Research article
Terrestrial ecosystem collapse and soil erosion before the end-Permian marine extinction: Organic geochemical evidence from marine and non-marine records

https://doi.org/10.1016/j.gloplacha.2020.103327Get rights and content

Highlights

  • Plant extinction was followed by soil erosion and the end-Permian marine extinction.

  • Bacteria flourished during the plant extinction in the non-marine section.

  • Bacteria flourished during the end-Permian marine extinction in the marine section.

  • Proto-recovery of vegetation coincided with global warming and oceanic euxinia.

Abstract

A terrestrial ecosystem collapse event accompanied by extensive soil erosion has been widely recorded in marine sedimentary rocks at the vicinity of the end-Permian mass extinction. However, the precise timing of this event and its impact on the marine extinction have not yet been ascertained. Here we present an organic geochemical study of non-marine and marine sections from the South China Craton, which shows that terrestrial ecosystem collapse was accompanied by a soil erosion event, and was followed by the end-Permian marine extinction. Two separate events devastated the terrestrial ecosystem prior to the marine extinction event, over a timespan of dozens of kyr. Bacteria flourished in the non-marine section coeval with a decline in terrestrial plants and in the marine section during the end-Permian marine extinction. A proto-recovery of herbaceous plants (not woody plants) occurred dozens of kyr after the end-Permian marine extinction and coincided with a global warming maximum and oceanic anoxia/euxinia.

Introduction

The Permian–Triassic (P–Tr) mass extinction, which occurred approximately 252 Myr ago, was the most devastating extinction in Phanerozoic history. It is estimated that more than 90% of marine species and about 70% of terrestrial vertebrate families were eliminated across the P–Tr transition (Erwin, 1994; Shen et al., 2011; Benton, 2018). There was a major loss of terrestrial flora, mostly coinciding with the end-Permian extinction of terrestrial and marine fauna (Twitchett et al., 2001; Ward et al., 2005; Hochuli et al., 2010). This terrestrial devastation is demonstrated globally by the mass disappearance of the Glossopteris and Gigantopteris megaflora, the reduction in palynomorphs, the last appearances of plant remains and abundant charcoal fossils from the terminal Changhsingian (latest Permian) age in non-marine sections (Hochuli et al., 2010; Cui et al., 2015; Zhang et al., 2016; Fielding et al., 2019; Chu et al., 2020), as well as a sedimentary facies change from meandering to braided river systems and a pronounced coal gap after the mass extinction event (Retallack, 1995; Newell et al., 1999; Ward et al., 2000; Benton and Newell, 2014). However, the dissimilar taxonomic diversity of gymnosperm pollen as well as the low abundance of gymnosperm megafossils indicate that >50% plant species became extinct, the worst crisis in plant history (Nowak et al., 2019).

The first geological evidence of excessive soil erosion was provided by pedoliths (redeposited paleosols) at the end-Permian crisis (Retallack, 2005). The change from meandering to braided stream systems indicates a decrease in riverbank sediments after a loss of rooted vegetation along with global warming during the end-Permian mass extinction (Newell et al., 1999; Ward et al., 2000; Benton and Newell, 2014). Higher resolution organic geochemical data in shallow marine sections show that the soil and rock erosion event slightly preceded the end-Permian extinction (EPE) in the ocean (Sephton et al., 2005; Fenton et al., 2007; Kaiho et al., 2016; Xie et al., 2017). Wildfire indicated by increased charcoal followed by high mercury (Hg) concentrations from southwestern China coincided with the end-Permian plant extinction and end-Permian terrestrial ecosystem devastation event (EPTD), which occurred prior to the EPE and the peak of volcanism (Chu et al., 2020). Paired coronene (six-ring polycyclic aromatic hydrocarbon [PAH], high-temperature combustion proxy)–mercury spikes as a refined proxy for LIP emplacement indicate that discrete volcanic eruptions could have caused the terrestrial ecosystem crisis followed by the marine ecosystem crisis, with the terrestrial ecosystem being disrupted by smaller global environmental changes than the marine ecosystem (Kaiho et al., 2020). The soil erosion event is demonstrated by the high excursions of inorganic weathering indices (Chemical Index of Alteration [CIA], Plagioclase Index of Alteration, and Chemical Index of Weathering) spanning the end-Permian plant extinction (Cao et al., 2019). The dramatic collapse in the soil system associated with rapid deforestation, drying, weathering, and the last occurrences of Gigantopteris and Glossopteris were recorded before the EPE in non-marine sections in South China and Australia (Zhang et al., 2016; Fielding et al., 2019) followed by temporary gymnosperm recovery in the negative carbon isotope (CI) shift (Hochuli et al., 2010, Hochuli et al., 2016). The extensive soil erosion at the end of the EPTD impacted the marine ecosystem during the P–Tr transition (Kaiho et al., 2016). Biomarker evidence from shallow marine sections suggests that the erosion event led to an algal bloom, the release of toxic components, asphyxiation, and oxygen-depleted near-shore bottom seawater, which served as environmental stresses for near-shore marine animals (Kaiho et al., 2016; Xie et al., 2017). The sudden disappearance of marine reef systems together with fusulinids and coral, followed by the mortality of benthic fauna, occurred at the EPE (Song et al., 2013; Kaiho et al., 2016).

