Pavel P. Povinec¹, Jozef Masarik¹, Ivan Sýkora¹, Andrej Kováčik¹, Juraj Beňo¹, Matthias M. M. Meier^2,3, Rainer Wieler², Matthias Laubenstein⁴ and Vladimir Porubčan^5,6

¹Department of Nuclear Physics and Biophysics, Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia
²Department of Earth Sciences, ETH Zürich, Zürich, Switzerland
³Centre de Recherches Pétrographiques et Géochimiques, CNRS Nancy, Vandœuvre les Nancy, France
⁴National Laboratory of Gran Sasso, INFN, I-67100, Assergi (AQ), Italy
⁵Department of Astronomy, Physics of the Earth and Meteorology, Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia
⁶Astronomical Institute, Slovak Academy of Sciences, Bratislava, Slovakia

Results of nondestructive gamma-ray analyses of cosmogenic radionuclides (7Be, 22Na, 26Al, 46Sc, 48V, 54Mn, 56Co, 57Co, 58Co, and 60Co) in 19 fragments of the Košice meteorite are presented and discussed. The activities varied mainly with position of fragments in the meteoroid body, and with fluxes of cosmic-ray particles in the space affecting radionuclides with different half-lives. Monte Carlo simulations of the production rates of 60Co and 26Al compared with experimental data indicate that the pre-atmospheric radius of the meteoroid was 50 ± 5 cm. In two Košice fragments, He, Ne, and Ar concentrations and isotopic compositions were also analyzed. The noble-gas cosmic-ray exposure age of the Košice meteorite is 5–7 Myr, consistent with the conspicuous peak (or doublet peak) in the exposure age histogram of H chondrites. One sample likely contains traces of implanted solar wind Ne, suggesting that Košice is a regolith breccia. The agreement between the simulated and observed 26Al activities indicate that the meteoroid was mostly irradiated by a long-term average flux of galactic cosmic rays of 4.8 particles cm−2 s−1, whereas the short-lived radionuclide activities are more consistent with a flux of 7.0 protons cm−2 s−1 as a result of the low solar modulation of the galactic cosmic rays during the last few years before the meteorite fall.

Reference
Povinec PP, Masarik J, Sýkora I, Kováčik A, Beňo J, Meier MMM, Wieler R, Laubenstein M and Porubčan V (2015) Cosmogenic nuclides in the Košice meteorite: Experimental investigations and Monte Carlo simulations. Meteoritics & Planetary Sciences (in Press)
Link to Article [doi:10.1111/maps.12380]

Published by arrangement with John Wiley & Sons

Xenia Ritter1,*, Alexander Deutsch2, Jasper Berndt1 andEric Robin3

¹Institut für Mineralogie, Westfälische Wilhelms-Universität Münster (WWU), Münster, Germany
²Institut für Planetologie, Westfälische Wilhelms-Universität Münster (WWU), Münster, Germany
³CEA-Grenoble INAC/SP2M/LEMMA, Grenoble Cedex 9, France

We have investigated six impact glass spherules from the K-Pg event bed at Beloc, Haiti, using optical and electron microscopy, electron microprobe and in situ laser ablation–mass spectrometry (LA-ICP-MS; 37 trace elements, spot size 90–35 μm), in order to understand geochemical changes during alteration. The mm-sized glass spherules are partly or totally altered to smectite, but original textural features are preserved. The average trace-element composition of glass matches that one of the upper continental crust. Hints for a “meteoritic component” are lacking (Ni/Cr < 1.3; Pt below detection limit). Compared to this fresh glass, smectites are strongly depleted in trace elements, except for Li, Sc, V, Ni, Ga, Ge, and Ba. The chondrite-normalized REE distribution patterns are flat with subchondritic abundances, related to their very low degree of crystallinity. We observe a positive Eu and a strong negative Ce anomaly; the latter is explained by formation of an organic Ce4+-complex, soluble under reducing conditions. Zr/Hf of glasses and smectites is chondritic to superchondritic (35–40), whereas Nb/Ta in smectite is subchondritic (5–12) compared to Nb/Ta in the glass (~14–18). The low Nb/Ta is due to the low Nb concentrations in the smectite. Using in situ techniques with high spatial resolution, we have documented for the first time the significant changes in diagnostic elemental ratios during alteration of glass spherules. This has to be taken into account in the interpretation of geochemical data of not only impact materials but also volcanic glass, especially if bulk rock methods are used.

Reference
Ritter X, Deutsch A, Berndt J and Robin E (2015) Impact glass spherules in the Chicxulub K-Pg event bed at Beloc, Haiti: Alteration patterns. Meteoritics & Planetary Sciences (in Press)
Link to Article [doi:10.1111/maps.12432]

Published by arrangement with John Wiley & Sons

Li Li^1,2, Zongyu Yue¹, Kaichang Di¹ and Man Peng¹

¹State Key Laboratory of Remote Sensing Science, Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Beijing, China
²University of Chinese Academy of Sciences, Beijing, China

The formation mechanism of layered ejecta craters on Mars has remained a topic of intense debate since their discovery. In this study, we perform a global morphological analysis of Martian layered ejecta craters using Thermal Emission Imaging System (THEMIS) images and Mars Orbiter Laser Altimeter (MOLA) data. The study focuses on the ejecta morphologies and well-defined distal rampart characteristics associated with 9945 layered ejecta craters with a diameter greater than 1.5 km distributed across the entire Martian surface. Data analysis based on the new database provides new information on the distribution and morphological details of the three major layered ejecta morphologies (single layer ejecta [SLE], double layer ejecta [DLE], and multiple layer ejecta [MLE]). Global analysis is applied to the latitudinal distribution of characteristic parameters, including the ejecta mobility, lobateness values, and onset diameter. Our survey of the distribution and characteristics of layered ejecta craters reveals that strong correlations exist between ejecta mobility and latitude, and there is a latitudinal dependence of onset diameter. Our study of Martian layered ejecta craters provides more detailed information and insights of a connection between the layered ejecta morphologies and the subsurface volatiles.

Reference
Li L, Yue Z, Di K and Peng N (2015) Observations of Martian layered ejecta craters and constraints on their formation mechanisms. Meteoritics & Planetary Sciences (in Press)
Link to Article [doi:10.1111/maps.12438]

Published by arrangement with John Wiley & Sons