Mass Extinction In South China Research Articles

Coupling of nitrogen biogeochemical cycling and phytoplankton community structure before and after the Late Ordovician mass extinction in South China

The Ordovician–Silurian transition (OST) is a crucial geological interval in Earth history, coinciding with the first of the ‘Big Five’ Phanerozoic mass extinction events (ca. 445 Ma). In addition to the dramatic loss of biodiversity, significant environmental change course such as redox conditions and nutrient availability have been the focus of debate. Previous studies have used isotopes of nitrogen (N) to reconstruct the redox evolution of the paleo-ocean and have identified biological nitrogen fixation as the main mode of nitrogen cycling during the OST. However, low δ15N values, ranging from −2‰ to +1‰, possibly correspond to four different redox conditions. The precise roles of these redox conditions and the spatial distributions of phytoplankton communities under different nitrogen cycles remain elusive. Here we present high-resolution nitrogen isotope, carbon isotope and lipid biomarker datasets from two drilled sections located on a submerged high of the Yangtze Basin to unravel the coupling between nitrogen biogeochemical cycling and phytoplankton community structure across the OST. The results suggest that there was a dominantly biological nitrogen fixation with local aerobic nitrogen cycling in the Yangtze Sea, and the nitrate inventory during the OST was smaller than that in the modern ocean. Particularly, before the Late Ordovician mass extinction (LOME), N-fixing cyanobacteria were likely extensively developed in the photic zone, while eukaryotic algae were limited. After the LOME, sea levels rose and the chemocline was higher than before the LOME. There was probably some NO3− that did not undergo denitrification in the surface ocean, favoring the development of eukaryotic algae. The ecological diversification from prokaryotic cyanobacteria to eukaryotic phytoplankton to eukaryotic zooplankton is likely to be a response to the enhanced biological pump, which generates positive feedbacks among the evolution of eukaryotic phytoplankton, organic matter enrichment, ocean oxygenation and atmospheric oxygen levels.

Biogeographic dynamics of graptolite species during the end-Ordovician mass extinction in South China

Biogeographic dynamics of graptolite species during the end-Ordovician mass extinction in South China

Nearshore warm-water biota development in the aftermath of the Late Ordovician Mass Extinction in South China

The Late Ordovician Mass Extinction (LOME) occurred between two significant biotic diversifications: the Great Ordovician Biodiversification Event and the Silurian–Devonian Nekton Revolution. Upper Hirnantian carbonate deposits therefore are critical archives for understanding warm-water biotas, biodiversity resurgence and trophic chain development in the immediate aftermath of the LOME. In this study, we use microfacies analysis to investigate composition and biodiversity of the upper Hirnantian carbonates developed in northeastern Guizhou Province of China. These carbonates lay along the northern margins of the Dianqiangui landmass and are composed of intraclastic pack- to grainstone, mud- to wackestone, and bioclastic wacke- to packstone. Depositional age of the carbonates is estimated to be late Hirnantian, chiefly indicated by their coincidence with the Hirnantian Carbon Isotope Excursion and the brachiopods Cathaysiorthis and Eospirigerina. The development of carbonates containing diverse warm-water fossils at this transitional time reflects glacio-eustatic changes in the aftermath of the maximum Hirnantian glaciation and LOME, and the consequence of regional Kwangsian Orogeny in South China. Supposed autotrophic organisms in the carbonates are represented by calcimicrobes Allonema and Girvanella, and calcareous algae Amsassia, Dasyporella and Dimorphosiphon. Heterotrophic organisms are also abundant, including bryozoans (Atactoporella, Dekayia, Eridotrypa, Hallopora, Moorephylloporina and Ptilodictya?), trilobites (Dicranopeltis, Eoleonaspis, Mucronaspis (Songxites), Niuchangella and an aulacopleurid-like trilobite), rugose corals (Axiphoria, Eurogrewingkia, Meitanolasma and Grewingkia), tabulate corals (auloporid coral, Catenipora, Halysites, Paleofavosites and Propora), stromatoporoids (Camptodictyon, Ecclimadictyon and Cystostroma), conodonts (Ozarkodina and Walliserodus), benthic graptolites (Desmograptus), gastropods (at least two genera), and ostracods. Such a high biodiversity is evidence of a complex trophic web after the extinction pulses in South China. The biotic development of the warm-water benthic community might have been triggered by a short-lived localized favourable environment that facilitated the survival of warm-water biota during the Hirnantian, which is postulated to have pioneered further Silurian reef recovery in South China.

