Marine anoxia and delayed Earth system recovery after the end-Permian extinction.

Delayed Earth system recovery following the end-Permian mass extinction is often attributed to severe ocean anoxia. However, the extent and duration of Early Triassic anoxia remains poorly constrained. Here we use paired records of uranium concentrations ([U]) and (238)U/(235)U isotopic compositions (δ(238)U) of Upper Permian-Upper Triassic marine limestones from China and Turkey to quantify variations in global seafloor redox conditions. We observe abrupt decreases in [U] and δ(238)U across the end-Permian extinction horizon, from ∼3 ppm and -0.15‰ to ∼0.3 ppm and -0.77‰, followed by a gradual return to preextinction values over the subsequent 5 million years. These trends imply a factor of 100 increase in the extent of seafloor anoxia and suggest the presence of a shallow oxygen minimum zone (OMZ) that inhibited the recovery of benthic animal diversity and marine ecosystem function. We hypothesize that in the Early Triassic oceans-characterized by prolonged shallow anoxia that may have impinged onto continental shelves-global biogeochemical cycles and marine ecosystem structure became more sensitive to variation in the position of the OMZ. Under this hypothesis, the Middle Triassic decline in bottom water anoxia, stabilization of biogeochemical cycles, and diversification of marine animals together reflect the development of a deeper and less extensive OMZ, which regulated Earth system recovery following the end-Permian catastrophe.

First Balanced Cross Section Across the Taurides Fold-Thrust Belt: Geological Constraints on the Subduction History of the Antalya Slab in Southern Anatolia.

Eastern Mediterranean subduction accommodated Africa-Eurasia convergence since Mesozoic time and produced multiple subducted slab fragments in the mantle below Anatolia. These included the north dipping Cyprus and ENE-dipping Antalya slabs, which are currently separated by an upper mantle slab gap. Segmentation of these slabs, and associated mantle flow, may have contributed to <8 Ma uplift of the Central Anatolian Plateau. The western Central Taurides fold-thrust belt in southern Turkey is in the upper plate above the Antalya slab and contains a geological record of its subduction. We present the first orogen-scale balanced cross section of the Taurides and find that it formed in two stages: (1) Cretaceous to middle Eocene thrusting resulted in a minimum of 73-km shortening, and (2) Mio-Pliocene thrusting resulted in a minimum of 17.5-km shortening. Eocene shortening accounts for only ~5 Myr of Africa-Eurasia plate convergence. It is unlikely that >400 km of post to middle Eocene plate convergence was accommodated between the Taurides and its Beydaglari platform foreland and instead must have been accommodated south of Beydaglari. The associated southward plate boundary jump separated the Antalya slab from the African plate and the Cyprus slab. The isolated Antalya slab was left in an intraplate setting and is probably still attached to Beydaglari today. We suggest the continental composition of the Antalya slab may have prevented its detachment. Finally, the gap between the Antalya and Cyprus slabs existed since at least Eocene time; their decoupling likely did not contribute to late Neogene Central Anatolian Plateau uplift.