Friday, December 04, 2015

Emeishan Volcanism's Impact on the Guadalupian/Capitanian Permian Mass Extinction

Submarine palaeoenvironments during Emeishan flood basalt volcanism, SW China: Implications for plume–lithosphere interaction during the Capitanian, Middle Permian (‘end Guadalupian’) extinction event


Jerram et al


Plume-induced lithospheric uplift and erosion are widely regarded as key features of large igneous province (LIP) emplacement, as is the coincidence of LIP eruption with major extinction and oceanic anoxic events (OAE). The Emeishan LIP, which erupted during the Capitanian (previously termed ‘end Guadalupian’) extinction event, has provided the most widely discussed example of axisymmetric doming above a rising mantle ‘plume’; advocates have argued that in excess of 500 m of uplift occurred over greater than 30 000 km2 causing extensive radially distributed erosion and alluvial fan formation. However, the recognition of submarine hydromagmatic and phreatomagmatic-style volcanism, as well as syn-volcanic marine sediments interbedded in the eruptive succession, now requires further examination to this simple plume–uplift model.

Here we present data from newly discovered sections from the center of the putative uplifted area (around Lake Er Hai, SW Yunnan Province,) that provide a more complete history of the Emeishan volcanism. These reveal that platform carbonate deposition was terminated by rapid subsidence, followed quickly by the onset of volcanism. Importantly, these eruptions also coincide with widespread losses amongst fusulinacean foraminifera and calcareous algae. For at least the lower two thirds of the 4–5 km thick lava pile, eruptions continued at or below sea level, as testified by the presence of voluminous mafic volcaniclastic deposits, pillow lavas, and development of syn-volcanic reefal limestones in the Emeishan inner zone. Only in the later stages of eruption did terrestrial lava flows become widely developed. This onset of volcanism in a submarine setting and the consequent violent, phreatomagmatic-style eruptions would have had a profound effect on marine fauna and exacerbated any volcanically induced climate effects during the Capitanian. The late Permian of SW China at the time of the Emeishan was an extended area of thinned lithosphere with epeiric seas, which appear to have been sustained through the onset of LIP emplacement. Therefore, while there remains substantial geochemical support of a plume origin for Emeishan volcanism, LIP emplacement cannot be ubiquitously associated with regional pre-eruption uplift, particularly where complex lithospheric structure exists above a plume.

No comments: