Refined Permian–Triassic Floristic Timeline Reveals Early Collapse And
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Refned Permian–Triassic foristic timeline reveals early collapse and delayed recovery of south polar terrestrial ecosystems Chris Mays1,†, Vivi Vajda1, Tracy D. Frank2, Christopher R. Fielding2, Robert S. Nicoll3, Allen P. Tevyaw2, and Stephen McLoughlin1 1 Swedish Museum of Natural History, Box 50007 S-104 05 Stockholm, Sweden 2 Department of Earth & Atmospheric Sciences, University of Nebraska-Lincoln, 126 Bessey Hall, Lincoln, NE 68588-0340, USA 3 72 Ellendon Street, Bungendore, NSW 2621, Australia ABSTRACT Smithian–Spathian boundary (ca. 249 Ma), disappearance of coals across Gondwana (Re- indices of increased weathering, thick red- tallack et al., 1996), the extinction of the primary The collapse of late Permian (Lopingian) beds, and abundant pleuromeian lycophytes coal-forming glossopterid gymnosperms (Class Gondwanan foras, characterized by the likely signify marked climate change and Dictyopteridiopsida; McLoughlin, 2011), and extinction of glossopterid gymnosperms, intensifcation of the Gondwanan monsoon the disappearance of key herbaceous to arbo- heralded the end of one of the most endur- climate system. This is the frst record of the rescent accessory taxa including a range of ing and extensive biomes in Earth’s history. Smithian–Spathian foral overturn event in sphenophytes, ferns, cordaitaleans, and conifers The Sydney Basin, Australia, hosts a near- high southern latitudes. (Hill et al., 1999). Glossopterids constituted an continuous, age-constrained succession of overwhelming proportion of the Lopingian (late high southern paleolatitude (∼65–75°S) ter- INTRODUCTION Permian) terrestrial biomass across Gondwana restrial strata spanning the end-Permian (e.g., Miller et al., 2016) and were the keystones extinction (EPE) interval. Sedimentological, Several mass extinction intervals in Earth’s of Lopingian component communities incor- stable carbon isotopic, palynological, and history have been linked to rapid warming driv- porating a broad range of invertebrates, verte- macroforal data were collected from two en by elevated levels of greenhouse gases (Bond brates, and fungi (Zavada and Mentis, 1992; cored coal-exploration wells and correlated. and Wignall, 2014), e.g., the end-Triassic ex- Prevec et al., 2009; Slater et al., 2012, 2015). Six palynostratigraphic zones, supported by tinction (McElwain et al., 1999; Steinthorsdottir Consequently, the loss of these primary produc- ordination analyses, were identifed within et al., 2011) and Toarcian oceanic anoxic event ers would have had an unprecedented impact the uppermost Permian to Lower Triassic (McElwain et al., 2005; Suan et al., 2010). The on herbivore populations (van de Schootbrugge succession, corresponding to discrete vegeta- end-Permian mass extinction (EPE), an episode and Gollner, 2013) even if gross plant diversity tion stages before, during, and after the EPE of Earth history associated with the single great- changes were modest. interval. Collapse of the glossopterid biome est loss of biodiversity, is no exception. Extreme Systematic analysis of the amplitude and marked the onset of the terrestrial EPE and warming driven by greenhouse gas emissions timing of foral productivity changes across the may have signifcantly predated the ma- from the Siberian Traps Large Igneous Prov- Permian–Triassic will elucidate the progressive rine mass extinctions and conodont-defned ince has been implicated as a proximate cause patterns of environmental change and the cata- Permian–Triassic Boundary. Apart from ex- of this cataclysm (Brand et al., 2012; Payne strophic diversity losses at higher trophic levels. tinction of the dominant Permian plant taxa, and Clapham, 2012; Song et al., 2014; Burgess Moreover, previous reports of a few glossopterids the EPE was characterized by a reduction et al., 2017). Approximately 50% of marine in- post-dating the initial stages of the EPE interval in primary productivity, and the immediate vertebrate families were eliminated during this in Gondwana (see Bomfeur et al., 2018) require aftermath was marked by high abundances episode of extinctions (Raup and Sepkoski, testing to assess the timing and signifcance of of opportunistic fungi, algae, and ferns. 