Xulong Lai

Lethally Hot Temperatures During the Early Triassic Greenhouse

Too-Hot Times Climate warming has been invoked as a factor contributing to widespread extinction events, acting as a trigger or amplifier for more proximal causes, such as marine anoxia. Sun et al. (p. 366; see the Perspective by Bottjer) present evidence that exceptionally high temperatures themselves may have caused some extinctions during the end-Permian. A rapid temperature rise coincided with a general absence of ichthyofauna in equatorial regions, as well as an absence of many species of marine mammals and calcareous algae, consistent with thermal influences on the marine low latitudes. Sea surface temperatures approached 40°C, which suggests that land temperatures likely fluctuated to even higher values that suppressed terrestrial equatorial plant and animal abundance during most of the Early Triassic. Global warming in the Early Triassic was so severe that equatorial latitudes were uninhabitable for many plants and animals. Global warming is widely regarded to have played a contributing role in numerous past biotic crises. Here, we show that the end-Permian mass extinction coincided with a rapid temperature rise to exceptionally high values in the Early Triassic that were inimical to life in equatorial latitudes and suppressed ecosystem recovery. This was manifested in the loss of calcareous algae, the near-absence of fish in equatorial Tethys, and the dominance of small taxa of invertebrates during the thermal maxima. High temperatures drove most Early Triassic plants and animals out of equatorial terrestrial ecosystems and probably were a major cause of the end-Smithian crisis.

Climate warming in the latest Permian and the Permian-Triassic mass extinction

High-resolution oxygen isotope records document the timing and magnitude of global warming across the Permian-Triassic (P-Tr) boundary. Oxygen isotope ratios measured on phosphate-bound oxygen in conodont apatite from the Meishan and Shangsi sections (South China) decrease by 2‰ in the latest Permian, translating into low-latitude surface water warming of 8 °C. The oxygen isotope shift coincides with the negative shift in carbon isotope ratios of carbonates, suggesting that the addition of isotopically light carbon to the ocean-atmosphere system by Siberian Traps volcanism and related processes resulted in higher greenhouse gas levels and global warming. The major temperature rise started immediately before the main extinction phase, with maximum and harmful temperatures documented in the latest Permian (Meishan: bed 27). The coincidence of climate warming and the main pulse of extinction suggest that global warming was one of the causes of the collapse of the marine and terrestrial ecosystems. In addition, very warm climate conditions in the Early Triassic may have played a major role in the delayed recovery in the aftermath of the Permian-Triassic crisis.

Changes in the global carbon cycle occurred as two episodes during the Permian–Triassic crisis

Coeval records of ocean, atmosphere, and terrestrial change are crucial to understanding the pattern and causes of global mass extinction across the Permian-Triassic boundary (PTB). However, relationships among changes in different settings remain largely unclear, primarily due to the challenges associated with the correlation among disparate records. Here we compare marine carbon isotopic records with marine and terrestrial environmental and biotic events recorded in sediments from the Meishan PTB section of south China. Time-scaled carbonate carbon isotopes exhibit two gradual major shifts across the PTB at Meishan, and these are duplicable elsewhere around the Tethys Ocean. The two shifts are associated with two episodes of enhanced terrestrial weathering indicated by an increased abundance of 13 C-enriched moretanes relative to hopanes and an elevated abundance of black carbon fragments. Key marine events previously reported for the PTB, including photic zone euxinia, faunal mass extinction, and cyanobacterial expansion, also occur as two episodes, coinciding with both of the progressive shifts to negative δ 13 C values and enhanced weathering. The temporal sequence of the duplicable events suggests that the biotic crisis was a consequence of prolonged and episodic changes in the marine and continental systems, and argues against an extraterrestrial impact as the main cause.

Volcanism, mass extinction, and carbon isotope fluctuations in the middle permian of China

Middle Permian Extinction A major extinction in the Middle Permian 260 to 270 million years ago preceded the huge end-Permian extinction. Wignall et al. (p. 1179) present a detailed analysis of the Middle Permian event from rocks in southwest China. The extinction coincided with extensive nearby volcanic eruptions. A major drop in carbon isotope values followed the extinction event, implying massive disruption of the carbon cycle. Fossiliferous rocks from southwest China show that a major extinction in the Middle Permian coincided with extensive volcanic eruptions. The 260-million-year-old Emeishan volcanic province of southwest China overlies and is interbedded with Middle Permian carbonates that contain a record of the Guadalupian mass extinction. Sections in the region thus provide an opportunity to directly monitor the relative timing of extinction and volcanism within the same locations. These show that the onset of volcanism was marked by both large phreatomagmatic eruptions and extinctions amongst fusulinacean foraminifers and calcareous algae. The temporal coincidence of these two phenomena supports the idea of a cause-and-effect relationship. The crisis predates the onset of a major negative carbon isotope excursion that points to subsequent severe disturbance of the ocean-atmosphere carbon cycle.

Recovery tempo and pattern of marine ecosystems after the end-Permian mass extinction

High-resolution sampling of more than 10,000 microfossils from seven Late Permian−Middle Triassic paleoequatorial sections in south China refutes claims for a 5 m.y. recovery delay after the end-Permian mass extinction. We show that level-bottom seafloor diversity began to recover in the early Smithian, little more than 1 m.y. after the mass extinction, while recovery of reef-building metazoans began 4 m.y. later, in the Anisian. A further mass extinction in the late Smithian, identified in the pelagic fossil record, is weakly manifest as a temporary pause in diversification among benthic communities. In the Early Triassic of south China, the offshore diversity increase began before then, in shallower settings. The recovery from the end-Permian mass extinction in south China was therefore significantly more rapid and environmentally more complex than hitherto known.

