Age and Paleoenvironmental Significance of the Frazer Beach
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University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Earth and Atmospheric Sciences, Department Papers in the Earth and Atmospheric Sciences of 2021 Age and Paleoenvironmental Significance of the rF azer Beach Member—A New Lithostratigraphic Unit Overlying the End- Permian Extinction Horizon in the Sydney Basin, Australia Stephen McLoughlin Robert S. Nicoll James L. Crowley Vivi Vajda Chris Mays See next page for additional authors Follow this and additional works at: https://digitalcommons.unl.edu/geosciencefacpub Part of the Earth Sciences Commons This Article is brought to you for free and open access by the Earth and Atmospheric Sciences, Department of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Papers in the Earth and Atmospheric Sciences by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Authors Stephen McLoughlin, Robert S. Nicoll, James L. Crowley, Vivi Vajda, Chris Mays, Christopher R. Fielding, Tracy D. Frank, Alexander Wheeler, and Malcolm Bocking ORIGINAL RESEARCH published: 08 January 2021 doi: 10.3389/feart.2020.600976 Age and Paleoenvironmental Significance of the Frazer Beach Member—A New Lithostratigraphic Unit Overlying the End-Permian Extinction Horizon in the Sydney Basin, Australia Stephen McLoughlin 1*, Robert S. Nicoll 2, James L. Crowley 3, Vivi Vajda 1, Chris Mays 1, Christopher R. Fielding 4, Tracy D. Frank 4, Alexander Wheeler 5 and Malcolm Bocking 6 1Department of Paleobiology, Swedish Museum of Natural History, Stockholm, Sweden, 2Independent Researcher, Bungendore, NSW, Australia, 3Isotope Geology Laboratory, Boise State University, Boise, ID, United States, 4Department of Earth and Atmospheric Sciences, University of Nebraska-Lincoln, Lincoln, NE, United States, 5School of Earth and Environmental Sciences, The University of Queensland, St. Lucia, QLD, Australia, 6Bocking Associates, Castle Hill, NSW, Australia Edited by: The newly defined Frazer Beach Member of the Moon Island Beach Formation is identified Evelyn Kustatscher, Museum of Nature South Tyrol, Italy widely across the Sydney Basin in both outcrop and exploration wells. This thin unit was Reviewed by: deposited immediately after extinction of the Glossopteris flora (defining the terrestrial end- Johann Neveling, Permian extinction event). The unit rests conformably on the uppermost Permian coal Council for Geoscience, South Africa seam in most places. A distinctive granule-microbreccia bed is locally represented at the Cindy Virginia Looy, University of California, Berkeley, base of the member. The unit otherwise consists of dark gray to black siltstone, shale, United States mudstone and, locally, thin lenses of fine-grained sandstone and tuff. The member *Correspondence: represents the topmost unit of the Newcastle Coal Measures and is overlain Stephen McLoughlin [email protected] gradationally by the Dooralong Shale or with a scoured (disconformable) contact by coarse-grained sandstones to conglomerates of the Coal Cliff Sandstone, Munmorah Specialty section: Conglomerate and laterally equivalent units. The member is characterized by a This article was submitted to “ ” Paleontology, palynological dead zone represented by a high proportion of degraded wood a section of the journal fragments, charcoal, amorphous organic matter and fungal spores. Abundant Frontiers in Earth Science freshwater algal remains and the initial stages of a terrestrial vascular plant recovery Received: 31 August 2020 flora are represented by low-diversity spore-pollen suites in the upper part of the unit in Accepted: 11 November 2020 Published: 08 January 2021 some areas. These assemblages are referable to the Playfordiaspora crenulata Citation: Palynozone interpreted as latest Permian in age on the basis of high precision McLoughlin S, Nicoll RS, Crowley JL, Chemical Abrasion Isotope Dilution Thermal Ionization Mass Spectrometry (CA-IDTIMS) Vajda V, Mays C, Fielding CR, Frank TD, Wheeler A and Bocking M dating of thin volcanic ash beds within and stratigraphically bracketing the unit. Plant (2021) Age and Paleoenvironmental macrofossils recovered from the upper Frazer Beach Member and immediately Significance of the Frazer Beach succeeding strata are dominated by Lepidopteris (Peltaspermaceae) and Voltziopsis Member—A New Lithostratigraphic Unit Overlying the End-Permian (Voltziales) with subsidiary pleuromeian lycopsids, sphenophytes, and ferns. Sparse Extinction Horizon in the Sydney vertebrate and invertebrate ichnofossils are also represented in the Frazer