Early-Middle Triassic Boundary Research Articles

The Early–Middle Triassic Supervolcano in the Yangtze Block, South China and associated obstacles to biotic recovery

The end–Permian mass extinction was one of the major global crises spanning the entire Early Triassic or longer. Eruptions of volcanos were one of the factors that delayed the biotic recovery after this event. Supervolcano eruptions can cause catastrophic effects on global environment, climate, and life. Here we investigate the tuff layers from Early–Middle Triassic boundary in the Yangtze Block and identify a supervolcano eruption event. The zircon U–Pb ages of the section–Langdai, section–Daijiagou and section–Longmendong tuff samples are 247.1 ± 1.9 Ma, 247.6 ± 2.0 Ma and 247.7 ± 1.7 Ma, respectively. These ages mark the Olenekian–Anisian boundary. The zircon grains from the tuff layers have negative εHf(t) (−15.3 to −0.8), two–stage Hf model (TDM2) ages (1.7 to 2.2 Ga) and display high–δ18O values (mostly > 10‰). Clay minerals and quartz dominate the rock composition. The whole rock compositions show that the tuff layers were derived from magma of intermediate to felsic composition, which formed by the remelting of Paleoproterozoic materials of continental crust. The volcanic eruption site is located in the Jinshajiang–Ailaoshan–Song Ma suture zone in the southwestern margin of the Yangtze Block. A combination of the closure of the Paleo–Tethys Ocean Basin and the collision of the Indochina Block and South China contributed to the eruption, which was a supervolcano eruption under the active continental margin arc settings. We speculate that this supervolcano eruption might have contributed to the delayed biotic recovery after the end–Permian mass extinction.

Geochronology and geochemistry of lithium-rich tuffs in the Sichuan basin, western Yangtze: Implication for the magmatic origin and final closure of eastern Paleo-Tethys

The felsic volcanogenic tuffs named “green-bean rocks” (GBRs), characterized by a green or yellowish green color, are widely distributed in the western Yangtze platform and have a high lithium content (286–957 ppm). This paper studies the ages, origin and tectonic setting of the GBRs in the Sichuan basin on the western margin of the Yangtze platform through the whole-rock geochemistry and zircon trace elements by using U–Pb dating and Hf–O isotopes. The GBR samples from the Quxian and Beibei sections yielded zircon U–Pb ages of 245.5 ± 1.8 Ma and 244.8 ± 2.2 Ma. These samples can be used as the isochronous stratigraphic marker of the Early–Middle Triassic boundary (EMTB) for regional correlation. The whole-rock and zircon geochemistry, and zircon Hf–O isotopes exhibited S-type geochemical affinities with high positive δ18O values (9.28‰–11.98‰), low negative εHf(t) values (−13.87 to − 6.79), and TDM2 ages of 2150–1703 Ma, indicating that the lithium-rich GBRs were generated by the remelting of the pre-existing ancient Paleoproterozoic layer without mantle source contamination in the arc-related/orogenic tectonic setting. The results of this study demonstrate that the lithium-rich GBRs in the western Yangtze platform were derived from arc volcanic eruptions along the Sanjiang orogen, triggered by the closure of the eastern Paleo-Tethys Ocean and the syn-collision between the continental Indochina and Yangtze blocks at ca. 247 Ma. This was marked by a major shift from I-type magmas with intermediate εHf(t) values to S-type magmas with low negative εHf(t) values. Collectively, our results provide new insights into the origin of the GBRs and decodes the closure of the eastern Paleo-Tethys.

THE OLENEKIAN-ANISIAN/EARLY-MIDDLE TRIASSIC BOUNDARY, AND ASSESSMENT OF THE POTENTIAL OF CONODONTS FOR CHRONOSTRATIGRAPHIC CALIBRATION OF THE TRIASSIC TIMESCALE