High resolution C-isotopic data from microbialites in the aftermath of the end-Permian mass extinction in South China

Globally, Late Permian to Early Triassic carbonate rocks record several pronounced positive and negative C-isotope excursions, indicating a dramatic reorganization of the global carbon cycle. These C-isotopic anomalies provide important constraints on environmental changes that occurred during the end-Permian extinction and the subsequent delayed biotic recovery. In this study, we present high-resolution carbonate C-isotopic data (δ13Ccarb) spanning the Permian-Triassic transition at Dajiang, South China. Our results reveal a general decrease in δ13Ccarb of ∼3.3‰ during the microbialite formation which was followed by an increase. C-isotopic chemostratigraphic correlation between the Dajiang section and the Global Boundary Stratotype Section and Point (GSSP) at Meishan suggest a hiatus of several thousands of years between the pre-extinction skeletal limestones and the microbialite deposition in the aftermath of the end-Permian extinction in South China. We suggest that multiple sources of 13C-depleted dissolved carbon are required to explain the negative δ13Ccarb excursions as well as the δ13Ccarb differences among microbialites deposited in various paleogeographic locations. Our study shows that carbon cycles during the formation of microbialite may have been more complex than previously thought, and cessation of microbialite formation may have been controlled by both global and local environmental changes.

Different controls on the Hg spikes linked the two pulses of the Late Ordovician mass extinction in South China

The Late Ordovician mass extinction (LOME, ca. 445 Ma; Hirnantian stage) is the second most severe biological crisis of the entire Phanerozoic. The LOME has been subdivided into two pulses (intervals), at the beginning and the ending of the Hirnantian glaciation, the LOMEI-1 and LOMEI-2, respectively. Although most studies suggest a rapid cooling and/or oceanic euxinia as major causes for this mass extinction, the driver of these environmental changes is still debated. As other Phanerozoic’s mass extinctions, extensive volcanism may have been the potential trigger of the Hirnantian glaciation. Indirect evidence of intense volcanism comes from Hg geochemistry: peaks of Hg concentrations have been found before and during the LOME, and have all been attributed to global volcanism in origin. Here, we present high-resolution mercury (Hg) profiles in three study sections, from a shelf to slope transect, on the Yangtze Shelf Sea (South China) to address the origin of Hg anomalies across the Ordovician–Silurian (O–S) boundary. The results show Hg anomaly enrichments in the middle Katian, late Katian, the LOMEI-1 at the beginning of the Hirnantian glaciation, the LOMEI-2 in the late Hirnantian glaciation, and late Rhuddanian. The Hg anomaly enrichments during the middle–late Katian and late Rhuddanian would probably reflect a volcanic origin. We find two different controls on the recorded Hg anomalies during the extinction time: i.e., primarily volcanism for the Hg anomaly at the LOMEI-1 and euxinia for the Hg anomaly at the LOMEI-2. Expansion of euxinia at the LOMEI-1 would have been probably enhanced by volcanic fertilization via weathering of volcanic deposits during the Middle and late Katian, and combined with euxinia at the LOMEI-2 to finally be responsible for the two pulses of the LOME.

Carbonate associated sulfate (CAS) δ34S heterogeneity across the End-Permian Mass Extinction in South China

The dynamics of the marine sulfur cycle across the End-Permian Mass Extinction (EPME) have been obscured by disagreement between sulfur isotopic records from different archives. Here, we attempt to resolve this disagreement with new measurements of carbonate associated sulfate (CAS) δ34S (i.e., δ34SCAS) from three Permian-Triassic boundary (PTB) sections in South China. We observe substantial δ34SCAS variation within single hand samples, with most samples having a δ34SCAS range exceeding 5‰ and some reaching ∼20‰. We also find evidence for mixing between low CAS abundance, high δ34SCAS and high CAS abundance, low δ34SCAS phases. A simple model of reduced sulfur oxidation and incorporation as CAS suggests that sedimentary redox oscillations may plausibly explain the δ34SCAS heterogeneity within many EPME carbonates; rapid variation in the δ34S of the marine SO42− reservoir is not necessary. Additional work to examine how synchronous changes in organic carbon fluxes, sedimentation rates, or other parameters that impact sediment redox and sulfur diagenesis is needed to evaluate the environmental implications of the δ34SCAS heterogeneity.

