From rainforest to herbland: New insights into land plant responses to the end-Permian mass extinction

The newly defined Frazer Beach Member of the Moon Island Beach Formation is identified widely across the Sydney Basin in both outcrop and exploration wells. This thin unit was deposited immediately after extinction of the Glossopteris flora (defining the terrestrial end-Permian extinction event). The unit rests conformably on the uppermost Permian coal seam in most places. A distinctive granule-microbreccia bed is locally represented at the base of the member. The unit otherwise consists of dark gray to black siltstone, shale, mudstone and, locally, thin lenses of fine-grained sandstone and tuff. The member represents the topmost unit of the Newcastle Coal Measures and is overlain gradationally by the Dooralong Shale or with a scoured (disconformable) contact by coarse-grained sandstones to conglomerates of the Coal Cliff Sandstone, Munmorah Conglomerate and laterally equivalent units. The member is characterized by a palynological “dead zone” represented by a high proportion of degraded wood fragments, charcoal, amorphous organic matter and fungal spores. Abundant freshwater algal remains and the initial stages of a terrestrial vascular plant recovery flora are represented by low-diversity spore-pollen suites in the upper part of the unit in some areas. These assemblages are referable to the Playfordiaspora crenulata Palynozone interpreted as latest Permian in age on the basis of high precision Chemical Abrasion Isotope Dilution Thermal Ionization Mass Spectrometry (CA-IDTIMS) dating of thin volcanic ash beds within and stratigraphically bracketing the unit. Plant macrofossils recovered from the upper Frazer Beach Member and immediately succeeding strata are dominated by Lepidopteris (Peltaspermaceae) and Voltziopsis (Voltziales) with subsidiary pleuromeian lycopsids, sphenophytes, and ferns. Sparse vertebrate and invertebrate ichnofossils are also represented in the Frazer Beach Member or in beds immediately overlying this unit. The Frazer Beach Member is correlative, in part, with a thin interval of organic-rich mudrocks, commonly known as the “marker mudstone” capping the Permian succession further to the north in the Bowen, Galilee and Cooper basins. The broad geographic distribution of this generally <5-m-thick mudrock unit highlights the development in eastern Gondwana of extensive, short-lived, shallow lacustrine systems with impoverished biotas in alluvial plain settings in the immediate aftermath of the end-Permian biotic crisis.

Section: Discussionmentioning

confidence: 87%

Age and Paleoenvironmental Significance of the Frazer Beach Member—A New Lithostratigraphic Unit Overlying the End-Permian Extinction Horizon in the Sydney Basin, Australia

McLoughlin

Nicoll²,

Crowley

et al. 2021

“…The taxonomic division of Early Triassic isoëtaleans into genera is based on variations in stem shape and length, strobilus characteristics, and morphology of sporophylls, leaves, microspores and megaspores. Their size ranged from very small herbaceous species to subarborescent ones (e.g., Retallack, 1997;Grauvogel-Stamm and Lugardon, 2001;Kustatscher et al, 2015;Feng et al, 2020). What all isoëtaleans have in common is their spirally arranged succulent leaves, sporophylls, and roots on a corm or elongated trunk.…”

Section: Taxonomic Remarks On the Order Isoëtalesmentioning

confidence: 99%

“…In the lower temporal resolution typical for the discontinuous megafossil record, a megafloral analysis by Grauvogel-Stamm and Ash (2005) revealed a similar pattern. Early-Middle Triassic macrofossil assemblages include the subarborescent Pleuromeia (Figure 2A) and its segregates, and the more Isoëtes-like, short-statured Tomiostrobus, Lepacyclotes ( Annalepis), Skilliostrobus and Isoetites (e.g., Retallack, 1997;Grauvogel-Stamm and Ash, 2005;Vajda and McLoughlin, 2007;Kustatcher et al, 2010;Hermann et al, 2011;Feng et al, 2020;Zhang et al, 2020). The partial, sometimes temporary, replacement of dominant flora province endemics with more cosmopolitan taxa resulted in a loss of floral provinciality-at the very least in the range of environments that is preserved in the fossil record.…”

