Microtektite-like impact glass associated with the Frasnian-Famennian boundary mass extinction

Glass spherules of probable impact origin occur in the Late Devonian Hony section in Belgium. They are found at the stratigraphic level of the Frasnian-Famennian boundary, which is marked by one of the largest mass extinctions in the Phanerozoic. The Hony glass spherules are chemically identical to those previously described from the stratigraphically equivalent Senzeille section located 90 km to the west-southwest. In contrast to the Senzeille layer, the age of the Hony spherule layer is well constrained by conodont biostratigraphy. The spherules have morphological and chemical characteristics similar to tektites and microtektites. They have a broad range of chemical composition with generally high [K ₂O/Na ₂O] and [Al ₂O ₃(Na ₂O/+K ₂O)]. Their water content is in the range measured for tektites and impact glasses. Small inclusions of lechatelierite may be present in the spherules. These glass spherules are likely to be the product of an impact event that occurred at or very near the Frasnian-Famennian boundary. The target rock was probably a clay-rich pelitic sediment intermixed with carbonates. The 368 ± 1 Ma Siljan Ring crater (Sweden) is the most likely impact-site candidate. The Hony and Senzeille glass spherules represent the first substantial evidence that an impact event may be linked to the Frasnian-Famennian mass extinction.