Article

Isotopic evidence bearing on Late Triassic extinction events, Queen Charlotte Islands, British Columbia, and implications for the duration and cause of the Triassic/Jurassic mass extinction

August 2004
Earth and Planetary Science Letters 224(3-4):589-600

August 2004
224(3-4):589-600

DOI:10.1016/j.epsl.2004.04.034

Authors:

Peter Ward

University of Washington Seattle

Geoff Garrison

AltaRock Energy, Inc.

James W. Haggart

Geological Survey of Canada

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Stable isotope analyses of Late Triassic to earliest Jurassic strata from Kennecott Point in the Queen Charlotte Islands, British Columbia, Canada shows the presence of two distinct and different organic carbon isotope anomalies at the Norian/Rhaetian and Rhaetian/Hettangian (=Triassic/Jurassic) stage boundaries. At the older of these boundaries, which is marked by the disappearance of the bivalve Monotis, the isotope record shows a series of short-lived positive excursions toward heavier values. Strata approaching this boundary show evidence of increasing anoxia. At the higher boundary, marked by the disappearance of the last remaining Triassic ammonites and over 50 species of radiolarians, the isotopic pattern consists of a series of short duration negative anomalies. The two events, separated by the duration of the Rhaetian age, comprise the end-Triassic mass extinction. While there is no definitive evidence as to cause, the isotopic record does not appear similar to that of the impact-caused Cretaceous/Tertiary boundary extinction.

Morphological trends across the Norian/Rhaetian boundary within Late Triassic conodonts in western Canada: Implications for protracted paleoenvironmental disturbance preceding the end-Triassic mass extinction

Article

Full-text available

Dec 2023
PALEOBIOLOGY

The Late Triassic conodont species Mockina ex gr. carinata and Mockina ex gr. englandi were exceptionally prevalent among the marine fauna of the Panthalassan realm from the middle Norian through to the Rhaetian. Leading into the complete extinction of conodonts near the Triassic/Jurassic boundary, a significant turnover event occurred in conodont fauna across the Norian/Rhaetian boundary (NRB), with the pectiniform elements of common Rhaetian genera from Tethys exhibiting minimal or absent platforms. This intergeneric trend of platform reduction is not as evident in Panthalassa, where these genera are very rare, but morphometric analyses of M. ex gr. carinata and M. ex gr. englandi specimens from across the Canadian Cordillera demonstrate that comparable shifts in morphology occurred intraspecifically in Panthalassa across the NRB, confirming the global extent of these trends. Pectiniform elements of M. ex gr. carinata display a sequential reduction of platform width from the middle Norian to late Norian to Rhaetian, whereas pectiniform elements of M. ex gr. englandi display a reduction of platform width only from the late Norian to Rhaetian. Specimens of both species that have a mid-platform length to breadth ratio greater than 3:1 are restricted to the Rhaetian. Specimens from the Kennecott Point section on Haida Gwaii, British Columbia, demonstrate that this morphological shift occurred somewhat later than other biostratigraphic proxies for the NRB. The global trend of platform width reduction in many conodont pectiniform elements may reflect a change in primary diet away from hard food sources, perhaps suggesting some degree of carbonate biomineralization suppression beginning around the NRB. This interpretation would support CO 2 outgassing as the causal mechanism of the environmental disturbance at the NRB and identify the NRB as a significant turning point for Late Triassic ecosystems, marking the beginning of a protracted, multiphase end-Triassic mass extinction.

Triassic/Jurassic bivalve biodiversity dynamics: Biotic versus abiotic factors

Article

Oct 2023

Based on the global occurrence dataset, the shift in taxonomic and functional diversity of bivalves at the Triassic/Jurassic transition was examined herein. There is a noticeable decline in diversity at many taxonomic levels (generic, family, and order) along the Triassic/Jurassic boundary. Test changes in the functional diversity (e.g., life habits, mobility levels, and feeding mode) revealed that the percentage of mobile exceeded stationary taxa after the end of the Triassic crisis, while no major changes were observed in the life habit or feeding mode. By the Sinemurian, diversity reached the pre-extinction levels. A significant difference was also found between survivors’ longevity and extinct taxa, where the Early Jurassic (Hettangian) fauna have a longer duration relative to those that became extinct. The Triassic/Jurassic boundary is marked by a marked sea-level fall and a decrease in the mean Sea Surface Temperature (SST), which is associated with increasing siliciclastic and decreasing carbonate rocks. The latter may also point to ocean acidification at the Triassic/Jurassic boundary. The geographic range size of bivalves is slightly changed by the end of the Triassic, where the taxa are slightly characterized by narrower ranges. Hence, the geographic range size, the result of ecophysiology, plays a major role in determining the extinction risk. The difference in the magnitude of the diversity loss (i.e., taxonomically vs. functionally) indicated that the shallower marine habitat destruction resulting from the sea-level fall is the primary cause of the Triassic/Jurassic mass extinction.

Paleoenvironmental interpretation of the Late Triassic Norian – Rhaetian boundary interval in the Whitehorse Trough (Stikine Terrane, northern Canadian Cordillera)

Article

Nov 2022
PALAEOGEOGR PALAEOCL

The Norian – Rhaetian boundary (NRB) is associated with significant faunal turnover in a wide variety of groups. Following the relative stability of the Norian Stage, this boundary potentially marks the beginning of a protracted and continuous episode of elevated extinction rates, which culminated with the end-Triassic mass extinction. Despite the importance of the NRB to paleontological trends in the Late Triassic, much about this event remains enigmatic, including potential causal mechanisms as well as the characteristics of the resulting paleoenvironmental changes. Fossiliferous limestone of the Sinwa Formation occurs in extensive outcrops throughout northwestern British Columbia and provides an exceptional record of Upper Triassic stratigraphy that represents a paleogeographic region largely uninvestigated prior. The present study integrates lithostratigraphic, paleontological, and geochemical data to reconstruct the shallow marine paleoenvironments recorded by the Sinwa Formation in two sections on Mount Sinwa, south of Atlin, within the Stikine Terrane. The progression of lithological facies observed in these sections suggests a gradual base level rise throughout the late Norian. Following this steady facies progression is a prominent shift from coral reef boundstone to shale near the top of both sections. This facies change approximately coincides with the NRB interval as evidenced by the first occurrence of the latest Norian – Rhaetian conodont species Mockina mosheri morphotype B, as well as by Re – Os isochron ages of organic-rich limestone. Although the base level rise observed at the NRB interval could be due to regional tectonics, it could also potentially be recording eustatic sea level rise given the lack of consensus around sea level change at the NRB. Measurements of late Norian ⁸⁷Sr/⁸⁶Sr ratios on Mount Sinwa are consistent with those recorded in Tethyan studies, but the Panthalassan record overall does not replicate the same drop across the NRB observed in the Tethys. The lithological facies shift is also immediately preceded by a negative excursion in the δ¹³C values of carbonate, indicating that the NRB interval on Mount Sinwa is associated with coral reef collapse as well as the globally observed disruption of carbon cycling.