The conodont Chiosella timorensis (Nogami, 1968) has for a long time been considered to be a suitable biotic proxy for the Olenekian-Anisian/Early-Middle Triassic boundary. The recently acquired ammonoid record around that boundary clearly shows that the FAD of this conodont is located well below the boundary, i.e., in the late Spathian. In the present paper, it is underlined that the conodont Chiosella timorensis was promoted as a proxy for the nominated boundary in the early 1980s when the ammonoid record around the boundary was not yet well established. On the other side, until the mid 1990s the taxonomic definition and the lineage of the conodont Chiosella timorensis were not well stated, and even now there are still controversial interpretations of the taxonomic content of this conodont species. The new data achieved from the ammonoid/conodont record around the nominated boundary, especially in the western USA, and also in the Deşli Caira section in Romania, firmly demonstrate that the conodont Chiosella timorensis is a defunct proxy for the Olenekian-Anisian/Early-Middle Triassic boundary. As a consequence, the present data on the ammonoid-documented Olenekian-Anisian/Early-Middle Triassic boundary requires the recalibration of all physical events that have been tied to the FAD of the conodont Chiosella timorensis. The case of the Albanian Kçira-section, for which the chronostratigraphic interpretation of the ammonoid record is proved incorrect, definitely makes the conodont Chiosella timorensis a defunct proxy for the nominated boundary. Also, the case of the two Chinese sections recently proposed as being “exceptional” GSSP candidates for the Early-Middle Triassic boundary, which is based on an inconsistent ammonoid/conodont biochronology, fully strengthens this conclusion. The history of the controversial usage of the conodont species Chiosella timorensis in defining the Olenekian-Anisian boundary justifies a discussion about the usefulness of conodonts in the chronostratigraphic calibration of the standard Triassic timescale. One may conclude that the conodonts are not qualified, and have not a reasonable potential, to be used to define or to redefine the boundaries of chronostratigraphic units in the standard Triassic timescale, which have been basically defined on ammonoid biochronology.

Early-Middle Triassic boundary interval: Integrated chemo-bio-magneto-stratigraphy of potential GSSPs for the base of the Anisian Stage in South China

The Wantou and Youping sections of Guangxi, South China provide a detailed high-resolution integrated calibration of the Early-Middle Triassic boundary succession for lithostratigraphy, volcanic episodes, conodont first occurrences (FOs), ammonoid biostratigraphy, geomagnetic polarity, inorganic carbon isotopes, sea-surface temperatures derived from conodont-apatite oxygen-isotopes, and ID-TIMS U–Pb radiometric dating. The upper Spathian (late Early Triassic) magnetostratigraphy is characterized by normal polarity (magnetozone LT9n) that encompasses the FOs of the typical Spathian conodonts Triassospathodus homeri and Gladigondolella carinata, the late Spathian Neopopanoceras haugi ammonoid zone and the beginning of a progressive positive shift in inorganic carbon isotopes. The overlying reversed polarity interval (LT9r) contains two brief normal-polarity subzones (MT1n and MT2n) that can be recognized in several other marine and terrestrial sections. The FO of conodont Chiosella timorensis sensu stricto, a proposed base-Anisian global marker, is near MT1n and near the end of the positive δ13Ccarb excursion. Sea-surface temperatures were reported to have cooled by 4°C during this rise in δ13Ccarb, suggesting a sequestration of carbon dioxide. The lowermost Anisian at Wantou and Youping is dominated by normal polarity (MT3n, with the presence of one major reversed-polarity subzone MT3n.1r), contains the FO of typical Anisian conodonts (Gladigondolella tethydis/Magnigondolella alexanderi), and has the onset of a plateau in inorganic carbon isotopes values (stabilizing around +4‰). The combination of the FO of conodont Chiosella timorensis s.s., the brief normal polarity zone (MT1n) and the last portion of the rising carbon-isotope trend are suitable for primary proxies for global correlation of the Early-Middle Triassic boundary (base of Anisian) to other marine and non-marine settings. Radiometric dates at the Wantou and at the Guandao sections, coupled with a composite cyclostratigraphy for Early Triassic through Anisian, indicate that the FO of the conodont Chiosella timorensis s.s. is at approximately 246.7 Ma.

