These extracts were analyzed using mass spectrometry with the soft-ionization techniques, Atmospheric Pressure Chemical Ionization (APCI) and Electrospray Ionization (ESI), which have not been shown to form fullerenes in-situ. In no case were we able to detect C60, nor could we corroborate previous reports of its occurrence in these sediments, thereby challenging the utility of fullerene as a proxy for bolide impacts or mass extinction events.

Reference
Carrasquillo AJ,Cao C,Erwin DH,Summons RE (2015) Non-detection of C60 fullerene at two mass extinction horizons. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.12.017]
Copyright Elsevier

¹J.D. Gilmour, ¹G. Holland, ²A.B. Verchovsky, ³A.V. Fisenko, ¹S.A. Crowther, ¹G. Turner
¹School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester M13 9PL, United Kingdom
²Centre for Earth, Planetary, Space and Astronomical Research, The Open University, Walton Hall, Milton Keynes MK7 6AA, United Kingdom
³Vernadsky Inst Geochem & Analyt Chem RAS, 19 Kosygin St, Moscow 119991, Russia

We identify new xenon components in a nanodiamond-rich residue from the reduced CV3 chondrite Efremovka. We demonstrate for the first time that these, and the previously identified xenon components Xe-P3 and Xe-P6, are associated with elevated I/Xe ratios. The 129I/127I ratio associated with xenon loss from these presolar compositions during processing on planetesimals in the early solar system was (0.369 ± 0.019) x 10-4, a factor of 3-4 lower than the canonical value. This suggests either incorporation of iodine into carbonaceous grains before the last input of freshly synthesized 129I to the solar system’s precursor material, or loss of noble gases during processing of planetesimals around 30 Myr after solar system formation. The xenon/iodine ratios and model closure ages were revealed by laser step pyrolysis analysis of a neutron-irradiated, coarse-grained nanodiamond separate.

Three distinct low temperature compositions are identified by characteristic I/Xe ratios and 132Xe/136Xe ratios. There is some evidence of multiple compositions with distinct I/Xe ratios in the higher temperature releases associated with Xe-P6. The presence of iodine alongside Q-Xe and these components in nanodiamonds constrains the pathway by which extreme volatiles entered the solid phase and may facilitate the identification of their carriers.

There is no detectable iodine contribution to the presolar Xe-HL component, which is released at intermediate temperatures; this, suggests a distinct trapping process. Releases associated with the other components all include significant contributions of 128Xe produced from iodine by neutron capture during reactor irradiation.

We propose a revised model relating the origin of Xe-P3 (which exhibits an s-process deficit) through a “Q-process” to the Q component (which makes the dominant contribution to the heavy noble gas budget of primitive material). The Q-process incorporates noble gases and iodine into specific carbonaceous phases with mass dependent fractionation relative to the ambient composition. Q-Xe is dominated by the products of this “Q-process” occurring shortly before or during solar system formation. Carriers that trapped xenon by earlier Q-process events were altered, perhaps by supernova shocks, converting some Q carriers into P3 carriers. Unlike Q carriers, these carriers preserve the isotopic signature of the xenon they trapped through oxidation of samples in the laboratory. P3 carriers thus disproportionately sample xenon that was incorporated before galactic chemical evolution had produced the solar xenon signature by enriching ambient xenon with s-process material.

Reference
Gilmour JD, Holland G, Verchovsky AB, Fisenko AV, Crowther SA, Turner G (2016) Xenon and iodine reveal multiple distinct exotic xenon components in Efremovka “nanodiamonds”. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.12.028]
Copyright Elsevier