Tracing volcanic emissions from the Central Atlantic Magmatic Province in the sedimentary record

Article

Full-text available

Nov 2020
EARTH-SCI REV

The end-Triassic mass extinction (ETME) is thought to have been caused by voluminous, pulsed volcanic activity of the Central Atlantic Magmatic Province (CAMP). Over the last decades, various geochemical signals and proxy records, including δ13C, pCO2, iridium and other platinum-group elements, mercury, polycyclic aromatic hydrocarbons (PAH), charcoal and SO2, have been directly or indirectly attributed to CAMP magmatism. Here, we compile these various records in a stratigraphic framework to present a cohesive chain of events for the CAMP and the end-Triassic mass extinction. Mercury and iridium anomalies in sediments indicate that CAMP activity commenced prior to the onset of the marine extinctions (as marked by the last occurrence of the Triassic ammonoid Choristoceras marshi or closely related species), and a negative δ13C excursion in organic matter (the Marshi CIE). This CIE may be explained by input of light carbon to the atmosphere from CAMP lavas of the Tiourjdal and Prevalent groups. Pedogenic carbonate below and above the Prevalent group in North America indicates a more than twofold increase in atmospheric pCO2. Subsequent n-alkane C-isotopes, and stomatal pCO2 data seem to indicate a temporary cooling after the Marshi CIE, which is consistent with climate models incorporating volcanic emissions of both CO2 and SO2. Records of excess iridium and Hg/TOC indicate intensified magmatism during the extinction interval. Tectonic and perhaps epeirogenic (i.e. doming due to rise of magma) activity is suggested by the occurrence of multiple and widespread seismites in Europe. Atmospheric pCO2 proxies indicate global warming, which culminated contemporaneously with the Spelae CIE. Global warming is corroborated by increased wildfire activity testified by charcoal and pyrolytic PAH records. Increased isotopic ratios of Os and Sr from sections that record global ocean signatures suggest increased weathering of continental crust likely due to climatic changes. Just prior to the increase in pCO2 from stomatal proxy data, fossil plants exhibit SO2-induced damage indicating excess sulfur dioxide deposition priot to and across the Triassic–Jurassic boundary. At the same time, increased ratios of heavy molecular PAHs (coronene/benzo(a)pyrene) in sediments suggest metamorphism of organic sediments also occurred across the Triassic–Jurassic boundary. These proxies may suggest that thermogenic release of light carbon and sulfur from sill intrusions in the Trans-Amazonian basins, where both evaporate- and organic-rich sediments are known to have been intruded, may have played an important role during the course of the ETME. Geochemical traces of magmatism, i.e. Ir and Hg, appear to have gradually disappeared during the Hettangian, suggesting that later phases of CAMP were less voluminous. Stomatal proxy data from Greenland and n-alkane C-isotope data from the UK, together with oxygen isotope data from carbonate fossils in the UK, may indicate that the global warming at the Spelae CIE was succeeded by another short-term cooling event. A gradual decrease in δ13C culminated at the top-Tilmanni CIE, marking the beginning of a long-term steady state with more negative C-isotope values than prior to the ETME. At this time, terrestrial ecosystems appear to have stabilized globally and ammonoids had begun to rediversify.

The Late Triassic Extinction at the Norian/Rhaetian boundary: Biotic evidence and geochemical analysis

Article

Apr 2020
EARTH-SCI REV

The latest Triassic was an interval of prolonged biotic extinction culminating in the end-Triassic Extinction (ETE). The ETE is now associated with a perturbation of the global carbon cycle just before the end of the Triassic that has been attributed to the extensive volcanism of the Circum-Atlantic Magmatic Province (CAMP). However, we attribute the onset of declining latest Triassic diversity to an older perturbation of the carbon cycle (δ¹³Corg) of global extent at or very close to the Norian/Rhaetian boundary (NRB). The NRB appears to be the culmination of stepwise biotic turnovers that characterize the latest Triassic and includes global extinctions of significant marine and terrestrial fossil groups. These biotic events across the NRB have been largely under-appreciated, yet together with a coeval disturbance of the carbon cycle were pivotal in the history of the Late Triassic. Here, we present new and published δ¹³Corg data from widespread sections (Italy, Greece, Australia, New Zealand,USA, Canada). These sections document a previously unknown perturbation in the carbon cycle of global extent that spanned the NRB. The disturbance extended across the Panthalassa Ocean to both sides of the Pangaean supercontinent and is recorded in both the Northern and Southern Hemispheres. The onset of stepwise Late Triassic extinctions coincides with carbon perturbation (δ¹³Corg) at the NRB, indicating that a combination of climatic and environmental changes impacted biota at a global scale. The NRB event may have been triggered either by gas emissions from the eruption of a large igneous province pre-dating the NRB, by a bolide impact of significant size or by some alternative source of greenhouse gas emissions. As yet, it has not been possible to clearly determine which of these trigger scenarios was responsible; the evidence is insufficient to decisively identify the causal mechanism and merits further study.