The Mesozoic maximum of 87Sr/86Sr ratio: a critical turning point after the end-Permian mass extinction

The secular change in 87Sr/86Sr ratio of the Mesozoic recorded the highest value above 0.7083 in Early–Middle Triassic boundary, i.e., the Triassic maximum, suggesting that a major reform in oceanography occurred after the end-Permian mass extinction. We have detected correlative highest 87Sr/86Sr value from the Triassic carbonate, including our data. The stratigraphic horizon of the maximum was constrained to the Olenekian–Anisian boundary (OAB) (247.2 Ma), by conodont. As the oceanic data represent the global average, the present study confirmed the chemostratigraphical utility of the “Triassic maximum” of 87Sr/86Sr ratio in global correlation. After the sharp rise throughout Early Triassic since the end-Permian mass extinction, a remarkable turnover of seawater-87Sr/86Sr values appeared in the OAB. A major global change likely appeared in the OAB to change the Sr-isotope balance in seawater from a continental flux-dominated to a mantle flux-dominated regime. The sharp turning point in 87Sr/86Sr values likely has recorded the timing of the biological influence on the environment.

Lower-Middle Triassic conodont biostratigraphy of the Mingtang section, Nanpanjiang Basin, South China

The well-exposed stratigraphic sequences on the Great Bank of Guizhou (GBG) in South China provide important information for the understanding of various environmental settings during the Permian-Triassic mass extinction and the subsequent recovery, including one of the oldest Triassic marginal reef complexes, which is viewed as an important indicator of biotic recovery following the end-Permian mass extinction. Here we report a systematic conodont study on a newly exposed Lower-Middle Triassic section, the Mingtang section, at the margin of the GBG to provide more data for the time scale of the post-extinction recovery. Twenty-four species in 11 conodont genera are identified and assigned to Hindeodus parvus, Neoclarkina discreta, Neospathodus dieneri, Novispathodus waageni, Neospathodus triangularis-Triassospathodus homeri, Chiosella timorensis, Nicoraella germanica, and Nicoraella kockeli zones in ascending order. These zones correlate well with the conodont successions in South China and over the world. The Induan-Olenekian boundary can be well defined by the first occurrence of Novispathodus waageni in the lower-middle part of the Luolou Formation, while the Early-Middle Triassic boundary was placed at 0.2m below the top of the Luolou Formation according to the first occurrence of Chiosella timorensis. These conodont data suggest that the Tubiphytes-reef began to recover in the Bithynian (early Middle Triassic), later than benthonic organisms such as foraminifers and calcareous algae.

A large aberrant stem ichthyosauriform indicating early rise and demise of ichthyosauromorphs in the wake of the end-Permian extinction.

Contrary to the fast radiation of most metazoans after the end-Permian mass extinction, it is believed that early marine reptiles evolved slowly during the same time interval. However, emerging discoveries of Early Triassic marine reptiles are questioning this traditional view. Here we present an aberrant basal ichthyosauriform with a hitherto unknown body design that suggests a fast radiation of early marine reptiles. The new species is larger than coeval marine reptiles and has an extremely small head and a long tail without a fluke. Its heavily-built body bears flattened and overlapping gastral elements reminiscent of hupehsuchians. A phylogenetic analysis places the new species at the base of ichthyosauriforms, as the sister taxon of Cartorhynchus with which it shares a short snout with rostrally extended nasals. It now appears that ichthyosauriforms evolved rapidly within the first one million years of their evolution, in the Spathian (Early Triassic), and their true diversity has yet to be fully uncovered. Early ichthyosauromorphs quickly became extinct near the Early-Middle Triassic boundary, during the last large environmental perturbation after the end-Permian extinction involving redox fluctuations, sea level changes and volcanism. Marine reptile faunas shifted from ichthyosauromorph-dominated to sauropterygian-dominated composition after the perturbation.

