PALEOENVIRONMENTAL AND BIOTIC CHANGES ACR OSS THE CRETACEOUS TERTIARYBOUNDARY IN THE OMAN MOUNTAINS/

Two new sites, revealing a record of the events at the K/T boundary, h ave been recently discovered in the Oman Mountains at the eastern end of the Arabian plate. In the Buraymi Basin. located at the northwester n flank of the chain, the KIT boundary is intersected by a basinal fac ies succession, whilst in the Sur area, the transition is illustrated within a confined carbonate platform sequence. This period exhibits im portant palaeoenvironmental and biotic changes which originated from t he conjunction of multiple factors. These came together over differing intervals of time, i.e., long period of time, short time scale and in stantaneous event. At the scale of the long period of time (4 Ma) stre tching from late Maastrichtian to the Danian (P1c), the Oman Mountains recorded profound modifications in terms of their palaeogeographic co ntext, undoubtedly linked to plate reorganisation. This was initially shown by the emersion of the rudist platforms and the flooding of the margins in the late, but not terminal, Maastrichtian. This first tecto nic event introduced an hemipelagic and a turbiditic sedimentation. As a consequence, this episode created, at the southern limb of the chai n, the confined Murka sub-basin characterised by a carbonate platform sedimentation. Because the transition terminal Maastrichtian-earliest Danian correspond to a period of tectonic quiescence, the sedimentatio n persisted through the K/T boundary without any notable modification. A second tectonic episode in the Danian P1b/P1c interval, accentuated the flooding of the plate margins where basin deposits were accumulat ing. The renewal of planktic foraminifera took place in stages suggest ing a gradation of palaeoecological conditions spread over a short tim e scale (1 to 2 Ma). This gradation is marked by the succession of thr ee waves of extinction which took place from the late Maastrichtian to the KIT boundary. Diversity of the benthic foraminifera then increase d progressively from subzone P1b onwards, showing the re-establishment of the ecosystem in P1c. The iridium anomaly detected at the WT bound ary at both sites would tend to reinforce the hypothesis of a meteorit e impact. the effects of which would have added to these events that u nfolded over a longer rime scale.