The asynchronous disappearance of conodonts: New constraints from Triassic − Jurassic boundary sections in the Tethys and Panthalassa

Article

Full-text available

Apr 2020
EARTH-SCI REV

The End-Triassic Extinction event (ETE) has been recognized in numerous sections worldwide and it is usually marked by three negative carbon isotope excursions (NCIEs), named “precursor” (P-NCIE), “initial” (I-NCIE) and “main” (M-NCIE) negative carbon isotope excursions. These three NCIEs are significant characteristics of this time interval, and they are likely related to the emplacement of the Central Atlantic Magmatic Province (CAMP) that is considered the main trigger of the ETE. Stable carbon isotope excursions, commonly related to biotic turnovers and extinctions, play an important role in stratigraphic correlations, particularly around the Triassic/Jurassic boundary (TJB). This time interval records the disappearance of conodonts, elements of a feeding apparatus belonging to marine organisms that populated the Paleozoic-early Mesozoic seas, and which became extinct across the TJB. So far, the interpretation of conodont extinction has remained ambiguous, as the timing of its last occurrence was debated which in turn hindered our understanding of the main cause(s) that could have led to their disappearance. Here we present and compare integrated data of nine TJB sections from different areas, Tethys and Panthalassa, and different depositional environments, i.e. shallow vs deep water or proximal vs distal shelf. Each of these sections record both the last occurrences of latest Triassic conodont taxa and pronounced changes in the carbon isotopic composition of organic matter across the TJB interval. Our analysis of chemo- and integrated biostratigraphic correlation suggests that the final extinction of the taxon Conodonta was asynchronous.

Chemostratigraphy Across the Triassic–Jurassic Boundary

Chapter

Full-text available

Jan 2019

The Triassic‐Jurassic transition (~201.5 Ma) is marked by one of the largest mass extinctions in Earth's history. This was accompanied by significant perturbations in ocean and atmosphere geochemistry, including the global carbon cycle, as expressed by major fluctuations in carbon isotope ratios. Central Atlantic Magmatic Province (CAMP) volcanism triggered environmental changes and played a key role in this biotic crisis. Biostratigraphic and chronostratigraphic studies link the end‐Triassic mass extinction with the early phases of CAMP volcanism, and notable mercury enrichments in geographically distributed marine and continental strata are shown to be coeval with the onset of the extrusive emplacement of CAMP. Sulfuric acid induced atmospheric aerosol clouds from subaerial CAMP volcanism can explain a brief, relatively cool seawater temperature pulse in the mid‐paleolatitude Pan‐European seaway across the T–J transition. The occurrence of CAMP‐induced carbon degassing may explain the overall long‐term shift toward much warmer conditions. The effect of CAMP volcanism on seawater 87Sr/86Sr values might have been indirect by driving enhanced continental weathering intensity. Changes in ocean‐atmosphere geochemistry and associated (causative) effects on paleoclimatic, paleoenvironmental, and paleoceanographic conditions on local, regional, and global scales are however not yet fully constrained.

The Norian “chaotic carbon interval”: New clues from the δ 13 C org record of the Lagonegro Basin (southern Italy)

Article

Full-text available

Jun 2017
GEOSPHERE

A global carbon-isotope curve for the Late Triassic has the potential for global correlations and new insights on the complex and extreme environmental changes that took place in this time interval. We reconstruct the global δ¹³Corg profile for the late Norian, improving on sparse published data from North American successions that depict a "chaotic carbon-isotope interval" with rapid oscillations. In this context, we studied three sections outcropping in the Lagonegro Basin (southern Italy), originally located in the western Tethys. The carbon-isotope profiles show four negative excursions correlatable within the Lagonegro Basin. In particular, a negative shift close to the Norian/Rhaetian boundary (NRB) appears to correlate with that observed in the North American δ¹³Corg record, documenting the widespread occurrence of this carbon cycle perturbation. The ⁸⁷Sr/⁸⁶Sr and ¹⁸⁷Os/¹⁸⁸Os profiles suggest that this negative shift was possibly caused by emplacement of a large igneous province (LIP). The release of greenhouse gases (CO2) to the atmosphere- ocean system is supported by the ¹²C enrichment observed, as well as by the increase of atmospheric pCO2 inferred by different models for the Norian/Rhaetian interval. The trigger of this strongly perturbed interval could thus be enhanced magmatic activity that could be ascribed to the Angayucham province (Alaska, North America), a large oceanic plateau active ca. 214 ± 7 Ma, which has an estimated volume comparable to the Wrangellia and the Central Atlantic Magmatic Province (CAMP) LIPs. In fact, these three Late Triassic igneous provinces may have caused extreme environmental and climate changes during the Late Triassic.

Si isotope ratio of radiolaria across Triassic–Jurassic transition in a pelagic deep-sea bedded chert (Inuyama, Japan)

Article

Jun 2022
GLOBAL PLANET CHANGE

The end-Triassic extinction event (ETE) marks one of the “Big five” mass extinction events of the Phanerozoic, yet the timing and nature of environmental changes on a global scale remain elusive. Here we report a mm-scale high-resolution δ³⁰Si profile of sea surface-dwelling radiolaria, preserved as moulds, spanning the end-Triassic radiolarian turnover interval of the deep-sea succession at the Katsuyama section, Inuyama, Japan. The δ³⁰Si of the Triassic-Jurassic radiolaria between − 0.6 ± 0.5‰ and 2.6 ± 0.3‰ overlap with available radiolarian δ³⁰Si data for Triassic to Cenozoic, including modern samples. The mass balance of Si with dominant radiolaria up to 90% in chert supports negligible impact of diagenesis on δ³⁰Si of radiolarian moulds. The cm-scale δ³⁰Si variations up to 2 ‰ are overall associated with changes in silica contents. Here we hypothesize that the δ³⁰Si of radiolarian reflect radiolarian productivity. We detected negative silicon isotope excursions within and above the end-Triassic radiolarian turnover interval, named here the SIE 1 and 2. The first SIE of 2 ‰ is detected from 0 mm to 10 mm above the base of purple chert interval, probably linked with the initial massive volcanism in the Central Atlantic magmatic provinces (CAMP) and associated deep-sea acidification and the onset of the end-Triassic radiolarian turnover. Subsequent positive SIE up to 2 ‰ ca. 10 mm above the first negative SIEs may record recovery of biosiliceous productivity, which could may be related with the first appearance of several Jurassic radiolarian taxa within the radiolarian turnover interval. We also detected data that is suggestive of SIE 2 in the lowermost dusky red chert bed, suggesting similar changes in productivity. These negative SIEs occurred within ~ 1 mm interval, implying the occurrence of kyr- or shorter-scale drastic environmental perturbations across the end-Triassic radiolarian turnover interval.

