Method for finding grains created by lightning discharge from the Younger Dryas Boundary layer GP51A-1304 Melted materials at the Younger Dryas boundary (YDB) are proposed to have been produced by an extraterrestrial impact. Critical evidence for this scenario is an unusual increase in the number of magnetic spherules in the YDB layer, dated to 12.9 ka. To investigate their origin, we separated sediment samples by density (2.89 g/cm^3) and size (greater than 0.15, 0.08, 0.05, and 0.036 mm). Next, the samples containing these spherules were subjected to repeated magnetic scanning. Initial scans were done over the grains smeared across the microscope glass and sandwiched with another microscopy glass cover and thin sheet of paper. After scanning, this sandwich was exposed to a 1-Tesla magnetic pulse, and more scans were obtained. Results indicate that a few magnetic grains displayed close to saturated remanent magnetism, consistent with having been exposed to lightning, while most of the spherules had not been exposed. This supports the hypothesis that some of these grains and spherules, which were associated with the extraterrestrial impact, could have been present in the plume cloud where lightning discharges formed due to convective air masses. If so, then a few may have formed after the impact during exposure to electric discharge along their flight path. Most of the spherules displayed no remanent magnetism, consistent with formation during the impact event, but inconsistent with formation by lightning.
Gunther Kletetschka1, 2, Ladislav Nabelek1, 2, Allen West3, Richard B Firestone4 1. Faculty of Science, Charles University in Prague, Prague, Czech Republic; 2. Institute of Geology, Czech Academy of Science of the Czech Republic, v.v.i., Prague, Czech Republic; 3. GeoScience Consulting, Dewey, AZ, USA; 4. Lawrence Berkeley National Laboratory, Berkeley, CA, USA