Section: Setting the Stagementioning

confidence: 99%

“…In equatorial Euramerica, evidence for walchian conifers was last recorded in late Permian sediments (e.g., Poort et al, 1997). In Cathaysia, the seed fern order Gigantopteridales and the arborescent lycophytes (Lepidodendrales) had their last fossil appearances (Zhang et al, 2016;Feng et al, 2020). In the mid to high northern latitudes of (Sub)Angara, the coniferophyte Cordaitales went extinct (e.g., Dobruskina, 1994).…”

Section: Introductionmentioning

confidence: 99%

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Proliferation of Isoëtalean Lycophytes During the Permo-Triassic Biotic Crises: A Proxy for the State of the Terrestrial Biosphere

Looy¹,

Cittert²,

Duijnstee³

2021

Throughout their 420-Ma-long history, Lycopodiopsida have played a subordinate role at the landscape level with very few exceptions. One being the arborescent Lepidodendrales that dominated Pennsylvanian peat swamps in equatorial regions. Another is the enigmatic world-wide proliferation of sub-arborescent Isoëtales during, and in the aftermath of the Permo-Triassic terrestrial biosphere crisis that extended deep into the Triassic. Palynological as well as megafossil data shows that in a great proportion of locations around the globe that produced a fossil record, the provincial floras characteristic for the latest Permian were replaced by communities dominated by Isoëtales such as Pleuromeia and its allies. Our analysis of the isoëtalean biology, especially of the genus Pleuromeia, reveals an unusual suite of physiological and life-history traits, all indicating that it was an excellent stress-tolerator, but also a slow-growing weak competitor. This enabled Pleuromeia to thrive during environmental crises and occupy diverse habitats following the decline of other plants groups. Given their unusual biology, Isoëtales’ repeated ubiquity throughout the Early Triassic implies prolonged and repeated environmental stress in localities worldwide. Additionally, it demonstrates that the cosmopolitan isoëtalean-dominated systems produced a low-productivity, low-diversity terrestrial trophic base of the food web that no longer provided the same level of ecological and evolutionary goods and services (energy source, niche construction, ecosystem engineering, etc.) as the communities they replaced.

“…Roots of these lycophytes were composed of rhizospheres or corms with rootlets extending from it. With their rather simple rooting systems, they were adapted to unstabilized soil, and able to grow in waterlogged disturbed ecosystems (Retallack, 1975;Retallack, 1997;Feng et al, 2020) such as in riparian ecosystems (Kustatscher et al, 2014). Plant associations are sensitive to climatic changes not only under the modern global change (e.g.…”

Section: Stabilizing Factors Of Each Regimementioning

confidence: 99%

Regime Shifts in an Early Triassic Subtropical Ecosystem

Schneebeli‐Hermann

2020

The Early Triassic was one of the most remarkable time intervals in Earth History. To begin with, life on Earth had to face one of the largest subaerial volcanic degassing, the Siberian Traps, followed by a plethora of accompanying environmental hazards with pronounced and repeated climatic changes. These changes not only led to repeated and, for several marine nektonic clades, intense extinction events but also to significant changes in terrestrial ecosystems. The Early Triassic terrestrial ecosystems of the southern subtropical region (Pakistan) are not necessarily marked by abrupt extinction events but by extreme shifts in composition. Modern ecological theories describe such shifts as catastrophic regime shifts. Here, the applicability of modern ecological theories to these past events is tested. Abrupt shifts in ecosystems can occur when protracted changing abiotic drivers (e.g. climate) reach critical points (thresholds or tipping points) sometimes accentuated by stochastic events. Early Triassic terrestrial plant ecosystem changes stand out from the longer term paleobotanical records because changes of similar magnitude have not been observed for many millions of years before and after the Early Triassic. To date, these changes have been attributed to repeated severe environmental perturbations, but here an alternative explanation is tested: the initial environmental perturbations around the Permian–Triassic boundary interval are regarded here as a main cause for a massive loss in terrestrial ecosystem resilience with the effect that comparatively small-scale perturbations in the following ∼5 Ma lead to abrupt regime shifts in terrestrial ecosystems.