ENVIRONMENTAL STRESSES PRECEDING THE END-TRIASSIC EXTINCTION IN THE PANTHALASSIC OCEAN

Conference Paper

Jan 2022

Onset of environmental disturbances in the Panthalassic Ocean over one million years prior to the Triassic-Jurassic boundary mass extinction

Article

Nov 2021
EARTH-SCI REV

While the end-Triassic mass extinction has been linked to emplacement of the Central Atlantic Magmatic Province (CAMP), evidence for environmental stresses appears hundreds of thousands of years prior to the extinction in some sections from the Panthalassic Ocean. In this study, we measured carbon, sulfur, and mercury concentrations in the Kurusu section, near Inuyama, Japan. These bedded radiolarian cherts are part of the Mino Terrane, an accretionary complex of late Paleozoic and Mesozoic sediments deposited at abyssal water depths in the open ocean, providing a unique window into the Triassic-Jurassic transition in pelagic settings. The rhythmically bedded nature of the sediments allowed construction of a floating astronomical age model tied to the radiolarian-defined Triassic-Jurassic boundary. Average linear sedimentation rates (LSR) of 0.07–0.48 cm kyr⁻¹ and total organic carbon (TOC) concentrations of 0.07–0.22% yielded estimates of primary productivity rates (PPR) based on published transfer functions ranging from 2400 to 63,000 mg C cm⁻² kyr⁻¹, which are generally comparable to PPRs in the modern equatorial and subtropical Pacific. While mercury (Hg) concentrations are strongly correlated with sedimentary sulfide content throughout the section, a distinct increase in the ratio of Hg to sulfide near the Triassic-Jurassic boundary may record Hg input from CAMP volcanism. Below this level, a series of discrete spikes in sulfide content appear during the ~ 1.2 Myr before the extinction, recording a precursor interval of environmental stress that also correlates with changes in the composition of the planktonic community. We infer that these changes reflect the development of stratification in the water column, with more reducing conditions characterizing the thermocline below the surface mixed layer. Based on the evidence from Kurusu and comparisons to other Panthalassic sections, we propose a model in which water-column stratification began to develop in the open Panthalassic Ocean over one million years before the Triassic-Jurassic boundary. Evidence from sections deposited at slope depths suggests that this rising chemocline may have begun to impinge on the slopes of island arcs and the South American continental margin by ~ 400 kyr before the boundary. The end-Triassic extinction coincided with both the main phase of CAMP eruptions and the irruption of acidic, reducing deep waters into photic zone and shelf environments.

Dasycladacean alga Palaeodasycladus in the northern Tethys (West Carpathians, Poland) and its new palaeogeographic range during the Early Jurassic

Article

Feb 2018

The green alga Palaeodasycladus was recognized in Lower Jurassic shallow-marine high-energy calcarenites of the Choč Nappe (Hronicum Domain) in the Tatra Mts in Poland. This occurrence indicates the most Northern record of Palaeodasycladus as it is known mostly from the southern part of the Western Tethys. The stratigraphic range of Palaeodasycladus (Norian, Sinemurian–Pliensbachian) and the upper Pliensbachian age of the overlying calcarenites (previous data on the basis of brachiopods) suggest that the studied part of the section was deposited during the Sinemurian–early Pliensbachian. The previous and current reports on occurrences of Palaeodasycladus allowed determination of a new northern palaeogeographic range of the shallow-marine Mediterranean biota during the Early Jurassic time.

A new Rhaetian δ 13 C org record: Carbon cycle disturbances, volcanism, End-Triassic mass Extinction (ETE)

Article

Full-text available

Jan 2018
EARTH-SCI REV

The links between large-scale volcanism, carbon cycle perturbations and the biotic crises at the End-Triassic Extinction event (ETE) are not well understood. The ETE seems to be marked by three carbon isotope excursions (CIEs) likely triggered by different eruptive phases of the Central Atlantic Magmatic Province (CAMP). These three CIEs appear to occur during the late Rhaetian, close to the Triassic/Jurassic boundary (TJB), but the relative timing connecting the volcanism, carbon perturbations and extinctions is still subject to debate resulting from: i) the difficulties in long-distance biostratigraphic correlations of Rhaetian successions due to the step-like extinction pattern characterizing the ETE, and to the lack of globally correlatable key-fossil group(s) across the system boundary; ii) the limit of coverage of available δ¹³C profiles to the system boundary interval, rather than the entire Rhaetian; iii) the inherent difficulties in correlating CIEs without clear biostratigraphic markers. Here we present a δ¹³Corg curve from the Lombardy Basin which covers for the first time the entire Rhaetian. Using this chemostratigraphy, we propose two possible correlations (option 1 and option 2) with other late Rhaetian to early Hettangian successions worldwide. These two possible correlations rely on a combination of paleontological (ammonoids, pollens, conodonts), lithostratigraphic and geochemical constraints. Option 2 in particular has important implications for the causality and geochronology of the ETE events by suggesting that the sharp negative peak usually considered to be the “initial” CIE in the Lombardy might represent a carbon perturbation within the negative trend of the “main” CIE. This implies that a reconsideration of the succession of biotic events occurring during this time interval is required.

Synchrony between the Central Atlantic magmatic province and the Triassic–Jurassic mass-extinction event?

Article

Feb 2007
PALAEOGEOGR PALAEOCL

Weathering trends in the Norian through geochemical and rock magnetic analyses from the Pignola–Abriola section (Lagonegro Basin, Italy)

Article

Full-text available

Mar 2024
CLIM PAST

We investigated the geochemical and rock magnetic properties of the magnetostratigraphically calibrated Pignola–Abriola section (Italy) in order to understand the climatic perturbations that characterize the late Norian–early Rhaetian interval (Late Triassic). We performed experiments on anhysteretic and isothermal remanence (ARM and IRM) and on magnetic susceptibility (χ) to obtain the rock magnetic parameters necessary for our paleoclimatic investigation. An episode of increase in the relative quantity of hematite, suggesting the enhanced subaerial oxidation of iron minerals, was identified in the Norian from ∼ 217 Ma in the Alaunian up to ∼ 211 Ma in the early Sevatian, followed by a decline up to 207–206 Ma at the end of the Norian (late Sevatian). The results of geochemical and multivariate statistical analyses support a long-term increase and reduction in rock weathering, confirming and extending previous 87Sr / 86Sr data from the Pizzo Mondello section (Italy). Possible causes of these long-term weathering trends are the multiphase uplifting of the Cimmerian orogen, occurring at mid-northern latitudes along the southern margin of Asia in the Late Triassic, and/or the northward motion of Pangea across the equatorial humid belt. Rapid excursions in oxidized iron minerals have also been observed across the Norian–Rhaetian boundary, the origin of which still has to be determined.

