Refined Permian–Triassic floristic timeline reveals early collapse and delayed recovery of south polar terrestrial ecosystems

Abstract

The collapse of late Permian (Lopingian) Gondwanan floras, characterized by the extinction of glossopterid gymnosperms, heralded the end of one of the most enduring and extensive biomes in Earth’s history. The Sydney Basin, Australia, hosts a near-continuous, age-constrained succession of high southern paleolatitude (∼65–75°S) terrestrial strata spanning the end-Permian extinction (EPE) interval. Sedimentological, stable carbon isotopic, palynological, and macrofloral data were collected from two cored coal-exploration wells and correlated. Six palynostratigraphic zones, supported by ordination analyses, were identified within the uppermost Permian to Lower Triassic succession, corresponding to discrete vegetation stages before, during, and after the EPE interval. Collapse of the glossopterid biome marked the onset of the terrestrial EPE and may have significantly predated the marine mass extinctions and conodont-defined Permian–Triassic Boundary. Apart from extinction of the dominant Permian plant taxa, the EPE was characterized by a reduction in primary productivity, and the immediate aftermath was marked by high abundances of opportunistic fungi, algae, and ferns. This transition is coeval with the onset of a gradual global decrease in δ13Corg and the primary extrusive phase of Siberian Traps Large Igneous Province magmatism. The dominant gymnosperm groups of the Gondwanan Mesozoic (peltasperms, conifers, and corystosperms) all appeared soon after the collapse but remained rare throughout the immediate post-EPE succession. Faltering recovery was due to a succession of rapid and severe climatic stressors until at least the late Early Triassic. Immediately prior to the Smithian–Spathian boundary (ca. 249 Ma), indices of increased weathering, thick redbeds, and abundant pleuromeian lycophytes likely signify marked climate change and intensification of the Gondwanan monsoon climate system. This is the first record of the Smithian–Spathian floral overturn event in high southern latitudes.

The base of the Lystrosaurus Assemblage Zone, Karoo Basin, predates the end-Permian marine extinction

“…This floral change is observed in many areas of Gondwana and was, until recently, interpreted as the terrestrial equivalent of the marine end-Permian biotic crisis 37,38 . More recent discoveries from the Sydney Basin in Australia, however, showed that the collapse of glossopterid dominated forests occurred about 370k years prior to the marine event 6 , although we note the presence there of a long diastem between the last Permian taxa characteristic of the Glossopteris flora and the first post-extinction pollen record 39,40 .…”

“…Hg and TOC values are the average of triplicate analyses of each horizon sampled. Palynological zone assignments, correlated with Australia 39,40 , appear against recovered pollen-and-spore assemblages. See supplemental information for legend.…”

“…The pollen assemblage immediately above the ash-fall tuff (Fig. 2) is correlative with the Dulhuntyispora parvithola zone 39,40 and the assemblage preserved stratigraphically higher is correlative with the Playfordiaspora crenulata zone 39,40 . It is at the base of the P. crenulata zone that a major floral change is interpreted as the demise of the Glossopteris flora in the Sydney Basin, Australia (Fig.…”

“…Global chronostratigraphy time scale Magnetic polarity (34,35) Australian palynological assemblage zones (6,39,40) Karoo basin palynological assemblage zones (this paper) Karoo basin vertebrate assemblage zones (27,28) Siberian trap magmatic activity (7) P. crenulata Smithian Fig. 4 Diagram synthesis of late Permian and early Triassic global chronostratigraphic time scale in Ma; magnetostratigraphy and polarity intervals 34,35 (black = normal, white = reverse); duration of Siberian Trap magmatic lava, pyroclastic, and sill emplacement activity 7 ; Australian palynological assemblage zones 39,40 and geochronometric age placed on vegetation collapse in the Sydney Basin; 6 compared with the results of the present study. Ages of the Dulhuntyispora parvithola palynological assemblage are provided for the upper Daptocephalus 20,21 and lower Lystrosaurus AZ (this paper) against magnetostratigraphic context based on interpreted magnetic stratigraphy at Old Lootsberg Pass and Bethel farm 21,28 .…”

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“…Most importantly, the end-Permian mass extinction constituted the most severe extinction event for marine animals (e.g., Benton and Twitchett, 2003;Stanley, 2016;Delfino et al, 2020). The timing and impact of this event on the biodiversity of terrestrial animals and land plants is not yet settled (e.g., Benton and Newell, 2014;Cleal, 2014, Cascales-Miñana et al, 2016;Fielding et al, 2019;Nowak et al, 2019;Gastaldo et al, 2020;Mays et al, 2020). However, it is generally accepted that the community structure of terrestrial floras underwent important changes, and there is a growing consensus that these changes should primarily be understood as a matter of successive ecological disturbances, rather than a question of abrupt biodiversity loss (Hochuli et al, 2016;Mishra et al, 2017;Fielding et al, 2019;Nowak et al, 2019;Vajda et al, 2020).…”