Some aspects of the Permian–Triassic boundary (PTB) and of the possible causes for the biotic crisis around this boundary

Abstract

The first appearance datum (FAD) of Hindeodus parvus is an excellent datum very close to the base of the Otoceras woodwardi Zone (priority base of the Triassic). For the first time, it allows an exact correlation of the PTB in all marine facies and faunal realms. The following features of the extinction and recovery patterns near the PTB are most important for the search for causes of the PTB biotic crisis: (1) most strongly affected were the (siliceous) plankton (radiolarians) and the warm-water benthos and nekton; (2) most of the cold-water faunas were not significantly affected; (3) the recovery of the warm-water benthos and siliceous plankton occurred only after an unusually long time (during the late Olenekian and Middle Triassic); (4) the productivity of the terrestrial plants dropped strongly and the recovery was mainly in the upper Olenekian and in the Middle Triassic; (5) several terrestrial extinction events occurred at different levels within the Upper Permian, considerable before the marine PTB; at or close to the FAD of Lystrosaurus no extinction event in the terrestrial faunas can be observed; (6) terrestrial faunal elements that survived the Dzhulfian–Dorashamian extinctions were able to survive some months of extreme climatic conditions by hibernation-like life stages (vertebrates), or by dry- and freezing-resistant eggs (conchostracans); (7) about 50% of the genera that disappeared at the PTB re-appeared in the Olenekian–Middle Triassic interval (Lazarus taxa), or in this time interval genera appeared that had undoubtedly evolved from genera that had disappeared at the PTB; and (8) the PTB is preceded by mass occurrences of marine (and continental?) fungi, and the fungal spike ends abruptly a little before the PTB. A scenario for the PTB biotic crisis is elaborated that takes into consideration: the real (not interpolated) diversity patterns of different marine and continental fossil groups, the exact correlation of bioevents in different faunal realms and facies, the strong biotic crisis in the Tethyan warm-water faunas in contrast to the much weaker biotic event in cold-water faunas, the severe Dzhulfian–Dorashamian climate in many parts of the world caused by the continent–ocean configuration and by Siberian Trap volcanism, the cooling of the Boreal area by the northward drift of Pangaea that interrupted the exchange of warm-water benthos between the Tethys and western North America during the Guadalupian, the extinction event at the Guadalupian–Lopingian boundary that restricted most of the affected warm-water faunas to the Tethys, the importance of lower Scythian anoxia that reached an unusually shallow level, and above all the effects of the contemporaneous huge volcanic events about 250 m.y. ago on the Siberian Platform and in the eastern Tethys that caused a 3–6-months-lasting volcanic winter with strong cooling in low latitudes, followed by a strong global warming.