Lujun Liu

Calibrating the End-Permian Mass Extinction

High-precision geochronologic dating constrains probable causes of Earths largest mass extinction. The end-Permian mass extinction was the most severe biodiversity crisis in Earth history. To better constrain the timing, and ultimately the causes of this event, we collected a suite of geochronologic, isotopic, and biostratigraphic data on several well-preserved sedimentary sections in South China. High-precision U-Pb dating reveals that the extinction peak occurred just before 252.28 ± 0.08 million years ago, after a decline of 2 per mil (‰) in δ13C over 90,000 years, and coincided with a δ13C excursion of −5‰ that is estimated to have lasted ≤20,000 years. The extinction interval was less than 200,000 years and synchronous in marine and terrestrial realms; associated charcoal-rich and soot-bearing layers indicate widespread wildfires on land. A massive release of thermogenic carbon dioxide and/or methane may have caused the catastrophic extinction.

A typical Euramerican floral element from the Shanxi Formation (Cisuralian, lower Permian) in the Wuda Coal Field, Inner Mongolia, North China

Autunia conferta (Sternberg) Kerp is one of the best known, earliest and most widespread callipterids in Euramerica during the Cisuralian. Unambiguous A. conferta foliage is for the first time recorded from Cathaysia in the Shanxi Formation of Wuda, Inner Mongolia, North China. Together with the find of Autunia naumannii (Gutbier) Kerp in the lowermost Permian strata of the same region, it proves that the radiation and spatio-temporal distribution of peltasperms was apparently not hampered by the floral provincialism, and it also indicates a mutual migration of floral elements between Cathaysia and Euramerica. Their long stratigraphic range, from the Cisuralian to the Lopingian, demonstrates that callipterids played an important role in the palaeotropical landscape and had a long history in North China during the Permian. The nearly absence of callipterids in typical Cisuralian wetland floras indicates their preference for well-drained settings and uplands. It is inferred that A. conferta lived contemporaneously with the wetland floral elements in Cathaysia during the Cisuralian, but commonly outside the window of preservation.