Showing papers on "Permian published in 2020"

The Jurassic Period

Abstract: Ammonites underwent an evolutionary diversification after the mass extinction of the end Triassic induced by the formation of a Large Igneous province (LIP), and this group provides the most useful marine biostratigraphy. Only two levels within the Jurassic are relatively well determined using U–Pb dating from single zircons in ash beds, at the base Hettangian and the Pliensbachian–Toarcian boundary. Otherwise the Lower Jurassic is scaled using astrochronology and the Middle and Upper Jurassic scaled from Pacific seafloor spreading rates correlated to magnetic reversals. LIP activity during the Early Jurassic (Triassic–Jurassic boundary and Toarcian) perturbed global environments to extents not evidenced since the end Permian, and age relationships allow for a strong causal connection between these LIP eruptions and mass extinctions caused by major paleoenvironmental change, including ocean anoxia. Breakup of the supercontinent Pangea dominated paleogeography and paleoceanography and created shallow seaways that form sources and traps for hydrocarbons. Calcareous planktonic algae diversified and migrated from shallow seaways to open oceans to set the stage for the beginning of modern oceanic biogeochemical cycling; calcareous nannofossils provide additional widely used correlation tools.

Permian–Triassic mass extinction pulses driven by major marine carbon cycle perturbations

Abstract: The Permian/Triassic boundary approximately 251.9 million years ago marked the most severe environmental crisis identified in the geological record, which dictated the onwards course for the evolution of life. Magmatism from Siberian Traps is thought to have played an important role, but the causational trigger and its feedbacks are yet to be fully understood. Here we present a new boron-isotope-derived seawater pH record from fossil brachiopod shells deposited on the Tethys shelf that demonstrates a substantial decline in seawater pH coeval with the onset of the mass extinction in the latest Permian. Combined with carbon isotope data, our results are integrated in a geochemical model that resolves the carbon cycle dynamics as well as the ocean redox conditions and nitrogen isotope turnover. We find that the initial ocean acidification was intimately linked to a large pulse of carbon degassing from the Siberian sill intrusions. We unravel the consequences of the greenhouse effect on the marine environment, and show how elevated sea surface temperatures, export production and nutrient input driven by increased rates of chemical weathering gave rise to widespread deoxygenation and sporadic sulfide poisoning of the oceans in the earliest Triassic. Our findings enable us to assemble a consistent biogeochemical reconstruction of the mechanisms that resulted in the largest Phanerozoic mass extinction. The end-Permian mass extinction was linked with ocean acidification due to carbon degassing associated with Siberian Trap emplacement, according to boron isotopes from fossil shells and reconstruction of the carbon cycle.

The Base of the Lystrosaurus Assemblage Zone, Karoo Basin, Predates the end-Permian Marine Extinction

Abstract: The current model for the end-Permian terrestrial ecosystem crisis holds that systematic loss exhibited by an abrupt turnover from the Daptocephalus to the Lystrosaurus Assemblage Zone (AZ; Karoo Basin, South Africa) is time equivalent with the marine Permian–Triassic boundary (PTB). The marine event began at 251.941 ± 0.037 Ma, with the PTB placed at 251.902 ± 0.024 Ma (2σ). Radio-isotopic dates over this interval in the Karoo Basin were limited to one high resolution ash-fall deposit in the upper Daptocephalus AZ (253.48 ± 0.15 (2σ) Ma) with no similar age constraints for the overlying biozone. Here, we present the first U-Pb CA-ID-TIMS zircon age (252.24 ± 0.11 (2σ) Ma) from a pristine ash-fall deposit in the Karoo Lystrosaurus AZ. This date confirms that the lower exposures of the Lystrosaurus AZ are of latest Permian age and that the purported turnover in the basin preceded the end-Permian marine event by over 300 ka, thus refuting the previously used stratigraphic marker for terrestrial end-Permian extinction. The end-Permian is associated with major changes in both marine and terrestrial biodiversity. Here, Gastaldo et al. present high resolution dating of the Lystrosaurus Assemblage Zone in the Karoo Basin, South Africa, demonstrating that the marine crisis did not mirror a coeval event on land.