Upper Norian conodonts from the Baoshan block, western Yunnan, southwestern China, and implications for conodont turnover

Article

Full-text available

Jan 2023

The Sevatian of the late Norian is one of the key intervals in biotic turnover and in changes of paleoclimate and paleoenvironments. Conodont faunas recovered from two sections of upper Norian strata of the Dashuitang and Nanshuba formations near Baoshan City in western Yunnan province provide new insights into the diversity and biostratigraphy of the Sevatian conodonts within China as well as globally. A lower Mockina ( M .) bidentata Zone and an upper Parvigondolella ( P .) andrusovi Zone are identified in this area according to the first occurrences of M. bidentata and of P. andrusovi . Rich conodont fauna of M. zapfei is detailed and presents various intraspecific forms. A total of 19 forms of P 1 elements are presented, which, when combined with the reported conodonts in the M. bidentata Zone, suggest that there was a peak in conodont diversity within the M. bidentata Zone. A biotic crisis in the uppermost M. bidentata Zone is recognized from the contrast between the diverse conodont fauna in the M. bidentata Zone and the rare conodonts in the P. andrusovi Zone. The conodont turnover during the middle Sevatian highlights the fact that the prolonged phases of the end-Triassic mass extinction probably began in the transition interval from M. bidentata Zone to P. andrusovi Zone.

Storms and deforestation prior to Triassic – Jurassic Boundary? Evidence from woody fossils at upmost Xujiahe Formation, Southwestern China

Preprint

Full-text available

Oct 2022

Global climate and environmental changes were the main causes of the end-Triassic mass extinction. However, direct sedimentological evidence of environmental catastrophes is rare in Triassic – Jurassic interval, especially in the eastern Tethys region. The newly discovered in-situ trunk fossils in paleosol surface and a set of unique branch-supported sandstones below may record the environmental disaster at the Triassic-Jurassic interval in the northern Sichuan Basin. Sedimentological data showed the strong storm prevalent induced the lodging direction of in-situ trunks is opposite to the direction of paleocurrent. Enhancement of large-scale runoff along with the dramatic increase of woody detrital input may indicate the deforesting at the Triassic -Jurassic boundary in eastern Tethys, Sichuan Basin.

Geochemical records of the end-Triassic Crisis preserved in a deep marine section of the Budva Basin, Dinarides, Montenegro.

Article

Sep 2022
PALAEOGEOGR PALAEOCL

The end-Triassic extinction event (~ 201.5 Ma) is one of the five major mass extinction events in Earth's history, however, considerable discussion continues on the exact causes and timing of the event. This is because, whilst certain geochemical data on T-J sections appears to be largely comparable globally, with for example a significant (up to 6‰) negative carbon-isotope (δ¹³C) excursion at the extinction horizon, more often than not other geochemical variations are neither uniform nor fully consistent between sections. Critical to this discussion is that the majority of the studied sections containing the end-Triassic extinction event are limited to shallow marine or terrestrial sections, which are prone to discontinuities and hiatuses. In this study, we present carbon isotopes (δ¹³Ccarb), total organic carbon (TOC), major and trace, mercury (Hg) and highly siderophile elements (HSE), osmium-isotope compositions and paleomagnetic data of a relatively less studied deep-marine T-J succession in the Budva Basin, Čanj, Montenegro. At Čanj, deep-marine Triassic limestones are abruptly interrupted by a ~ 6 cm finely laminated clay layer, before transitioning to more argillaceous Jurassic red beds. The clay layer is interpreted to represent the end-Triassic extinction interval and is characterized by a negative carbon isotope excursion, relative heavy rare earth element (HREE) enrichment, Hg increase, HSE enrichment and a sharp shift to unradiogenic osmium-isotopic ratios. This establishes the Čanj section as a unique and well-preserved outcrop that exquisitely encapsulates the end-Triassic extinction in the Tethyan marine realm. The distinct geochemical markers recorded at Čanj are consistent with the Central Atlantic Magmatic Province as the main driver behind the end-Triassic extinction.

Anisian (Middle Triassic) stromatolites from Southwest China: Biogeological features and implications for variations of filament size and diversity of Triassic cyanobacteria

Article

Jul 2022
PALAEOGEOGR PALAEOCL

This study documents new stromatolite deposits from the Anisian succession of the Guanling Formation in the Boyun section of eastern Yunnan Province, southwestern China. The Boyun stromatolites are characterized by undulating laminations, which yield a variety of biostructures and abiotic grains, such as cyanobacteria Bevocastria and Renalcis, microclots, fecal pellets, coccoid-like spheroids, and authigenic quartz. Filamentous cyanobacteria Bevocastria are likely the major builder constructing the Boyun stromatolite build-ups. Stromatolites in the Boyun section likely grew in an open, oxic marine environment, differing from the Lower Triassic stromatolites that were mostly formed in relatively oxygen-poor conditions of shallow marine settings, strengthening the view that stromatolites are not necessarily indicative of harsh environments. In addition, the global dataset of cyanobacteria filament sizes through the Triassic deciphers that a pronounced increase in the diameter of filamentous cyanobacteria through the Early-Middle Triassic, followed by a decline during the Late Triassic. The developments of marine deoxygenation in the Early Triassic and Rhaetian broadly coincided with the reduction in cyanobacteria filament diameter, suggesting a possible causal link between the two. Our data also show that the diversity of cyanobacteria does not show a significant correlation relationship with any modeled estimates of CO2, indicating that their might be more complex when CO2 levels below ∼2800 ppm (10 times present atmospheric level).

