Reply to comment on “Mantle plume: the invisible serial killer — Application to the Permian–Triassic boundary mass extinction” by E. Heydari, N. Arzani and J. Hassanzadeh [Palaeogeography, Palaeoclimatology, Palaeoecology 264 (2008) 147–162]
Abstract In a recent paper (Heydari, E., Arzani, N., Hassanzadeh, J., 2008. Mantle plume: the invisible serial killer — application to the Permian–Triassic boundary mass extinction. Palaeogeography, Palaeoclimatology, Palaeoecology 264, 147–162) the cause of the end-Permian mass extinction was once again associated with the eruption of the Siberian Traps. However, this work considered the vast outpouring of flood basalts to be an incidental sideshow to the main event: the catastrophic release of huge volumes of methane to the atmosphere. This was attributed to a selection of sources – marine gas hydrates, thermogenic methane and methane from permafrost – that have been proposed by many authors previously. Uniquely, they suggest that the mantle plume (envisaged to have sourced the flood basalts) impinged beneath oceanic crust to the north of the Siberian flood basalts and that feeder dykes in the continental slope to the south heated sediments and released methane. There is no evidence for either of these two new proposed facets to end–Permian volcanism. The paper invokes an "oceanic acid bath" kill mechanism and dismisses claims for ocean anoxia at this time instead suggesting that end–Permian oceans were as well ventilated as those pertaining today. This latter claim simply ignores a vast body of sedimentological, palaeoecological and geochemical evidence for widespread anoxia in ocean and shelf settings at this time. The former claim for ocean acidity is equally suspect and based on the notion that a transition from calcite to aragonite-precipitating seas occurred at the Permian–Triassic boundary. However, previous studies have suggested that this interval occurs within a phase of "aragonite seas" and it is significant that most of the principal contributors to carbonate sediment in the Late Permian (calcareous algae and foraminifera) secreted aragonite.