Quantitative constraints on carbon cycling and temporal changes in episodic euxinia during the end-Permian mass extinction in South China

We report the temporal and spatial C-isotopic variations of carbonate (δ13Ccarb) and organic carbon (δ13Corg) spanning the Permian-Triassic transition at the Xiakou and Chaotian sections in South China. The C-isotope data from the two sections show two episodes of δ13Ccarb decrease. However, in contrast to most of the C-isotopic records of the Phanerozoic, the changes in δ13Corg are not paralleled by those of δ13Ccarb: rather, they show a gradual increase followed by a consistent negative excursion. Accordingly, the C-isotopic data exhibit two episodes of decreased Δ13Ccarb-org (Δ13Ccarb-org = δ13Ccarb – δ13Corg). A dual-reservoir model was used to study the main factors responsible for the C-isotopic excursions. We show that two episodes of decrease in δ13Ccarb and Δ13Ccarb-org may be best explained by the remineralization of organic carbon and the proliferation of green sulfur bacteria, which may have been driven by the episodic incursion of sulfidic waters. The temporal and spatial variations of δ13Ccarb and δ13Corg reveal two episodic incursions of sulfidic waters into shallow water areas with resulting photic zone euxinia. The first incursion of sulfidic waters occurred before the end-Permian mass extinction (EPME) event, while the second incursion occurred across the EPME event. The modeling results show that the amount of 13C-depleted carbon input from remineralization across the EPME is ~1.5-times that before the EPME, providing quantitative evidence for the temporal changes in episodic euxinia. This conclusion is strengthened by the observed δ13C depth gradient between the two sections. Our results provide quantitative constraints on carbon cycling in the Permian-Triassic oceans and suggest that the expanded euxinia may have crossed a threshold that led to the most severe biotic crisis in Earth's history.

Constraining the biotic transitions across the end‐Ordovician mass extinction in South China: Bio‐ and chemostratigraphy of the Wulipo Formation in the Meitan area of northern Guizhou

The richly fossiliferous succession of the Wulipo Formation in the Huangjiaba area near Meitan in northern Guizhou, SW China, represents one of the very rare records of shelly fauna across the Ordovician and Silurian transition worldwide. This area is therefore crucial for understanding the pattern and dynamics of the end‐Ordovician mass extinction (EOME). Historically, the Wulipo Formation was dated as middle Rhuddanian (early Silurian). However, its fauna shows a close affinity with Transitional Benthic Fauna 3 (TBF 3), now known to be confined within the late Hirnantian (latest Ordovician) in well‐constrained successions globally. Here we present for the first time, chemostratigraphic data from the Wulipo Formation which confirm the presence of the Hirnantian Isotope Carbon Excursion. A critical review of faunal evidence further indicates a late Hirnantian age for this formation, and thus the hitherto only known anomalous TBF 3 record documented from South China is convincingly redated. The important implication is that the substantial biotic recovery after the EOME commenced globally at the very beginning of the Silurian with an overall amelioration of physical conditions. The new findings also suggest a much wider distribution of postglacial warm‐water benthic faunas on the Yangtze Platform during the late Hirnantian than previously envisaged.

Mercury anomalies across the end Permian mass extinction in South China from shallow and deep water depositional environments

Life on Earth suffered its greatest bio-crisis since multicellular organisms rose 600 million years ago during the end-Permian mass extinction. Coincidence of the mass extinction with flood basalt eruptions in Siberia is well established, but the exact causal connection between the eruptions and extinction processes in South China is uncertain due to their wide spatial separation and the absence of direct geochemical evidence linking the two. The concentration and stable isotope analysis of mercury provides a way to test these links as its concentration is thought to be tied to igneous activity. Mercury/total organic carbon ratios from three Permian–Triassic boundary sections with a well-resolved extinction record in South China show elevated values (up to 900 ppb/wt.% relative to a background of <100 ppb/wt.%) that exactly coincides with the end-Permian mass extinction horizon. This enrichment does not show any correlation with redox and sedimentation rate variations during that time. Hg isotope mass-independent fractionation (Δ199Hg), with sustained positive values, indicate a predominant atmospheric-derived signature of volcanic Hg in deep-shelf settings of the Daxiakou and Shangsi sections. In contrast, the nearshore environment of the Meishan section displays a negative Δ199Hg signature, interpreted to be related to terrestrial Hg sources. Such temporal differences in Δ199Hg values shed new light on Hg geochemical behavior in marine settings, and also on the kill mechanisms associated with volcanism that were responsible for biotic mortality at the end of the Permian.