Extensive marine anoxia in the European epicontinental sea during the end-Triassic mass extinction

Article

Full-text available

Feb 2022
GLOBAL PLANET CHANGE

Warming-induced marine anoxia has been hypothesized as an environmental stressor for the end-Triassic mass extinction (ETME), but links between the spread of marine anoxia and the two phases of extinction are poorly constrained. Here, we report iron speciation and trace metal data from the Bristol Channel Basin and Larne Basin of the NW European epicontinental sea (EES), spanning the Triassic–Jurassic (T–J) transition (~ 202–200 Ma). Results show frequent development of anoxic-ferruginous conditions, interspersed with ephemeral euxinic episodes in the Bristol Channel Basin during the latest Rhaetian, whereas the contemporaneous Larne Basin remained largely oxygenated, suggesting heterogeneous redox conditions between basins. Subsequently, more persistent euxinic conditions prevailed across the T–J boundary in both basins, coinciding precisely with the second phase of the ETME. We propose that this later phase of benthic faunal loss in the NW EES was directly driven by the bottom-water oxygen crisis. Conversely, although anoxic conditions persisted into the early Hettangian, the benthos diversified at this time in nearshore areas. Post-extinction conditions were poised at a fluctuating redox state, but anoxia did not extend into the shallowest areas where benthic marine ecosystem recovery was occurring.

Facies stacking and distribution in the Gabbs Formation (late Triassic, west-Central Nevada, USA): An environmental baseline to the end-Triassic carbonate crisis

Article

Oct 2021
SEDIMENT GEOL

The primarily carbonate Gabbs Formation of west-central Nevada, U.S.A., remains an important, rare example of Panthalassan shallow-marine environments from the Late Triassic and through the Triassic–Jurassic boundary. Its relevance as a locality persists, particularly as the end-Triassic mass extinction interval is increasingly recognized as a carbonate crisis, evidenced by the global decline of carbonate facies and calcareous marine organisms. However, important transitions across key stratigraphic boundaries in this region have tended to be evaluated in isolation, producing an incomplete picture of sedimentation through the duration of the Late Triassic leading up to the geochemical crises and mass extinction at the close of the Triassic. In this work, multiple correlative measured sections are used to describe the facies in the mixed carbonate-siliciclastic ramp and characterize controls on carbonate facies. The outer ramp transition to inner ramp facies of the Gabbs represent a transgressive-regressive-transgression cycle culminating in a transition to terrigenous inputs and gradual decline of carbonate sediments stratigraphically below the mass extinction interval. This predictable loss of carbonate facies and the near continuous deposition of the Gabbs Formation allows for evidence of facies changes and acidifying conditions in the latest Triassic to be considered independently; in contrast to other global Late Triassic sections where depositional hiatuses or abrupt facies changes often compounds these records. Establishing a baseline sedimentation for the Late Triassic demonstrates that the final loss of carbonate facies can be decoupled from the onset of acidifying conditions, resulting in a more precise timeline of latest Triassic environmental upheaval.

Sedimentary record of Upper Triassic impact in the Lagonegro Basin, southern Italy: Insights from highly siderophile elements and Re Os isotope stratigraphy across the Norian/Rhaetian boundary

Article

Aug 2021
CHEM GEOL

The Norian and Rhaetian transition (Late Triassic) is characterized by a faunal turnover in major pelagic groups, such as radiolarians, conodonts, and ammonoids. Although catastrophic events such as emplacements of large igneous provinces and/or extraterrestrial impacts have been suggested to account for this biotic turnover, firm evidence based on geochemistry of sedimentary successions is still lacking. In order to assess environmental changes across the Norian/Rhaetian boundary (NRB), we report high–resolution stratigraphic variations for whole-rock major, trace, and highly siderophile element abundances, together with ReOs isotope ratios for the Sasso di Castalda section in Lagonegro Basin, southern Italy. The section consists of a continuously exposed sequence of upper Norian (Sevatian) through the lower Rhaetian of a deep basinal deposits. Our data demonstrated that the upper Norian section records important events in stratigraphically ascending order: (1) a depositional environment moved below the Carbonate Compensation Depth, leading to the carbonate-biosilica transition associated with a slight depletion of elements favored in heavy minerals such as Zr, Hf, and Ti, (2) an input of Rochechouart impact components detected by platinum-group element anomaly, and (3) a transient change of redox state into low oxygen (dysoxic to suboxic) conditions marked by increases of V, U, and Re. This sequence of events suggests that the Rochechouart impact predates the major environmental changes resulting in faunal turnover at the NRB. Although their direct causal relationships are highly questionable given the small size of impactor and the interval between the impact horizon and the NRB, the possibility of triggering subsequent environmental and biotic collapses cannot be ruled out. This study provides the first identification of Rochechouart impact horizon in marine strata, which could be an important event marker for further studies on contemporaneous sections in the Lagonegro Basin and other localities.

Correlation between the Warepan/Otapirian and the Norian/Rhaetian stage boundary: implications of a global negative δ 13 C org perturbation

Article

Full-text available

Mar 2021

The Norian/Rhaetian boundary interval (Late Triassic) is characterised by significant biotic turnover and severe climatic changes. However, this boundary still awaits formal definition. We have investigated the δ¹³Corg record within a well-preserved marine sequence exposed in the Kiritehere section, North Island, New Zealand. This section was located at higher latitudes (above 60°S) during the Triassic, and is considered the best exposed section representative of the New Zealand Warepan/Otapirian stage boundary. This is a regional boundary pertaining to the Zealandia region of Gondwana; it is described in the New Zealand Geological Timescale (NZGT) and it has been recognised as being correlative with the Norian/Rhaetian boundary. Using an integrated chemo- and biostratigraphic approach, we have identified a negative δ¹³Corg shift close to the disappearance of the standard-sized monotids (fossil bivalves) in the Kiritehere section. We interpret this negative shift to be the same negative δ¹³Corg shift that has been proposed to define the base of the Rhaetian. However, the position of the negative δ¹³Corg shift in the Kiritehere section is ca. 6.40 m below the accepted position of the Warepan/Otapirian boundary, based on biostratigraphy. This δ¹³Corg isotopic shift, best thought of as a chemostratigraphic event, is regarded here as a global phenomenon.