The relationship between the “Green-bean Rock” layers and conodont Chiosella timorensis and implications on defining the Early-Middle Triassic boundary in the Nanpanjiang Basin, South China

The Triassic “Green-bean Rock” (GBR) layers were widely recognized around the Early-Middle Triassic boundary interval in the Nanpanjiang Basin, South China. To determine the precise relationship between the GBR layers and the first appearance datum (FAD) of the conodont Chiosella timorensis, four Lower-Middle Triassic sections from the Nanpanjiang Basin, including the Gaimao, Bianyang II, Zuodeng and Wantou sections have been studied in detail. Detailed conodont biostratigraphy convinces us that there is no exact temporal relationship between the GBR layers and first occurrence of Ch. timorensis. Moreover, the numbers of the GBR layers are different from the place to place within the Nanpanjiang Basin, and the time span of the GBR layers was much longer than previously estimated. Global correlations show that the FAD of Ch. timorensis is contemporaneous basinwide and worldwide and more suitable marker defining the Olenekian-Anisian boundary (Early-Middle Triassic boundary) than any other proxies.

Carbon isotopic composition of Early Triassic marine carbonates, Eastern Sichuan Basin, China

As the interval following the biggest Phanerozoic mass extinction at the end of Permian, the Early Triassic is characterized by an immature, poorly functioned ecosystem. The effects of these extreme environmental conditions can be mirrored by the changes in the δ13C record of marine carbonates. However, the details about the carbon isotopic composition and evolution of the Early Triassic seawater remain poorly understood. A dataset of new δ13C and δ18O values as well as selected major and trace element data (including concentrations of CaO, MgO, Mn, and Sr) was obtained from 113 marine carbonate samples collected in Eastern Sichuan Basin. The isotopic and elemental data are used to evaluate effects of thermochemical sulfate reduction on δ13C. The δ13C values of a few samples affected by thermochemical sulfate reduction were corrected. By combining carbonate δ13C results in our investigated sections, we constructed a composite curve of the Lower Triassic. The results reveal a δ13C anomaly of carbonate rocks throughout the Early Triassic, accompanied by some rapid jumps and falls, such as those from approximately −2‰ to the extremely high value of 8‰ within a period of about 5 Ma. The Early Triassic δ13C profile derived from Eastern Sichuan Basin shows a close correspondence with Guandao section in Guizhou Province, whereas it yields an excursion pattern differing from Chaohu section in Anhui Province of the Lower Yangtze region (with the δ13C value from the minimum around −6‰ to the maximum near 4‰). The higher δ13C values and the positive carbon isotope excursions in the Lower Triassic from Eastern Sichuan Basin were most likely a consequence of the principal environmental change that may include: (1) the barren land surface due to the absence of vegetation, (2) the loss of diverse marine invertebrate groups and marine carbonates, (3) the thriving of bacteria, algae and methanogenus in ocean ecosystems, and (4) the local effect of the repositories of isotopically light carbon occurred in the form of methane hydrates. This process ended at the Early-Middle Triassic boundary, which indicates that the biotic recovery started at the end of the Lower Triassic. The terrestrial vegetation and marine invertebrates, as the regulators for carbon cycle, are irreplaceable and demand strong protections.

The elusive origin of Chiosella timorensis (Conodont Triassic)

The First Appearance Datum (FAD) of the conodont Chiosella timorensis has been recently proposed as an index for the worldwide recognition of the Olenekian-Anisian Boundary (OAB, Early-Middle Triassic boundary). We here report the co-occurrence of C. timorensis with the ammonoids Neopopanoceras haugi (Hyatt and Smith), Keyserlingites pacificus (Hyatt and Smith), Subhungarites yatesi (Hyatt and Smith) and Pseudacrochordiceras inyoense (Smith), which are diagnostic of the late Spathian Haugi Zone. This shows that the previously published first occurrences of C. timorensis were still too poorly constrained, and it questions the adequacy of its FAD as a marker of the OAB. It challenges the significance of some observed lower stratigraphic occurrences of C. gondolelloides compared with C. timorensis. We revise the current criterion for the taxonomic separation of these two species and define a new Chiosella species (left in open nomenclature). The origin of Chiosella timorensis remains unknown but multi-element analyses suggest an affinity with the late Olenekian Neogondolella ex gr. regalis. Our reassessment of the material from the most important OAB sections (Desli Caira, Romania and Guandao, China) allows us to propose a new and more reliable biochronological scheme based on conodont maximal associations for the OAB.