Geographic dynamics of some major graptolite taxa of the Diplograptina during the Late Ordovician mass extinction in South China

The study of graptolite paleobiogeography is important for understanding the relationship between geography and evolutionary dynamics in graptolites. However, there have been few detailed studies of graptolite paleobiogeography during the Late Ordovician, or the role that geography played in the Hirnantian Mass Extinction (HME). In this study, in order to investigate the geographic dynamics of major graptolite taxa during the HME, a data-set of graptolite occurrences in the late Katian–Hirnantian from 61 localities in South China was compiled using the GBDB online database. The minimum polygon method was used to reconstruct 14 distribution maps of 5 major taxa belonging to the Diplograptina. The geographic dynamics of most diplograptine taxa show a small reduction in their geographic ranges from the Dicellograptus complexus Zone to the Paraorthograptus pacificus Zone, probably because of the contractions in the distribution areas of the coeval marine sediments. A substantial reduction in the distributions of most diplograptine taxa from the P. pacificus Zone to the Metabolograptus extraordinarius Zone mainly represents the effect of the major extinction event. Our study also demonstrates a reduction in the geographic ranges of each taxon to the center of the Yangtze epicontinental sea during the HME. The changes in geographic ranges are mirrored by a similar reduction in species-level total diversity during the study interval.

Origin of volcanic ash beds across the Permian–Triassic boundary, Daxiakou, South China: Petrology and U–Pb age, trace elements and Hf-isotope composition of zircon

Abundant volcanic ash layers, largely altered to clay, characterize the Permian–Triassic boundary beds of the Daxiakou section, South China. Volcanism may have had an important role in the Permian–Triassic mass extinction, so it is important to understand the origin of these ash beds. The lithology of ash bed 260, as constrained by modes of crystal fragments (66.7% plagioclase, 7.2% alkali feldspar, and 26.1% quartz), suggests that the ash represents dacitic volcanism. The U–Pb ages, trace elements and Hf-isotope compositions of zircons from ten ash beds have been analyzed using LA-ICPMS and LA-MC-ICPMS. The zircons can be divided into two groups: magmatic zircons (~97%, 227–279Ma) and inherited zircons (~3%, 678–2424Ma). Magmatic zircons have Y, Hf, Th and U contents and Nb/Ta ratios typical of zircons from silicic calc-alkaline volcanism. εHf(t) values of magmatic zircons vary from −10.9 to +5.3, implying magmatic mixing between juvenile crustal material (probably Neoproterozoic in age) and ancient crustal material (probably Archean). Beds 252–259-b have relatively depleted Hf-isotope compositions with εHf(t) values of −10.9–+5.3 and averages of −5.0–−2.5, while other beds have εHf(t) values of −10.8–+4.4 (mostly −10.8–−3.5) and averages of −8.9–−6.8, implying more input of juvenile crustal material in the volcanism of Beds 252–259-b. Integration of the Hf-isotope and trace-element compositions of magmatic zircons suggests that the volcanism producing the ashes took place along the convergent continent margins during the formation of the Pangea supercontinent. This intense silicic volcanism may have played an important role in causing the Permian–Triassic mass extinction in South China.