Recent advances in heteromorph ammonoid palaeobiology

Article

Full-text available

Jan 2021
BIOL REV

Heteromorphs are ammonoids forming a conch with detached whorls (open coiling) or non-planispiral coiling. Such aberrant forms appeared convergently four times within this extinct group of cephalopods. Since Wiedmann's seminal paper in this journal, the palaeobiology of heteromorphs has advanced substantially. Combining direct evidence from their fossil record, indirect insights from phylogenetic bracketing, and physical as well as virtual models, we reach an improved understanding of heteromorph ammonoid palaeobiology. Their anatomy, buoyancy, locomotion, predators, diet, palaeoecology, and extinction are discussed. Based on phylogenetic bracketing with nautiloids and coleoids, hetero-morphs like other ammonoids had 10 arms, a well-developed brain, lens eyes, a buccal mass with a radula and a smaller upper as well as a larger lower jaw, and ammonia in their soft tissue. Heteromorphs likely lacked arm suckers, hooks, tentacles , a hood, and an ink sac. All Cretaceous heteromorphs share an aptychus-type lower jaw with a lamellar calcitic covering. Differences in radular tooth morphology and size in heteromorphs suggest a microphagous diet. Stomach contents of heteromorphs comprise planktic crustaceans, gastropods, and crinoids, suggesting a zooplanktic diet. Forms with a U-shaped body chamber (ancylocone) are regarded as suspension feeders, whereas orthoconic forms additionally might have consumed benthic prey. Heteromorphs could achieve near-neutral buoyancy regardless of conch shape or ontog-eny. Orthoconic heteromorphs likely had a vertical orientation, whereas ancylocone heteromorphs had a near-horizontal aperture pointing upwards. Heteromorphs with a U-shaped body chamber are more stable hydrodynamically than modern Nautilus and were unable substantially to modify their orientation by active locomotion, i.e. they had no or limited access to benthic prey at adulthood. Pathologies reported for heteromorphs were likely inflicted by crustaceans, fish, marine reptiles, and other cephalopods. Pathologies on Ptychoceras corroborates an external shell and rejects the endocochleate hypothesis. Devonian, Triassic, and Jurassic heteromorphs had a preference for deep-subtidal to offshore facies but are rare in shallow-subtidal, slope, and bathyal facies. Early Cretaceous heteromorphs preferred deep-subtidal to bathyal facies. Late Cretaceous heteromorphs are common in shallow-subtidal to offshore facies. Oxygen isotope data suggest rapid growth and a demersal habitat for adult Discoscaphites and Baculites. A benthic embryonic stage, planktic hatchlings, and a habitat change after one whorl is proposed for Hoploscaphites. Carbon isotope data indicate that some Baculites lived throughout their lives at cold seeps. Adaptation to a planktic life habit potentially drove selection towards smaller hatchlings, implying high fecundity and an ecological role of the hatchlings as micro-and mesoplankton. The Chicxulub impact at the Cretaceous/Paleogene (K/Pg) boundary 66 million years ago is the likely trigger for the extinction of ammonoids. Ammonoids likely persisted after this event for 40-500 thousand years and are exclusively represented by heteromorphs. The ammonoid extinction is linked to their small hatchling sizes, planktotrophic diets, and higher metabolic rates than in nautilids, which survived the K/Pg mass extinction event.

AMMONOIDS OF THE LATEST TRIASSIC GABBS FORMATION AT NEW YORK CANYON, MINERAL COUNTY, NEVADA

Chapter

Full-text available

Jan 2021

The Gabbs Formation in the New York Canyon area of the Gabbs Valley Range in west-central Nevada has one of the best successions of Rhaetian ammonoids in North America. Six new species and the species ranges of ammonoids of Rhaetian age from the Gabbs Formation are provided here, as well as documentation of ammonoid occurrences in each of the stratigraphic sections studied. The new species are Peripleurites gabbensis, Paracochloceras nunminensis, Arcestes lawsi, Placites heggi, Rhacophyllites mulleri, and Rhacophyllites volcanoensis. A carbon isotope curve demonstrates a negative δ 13 C anomaly at the limit between the Newyorkensis and Amoenum Zones. It is noteworthy that there is an overall slight negative trend in C13 values throughout the Rhaetian in this section, interrupted by the excursion at the Newyorkensis and Amoenum zone boundary, and leading up to the terminal Triassic negative excursion.

Widespread elevated iridium in Upper Triassic-Lower Jurassic strata of the Newark Supergroup: implications for use as an extinction marker

Article

Full-text available

Nov 2020

Anomalous levels of iridium in sedimentary strata are associated with mass extinction events caused by impact events. In the case of the end-Triassic extinction event, the anomalies as well as the extinctions are linked to the eruption of the Central Atlantic Magmatic Province (CAMP) flood basalts. We report new data on concentrations of iridium in continental strata of the Fundy, Deerfield, Hartford and Newark basins, both above and below the oldest CAMP flows in these basins, that demonstrate that these anomalies are more common than previously known. We conclude that the enrichments were at least in some instances likely derived locally by concentration due to leaching directly from the lavas into sediments proximal to the CAMP flows due to post-eruptive hydrothermal activity. In other instances, the enrichments likely record the global fallout of aerosols and/or ash particles during the eruptions of the CAMP basalts. The common association of the highest levels of enrichment with organic matter suggests either redox control or stabilization by formation of organometallic complexes following post-eruptive redistribution. These findings demonstrate the importance of considering the distribution and magnitude of iridium anomalies in considering the source of the iridium and possible extinction mechanisms.

A two-phase end-Triassic mass extinction

Article

Jul 2020

A two-phase end-Triassic mass extinction

Article

Jul 2020
EARTH-SCI REV

The end-Triassic mass extinction was one of the big five crises of the fossil record. It affected diverse marine groups, including bivalves, brachiopods, ostracods, calcareous algae, radiolarians, and tetrapods and coincided with major changes in palynological assemblages. The rapidity of the event has long been debated and here we show that it can be resolved into two distinct, short-lived extinction pulses separated by a several hundred-thousand-year interlude phase. Detailed collecting in the British Isles shows the first extinction in the lower Cotham Member eliminated many bivalves and ostracods. This event has been previously considered as the end-Triassic mass extinction horizon, however a second extinction is also seen at the top of the Langport Member after a phase of recovery marked by diversity increase. This younger crisis caused the loss of further bivalves, ostracods and the last of the conodonts. The two phases of marine extinctions coincide with marked turnovers amongst palynofloral assemblages with the interlude phase manifest as a fern spore-dominated interval (the Polypodiisporites polymicroforatus abundance interval). Correlation of Triassic-Jurassic boundary sections (and their associated extinction record) in Europe has been controversial. The most parsimonious correlation scheme assumes that a brief, high amplitude negative excursion of δ¹³Corg values, seen at the level of the first extinction phase in the UK, is manifest in other European sections in the same way. Alternative correlation schemes require complex scenarios with extinction occurring in some areas as recovery is happening elsewhere. In Europe, the first extinction coincides with regression whilst the second occurs at a flooding surface marked by the spread of anoxia. The extinction history of the terminal Triassic crisis is remarkably similar to that seen during other extinction events (end-Ordovician, Permo-Triassic, Toarcian) and suggests that, if the ultimate driver of these crises – large igneous province eruptions – is the same, then they show the same “double-punch” eruption history separated by a more benign interval of a few hundred-thousand-year duration.

