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We report paleomagnetic directions from the target rocks of the Tunnunik impact structure, as well as from lithic impact breccia dikes that formed during the impact event. The target sedimentary rocks have been remagnetized after impact-related tilting during a reverse polarity interval. Their magnetization is unblocked up to 350 °C. The diabase dikes intruding into these sediments retained their original magnetization which unblocks above 400 °C. The impact breccia records a paleomagnetic direction similar to that of the overprints in the target sedimentary rocks. The comparison of the resulting virtual geomagnetic pole for the Tunnunik impact structure with the apparent polar wander path for Laurentia combined with biostratigraphic constraints from the target sedimentary rocks is most consistent with an impact age in the Late Ordovician or Silurian, around 430–450 Ma, soon after the deposition of the youngest impacted sedimentary rocks. Our results from the overprinted sedimentary rocks and diabase dikes imply that the postimpact temperature of the studied rocks was about 350 °C.

Micrometeorites are estimated to represent the main part of the present flux of extraterrestrial matter found on the Earth's surface and provide valuable samples to probe the interplanetary medium. Here, we describe large and representative collections of micrometeorites currently available to the scientific community. These include Antarctic collections from surface ice and snow, as well as glacial sediments from the eroded top of nunataks—summits outcropping from the icesheet—and moraines. Collections extracted from deep-sea sediments (DSS) produced a large number of micrometeorites, in particular, iron-rich cosmic spherules that are rarer in other collections. Collections from the old and stable surface of the Atacama Desert show that finding large numbers of micrometeorites is not restricted to polar regions or DSS. The advent of rooftop collections marks an important step into involving citizen science in the study of micrometeorites, as well as providing potential sampling locations over all latitudes to explore the modern flux. We explore their strengths of the collections to address specific scientific questions and their potential weaknesses. The future of micrometeorite research will involve the finding of large fossil micrometeorite collections and benefit from recent advances in sampling cosmic dust directly from the air. This article is part of the theme issue 'Dust in the Solar System and beyond'. [ABSTRACT FROM AUTHOR]

We perform a systematic and detailed study of the 14C and 14C‐10Be dating systems for meteorite terrestrial ages. Physical model calculations indicate that neither the 14C production rates nor the 14C/10Be production rate ratios are constant enough to be reasonably approximated by average values. By using simple averages, one introduces a significant size‐dependent bias into the database for meteorite terrestrial ages. By combining modeled 14C production rates and 14C/10Be production rate ratios with (22Ne/21Ne)cos ratios and assuming ~80% ablation losses, relatively easy to use correlations of 14C production rates and 14C/10Be production rate ratios as a function of (22Ne/21Ne)cos are established. The new correlations enable the determination of terrestrial ages that are more accurate than ages based solely on average values for 14C and/or 14C/10Be. We validate the model predictions by measuring 14C activity concentrations, 14C/10Be production rate ratios, 21Necos concentrations, and (22Ne/21Ne)cos ratios in four recently fallen meteorites: Mt. Tazerzait, Boumdeid (2011), Bensour, and SaU 606. The experimental data confirmed the model predictions, although the available data are insufficient to be conclusive. More data from freshly fallen meteorites are needed for validating the model predictions for different chondrite sizes and chondrite types. [ABSTRACT FROM AUTHOR]

Through the investigation of terrestrial ages of meteorites from Oman, we aim to better understand the time scales of meteorite accumulation and erosion in Oman and the meteorite flux in the past. Here, we present 14C and 14C‐10Be terrestrial ages of seven ordinary chondrite strewn fields and two unpaired single meteorites from the Sultanate of Oman. After critical evaluation of multiple data for each strewn field, we propose "best estimate terrestrial ages," typically based on 14C/10Be. For objects for which complex irradiation histories are known or suspected, terrestrial ages were calculated solely using 14C. The best estimate strewn field ages range from 8.1 ± 3.0 ka (SaU 001) to 35.2 ± 5.1 ka (Dho 005). Including two previously dated strewn fields, the mean and median age of nine Oman strewn fields is 15.9 ± 12.3 and 13.6 ka, respectively. The new data show a general good agreement with data previously obtained in a different laboratory, and we observe a similar general correlation between strewn field ages and mean weathering grade as in previous work based on individual meteorites. Weathering degree W4 is reached for dated samples after 20–35 ka. While the age statistics of strewn fields does not show the previously observed lack of young events, the low abundance of young (0–5 ka) individual meteorites as compared with older (~20 ka) meteorites is confirmed by our data and remains unexplained. [ABSTRACT FROM AUTHOR]