Permian-Triassic magmatism and Ag-Sb mineralization in southeastern Altai and northwestern Mongolia

In the 1980s, Ag-Sb deposits were discovered in a new ore cluster of the Delyun-Yustyd back-arc rift basin in southeastern Altai and northwestern Mongolia. The Delyun-Yustyd basin is filled with up to 9 km thick Devonian volcanosedimentary and terrigenous rocks lying over Vendian-Cambrian carbonate-terrigenous strata. Volcanosedimentary rocks are intruded by D 3-C 1 granites of the Yustyd complex, as well as by pre-granite mafic rocks, post-granite gabbro-diabase, diabase porphyry dikes, and younger lamprophyre dikes of the Chuya complex (245–236 Ma Ar-Ar biotite age). Ag-Sb ores in the Yustyd cluster formed at the Early Mesozoic stage at 240±1.6 Ma (Early-Middle Triassic boundary) and were thus nearly coeval with the Chuya lamprophyre intrusion. The age of Cu-Ag-Sb-Hg mineralization is about 234.4±1.0 Ma (Ar-Ar, sericite). Sb-Hg mineralization is the latest in the province (231.5±1.0 Ma, Ar-Ar, sericite). Gradual change of Ag-Sb (siderite-tetrahedrite) ores to complex Cu-Ag-Sb-Hg (Hg-Ag-tetrahedrite) and Sb-Hg (cinnabar with Sb sulfosalts and stibnite) mineralization along the Kurai-Kobdo and Terekta-Tolbonur large faults is interpreted as development of stage metallogenic zoning along major ore-controlling faults.

Evolution of strontium isotopic composition of seawater from Late Permian to Early Triassic based on study of marine carbonates, Zhongliang Mountain, Chongqing, China

Collected from a Late Permian to Early Triassic sedimentary section in the Zhongliang Mountain of Chongqing, Southwest China, sixty marine carbonate samples were measured for the 87Sr/86Sr ratios, and corresponding evolution curve was constructed. The concentrations of SiO2, CaO, MgO, Mn and Sr are used to evaluate reservation of strontium isotopic composition for original seawater and the credibility of the dissolution method for sample preparation. The results show that most of the samples (except seven samples with the Mn/Sr ratios higher than 2) contain the original geochemistry signatures of ancient seawater. Compared to the published 87Sr/86Sr ratios from the Late Permian to Early Triassic, our database reported here is the largest and the curve constructed is the most complete. The strontium isotopic curve from Late Permian to Early Triassic is consistent globally and exhibits a general trend of steady increase during this period. The minimum of 87Sr/86Sr ratios (0.707011) occurs in the Late Permian (30 m in thickness below the Permian-Triassic boundary), and the maximum (0.708281), near the Early-Middle Triassic boundary. The lack of land plants and the rapid continental weathering result in the increase of 87Sr/86Sr ratios during the interval. The Permian-Triassic boundary in Zhongliang Mountain Section has been accepted internationally. The 87Sr/86Sr ratios of six samples near the boundary vary from 0.70714 to 0.70715 with an average of 0.70714, which is consistent with the value of 0.70715 (samples are from articulate brachiopod shells) from Korte et al. published in 2006 (within the error range in experiment). Accordingly, the strontium isotope composition in the Permian-Triassic boundary in this paper is of global significance. It can be confirmed that the 87Sr/86Sr ratios of the seawater in the Permian-Triassic transition are in the range of 0.70714–0.70715.

A TEST OF BIOGEOGRAPHICAL, ENVIRONMENTAL, AND ECOLOGICAL EFFECT ON MIDDLE AND LATE TRIASSIC BRACHIOPOD AND BIVALVE ABUNDANCE PATTERNS

Analysis of Middle Triassic data indicates that biogeography influences sample distributions, whereas depositional environment and stratigraphic position play secondary roles in governing sample patterns. During this time, taxa differed among biogeographic realms, while the general ecology remained the same: epifaunal benthos— pedunculate and epibyssate suspension feeders—dominate Middle Triassic samples much as they did in the Early Triassic. In contrast, Late Triassic data prove to be more complex in terms of ecology compared to Middle Triassic. Here, guild structure dictates the faunal patterns in addition to biogeographic realm and stratigraphic position, and an overall increase of infaunal life habits occurs—burrowing suspension and deposit feeders increase. Although diversity after mass extinction began to recover at the Early-Middle Triassic boundary, our results indicate that ecology remained stable through the Middle Triassic until the more modern life habits (e.g., infaunalization) increased in the Late Triassic. We conclude that the taxonomic and ecological differences among Late Triassic geographic regions recorded the initiation of a more mobile and infaunal life habit indicative of a modern lifestyle. Our results also indicate that this modernization did not necessarily unfold simultaneously and in coordinated fashion within regions and throughout time. Instead, details of guild expansion or stability may be region specific.

