A newly discovered sedimentary accumulation of micrometeorites in the Sør Rondane Mountains of East Antarctica, close to the Widerøefjellet summit at $2750 m above sea level, is characterized in this work. The focus here lies on 2099 melted cosmic spherules larger than 200 lm, extracted from 3.2 kg of sampled sediment. Although the Widerøefjellet deposit shares similarities to the micrometeorite traps encountered in the Transantarctic Mountains, both subtle and more distinct differences in the physicochemical properties of the retrieved extraterrestrial particles and sedimentary host deposits are discernable (e.g., types of bedrock, degree of wind exposure, abundance of metal-rich particles). Unlike the Frontier Mountain and Miller Butte sedimentary traps, the size fraction below 240 lm indicates some degree of sorting at Widerøefjellet, potentially through the redistribution by wind, preferential alteration of smaller particles, or processing biases. However, the cosmic spherules larger than 300 lm appear largely unbiased following their size distribution, frequency by textural type, and bulk chemical compositions. Based on the available bedrock exposure ages for the Sør Rondane Mountains, extraterrestrial dust is estimated to have accumulated over a time span of $1-3 Ma at Widerøefjellet. Consequently, the Widerøefjellet collection reflects a substantial reservoir to sample the micrometeorite influx over this time interval. Petrographic observations and 3D microscopic CT imaging are combined with chemical and triple-oxygen isotopic analyses of silicate-rich cosmic spherules larger than 325 lm. The major element composition of 49 cosmic spherules confirms their principally chondritic parentage. For 18 glassy, 15 barred olivine, and 11 cryptocrystalline cosmic spherules, trace element concentrations are also reported on.Based on comparison with evaporation experiments reported in literature and accounting for siderophile and chalcophile element losses during high-density phase segregation and ejection, the observed compositional sequence largely reflects progressive heating and evaporation during atmospheric passage accompanied by significant redox shifts, although the influence of (refractory) chondrite mineral constituents and terrestrial alteration cannot be excluded in all cases. Twenty-eight cosmic spherules larger than 325 lm analyzed for triple-oxygen isotope ratios confirm inheritance from mostly carbonaceous chondritic precursor materials ($55% of the particles). Yet, $30% of the measured cosmic spherules and $50% of all glassy cosmic spherules are characterized by oxygen isotope ratios above the terrestrial fractionation line, implying genetic links to ordinary chondrites and parent bodies currently unsampled by meteorites. The structural, textural, chemical, and isotopic characteristics of the cosmic spherules from the Sør Rondane Mountains, and particularly the high proportion of Mg-rich glass particles contained therein, imply a well-preserved and representative new sedimentary micrometeorite collect...

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At the French synchrotron facility SOLEIL, a new X-ray imaging facility PUMA (Photons Utilisé s pour les Maté riaux Anciens) has been made available to scientific communities studying materials from cultural heritage. This new instrument aims to achieve 2D and 3D imaging with microscopic resolution, applying different analytical techniques including X-ray fluorescence spectroscopy (XRF), X-ray absorption spectroscopy (XAS), X-ray diffraction and phase-contrast imaging. In order to discover its capabilities a detailed analytical characterization of this beamline as an analytical and imaging tool is deemed necessary. In this work, (confocal) XRF and XAS analyses are demonstrated using the Seymchan pallasite meteorite and an Antarctic unmelted micrometeorite as case studies. The obtained spatial resolution (2 mm  3 mm) and sensitivity (detection limits <10 p.p.m. for 1 s acquisition at 18 keV) show that PUMA is a competitive state-of-the-art beamline, providing several high-profile and high-in-demand analytical methods while maintaining applicability towards a wide range of heritage-oriented sciences.

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Large airbursts, the most frequent hazardous impact events, are estimated to occur orders of magnitude more frequently than crater-forming impacts. However, finding traces of these events is impeded by the difficulty of identifying them in the recent geological record. Here, we describe condensation spherules found on top of Walnumfjellet in the Sør Rondane Mountains, Antarctica. Affinities with similar spherules found in EPICA Dome C and Dome Fuji ice cores suggest that these particles were produced during a single-asteroid impact ca. 430 thousand years (ka) ago. The lack of a confirmed crater on the Antarctic ice sheet and geochemical and 18O-poor oxygen isotope signatures allow us to hypothesize that the impact particles result from a touchdown event, in which a projectile vapor jet interacts with the Antarctic ice sheet. Numerical models support a touchdown scenario. This study has implications for the identification and inventory of large cosmic events on Earth.