Intensive Wildfire Associated With Volcanism Promoted the Vegetation Changeover in Southwest China During the Permian−Triassic Transition

Yao-Feng Cai,Hua Zhang,Shu-Zhong Shen,Zhuo Feng

doi:10.3389/feart.2021.615841

Abstract

Palaeo-wildfire, which had an important impact on the end Permian terrestrial ecosystems, became more intense in the latest Permian globally, evidenced by extensive occurrence of fossil charcoals. In this study, we report abundant charcoals from the upper part of the Xuanwei Formation and the Permian–Triassic transitional Kayitou Formation in the Lengqinggou section, western Guizhou Province, Southwest China. These charcoals are well-preserved with anatomical structures and can be classified into seven distinctive types according to their characteristics. Organic carbon isotopic analyses of both bulk rocks and charcoals show that the δ13Corg values in the Kayitou Formation are notably more negative than those in the Xuanwei Formation, with a negative excursion of 4.08‰ immediately above the volcanic ash bed in the middle of the uppermost coal bed of the Xuanwei Formation. Charcoals with high reflectance values (Romean = 2.38%) are discovered below the ash bed. By contrast, the reflectance values (Romean = 1.51%) of the charcoals in the Kayitou Formation are much lower than those of the Xuanwei Formation, indicating the palaeo-wildfire types have changed from crown fires to surface fires, which was probably due to the retrogression of vegetation systems during the extinction. Based on the above evidence, we suppose that palaeo-wildfires became more frequent and more severe since the climate became drier during the latest Permian in Southwest China, and the eventual vegetation changeover of the terrestrial ecosystems in Southwest China could be caused by volcanism.

Highlights

Fire is a considerable disturbance that influences the Earth’s ecosystems over both short and long timescales (e. g., Scott, 2000; Sugihara et al, 2006; Belcher et al, 2013)
More and more investigations indicate that wildfire, which had an important impact on terrestrial ecosystems, could have contributed to the end-Permian mass extinction (EPME): a change in the maceral composition from Australia indicates that a major fire event resulted in the destruction of vegetation, and increased run-off and erosion on land during the late Permian (Glasspool, 2000); Wang and Chen (2001) proposed that highfrequency wildfires and water-stress might be the main extinction mechanisms for the forest vegetation dieback at the EPME in North China; large-scale combustion of coals and organic-rich sediments induced by the Siberian Traps, was suggested to have affected the global climate change and carbon cycle during the latest Permian (Grasby et al, 2011)
We report more than 50 horizons in the Lengqinggou section containing charcoal fragments from the upper Xuanwei and the Kayitou formations, indicating that palaeo-wildfires are common and frequent phenomena during the latest Permian in Southwest China

Summary

Introduction

Fire is a considerable disturbance that influences the Earth’s ecosystems over both short and long timescales (e. g., Scott, 2000; Sugihara et al, 2006; Belcher et al, 2013). More and more investigations indicate that wildfire, which had an important impact on terrestrial ecosystems, could have contributed to the end-Permian mass extinction (EPME): a change in the maceral composition from Australia indicates that a major fire event resulted in the destruction of vegetation, and increased run-off and erosion on land during the late Permian (Glasspool, 2000); Wang and Chen (2001) proposed that highfrequency wildfires and water-stress might be the main extinction mechanisms for the forest vegetation dieback at the EPME in North China; large-scale combustion of coals and organic-rich sediments induced by the Siberian Traps, was suggested to have affected the global climate change and carbon cycle during the latest Permian (Grasby et al, 2011). The published charcoal records from Permian and Triassic sediments were summarized by Abu Hamad et al (2012), showing a “charcoal gap” in the Early Triassic

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