Siberian Trap volcanism, global warming and the Permian-Triassic mass extinction: New insights from Armenian Permian-Triassic sections

Abstract: Permian-Triassic boundary sections from Armenia were studied for carbon isotopes of carbonates as well as oxygen isotopes of conodont apatite in order to constrain the global significance of earlier reported variations in the isotope proxies and elaborate the temporal relationship between carbon cycle changes, global warming and Siberian Trap volcanism. Carbon isotope records of the Chanakhchi and Vedi II sections show a 3–5‰ negative excursion that start in the Clarkina nodosa (C. yini) conodont Zone (latest Permian) with minimum values recorded in Hindeodus parvus to Isarcicella isarcica conodont zones (earliest Triassic). Sea surface temperatures (SST) reconstructed from oxygen isotopes of conodont apatite increase by 8–10 °C over an extrapolated time interval of ∼39 ka with the onset of global warming occurring in the C. iranica (C. meishanensis) Zone of the latest Permian. Climate warming documented in the Armenian sections is comparable to published time-equivalent shifts in SST in Iran and South China suggesting that this temperature change represents a true global signature. By correlating the Armenian and Iranian section with the radiometrically well-dated Meishan GSSP (Global Stratotype Section and Point) section (South China), the negative shift in δ13C is estimated to have occurred 12–128 ka prior to the onset of global warming. This temporal offset is unexpected given the synchrony in changes in atmospheric CO2 and global temperature as seen in Pleistocene ice core records. The negative δ13C excursion is explained by the addition of emission of isotopically light CO2 and CH4 from thermogenic heating of organic carbon-rich sediments by Siberian Trap sill intrusions. However, the observed time lag in the δ13C and δ18O shifts questions the generally assumed cause-effect relationship between emission of thermogenically produced greenhouse gases and global warming. The onset of temperature rise coincides with a significant enrichment in Hg/TOC (total organic carbon) ratios arguing for a major volcanic event at the base of the extinction interval. Whether global warming was a major factor for the Late Permian mass extinction depends on the duration of the extinction interval. Warming only starts at the base of the extinction interval, but with the extinction encompassing a time interval of 60 ± 48 ka, global climate warming in conjunction with temperature-related stressors as hypoxia and reduced nutrient availability may have been one of the major triggers of the most devastating biotic crisis in Earth history.

Toxic mercury pulses into late Permian terrestrial and marine environments

Abstract: Large spikes in mercury (Hg) concentration are observed globally at the latest Permian extinction (LPE) horizon that are thought to be related to enhanced volcanic emissions of the Siberian Traps large igneous province (LIP). While forming an effective chemostratigraphic marker, it remains unclear whether such enhanced volcanic Hg emissions could have generated toxic conditions that contributed to extinction processes. To address this, we examined the nature of enhanced Hg emissions from the Siberian Traps LIP and the potential impact it may have had on global ecosystems during the LPE. Model results for a LIP eruption predict that pulses of Hg emissions to the atmosphere would have been orders of magnitude greater than normal background conditions. When deposited into world environments, this would have generated a series of toxic shocks, each lasting >1000 yr. Such repeated Hg loading events would have had severe impact across marine trophic levels, as well as been toxic to terrestrial plant and animal life. Such high Hg loading rates may help explain the co-occurrence of marine and terrestrial extinctions.

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.

Provenance of Pennsylvanian–Permian sedimentary rocks associated with the Ancestral Rocky Mountains orogeny in southwestern Laurentia: Implications for continental-scale Laurentian sediment transport systems

Abstract: 2School of Earth and Sustainability, Northern Arizona University, Flagstaff, AZ 86011 3Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX 77204 4 Department of Earth and Space Sciences, University of Washington, Seattle, WA 98195 Leary, R.J., Umhoefer, P., Smith, M.E., Smith, T.M., Saylor, J.E., Riggs, N., Burr, G., Lodes, E., Foley, D., Licht, A., Mueller, M.A., and Baird, C., 2020, Provenance of Pennsylvanian–Permian sedimentary rocks associated with the Ancestral Rocky Mountains orogeny in southwestern Laurentia: Implications for continental-scale Laurentian sediment transport systems: Lithosphere, https://doi.org/10.1130/L1115.1. GSA Data Repository Item 2020103

İzmir‐Ankara suture as a Triassic to Cretaceous plate boundary – data from central Anatolia

Abstract: The Izmir‐Ankara suture represents part of the boundary between Laurasia and Gondwana along which a wide Tethyan ocean was subducted. In northwest Turkey, it is associated with distinct oceanic subduction‐accretion complexes of Late Triassic, Jurassic and Late Cretaceous ages. The Late Triassic and Jurassic accretion complexes consist predominantly of basalt with lesser amounts of shale, limestone, chert, Permian (274 Ma zircon U‐Pb age) metagabbro and serpentinite, which have undergone greenschist facies metamorphism. Ar‐Ar muscovite ages from the phyllites range from 210 Ma down to 145 Ma with a broad southward younging. The Late Cretaceous subduction‐accretion complex, the ophiolitic melange, consists of basalt, radiolarian chert, shale and minor amounts of recrystallized limestone, serpentinite and greywacke, showing various degrees of blueschist facies metamorphism and penetrative deformation. Ar‐Ar phengite ages from two blueschist metabasites are ca. 80 Ma (Campanian). The ophiolitic melange includes large Jurassic peridotite‐gabbro bodies with plagiogranites with ca. 180 Ma U‐Pb zircon ages. Geochronological and geological data show that Permian to Cretaceous oceanic lithosphere was subducted north under the Pontides from the Late Triassic to the Late Cretaceous. This period was characterized generally by subduction‐accretion, except in the Early Cretaceous, when subduction‐erosion took place. In the Sakarya segment all the subduction accretion complexes, as well as the adjacent continental sequences, are unconformably overlain by Lower Eocene red beds. This, along with the stratigraphy of the Sakarya Zone indicate that the hard collision between the Sakarya Zone and the Anatolide‐Tauride Block took place in Paleocene.