Timing of recovery from the end-Permian extinction: Geochronologic and biostratigraphic constraints from south China: COMMENT AND REPLY: COMMENT

[Lehrmann et al. (2006)][1] recently interpolated a new age of 247.2 Ma for the Early-Middle Triassic boundary in Guandao (Guizhou Province, south China) where four new U-Pb ages were measured from ash layers bracketing this boundary as defined by conodonts. Along with previous data of [Lehrmann et

Timing of recovery from the end-Permian extinction: Geochronologic and biostratigraphic constraints from south China

Research Article| December 01, 2006 Timing of recovery from the end-Permian extinction: Geochronologic and biostratigraphic constraints from south China Daniel J. Lehrmann; Daniel J. Lehrmann 1Department of Geology, University of Wisconsin–Oshkosh, Oshkosh, Wisconsin 54901, USA Search for other works by this author on: GSW Google Scholar Jahandar Ramezani; Jahandar Ramezani 2Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Search for other works by this author on: GSW Google Scholar Samuel A. Bowring; Samuel A. Bowring 2Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Search for other works by this author on: GSW Google Scholar Mark W. Martin; Mark W. Martin 2Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Search for other works by this author on: GSW Google Scholar Paul Montgomery; Paul Montgomery 3Department of Geology, University of Kansas, Lawrence, Kansas 66045, USA Search for other works by this author on: GSW Google Scholar Paul Enos; Paul Enos 3Department of Geology, University of Kansas, Lawrence, Kansas 66045, USA Search for other works by this author on: GSW Google Scholar Jonathan L. Payne; Jonathan L. Payne 4Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305, USA Search for other works by this author on: GSW Google Scholar Michael J. Orchard; Michael J. Orchard 5Geological Survey of Canada, Vancouver, BC V6B 5J3, Canada Search for other works by this author on: GSW Google Scholar Wang Hongmei; Wang Hongmei 6Guizhou Bureau of Geology and Mineral Resources, Guiyang, Guizhou, People's Republic of China Search for other works by this author on: GSW Google Scholar Wei Jiayong Wei Jiayong 6Guizhou Bureau of Geology and Mineral Resources, Guiyang, Guizhou, People's Republic of China Search for other works by this author on: GSW Google Scholar Author and Article Information Daniel J. Lehrmann 1Department of Geology, University of Wisconsin–Oshkosh, Oshkosh, Wisconsin 54901, USA Jahandar Ramezani 2Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Samuel A. Bowring 2Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Mark W. Martin 2Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Paul Montgomery 3Department of Geology, University of Kansas, Lawrence, Kansas 66045, USA Paul Enos 3Department of Geology, University of Kansas, Lawrence, Kansas 66045, USA Jonathan L. Payne 4Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305, USA Michael J. Orchard 5Geological Survey of Canada, Vancouver, BC V6B 5J3, Canada Wang Hongmei 6Guizhou Bureau of Geology and Mineral Resources, Guiyang, Guizhou, People's Republic of China Wei Jiayong 6Guizhou Bureau of Geology and Mineral Resources, Guiyang, Guizhou, People's Republic of China Publisher: Geological Society of America Received: 26 Mar 2006 Revision Received: 04 Jul 2006 Accepted: 14 Jul 2006 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 The Geological Society of America, Inc. Geology (2006) 34 (12): 1053–1056. https://doi.org/10.1130/G22827A.1 Article history Received: 26 Mar 2006 Revision Received: 04 Jul 2006 Accepted: 14 Jul 2006 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 Daniel J. Lehrmann, Jahandar Ramezani, Samuel A. Bowring, Mark W. Martin, Paul Montgomery, Paul Enos, Jonathan L. Payne, Michael J. Orchard, Wang Hongmei, Wei Jiayong; Timing of recovery from the end-Permian extinction: Geochronologic and biostratigraphic constraints from south China. Geology 2006;; 34 (12): 1053–1056. doi: https://doi.org/10.1130/G22827A.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 Four volcanic-ash beds bracket the Early-Middle Triassic boundary, as defined by conodont biostratigraphy, in a stratigraphic section in south China. High-precision U-Pb dates of single zircons allow us to place the Early to Middle Triassic (Olenekian-Anisian) boundary at 247.2 Ma. Magnetic-reversal stratigraphy allows global correlation. The new dates constrain the Early Triassic interval characterized by delayed biotic recovery and carbon-cycle instability to ∼5 m.y. This time constraint must be considered in any model for the end-Permian extinction and subsequent recovery. 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Newly Discovered Fish Faunas from the Early Triassic, Karoo Basin, South Africa, and their Correlative Implications

