Dr Janaína Ávila is a research fellow at the Australian National University (ANU). In 2011, she received her PhD in isotope cosmochemistry from the Research School of Earth Sciences (RSES, ANU). During her PhD research, she developed new protocols for measuring heavy isotopes (U, Th, Pb, W, Ba, Eu) in situ in presolar stardust SiC grains using the SHRIMP ion microprobe. Most of this work was carried out at RSES (ANU) under the supervision of Prof. Trevor Ireland, but she also had the opportunity to closely work with Prof. Ernst Zinner at Washington University in St. Louis, carrying out C, N, and Si isotope measurements with a NanoSIMS 50, and with Dr. Maria Lugaro from Monash University on s-process nucleosynthetic signatures.
Since her PhD award, Dr Ávila has held postdoctoral fellowships at the Astronomy Department, University of São Paulo, where she continued research on nucleosynthetic signatures of heavy elements in AGB stars, and then at RSES-ANU, first as a Researcher in Business Postdoctoral Fellow and then as a research fellow. Dr Ávila research centres around the application of ion microprobes to the understanding of the isotopic nature of solar and presolar materials at the microscale. Dr Ávila is particularly interested in presolar grains recovered from primitive meteorites and the scientific implications of their isotopic signatures to the understanding of the origin of the elements and the chemical evolution of the galaxy and solar neighbourhood. Current interests include: (1) isotopic signatures of nucleosynthetic processes that occur inside stars, (2) environmental and biological evolutions on early Earth, and (3) factors influencing isotopic fractionation (mass-dependent and mass-independent fractionation) associated to sulfur and oxygen isotopes.
- Development and applications of secondary ion mass spectrometry within the planetary sciences
- Stable isotopes
- Cosmochemistry and Cosmochronology
- Meteorites and stardust grains
The great oxygenation of the Earth's atmosphere revisited
To understand when, how, and how quickly oxygen has become a component of our atmosphere between about 2.5 and 2.2 billion years ago, an international research team involving RSES-ANU has studied the systematics of the four isotopes of sulfur in more than 700 meters of Australian sedimentary deposits. The results show that the oxygenation of the planet began much earlier than traditionally admitted and that its recording was not synchronous from one continent to another (Australia, South Africa, North America) but spread in time over almost 300 million years. This apparent shift reflects a local effect related to oxidative weathering of older continental surfaces.
In the absence of oxygen in the atmosphere, the UV photolysis of sulfur dioxide (SO2) released by volcanic activity results in the production of sulfur compounds characterized by very specific isotopic fractionations defined as “mass independent” (noted , MIF-S). When dissolved in the ocean, these sulfur compounds transfer this isotopic anomaly to the sedimentary record during their precipitation in the form of pyrite, for example. In the presence of atmospheric oxygen, these particular mass-independent isotopic fractionations disappear. The great oxygenation of the Earth's atmosphere (Great Oxidation Event, GOE) between 2.5 and 2.2 billion years ago (Ga) was defined as the time interval during which a sufficient amount of atmospheric oxygen was present to prevent the production and transfer of these isotopic anomalies into the sedimentary record. The disappearance of these isotopic anomalies in South African sediments over a few meters of sediment thickness, led previous studies to propose that the increase of oxygen in the atmosphere was rapid (less than 10 million years) and globally synchronous at around 2.32 Ga worldwide. However, the presence of large sedimentary gaps in the South African sequences implies that this oxygenation model remains loosely constrained.
“In order to better constrain the mechanisms, magnitude, and duration of the GOE, we conducted a drilling campaign in the Hamersley Basin in Western Australia to study a representative sampling that intersects the period between 2.5 and 2.2 Ga associated with the GOE. Unlike its equivalents in South Africa and North America, the sedimentary sequence studied, the Turee Creek Group, does not show major sedimentary discontinuities,” said Professor Pascal Philippot from University of Montpellier and IPGP, lead investigator of the study.
The analysis of isotopes of sulfur with high stratigraphic resolution shows a relatively homogeneous MIF-S signal of low amplitude (1 ± 0.5 ‰) on all the cores. This signal is punctuated by several sedimentary intervals in which the sulphides do not exhibit MIF-S anomalies. The presence of deposits without MIF-S implies that a significant amount of oxygen were present in the atmosphere as early as 2.45 Ga. The MIF-S signal on the order of 1 ‰ represents the average of the isotopic anomalies measured in the sulphides of the Archean period (4.0 to 2.5 Ga) prior to the GOE. The record of such an anomaly over more than 700 meters of drill cores cannot be explained by atmospheric processes, but it is best attributed to oxidative weathering of older (Archean) continental surfaces and the recycling of a sulphate reservoir of homogeneous isotopic composition of the order of 1‰ in the ocean. “This model allows us to explain that the MIF-S record in sediments of South Africa, North America, and Australia is not synchronous because it depends on local weathering surfaces. These results imply that the current paradigm of defining the GOE at 2.33-2.32 Ga based on the last occurrence of MIF-S in South Africa must be abandoned”, said Professor Pascal Philippot.
