The Hirnantian (Late Ordovician) and end-Guadalupian (Middle Permian) mass-extinction events compared
Résumé
The so-called Big Five mass extinctions of the Phanerozoic include two prominent
Palaeozoic episodes: the end-Ordovician and end-Permian events, both with large biodiversity
loss. We consider that the end-Ordovician (Hirnantian) extinction could be
best compared to the Middle Permian end-Guadalupian (=Capitanian) extinction,
rather than to the end-Permian (Permo-Triassic boundary; PTB) extinction. The end-
Guadalupian extinction, ca. 8 Myr before the PTB extinction, occurred as an independent
episode under extremely unique global setting with the lowest sea level and lowest
Sr isotopic ratios in seawater of the Phanerozoic. Multiple similarities exist between
the end-Ordovician (Hirnantian) and the end-Guadalupian (Capitanian) events, such
as the preferential elimination of sessile biota in the tropics, a global sea-level drop
and secular changes in seawater C and Sr isotope ratios, occurring under global cooling.
The limited development of land vegetation suggests that the Ordovician extinction
was restricted solely to the marine realm, with no prominent damages on land,
and no large igneous province (LIP) recognized in the Ordovician. The comparison
indicates that the two extinctions of the Hirnantian and of the Capitanian have been
essentially triggered by similar causes/processes; nonetheless, biotic responses were different,
owing to the more oxygenated status of surface environments in the Permian
after the mid-Palaeozoic terrestrialization. □ Atmospheric oxygen level, Capitanian,
carbon isotope, global cooling, Hirnantian, mass extinction, Ordovician, Permian, superchron,
terrestrialization.