Carbon and sulfur isotopic fluctuations associated with the end-Guadalupian mass extinction in South China

Concentrations of total organic matter (TOC), carbon isotopic compositions of carbonate and organic matter (δ13Ccarb, δ13Corg), and sulfur isotopic compositions of carbonate associated sulfate (δ34Ssulfate) across the Guadalupian–Lopingian (G–L) boundary were analyzed from identical samples of Tieqiao section, Laibin, Guangxi province, South China. The δ13Ccarb values show a positive excursion from −0.45‰ to the peak of 3.80‰ in the Laibin limestone member of the Maokou Formation, followed by a drastic drop to −2.60‰ in the lowest Heshan formation, then returned to about 1.58‰. Similar to the trends of the δ13Ccarb values, Δ13Ccarb–org values also show a positive excursion followed by a sharp negative shift. The onset of a major negative carbon isotope excursion postdates the end Guadalupian extinction that indicates subsequent severe disturbance of the ocean–atmosphere carbon cycle. The first biostratigraphic δ34Ssulfate values during the G–L transition exhibit a remarkable fluctuation: a dramatic negative shift followed by a rapid positive shift, ranging from 36.88‰ to −37.41‰. These sulfate isotopic records suggest that the ocean during the G–L transition was strongly stratified, forming an unstable chemocline separating oxic shallow water from anoxic/euxinic deep water. Chemocline excursions, together with subsequent rapid transgression and oceanic anoxia, were likely responsible for the massive diversity decline of the G–L biotic crisis.

An oxygenation event occurred in deep shelf settings immediately after the end-Permian mass extinction in South China

Widespread oceanic anoxia has been consistently considered as a main characteristic of the oceanic environment after the end-Permian mass extinction. However, newly obtained pyrite framboid data suggest otherwise from a deep shelf setting (Changtanhe section) of northwestern Hunan province in South China. Our results reveal that an oxygenation event occurred immediately after the end-Permian mass extinction in this section, where the redox conditions of bottom water changed from lower dysoxic to upper dysoxic during the Permian–Triassic (P/Tr) transition. The oxygenation event likely resulted from mixing of deep dysoxic bottom waters with shallow, oxygenated waters triggered by enhanced upwelling and seawater circulation as well as the large regression during the P/Tr transition. These may also be the cause of the partial remission of dysoxic conditions immediately after the end-Permian mass extinction in other deep shelf settings, especially in South China.

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

Research Article| August 01, 2011 Recovery tempo and pattern of marine ecosystems after the end-Permian mass extinction Haijun Song; Haijun Song 1State Key Laboratory of Biogeology and Environmental Geology of Ministry of Education, China University of Geosciences, Wuhan 430074, China2School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK Search for other works by this author on: GSW Google Scholar Paul B. Wignall; Paul B. Wignall * 2School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK *E-mails: p.wignall@see.leeds.ac.uk; jntong@cug.edu.cn. Search for other works by this author on: GSW Google Scholar Zhong-Qiang Chen; Zhong-Qiang Chen 3School of Earth and Geographical Sciences, University of Western Australia, Perth, WA 6009, Australia Search for other works by this author on: GSW Google Scholar Jinnan Tong; Jinnan Tong * 1State Key Laboratory of Biogeology and Environmental Geology of Ministry of Education, China University of Geosciences, Wuhan 430074, China *E-mails: p.wignall@see.leeds.ac.uk; jntong@cug.edu.cn. Search for other works by this author on: GSW Google Scholar David P.G. Bond; David P.G. Bond 2School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK Search for other works by this author on: GSW Google Scholar Xulong Lai; Xulong Lai 1State Key Laboratory of Biogeology and Environmental Geology of Ministry of Education, China University of Geosciences, Wuhan 430074, China Search for other works by this author on: GSW Google Scholar Xiaoming Zhao; Xiaoming Zhao 4Wuhan Institute of Geology and Mineral Resources, Wuhan 430205, China Search for other works by this author on: GSW Google Scholar Haishui Jiang; Haishui Jiang 1State Key Laboratory of Biogeology and Environmental Geology of Ministry of Education, China University of Geosciences, Wuhan 430074, China Search for other works by this author on: GSW Google Scholar Chunbo Yan; Chunbo Yan 1State Key Laboratory of Biogeology and Environmental Geology of Ministry of Education, China University of Geosciences, Wuhan 430074, China Search for other works by this author on: GSW Google Scholar Zhijun Niu; Zhijun Niu 4Wuhan Institute of Geology and Mineral Resources, Wuhan 430205, China Search for other works by this author on: GSW Google Scholar Jing Chen; Jing Chen 1State Key Laboratory of Biogeology and Environmental Geology of Ministry of Education, China University of Geosciences, Wuhan 430074, China Search for other works by this author on: GSW Google Scholar Hao Yang; Hao Yang 1State Key Laboratory of Biogeology and Environmental Geology of Ministry of Education, China University of Geosciences, Wuhan 430074, China Search for other works by this author on: GSW Google Scholar Yongbiao Wang Yongbiao Wang 1State Key Laboratory of Biogeology and Environmental Geology of Ministry of Education, China University of Geosciences, Wuhan 430074, China Search for other works by this author on: GSW Google Scholar Geology (2011) 39 (8): 739–742. https://doi.org/10.1130/G32191.1 Article history received: 18 Feb 2011 accepted: 14 Mar 2011 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Haijun Song, Paul B. Wignall, Zhong-Qiang Chen, Jinnan Tong, David P.G. Bond, Xulong Lai, Xiaoming Zhao, Haishui Jiang, Chunbo Yan, Zhijun Niu, Jing Chen, Hao Yang, Yongbiao Wang; Recovery tempo and pattern of marine ecosystems after the end-Permian mass extinction. Geology 2011;; 39 (8): 739–742. doi: https://doi.org/10.1130/G32191.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract 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. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Composition and structure of microbialite ecosystems following the end-Permian mass extinction in South China