Beach Basin, Australia. Front. Earth Sci. 8:600976. Member or in beds immediately overlying this unit. The Frazer Beach Member is doi: 10.3389/feart.2020.600976 correlative, in part, with a thin interval of organic-rich mudrocks, commonly known as Frontiers in Earth Science | www.frontiersin.org 1 January 2021 | Volume 8 | Article 600976 McLoughlin et al. Frazer Beach Member 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. Keywords: Permian-Triassic, mass extinction, CA-IDTIMS, plant fossils, palynology, fluvial sedimentology, stable isotope geochemistry, anachronistic facies INTRODUCTION Permian coal seam (McElroy, 1969). However, early palynological studies employing floristic correlations with Coalfield geologists in New South Wales, Australia, have long other regions (Evans, 1966; Balme, 1969; Helby, 1970; Helby, recognized a unit of dark gray to black shales, mudstones and 1973; Helby et al., 1987) inferred the PTB to be positioned higher siltstones, typically <2m thick, capping the uppermost Permian (within the Narrabeen Group) than the major floral turnover coal seam across the Sydney Basin. Historically, this interval has (EPE). Some workers have invoked a significant hiatus and an been termed the Bulli or Vales Point “roof strata” (Diessel et al., erosional unconformity around the Permian-Triassic transition 1967), “roof shales” (Townrow, 1967b; White, 1981), (base of the Narrabeen Group) in various parts of the basin “transitional zone/beds” (Hennelly, 1958; Wu et al., 2019), (Rattigan and McKenzie, 1969; Helby, 1970; Helby, 1973; “blacks” (in part: Clark, 1992) or, in a paleontological sense, Herbert, 1997), whereas others argued that the transition is the “dead zone” (Vajda et al., 2020). Traditionally, the top of the conformable (Dun, 1910). Recent work integrating uppermost Permian coal seam has been used to define the sedimentology, palynostratigraphy and high-precision CA- boundary between the Newcastle Coal Measures (and Illawarra IDTIMS dating of zircon crystals from ash beds shows that Coal Measures in southern and western regions of the basin) and the transition is generally conformable in the basin’s main the overlying Narrabeen Group (Agnew et al., 1995; Armstrong depocenters and provides clarity to the positions of the EPE et al., 1995; Scheibner and Basden, 1998; Creech, 2002; Shi et al., and PTB within the succession (Metcalfe et al., 2015; Fielding 2010; Pinetown, 2014; Metcalfe et al., 2015; Laurie et al., 2016). et al., 2019; Fielding et al., 2020; Mays et al., 2020; Vajda et al., Consequently, previous studies have assigned the Vales Point/ 2020). Bulli “roof strata” to the basal Narrabeen Group. In contrast, Given that this package of mudrocks is lithologically distinct Hutton and Bamberry (1999, p. 122) recommended that these from the bracketing coal and sandstone units, has a unique fossil carbonaceous mudrocks should be treated as part of the Sydney content, has a broad geographic distribution, and is positioned in Subgroup (uppermost Newcastle/Illawarra Coal Measures), but an interval of global interest (between the EPE and PTB the unit has never been formally defined. horizons), we argue that it deserves recognition as a discrete The boundary between the Bulli/Katoomba/Vales Point coal lithostratigraphic unit. Here we formally describe this unit as the seams and the overlying shale/siltstone interval marks a major Frazer Beach Member of the Moon Island Beach Formation and change in fossil floras throughout the Sydney Basin and is the raise the Newcastle/Illawarra Coal Measures boundary to the top terrestrial expression of the end-Permian extinction event (EPE) of this new unit. We document the sedimentary characteristics, (Grebe, 1970; Helby, 1973; Retallack, 1977; Fielding et al., 2019; fossil biota, depositional setting, regional correlative units and Mays et al., 2020; Vajda et al., 2020). Recently, our team and global paleoenvironmental significance of this member. others have noted that this shale/mudstone/siltstone unit represents a distinctive lacustrine facies association (Facies Association G of Fielding et al., 2020) overprinted by paleosol MATERIAL AND METHODS development (Retallack, 2005), and is characterized by excursions in the values of carbon stable isotopes and chemical index of Sedimentological features and stratigraphic relationships were alteration (CIA) (Williams et al., 2017; Vajda et al., 2020). The compiled by logging numerous outcrop sections and bore cores unit hosts distinctive vertebrate ichnofossil (Retallack 1996; from sites across the Sydney Basin (see Fielding et al., 2020 for McLoughlin