Facies analysis and sea-level change at the Guadalupian–Lopingian Global Stratotype (Laibin, South China), and its bearing on the end-Guadalupian mass extinction

Abstract: The Guadalupian–Lopingian boundary stratotype at Penglaitan, and the nearby Tieqiao section, near Laibin, South China, record a series of major environmental changes within the Jiangnan Basin during a Mid-Permian biotic crisis. The sequence-stratigraphic, petrographic and palaeontological record of these sections has been studied and the associated strontium isotopic fluctuations have been assayed. Mass extinction of fusulinid foraminifers is most clearly associated in time with onset of volcanism and a relative sea-level fall that led to the establishment of mid-ramp conditions (Laibin Limestone) in settings that were previously dominated by radiolarian mudstones. The regression also coincides with a low point of 87Sr/86Sr ratios. The lowstand deposits contain mafic scoriaceous grains that record pyroclastic volcanism probably centred in the Emeishan flood basalt province 800 km to the west of Laibin. Thus, unusually violent eruptions associated with flood basalts in this province may have contributed to the environmental stresses responsible for the extinction event. Subsequent environmental changes included transgression, spread of dysoxic waters, indicated by populations of small pyrite framboids, and a major negative C-isotope excursion. All these phenomena have been previously related to the end-Guadalupian extinction but they in fact post-date the crisis because a post-extinction fauna of foraminifers is encountered at this time.

Palaeoecology of the conodonts Hindeodus and Clarkina during the Permian–Triassic transitional period

Abstract Detailed investigation of the distributions of the Hindeodus and Clarkina (Neogondolella) conodont faunas has been undertaken on the P/T boundary strata of the Meishan section, Zhejiang Province, South China, in association with detailed facies analysis. This reveals that Hindeodus increased and Clarkina sharply declined in abundance during a phase of relative sea-level rise which began at the end-Permian (Bed 25) and extended into Early Triassic. This was associated with the development of anoxic conditions. This distribution does not accord with previous suggestions that Hindeodus was a nearshore, shallow water taxon. The decline of the supposed deeper water genus Clarkina is also somewhat surprising but it may relate to the inhibition of a nektobenthic genus by dysoxic–anoxic bottom waters. The widespread facies and geographic distribution of Hindeodus suggests it was a pelagic type unaffected by anoxic bottom waters. Hence, the Hindeodus lineage provides a reliable criterion for identification of the Permian–Triassic boundary.

Permian-Triassic conodonts from Dajiang (Guizhou, South China) and their implication for the age of microbialite deposition in the aftermath of the End-Permian mass extinction

The widespread microbialites deposition that followed the End-Permian mass extinction in the Tethyan realm have been intensively studied because of the evidence they provide on the nature of this crisis and its aftermath. However, the age of the microbialite event remains controversial. New conodont collection across the Permian-Triassic (P-T) transition from Dajiang (Guizhou Province, South China) in this study enable us to discriminate four conodont zones, in ascending order, they are: Hindeodus parvus zone, Isarcicella lobata zone, Isarcicella isarcica zone and Hindeodus sosioensis zone. The age of microbialite in the P-T transition at the Dajiang Section is considered to be within the Hindeodus parvus zone and thus to clearly post-date the main extinction crisis. Reviewing the age of onset of microbialites throughout the Tethyan regions reveals two different ages: a Hindeodus changxingensis zone age is dominant in south-western and westernmost Tethys, whilst most other regions show microbialite deposition began in the Hindeodus parvus zone. Our investigation also indicates that two conodont changes occur at this time: an increase of hindeodid species immediately following a sequence boundary and the mass extinction, and a phase of extinction losses in the earliest Triassic Isarcicella isarcica zone during highstand development.

UPPERMOST PERMIAN TO LOWER TRIASSIC CONODONTS AT BIANYANG SECTION, GUIHZOU PROVINCE, SOUTH CHINA

ABSTRACT A new conodont biostratigraphic study is presented from a key section on the flanks of the Permian-Triassic Great Bank of Guizhou, an isolated carbonate platform from South China, that has recently provided much key data for understanding the nature of this mass extinction interval. Detailed investigation at Bianyang (Guizhou Province) has revealed ten conodont zones, in ascending order: Clarkina yini Zone; Hindeodus changxingensis Zone; Hindeodus parvus Zone; Sweetospathodus kummeli Zone; Neospathodus dieneri Zone; Neospathodus cristagalli Zone; Discretella discreta Zone; Pachycladina-Parachirognathus assemblage zone; Icriospathodus collinsoni Zone; Triassospathodus homeri Zone. This allowed the Permian-Triassic boundary (PTB) to be defined in the section based on the first occurrence of Hindeodus parvus. Furthermore, it is proposed that the first occurrence of Discretella discreta can be used as an auxiliary reference for defining the Induan-Olenekian boundary when Novispathodus waageni is absent both at Bianyang and elsewhere.

Size variation of conodonts during the Smithian-Spathian (Early Triassic) global warming event

The Early Triassic Smithian–Spathian Boundary (SSB) crisis coincided with an episode of extreme warmth. A high-resolution stratigraphic framework comprising six conodont zones is provided in the Jiarong section, Nanpanjiang Basin, in South China. Detailed size measurements of 441 conodont elements of the closely related genera Neospathodus, Triassospathodus, and Novispathodus show for the first time that this clade suffered a temporary, but significant, size reduction during the SSB crisis. The size reduction of conodonts was probably caused by an episode of global warming.