Annelies Van Hoesel^1,2, Wim Z. Hoek², Gillian M. Pennock¹, Knut Kaiser³, Oliver Plümper¹, Michal Jankowski⁴, Maartje F. Hamers¹, Norbert Schlaak⁵, Mathias Küster⁶, Alexander V. Andronikov⁷ and Martyn R. Drury¹

¹Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands
²Department of Physical Geography, Utrecht University, Utrecht, The Netherlands
³GFZ German Research Centre for Geosciences, Potsdam, Germany
⁴Department of Soil Science and Landscape Management, Nicolaus Copernicus University, Toruń, Poland
⁵State Agency for Mining, Geology and Resources Brandenburg (LBGR), Cottbus, Germany
⁶Institute of Geography and Geology, University of Greifswald, Greifswald, Germany
⁷Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA

The Younger Dryas impact hypothesis suggests that multiple airbursts or extraterrestrial impacts occurring at the end of the Allerød interstadial resulted in the Younger Dryas cold period. So far, no reproducible, diagnostic evidence has, however, been reported. Quartz grains containing planar deformation features (known as shocked quartz grains), are considered a reliable indicator for the occurrence of an extraterrestrial impact when found in a geological setting. Although alleged shocked quartz grains have been reported at a possible Allerød-Younger Dryas boundary layer in Venezuela, the identification of shocked quartz in this layer is ambiguous. To test whether shocked quartz is indeed present in the proposed impact layer, we investigated the quartz fraction of multiple Allerød-Younger Dryas boundary layers from Europe and North America, where proposed impact markers have been reported. Grains were analyzed using a combination of light and electron microscopy techniques. All samples contained a variable amount of quartz grains with (sub)planar microstructures, often tectonic deformation lamellae. A total of one quartz grain containing planar deformation features was found in our samples. This shocked quartz grain comes from the Usselo palaeosol at Geldrop Aalsterhut, the Netherlands. Scanning electron microscopy cathodoluminescence imaging and transmission electron microscopy imaging, however, show that the planar deformation features in this grain are healed and thus likely to be older than the Allerød-Younger Dryas boundary. We suggest that this grain was possibly eroded from an older crater or distal ejecta layer and later redeposited in the European sandbelt. The single shocked quartz grain at this moment thus cannot be used to support the Younger Dryas impact hypothesis.

Reference
Van Hoesel A, Hoek WZ, Pennock GM, Kaiser K, Plümper O, Jankowski M, Hamers MF, Schlaak N, Küster M, Andronikov AV and Drury MR (2015) A search for shocked quartz grains in the Allerød-Younger Dryas boundary layer. Meteoritics & Planetary Sciences (in Press)
Link to Article [doi:10.1111/maps.12435]

Published by arrangement with John Wiley & Sons