Buday'ah (Oman) and Arrow Rock (New-Zealand): from a similar to a divergent evolution of Permian-Triassic oceanic successions

International audienceThe Oman Mountains expose the middle Permian to lower Triassic Buday'ah section of oceanic sediments closeto the Tethyan Gondwana margin. The tectonically truncated Permian litho-units start with a basal volcanicsequence composed of pillow basalt showing transitional and enriched MORB signatures (Maury et al., 2003:Lapierre et al., 2004). In different parts of the pillow lava succession, inter-pillow cavities are filled up with redlime-mudstone with rare middle Permian ammonoids, and lenses up to 1.2 m thick red ammonoid- limestonecover the irregular upper surface of the pillows. A Clarkina conodont fauna of latest Capitanian age occurs nearthe top of the limestones (C. Henderson and A. Nicora in Baud & Bernecker, ed., 2010 and in Baud et al.,submitted). The following red radiolarian chert spans the latest Capitanian to Wuchiapingian age with theradiolarian assemblage Follicucullus ventricosus – F. scholasticus (F. Cordey in Baud & Bernecker, ed., 2010,and in Baud et al., submitted).Described by Spörli et al. (2006, 2007) and by Takemura et al. (2007), a similar Permian chert-dominated oceanfloor sequence, but accreted from Panthalassa, occurs at Arrow Rocks, Northland, New Zealand. LatestCapitanian to Wuchiapingian red radiolarian cherts overlies middle Permian red limestone lenses in basalticrocks with the same radiolarian assemblage in the lower part. The Changhsingan succession consists of darkgrey siliceous mudstone in Buday'ah and bedded siliceous mudstone and chert in Arrow Rocks. The mainchange between the two oceanic sections occurs in the Late Changhsingian: Arrow Rocks sedimentation gradesagain to pale green bedded cherts in late Changhsingian whereas Buday’ah displays calcareous clay mudstoneacross the Permian-Triassic boundary. Reported from Arrow Rocks there is a thin Permian/Triassic boundaryinterval consisting of alternating black siliceous shale and grey chert (Spörli et al., 2006) and above the basalTriassic (Induan) succession consists of red cherts and siliceous mudstone. No more chert nor siliceousmudstone are present in Buday’ah but Induan platy lime mudstone and calcareous shales with calcispheres (castsof radiolarians?) followed by Olenekian papery lime mudstones, thus showing a highly divergent evolution.The difference could be explained by differential plate tectonic displacement. Arrow Rocks sequence movedover a long distance from a relatively low latitude position in the Middle Permian to a high latitude one in mid-Triassic times (Spörli et al., 2007). Meanwhile Buday’ah’s succession on the Gondwana margin was displacedtowards a lower latitude position from Middle Permian to Triassic. Consequently, these oceanic successionsdifferences from the late Changhsingian onward may be related to the divergent geodynamic evolution