RSES-ANU scientists Dr Janaína Ávila and Professor Trevor Ireland, co-authors of the research published in Nature Communications, said the detailed and extensive dataset produced in this study has enable to constraint the timing of the Great Oxidation Event more accurately than previous studies. “Our data indicate that since ca. 2.45 Ga free oxygen was an important component of the Earth’s atmosphere being capable to drive oxidative weathering on land”, said Dr Janaína Ávila.
“Before 2.45Ga, the Earth’s atmosphere and oceans had extremely low levels of oxygen. Several studies indicate that the O2 content of the atmosphere was probably less than 0.001% of the present atmospheric level. During the GOE, the transition from a low oxygen atmosphere to an atmosphere characterized by oxic-suboxic conditions is linked in time with a series of global glacial events. Our data suggest that the rise of atmospheric oxygen occurred around 2.45 Ga or earlier and was not a rapid and synchronous event from one continent to another as previously thought”, said Dr Janaína Ávila.
“Due to recent advances on instrumental capabilities of SHRIMP-SI, an ion microprobe developed by the ANU-Research School of Earth Sciences, we now have the ability to measure with high precision the four isotopes of sulfur in individual domains in single grains. Ion microprobe analysis offers spatial control of measurements that is unmatched by any other technique, allowing isotopic data to be correlated with other geochronological, geochemical, and textural information”, said Dr Janaína Ávila.
Laboratories and organizations involved: Paris Institute of Earth Physics (IPGP / CNRS / Paris Diderot University) and Montpellier Geosciences (Montpellier Geosciences / OREME, University of Montpellier / CNRS / West Indies University), Research School of Earth Sciences (Australian National University, Australia), Ocean Geosciences Laboratory (LGO / IUEM, CNRS / UBO / UBS), John de Laeter Center for Isotope Research (Curtin University, Australia), Biogeosciences (EPHE / University of Bourgogne Franche-Comté / CNRS) and School of Biological, Earth and Environmental Sciences (University of New South Wales, Australia).
Source: Globally asynchronous sulphur isotope signals require re-definition of the Great Oxidation Event. 2018. Philippot, P., Ávila, J., Killingsworth, B., Tessalina, S., Baton, F., Caquineau, T., Muller, E., Pecoits, E., Cartigny, P., Lalonde, S., Ireland, T., Thomazo, C., Van Kranendonk, M.J. and Busigny, V., Nature Communications, DOI: 10.1038/s41467-018-04621-x, 8 juin 2018
Multiple sulfur isotope analysis of sedimentary pyrites with SHRIMP-SI: unravelling complex depositional and post-depositional processes
The sulfur isotopic record of Archean and Paleoproterozoic sedimentary rocks places important constraints on the timing of atmospheric oxygenation. However, many of these ancient rocks have endured several post-depositional processes (e.g., diagenetic, magmatic, hydrothermal, and metamorphic) over geological time so that the original isotopic signature from the early atmosphere and biosphere is now largely overprinted. In situ SHRIMP-SI measurements of multiple sulfur isotopes (32S, 33S, 34S, 36S) in pyrite now allow Δ33S to be determined with internal errors better than 0.05‰ (2SE) and reproducibility about 0.1‰ (2SD). Charge mode measurements  of 36S− allow Δ36S values to be determined with internal precisions of ± 0.2‰ (2SE) and reproducibility better than 0.25‰ (2SD). This level of precision permits identification, at the micron scale, of preserved isotopic signatures of ancient atmospheric chemical and biological activity, as well as overprinted secondary processes.
Measurements of oxygen isotope ratios with the new SHRIMP-SI: high precision analyses of zircon reference materials
The potential for oxygen isotopic analysis of zircon (ZrSiO4) has been recognized for quite some time. Due to its refractory nature and widespread occurrence in many geological environments, zircon d18O values offer unique insights into a wide range of geological processes. The recently commissioned SHRIMP-SI has been designed to be capable of levels of precision similar to conventional oxygen isotope bulk analysis, while maintaining the in situ relationship that is essential for the documentation and interpretation of geological samples. In order to assess SHRIMP-SI instrument performance, oxygen isotopic analyses have been carried out on a suite of zircon reference materials, many of which have been used previously for U-Pb and/or oxygen isotope standardization. We have been able to achieve analytical sessions with measurement stability of better than 0.3 ‰ (95% confidence level). Analyses of common reference materials (Mud Tank, FC1, Temora, R33) typically yield the expected offsets within 0.1 ‰.
