Abstract
The devastating end-Permian mass extinction is widely considered to have been caused by large-scale and rapid greenhouse gas release by Siberian magmatism. Although the proximate extinction mechanisms are disputed, there is widespread agreement that a major extinction pulse occurred immediately below the biostratigraphically defined Permian-Triassic boundary. Our statistical analyses of stratigraphic confidence intervals do not comply with a single end-Permian extinction pulse of ammonoids in Iran. High turnover rates and extinction pulses are observed over the last 700 k.y. of the Permian period in two widely separated sections representative of a larger area. Analyses of body sizes and morphological complexity support a gradual decline over the same interval. Similar pre-mass extinction declines and disturbances of the carbon cycle have sometimes been reported from other regions, suggesting a widespread, but often overlooked, environmental deterioration at a global scale, well before the traditional main extinction pulse.
Highlights
Patterns, ultimate causes, and consequences of the end-Permian mass extinction are increasingly well understood, but there is still controversy regarding the extinction mechanism (Baresel et al, 2017)
To test our hypothesis of a gradual decline, we studied the succession of latest Permian ammonoids in two classical Iranian areas, where fossils are uniformly distributed in sections of monotonous deep-water limestones: the Paratirolites Limestone at Julfa in northwest Iran facing the Paleotethys, and Baghuk Mountain in central Iran facing the Neotethys (Fig. 1)
A uniform distribution of fossil horizons is rejected for the entire thickness of the Paratirolites Limestone, but Kolmogorov-Smirnov (KS) tests and quantile-simulations sensu Solow et al (2006) suggest a uniform distribution in the upper 4 m
Summary
Ultimate causes, and consequences of the end-Permian mass extinction are increasingly well understood, but there is still controversy regarding the extinction mechanism (Baresel et al, 2017). The Siberian Traps are consistently being linked to the most profound mass extinction of the Phanerozoic (e.g., Brand et al, 2012; Burgess et al, 2017), the precise temporal match between volcanism and extinctions remains equivocal. There is an ongoing debate whether a single extinction pulse (Jin et al, 2000) or several extinction pulses (e.g., Xie et al, 2005; Song et al, 2013) are most likely. Authors arguing for two or more extinction pulses usually identify additional extinction pulses in younger strata. Gradual extinctions within the latest Permian (late Changhsingian) are sometimes suggested (Ward et al, 2005; Feng and Algeo, 2014; Wang et al, 2014) but not widely discussed in current extinction scenarios
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