End-Permian terrestrial disturbance followed by the complete plant devastation, and the vegetation proto-recovery in the earliest-Triassic recorded in coastal sea sediments

The Permian−Triassic mass extinction was the most severe biotic crisis of the past 540 million years, eliminating 80–90% of species in the ocean and ~ 70% of land-based vertebrate families. Researchers have debated whether terrestrial vegetation collapse occurred before or after the marine extinction, or if they were synchronous. We analyzed the ratios of normal alkanes of terrestrial plant origin to total normal alkanes (terrestrial plant index) as well as those of pristane to phytane, which are affected by terrestrial plant inflow and ocean redox, in shallow marine, terrestrial lagoon, and central deep-ocean sedimentary rocks from China, Italy, India, and Japan to elucidate the terrestrial vegetation history. Interpretation of pristane/phytane ratios was conducted through comparison with other seawater redox indices. Both proxies indicate that two terrestrial vegetation collapses occurred, before and at the end-Permian marine extinction in the coastal sea environment, followed by the complete plant devastation, and a subsequent terrestrial vegetation proto-recovery in the earliest Triassic. The two proxies showed opposite patterns in a terrestrial lagoon setting section, and those from a central deep-ocean setting indicate that little terrestrial plant material reached the central ocean. These differing responses of the pristane/phytane ratios among geographical settings are consistent with natural phenomena, indicating that the method proposed in this study results in valid reconstruction of vegetation changes. Cyanobacterial blooms occurred from the end-Permian vegetation collapse until after the massive plant-soil erosion, suggesting that terrestrial ecosystem disturbance caused deterioration of the environment for eukaryotic algae in the coastal sea and terrestrial lagoon.