After the end-Permian mass extinction, microbialites were widespread in the shallow marine environments in South China. Diverse microbialites are characteristic of the Early Triassic carbonate sequences. Their stratigraphic range is rather short, just across the Permian–Triassic (P–Tr) boundary, and defined by conodonts N. meishanensis, H. changxingensis, and H. parvus Zones. Thus, the P–Tr microbialites grew immediately after the first episode of the end-Permian mass extinction coinciding with the beginning of the conodont N. meishanensis Zone and ceased their growth at the beginning of the conodont I. staeschei Zone, which occurred just before the second episode of the end-Permian crisis at Meishan. They include three main types: stromatolites, thrombolites and dendrites in South China. The presence of abundant microbial remains of coccoid-type and Renalcis-like microbes strengthens the previous view that the P–Tr microbialites are biogenic. Both cyanobacteria and other microbes have participated to construct the microbial ecosystems. The thrombolite communities are dominated by the Renalcis-like microbes and foraminifers and also contain ostracods, microgastropods, and microconchids. The stromatolite communities are dominated by coccoidal microbes with minor constituents of other undetermined microbes. Metazoans are rare. The dendrolite assemblage contains few identifiable microfossils. Most of microbialite communities have a high-abundance, low-diversity community structure, characteristic of marine communities after the end-Permian mass extinction. Some metazoans of either opportunists or disaster forms dwelled in this special ecosystem. The microbialite-builders formed the primary producer communities and constructed the lowest level ecosystem structure. The lower-level ecosystem proliferated due to the collapse of the higher level of ecosystem structure characterized by benthic shelly and predator communities in the end-Permian crisis.

Reconstruction of ecosystem and biotic recovery following the end-Permian mass extinction in South China

Reconstruction of ecosystem and biotic recovery following the end-Permian mass extinction in South China

Large perturbations of the carbon and sulfur cycle associated with the Late Ordovician mass extinction in South China

High-resolution δ 13 C data of organic carbon from a continuous section of the Late Ordovician–Early Silurian reveal two positive δ 13 C excursions that are associated with the mass extinction in South China. The fi rst stratigraphic δ 34 S measurements on pyrite tied to well-established biostratigraphy indicate a large perturbation of the sulfur cycle, consistent with major sea-level changes related to the glaciation. The elevated δ 34 S values of pyrites and a large, short-lived negative δ 34 S excursion of ~20‰ associated with the decay of the glaciation suggest deep-water anoxia during the Hirnantian Stage, in contrast to the conventional view that the global oceans were oxygenated. We suggest that deep-water anoxia may have contributed to the Late Ordovician mass extinction in South China and possibly elsewhere.

