INTEGRATED PLUME WINTER SCENARIO FOR THE DOUBLE-PHASED EXTINCTION DURING THE PALEOZOIC-MESOZOIC TRANSITION

The Permian rocks recorded the double-phased major changes in the second half of the Permian in a global extent. Everything geologically unusual started in the Late Guadalupian (Middle Permian); i.e., 1) the first mass extinction, 2) onset of the superanoxia, 3) sea-level drop down to the Phanerozoic minimum, 4) onset of volatile fluctuation in carbon isotope ratio, 5) 87Sr/86Sr ratio of the Paleozoic minimum, 6) extensive felsic alkaline volcanism, and 7) Illawarra Reversal. The episodic magmatism was likely related to the activity of a mantle superplume that initially rifted Pangea. The superplume formed several LIPs that likely caused a “plume winter” with global cooling by dust/aerosol screens in the stratosphere, gas poisoning, acid rain damage to surface vegetation etc. Post-eruption global warming (plume summer) took over cooling and delayed the recovery of biodiversity and intensified the ocean stratification. A unique geomagnetic episode called the Illawarra Reversal around the Wordian-Capitanian boundary (ca. 265 Ma) recorded the appearance of a large instability in the geomagnetic dipole in the Earth’s outer core. This was triggered likely by the episodic fall-down of a cold megalith (subducted oceanic slabs) from the upper mantle to the D” layer above the 2,900 km-deep core-mantle boundary, in tight association with the launching of a mantle superplume. The Capitanian Kamura cooling event and the first biodiversity decline were probably led by the weakened geomagnetic intensity due to unstable dipole of geodynamo. Under the low geomagnetic intensity, the flux of galactic cosmic radiation increased to cause extensive cloud coverage over the planet and to drive the Kamura cooling event. The “Plume Winter” scenario is integrated to explain concordantly both the unique catastrophe in biosphere and the remarkable episode of the core’s geodynamo in terms of mantle superplume tectonics.