Recent collecting in exposures of the lowermost Burgersdorp Formation (Beaufort Group), of the Karoo Basin of South Africa, has revealed a previously unknown fish fauna from the Early Triassic (Scythian), lowermost Cynognathus Assemblage Zone (CAZ), which forms an important component of the total vertebrate assemblage. The newly discovered fish material includes lungfish, saurichthyids, and a large microfauna that includes numerous isolated chondrichthyan teeth, two fin spine fragments, and actinopterygian scales and teeth. The latest fish finds, together with the lowermost Cynognathus Assemblage Zone vertebrate faunas, make this Karoo Basin Assemblage Zone one of the most diverse Early Triassic faunal assemblages, comparable in faunal diversity to those from the Czatkowice Formation (Poland) and the Arcadia Formation (Australia). The presence of the lungfish Ptychoceratodus phillipsi in the early Middle Triassic Cynognathus Assemblage Zone (Subzone B), and in the underlying latest Early Triassic Cynognathus Assemblage Zone (Subzone A), indicates that these lungfish could serve as range index fossils within the CAZ, and thus are potentially useful biostratigraphic markers across the Early-Middle Triassic boundary. Furthermore the ‘new’ fish fauna provides a vital marine realm link in particular with the faunas of Madagascar and Australia, that is unavailable using the tetrapod faunal elements of the lower CAZ.

A Triassic Upwelling Zone: The Shublik Formation, Arctic Alaska, U.S.A.--Discussion

Parrish et al. (2001) recently described various facies from the Triassic Shublik Formation of northern Alaska and emphasized the presence of phosphate, glauconite, and a high content of organic carbon in the strata. They interpreted the Shublik Formation as having been deposited under the influence of an upwelling zone on the basis of these distinctive lithologic attributes and hence the title of their article. We wish to point out that, whereas such lithologies may possibly point to upwelling conditions, they certainly do not provide solid proof for the former existence of such a depositional setting. We base this statement on the nature of equivalent strata in adjacent Arctic areas, the Canadian Arctic Archipelago and Svalbard, which are briefly described below. First of all it is necessary to comment on the stratigraphic data provided by Parrish et al. (2001) for the Shublik Formation of the National Petroleum Reserve of Alaska and the Arctic National Wildlife Refuge (NPRA-ANWR) of northern Alaska. They state, The Shublik Formation is Upper Triassic (Carnian-Norian) whereas in the accompanying Fig. 1 they illustrate that the Shublik Formation of NPRA and ANWR ranges in age from mid-Early Triassic to Late Triassic. Unfortunately both of these age designations are unsubstantiated. Detterman et al. (1975) established that the Shublik Formation of northeastern Alaska ranges in age from early Middle Triassic (Anisian) to Late Triassic (Norian) (see their figure 4). This age range is important because the contact of the Shublik Formation with the underlying Ivishak Formation appears to mark a significant, Arctic-wide sequence boundary that coincides approximately with the Early-Middle Triassic boundary (Bird and Molenaar 1987; Embry 1989). Furthermore, the upper contact of the Shublik Formation with …