Lower Triassic bivalve assemblages after the end-Permian mass extinction in South China and North Vietnam

Lower Triassic bivalve assemblages are recognized in the Yinkeng Formation, South China, and the Hong Ngai Formation, North Vietnam. Basinal mudstones and deep ramp carbonates contain the mono- specific Claraia wangi assemblage. The Eumorphotis teilhardi-Towapteria scythica assemblage occurs in deep ramp deposits. The Claraia stachei-Claraia phobangensis assemblage is found in shallow ramp deposits. These bivalve assemblages are mainly composed of epifaunal species, and are characterized by low spe- cies diversity and parautochthonous elements. Most species of Claraia probably inhabited shallow to deep marine environments. Besides, Eumorphotis and Towapteria are useful indicators of Lower Triassic shallow marine environments above storm-wave base.

Survival strategies of brachiopod faunas from the end-Permian mass extinction

Global reviews reveal that 102 brachiopod species (including 40 indeterminate species) belonging to 43 genera within 27 families survived the end-Permian mass extinction in South China, the Himalayan regions (southern Tibet, Nepal, Salt Range and Kashmir), southern Alps (Italy), Arctic Canada, western USA and Western Australia. Of these, the surviving brachiopods are most abundant and widespread in South China where they occur in 32 of the 42 Permian–Triassic (P/T) boundary sections around the world. Brachiopod faunas are the most abundant and diverse post-extinction survivors, and their appearance above the end-Permian mass extinction horizon somewhat masks recognition of the end-Permian extinction. These surviving brachiopods occur in three stratal intervals corresponding to the “Mixed Fauna Beds” (MFB hereafter) 1–3 of the P/T boundary beds. A sharp drop in diversity of the brachiopod faunas coincides with the widely accepted end-Permian mass extinction horizon. The post-extinction brachiopods were also affected by a subsequent crisis corresponding to the boundary between MFB 2 and MFB 3 so that most survivors were extinct approximately 0.7 Ma after the end-Permian mass extinction. The surviving brachiopods were mainly Productida, followed by Spiriferida. In particular, small chonetids, chonetid-like productellids and smooth, thin-shelled ambocollid spiriferids are most abundant. Lingula is extraordinarily abundant and widespread approximately 0.7 Ma after the greatest extinction when many regions became devoid of articulate brachiopods. Widespread, broadly adapted and small-sized taxa preferentially survived. Frequent intrageneric speciation of widespread, widely adapted generalist genera enabled survival brachiopods to occupy rapidly and efficiently vacant ecospace in the aftermath of the end-Permian extinction. The ecological habitats of the post-extinction brachiopods are subdivided into nearshore, epeiric sea, restricted carbonate platform, open carbonate platform, ramp and outer shelf environments. Of these, the survival brachiopods are most diverse in the open platform environments. The nearshore zone provided ideal habitats for the nonarticulated brachiopods to occupy; whereas the survivors in the outer shelf are predominantly chonetids and chonetid-like productellids. The most successful survivors, the productid brachiopods, are widely distributed in six types of ecological habitats and thus have no apparent preference for specific environments. The end-Permian extinction resulted in the movement of biogeographical provinces towards the palaeo-equator. The brachiopods survived mostly in the palaeo-equatorial provinces and along the southern margins of the Palaeo-Tethys Ocean.

Calcimicrobialite after end-Permian mass extinction in South China and its pa-laeoenvironmental signifi-cance

Calcimicrobialites, which could be correlated to the layer 27 in Meishan section according to the Hindeodus parvus, occur abruptly on the end-Permian mass extinction boundary in South China. Microbialites mainly distribute on the top of reef facies or shallow carbonate platforms, thinning into deep facies. All the microbialites discovered are composed of micrite and coarse crystal digitate carbonate or patch carbonate. Microfossils usually dominate in the microbialites, and small gastropods, bivalves and ostracodes can also be found. This fossil assemblage represents a simple but particular remanent biota after the end-Permian mass extinction on the top of reefs or shallow carbonate platforms. Abrupt occurrence of microbialites above the mass extinction boundary is the ecological response to the end-Permian global event in reef or shallow carbonate facies. Many studies have been done on the Permian-Triassic boundary and event in deep water facies sections or middle to lower shelf facies sections. However, the calcimicrobialites in South China are mainly located above reef facies or shallow carbonate platform facies. It will surely be helpful for people to know more about the different responses in different depths of ancient marine environment during the transition between Permian and Triassic by the study of petrology, palaeontology and palaeoecology of the calcimicrobialites.