POSSIBLE MULTIPLE BOLIDE IMPACTS AT THE FRASNIAN-FAMENNIAN BOUNDARY: EVIDENCE FROM TWO SECTIONS, BOU TCHRAFINE AND JEBEL AMELANE, LOCATED IN THE ANTI-ATLAS OF MOROCCO

Previous work on the Frasnian-Famennian (F-F) boundary has produced clear evidence of multiple extraterrestrial impact events, but the question remains, is there evidence to support a direct cause and effect relationship between impacts and the Kellwasser mass extinctions that occurred? We have found several ejecta layers in two sections in Morocco, Bou Tchrafine and Jebel Amelane. Impact related evidence from these layers includes shocked quartz grains, microspherules and octahedral microcrysts, and high concentrations of Ni, Cr, As, and V, elements known to be associated with bolide impacts. In addition, we find very high Ga levels in concentrations above terrestrial background and known to be concentrated in some meteorites. Microprobe analyses of polished microspherules from these levels also show elevated values of Ni, V and As, similar to the chemistry of microspherules recently reported from the K-T and Eifelian-Givetian impact levels. At Jebel Amelane, a very thin microspherule layer (0.2 mm) containing octahedral microcrysts is located within 1 cm of the base of the Upper Kellwasser extinction level, while a second microspherule-microcryst layer is just 6 cm above it’s base. A third microspherule-microcryst level lies ~1 m higher in the section, above the Upper Kellwasser level and contains shocked quartz. At Bou Tchrafine we have found two distinctive ejecta levels, the lowest of these contains abundant shocked quartz grains and microspherules. A second microspherule level is found ~1.1 m higher in the section, above the Upper Kellwasser level. No microcrysts were found in this section. The close coincidence between the onset of the Upper Kellwasser extinctions and impact evidence suggests a connection between these two events. Although an impact may not have been the primary cause, if shelfal marine biota were destabilized due to environmental factors, an impact at that time could well have further destabilized the environment to the point that the Kellwasser mass extinctions occurred.