1982; Alroy et al., 2008), ∼81% of marine fos- relictual communities that might have harbored This transition is coeval with the onset of a sil species disappeared (Stanley, 2016), and it is plant groups that seeded subsequent taxonomic 13 gradual global decrease in δ Corg and the the only mass extinction interval with a similar radiations in the Triassic. It is particularly rel- primary extrusive phase of Siberian Traps impact on both marine and terrestrial faunas evant to establish the pace and extent of extinc- Large Igneous Province magmatism. The (Benton, 1995; Labandeira, 2005). tion and recovery in high-latitude biomes, which dominant gymnosperm groups of the Gond- The global fossil record of terrestrial foras may have provided the optimal settings for the wanan Mesozoic (peltasperms, conifers, and reveals a greater species turnover between the persistence of thermophobic and hygrophilic corystosperms) all appeared soon after the Permian and Triassic than any other interval in plant communities preferring cool and moist en- collapse but remained rare throughout the Earth’s history (McElwain and Punyasena, 2007; vironments, while illuminating the adaptations immediate post-EPE succession. Faltering Cascales-Miñana et al., 2016). Although it has promoting their survival. In this paper, we docu- recovery was due to a succession of rapid been argued that foral diversity changes across ment the foristic changes from the end-Permian and severe climatic stressors until at least the the EPE were modest compared to animals (e.g., ecological collapse through the stepwise pattern late Early Triassic. Immediately prior to the Schneebeli-Hermann et al., 2017; Nowak et al., of vegetation recovery in the southern high-lat- 2019), a major terrestrial ecosystem collapse itude Lower Triassic succession of the Sydney †[email protected]. is represented by the apparently synchronous Basin, eastern Australia. This foristic succession GSA Bulletin; Month/Month 2019; 0; p. 1–25; https://doi.org/10.1130/B35355.1; 12 fgures; Data Repository item 2020024. For permission to copy, contact [email protected] 1 © 2019 Geological Society of America Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/doi/10.1130/B35355.1/4871101/b35355.pdf by Univ Nebraska Lincoln user on 14 November 2019 Mays et al. provides context for the interpretation of climatic 2010; Esmeray-Senlet et al., 2017). Conse- which occurred long before the system bound- shifts and other global events through the latest quently, terrestrial biostratigraphic studies have ary sensu stricto based on correlations with the Permian and Early Triassic. proposed widely disparate placements of the sys- stratotype section at Meishan, South China. With tem boundary, especially in regions remote from recent improved chronostratigraphic controls on Timing of the End-Permian Extinction and the stratotype section. For example, some have the Sydney-Gunnedah-Bowen basin succession Permian–Triassic Boundary placed the PTB in stratigraphical proximity to the (Metcalfe et al., 2015; Laurie et al., 2016; Field- terrestrial EPE (e.g., Laurie et al., 2016), whereas ing et al., 2019), the Lopingian to Lower Trias- In continental settings, the EPE has tradi- others have favored its placement much higher sic palynozones of eastern Australia have been tionally been interpreted as a single, rapid de- in the stratigraphic successions (e.g., Looy et al., recalibrated herein (Fig. 1). This refned timeline stabilization and collapse of the terrestrial bio- 2001; Lindström and McLoughlin, 2007; Gastal- provides the context for interpreting the stage- sphere (e.g., Visscher et al., 1996), whereas in do et al., 2015; Zhang et al., 2016). Independent by-stage extinctions and recoveries of the latest the marine realm at least two prominent stages proxies have been increasingly employed to cor- Permian to Early Triassic south polar foras. of extinction have been identifed, e.g., at the relate both the PTB and EPE over broad regions, Permian–Triassic boundary (PTB)type section such as U-Pb radiogenic-isotope ages (Burgess Geological Setting at Meishan, southern China (Jin et al., 2000; Yin et al., 2014; Metcalfe et al., 2015), stable carbon et al., 2012; Song et al., 2013). These extinction isotope trends (e.g., Morante, 1996; Korte and During the Permian and Triassic, the Sydney pulses, and their associated sharp carbon isotope Kozur, 2010), and/or other geochemical signa- Basin was situated at ∼65–75°S (Veevers, 2006), excursions, are separated by ∼60 k.y. (Burgess tures (e.g., Grice et al., 2005; Williams et al., and it was the southernmost component of the et al., 2014) and have been employed to defne 2012, 2017). The combination of radioisotopic Sydney-Gunnedah-Bowen basin complex. This an “extinction interval.” Furthermore, the marine geochronology, chemostratigraphy, and high- large foreland basin system and the continental record shows a long-term carbon isotope excur- resolution biostratigraphy currently provides the volcanic belt to its east, the New England Oro- sion that predates the primary extinction phase most robust method for dating and correlating gen, developed in association with active sub- and the PTB by more than one million years, the key terrestrial bioevents associated with the duction of Panthalassan oceanic crust along