Sequence stratigraphy, paleogeography, and coal accumulation regularity of major coal-accumulating periods in China

Abstract: There are 9 major coal-accumulating periods during geological history in China, including the Early Carboniferous, Late Carboniferous-Early Permian, Middle Permian, Late Permian, Late Triassic, Early-Middle Jurassic, Early Cretaceous, Paleogene and Neogene. The coal formed in these periods were developed in different coal-accumulating areas (CAA) including the North China, South China, Northwest China, Northeast China, the Qinghai–Tibet area, and China offshore area. In this paper, we investigated depositional environments, sequence stratigraphy, lithofacies paleogeography and coal accumulation pattern of five major coal-accumulating periods including the Late Carboniferous to Middle Permian of the North China CAA, the Late Permian of the South China CAA, the Late Triassic of the South China CAA, the Early-Middle Jurassic of the North and Northwest China CAA, and the Early Cretaceous in the Northeast China CAA. According to distribution of the coal-bearing strata and the regional tectonic outlines, we have identified distribution range of the coal-forming basins, sedimentary facies types and coal-accumulating models. The sequence stratigraphic frameworks of the major coal-accumulating periods were established based on recognition of a variety of sequence boundaries. The distribution of thick coals and migration patterns of the coal-accumulating centers in the sequence stratigraphic framework were analyzed. The lithofacies paleogeography maps based on third-order sequences were reconstructed and the distribution of coal accumulation centers and coal-rich belts were predicted.

The Middle Permian South Ash Pasture Assemblage of North-Central Texas: Coniferophyte and Gigantopterid Herbivory and Longer-Term Herbivory Trends

Abstract: Premise of research. The South Ash Pasture (SAP) Flora is an unusual gymnosperm-dominated plant assemblage from the Middle Permian (Guadalupian) of Texas. It is the first Guadalupian Epoch flora fr...

Intensifying aeolian activity following the end‐Permian mass extinction: Evidence from the Late Permian–Early Triassic terrestrial sedimentary record of the Ordos Basin, North China

Abstract: Sedimentary successions provide direct evidence of climate and tectonics, and these give clues about the causes of the mass extinction around the Permian–Triassic boundary. Terrestrial Permian–Triassic boundary strata in the eastern Ordos Basin, North China, include the Late Permian Sunjiagou, Early Triassic Liujiagou and late Early Triassic Heshanggou formations in ascending order. The Sunjiagou Formation comprises cross-bedded sandstones overlaid by mudstones, indicating meandering rivers with channel, point bar and floodplain deposits. The Liujiagou Formation was formed in braided rivers of arid sand bars interacting with some aeolian dune deposits, distinguished by abundant sandstones where diverse trough and planar cross-bedding and aeolian structures (for example, inverse climbing-ripple, translatent-ripple lamination, grainfall and grainflow laminations) interchange vertically and laterally. The Heshanggou Formation is a rhythmic succession of mudstones interbedded with thin medium-grained sandstones mainly deposited in a shallow lacustrine environment. Overall, the sharp meandering to braided to shallow lake sedimentary transition documents palaeoenvironmental changes from semi-arid to arid and then to semi-humid conditions across the Permian–Triassic boundary. The die-off of tetrapods and plants, decreased bioturbation levels in the uppermost Sunjiagou Formation, and the bloom of microbially-induced sedimentary structures in the Liujiagou Formation marks the mass extinction around the Permian–Triassic boundary. The disappearance of microbially-induced sedimentary structures, increasingly intense bioturbation from bottom to top and the reoccurrence of reptile footprints in the Heshanggou Formation reveal gradual recovery of the ecosystem after the Permian–Triassic boundary extinction. This study is the first to identify the intensification of aeolian activity following the end-Permian mass extinction in North China. Moreover, while northern North China continued to be uplifted tectonically from the Late Palaeozoic to Late Mesozoic, the switch of sedimentary patterns across the Permian–Triassic boundary in Shanxi is largely linked to the development of an arid and subsequently semi-humid climate condition, which probably directly affected the collapse and delayed recovery in palaeoecosystems. 2691 © 2020 The Authors. Sedimentology © 2020 International Association of Sedimentologists Sedimentology (2020) 67, 2691–2720 doi: 10.1111/sed.12716