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 Philippot P., Ávila J.N., Killingsworth B.A., Tessalina S., Baton F., Caquineau T., Muller E., Pecoits E., Cartigny P., Lalonde S.V., Ireland T.R., Thomazo C., van Kranendonk M.J., Busigny V. 2018. Globally asynchronous sulphur isotope signals require re-definition of the Great Oxidation Event. Nature Communications 9: 2245.
 Rielli A., Tomkins A.G., Nebel O., Raveggi M., Jeon H., Martin L., Ávila J.N. 2018. Sulfur isotope and PGE systematics of metasomatised mantle wedge. Earth and Planetary Science Letters, 497: 181-192.
 Palke A.C., Wong J., Verdel C., Ávila J.N. 2018. A common origin for Thai/Cambodian rubies and blue and violet sapphires from Yogo Gulch, Montana, USA? American Mineralogist 103: 469-479.
 Ireland T.R., Ávila J.N., Lugaro M., Cristallo S., Holden P., Lanc P., Nittler L., Alexander C.M.O'D., Gyngard F., Amari S. 2018. Rare earth element abundances in presolar SiC. Geochimica et Cosmochimica Acta 221, 200-218.
 Babinski M., Rapela C.W., Ávila J.N (eds). 2016. 50 years of isotope geology in South America. Brazilian Journal of Geology 46.
 Ireland T.R., Schram N., Holden P., Lanc., Ávila J.N., Armstrong R., Amelin Y., Latimore D., Corrigan., Clement S., Foster J.J., Compston W. 2014. Charge-mode electrometer measurements of S-isotopic compositions on SHRIMP-SI. International Journal of Mass Spectrometry 359, 26-37.
 Ávila J.N., Ireland T.R., Gyngard F., Zinner E., Mallmann G., Lugaro M., Holden P., Amari S. 2013. Barium isotopic compositions in stardust SiC grains from the Murchison meteorite: Insights into the stellar origins of large SiC grains. Geochimica et Cosmochimica Acta 120, 628-647.
 Ávila J.N., Ireland T.R., Lugaro M., Gyngard F., Zinner E., Cristallo S., Holden P., Rauscher T. 2013. Europium s-process signature at close-to-solar metallicity in stardust SiC grains from AGB stars. Astrophysical Journal Letters 768, L18 (7p).
 Ávila J.N., Lugaro M., Ireland T.R., Gyngard F., Zinner E., Cristallo S., Holden P., Buntain J., Amari S., Karakas, A.I. 2012. Tungsten isotopic compositions in stardust SiC grains from the Murchison meteorite: Constrains on the s-process in the Hf-Ta-W-Re-Os region. Astrophysical Journal 744, 49 (13p).
 Barredo S., Chemale Jr. F., Marsicano C., Ávila J.N., Ottone E.G., Ramos V.A. 2012. Tectono-sequence stratigraphy and U-Pb zircon ages of the Rincon Blanco depocenter, Northern Cuyo Rift, Argentina. Gondwana Research 21,624-636.
 Mancuso A.C., Chemale F., Barredo S., Ávila J.N., Ottone E.G., Marsicano C. 2010. Age constraints for the northernmost outcrops of the Triassic Cuyana Basin, Argentina. Journal of South American Earth Sciences 30, 97-103.
 Heck P.R., Gyngard F., Ott U., Meier M.M.M., Ávila J.N., Amari S., Zinner E., Lewis R.S., Bauer H., Wieler R. 2009. Interstellar residence times of presolar SiC dust grains from the Murchison Carbonaceous meteorite. Astrophysical Journal 698, 1155-1164.
 Mallmann G., Chemale Jr. F., Ávila J.N., Kawashita K., Armstrong R.A., 2007. Isotope geochemistry and geochronology of the Nico Perez Terrane, Rio de la Plata Craton, Uruguay. Gondwana Research 12, 489-508.
 Ávila J.N., Chemale Jr. F., Mallmann G., Kawashita K., Armstrong R.A., 2006. Combined stratigraphic and isotopic studies of Triassic strata, Cuyo Basin, Argentine Precordillera. Geological Society of America Bulletin 118, 1088-1098.
 Ávila J.N., Chemale Jr. F., Mallmann G., Borba, A.W., Luft, F.F., 2005. Thermal evolution of inverted basins: Constraints from apatite fission track thermochronology in the Cuyo Basin, Argentine Precordillera. Radiation Measurements 39, 603-611.
 Luft F.F., Luft Jr J.L., Chemale Jr F., Vignol-Lelarge M.L.M., Ávila J.N. 2005. Post-Gondwana break-up record constraints from apatite fission track thermochronology in NW Namibia. Radiation Measurements 39, 675-679.