The transient expansion of anoxic/euxinic seawater to the surface water reached a maximum at the EPE (Kaiho et al., 2016), but ocean stratification, oceanic anoxia/euxinia, and global warming reached their maxima in the earliest Triassic, during a period of long duration (1.4 Myr), with fluctuations continuing until the end of the Smithian (Joachimski et al., 2012; Sun et al., 2012; Kaiho et al., 2016; Xie et al., 2017; Zhang et al., 2018). The most striking discovery of the Sydney Basin paleosol study was warming at the P–Tr boundary (PTB), characterized as a “post-apocalyptic greenhouse” (Retallack, 1999). Evidence from δ18O values of phosphate-bound conodont apatite in the Shangsi and Meishan sections and CIA data from North China indicates a ~10°C increase in surface seawater and atmosphere temperatures across the end-Permian crisis (Joachimski et al., 2012; Sun et al., 2012; Chen et al., 2016; Shen et al., 2018; Petsios et al., 2019).

Although both terrestrial and marine biotic and environmental investigations have progressed in recent decades, one of the remaining issues, as noted by Bottjer (2012), is that the correlations between land collapse, recovery, and environmental changes and marine devastation events must be clarified in detail. To establish the temporal patterns of these variables in both marine and terrestrial settings, and the dynamics thereof during the latest Permian to the earliest Triassic (late Changhsingian to Griesbachian), we used organic carbon isotopes and biomarkers to investigate the timing of terrestrial vegetation loss, the recovery of the terrestrial vegetation, bacteria/eukaryote ratios, marine mass mortality, and environmental stress recorded in a non-marine section at Xiaohebian and a marine section at Shangsi in the paleo-South China Craton spanning the end-Permian mass extinction (Fig. 1). Previously published paleontological data from these study sections provide a solid foundation for mapping high-resolution temporal patterns of both biotic and environmental changes.

Section snippets

Geological setting

The non-marine Xiaohebian section is located near the town of Halahe in Guizhou Province in South China (N26°50'08", E104°01'09"). The P–Tr successions of western Guizhou and eastern Yunnan are mainly composed of the Upper Permian Xuanwei Formation and the Lower Triassic Kayitou and Dongchuan Formations (Fig. 1). The Xiaohebian section consists of an Uppermost Permian coal-bearing Xuanwei Formation overlain by a coal-barren brownish-yellow Kayitou Formation 15 m thick. Above the Kayitou

Methods

Approximately 50 shale, mudstone, silty mudstone, and siltstone samples and 71 carbonate, shale, and marl samples were collected from the Xiaohebian and Shangsi sections for organic geochemical assessment, respectively. The organic compounds were identified using an Agilent 7890B GC interfaced to an Agilent 7000 triple-quadrupole mass spectrometer. The total organic carbon (TOC) and total nitrogen (TN) contents of the sedimentary rocks were determined using an Arlo-Erba elemental analyzer

Basic information

In the organic matter isotope (δ13Corg) data from the Xiaohebian section, level B shows the highest plateau of –22‰, followed by a slight decrease in level C. The negative shift starts in level C and continues from level D to level E, with the lowest values of –21‰ and –29‰, respectively. The δ13Corg data starts to increase from level E to level F until reaching –20‰ in the Xiaohebian section. In the δ13Ccarb data from the Shangsi section, the increase begins in level B and reaches the highest

Temporal pattern of terrestrial changes

The onset of the vegetation collapse occurred before the end-Permian extinction (EPE) in both the Xiaohebian and Shangsi sections, as indicated by the low terrestrial plant index value at CI level D (Fig. 5, Fig. 6). The soil erosion events coincided with the extinction event in both sections, as demonstrated by the high C30M/C30HP and DBF/Phe data. The complete devastation of vegetation occurred after the end-Permian terrestrial ecosystem devastation event (EPTD) in the non-marine Xiaohebian

Conclusion

This biomarker study in the non-marine section at Xiaohebian shows that a collapse of terrestrial higher plants marked by a low (C17+19)/(C17+19+27+29) n-alkane ratio, a soil erosion event marked by high DBF/Phe values, and the proliferation of bacteria marked by high hopane/sterane ratios occurred coincidentally at CI level D, followed by a negative excursion of δ13Corg at CI levels D–E, which was followed by the complete devastation of vegetation at CI level F. Significantly high n-C17/short n

Declaration of competing interest

None.

Acknowledgements

This work was supported by the Japan Society for the Promotion of Science (KAKENHI—Grants-in-Aid for Scientific Research, 25247084) and the National Science Foundation of China (grants nos. 41530104, 41602024, and 41661134047). We thank Megumu Fujibayashi for measuring organic carbon content and its isotopes, Hideko Takayanagi for helping to get the carbonate carbon isotope data.

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