INTRODUCTION The Cretaceous-Tertiary (K/T) boundary debate has trig- gered intense searches for evidence of possible impact-related mass extinctions in the fossil record. So far, only at the K/T boundary is there significant evidence to support an impact- extinction linkage. The Late Devonian, and more particularly the Frasnian-Famennian (F/F) boundary, corresponds to one of the five largest mass extinction periods in the fossil record (Sep- koski, 1982) and is characterized by the disappearance of pelagic and shallow benthic organisms and reef builders (McLaren, 1982). Possible impact products in the form of glassy microtektite- like spherules have been documented recently at or near the F/F boundary in Late Devonian sections in south China and Belgium (Wang, 1992; Claeys et al., 1992; Claeys and Casier, 1994). In China the glass spherules are found 1.5 to 2 m.y. above the F/F Geological Society of America Special Paper 307 1996 Geochemistry of the Frasnian-Famennian boundary in Belgium: Mass extinction, anoxic oceans and microtektite layer, but not much iridium? P. Claeys* Department of Geology and Geophysics, University of California, Berkeley, California 94720-4767 F. T. Kyte Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90024 A. Herbosch* Department of Geology and Geophysics, University of California, Berkeley, California 94720-4767 J.-G. Casier Paleontology Department, Belgian Royal Institute of Natural Sciences, 29 Rue Vautier, B-1040 Brussels, Belgium ABSTRACT The Late Devonian, and in particular the Frasnian-Famennian (F/F) boundary, records one of the five largest mass extinctions in the fossil record. Glassy spherules believed to be of impact origin are associated with the F/F boundary in two Belgian sections (Senzeille and Hony). They have also been reported in sediments deposited approximately 1.5 to 2 m.y. above the boundary in south China, and in the Canning Basin (Australia) this event coincides with a 300 pg/g Ir anomaly. In this study, the F/F boundary in the Hony section was analyzed for trace and major elements to test the possibility of an Ir anomaly associated with the spherule layer. No significant positive Ir anomaly was detected in the 2 m of section investigated. Nevertheless, chalcophile elements show an increase within the dark shale bed marking the F/F boundary. This increase is interpreted to represent a reduction in oxygen concentrations in the depo- sitional environment. This level must be equivalent to the upper part of the Kellwasser anoxic event recognized throughout the paleo-Tethys in what is now western Europe. The F/F boundary seems to be marked by a succession of major events, including impact, oxygen-depleted water on the shelf, and worldwide extinction of organisms. Claeys, P., Kyte, F. T., Herbosch,A., and Casier, J-G., 1996, Geochemistry of the Frasnian-Famennian boundary in Belgium: Mass extinction, anoxic oceans and microtektite layer, but not much iridium?, in Ryder, G., Fastovsky, D., and Gartner, S., eds., The Cretaceous-Tertiary Event and Other Catastrophes in Earth History: Boulder, Colorado, Geological Society of America Special Paper 307. 491 *Present addresses: Claeys, Institut für Mineralogie, Museum für Naturkunde, Invalidenstrasse 43, D-10015 Berlin, Germany; Herbosch, Earth and Environmental Sciences Department, CP 160, Free University of Brussels, 50 Avenue F. D. Roosevelt, B-1050 Brussels, Belgium.