Redox conditions and nitrogen cycling during the Triassic-Jurassic transition: A new perspective from the mid-Panthalassa

Article

Apr 2020
EARTH-SCI REV

Past, present, and future mass extinctions

Article

Feb 2020
J AFR EARTH SCI

Enigmatic catastrophic events, involving mass extinction of life forms, have been recorded several times in the Earth history. In many cases, the causes and mechanisms of these major and minor mass extinctions can be traced via the fossil record. A synthesis of the available information is herein made on the major catastrophic events through Earth history to understand the processes in the past and present with speculation into the future. The selective nature of major mass extinctions from the fossil record indicates the vanishing of s pecific taxa and the survival of others. The sudden extinction of organisms is almost accompanied by a grad ual disappearance of other forms, thus excluding any single cause for the killing mechanism. Consequently, the multiple causes’ scenario is the plausible mechanism responsible for the vanishing of biota through the history of the fossil record. On the other hand, the recovery of biota after mass extinctions is also an intrigui ng phenomenon, in which some groups had rapid recovery whereas others took a long time for a revival. B ased on multiple pieces of evidence from Africa, the end Permian extinction and the extinction of some Qu aternary megafauna may be related to severe drought. In addition, the current mass extinction is progressive ly underway; arising from multiple causes and mainly related to anthropogenic activities, widespread diseas es, as well as the possibility of extraterrestrial impacts. Reevaluation of the magnitude of the extinction eve nt is urgently needed to judge if these extinctions represent natural episodic fluctuation of the biodiversity c urve or unexpected catastrophe. Analyses of invertebrate occurrence data revealed that taxa originated duri ng stressful crises intervals have a wider geographic range size and lower extinction rates. Moreover, specie s durations, geographic range, and diversity are influencing each other. In addition, the ecological traits of a species may control their extinction pattern and recovery speed-limit. Furthermore, the wide geographical distribution provides potentially to survive mass extinctions. Therefore, narrower geographic-range taxa are facing higher extinction risk.

Sedimentological and paleoecological aspects of the Norian–Rhaetian transition (Late Triassic) in the Xuanhan area of the Sichuan Basin, Southwest China

Article

Full-text available

May 2019
Palaeoworld

The end-Triassic mass extinction is one of the five big extinction events in the Phanerozoic, and its impact on marine organisms has been extensively studied. However, whether the terrestrial ecosystem had begun to deteriorate or even collapsed prior to the end-Triassic mass extinction remains controversial and the related studies in Asia are very limited. In this study, we provide a comprehensive investigation of the sedimentary environments, their implications for floral changes, and the paleoecology during the Norian–Rhaetian transition in Xuanhan area, northeastern Sichuan Basin, Southwest China. The sedimentary environments and climatic conditions changed coupling the transgression and regression caused by the tectonic movements. Climatic oscillations were identified during the Norian–Rhaetian transition in the Xuanhan area, including a short-term cooling event. The diversity and composition of the plant communities changed through the Norian–Rhaetian transition in Xuanhan area, but the terrestrial ecosystem as a whole didn’t collapse or deteriorate prior to the end-Triassic mass extinction.

New magnetobiostratigraphic results from the Ladinian of the Dolomites and implications for the Triassic geomagnetic polarity timescale

Article

Mar 2019
PALAEOGEOGR PALAEOCL

Global perturbations of carbon cycle during the Triassic–Jurassic transition recorded in the mid-Panthalassa

Article

Aug 2018
EARTH PLANET SC LETT

To examine environmental changes in the biosphere during the Triassic-Jurassic transition, with a particular focus on the global carbon cycle related to Central Atlantic Magmatic Provinces (CAMP) volcanism in the mid-Panthalassa, we established stratigraphic δ 13 C org variations using Rhaetian (Late Triassic) to Hettangian (Early Jurassic) shales interbedded within deep-sea cherts in the Katsuyama section in the Mino-Tanba belt, SW Japan. High-resolution record of Rhaetian to Hettangian δ 13 C org values in the mid-Panthalassa contain three distinct negative carbon isotopic excursions (NCIEs) before and across the Triassic-Jurassic boundary (TJB): the Rhaetian NCIE1 and NCIE2 show a deviation of 5.0h from ca. −24.0h to ca. −29.0h, whereas NCIE3 across the TJB shows a 3.5h deviation from ca. −23.5h to ca. −27.0h. Our newly obtained NCIEs in the deep mid-Panthalassa can be correlated with the δ 13 C org records in the shallow-marine Tethyan regions (i.e., precursor, initial, and main CIEs), suggesting that three NCIEs in the Tethys and mid-Panthalassa likely reflected the global perturbations of the carbon cycle. Three NCIEs before and across the TJB can be interpreted as the consequence of the multiple CAMP volcanic episodes; i.e., the release of thermogenic methane from organic-rich sediments by CAMP intrusive rocks for NCIE1 and large-scale volcanically derived carbon species for NCIE2 and NCIE3. In addition, progressive increase of atmospheric pCO 2 throughout three NCIEs was possibly attributed to accumulation of volcanically derived CO 2 from multiple CAMP eruptions, which resulted in the development of ocean acidification across the TJB. On the other hand, in view of the oxic conditions in the deep mid-Panthalassa during three NCIEs, the development of coeval oceanic anoxic-euxinic conditions was restricted solely to shallow-marine regions. Therefore, ocean acidification together with localized shallow-marine anoxia acted as environmental stresses on the biosphere, which eventually resulted in the severe biotic crisis at the end of the Triassic.

New Upper Triassic Conodont Biozonation of the Tethyan Realm

Chapter

Full-text available

Nov 2018

Conodonts are biostratigraphically very important microfossils in the Upper Triassic, occurring in different marine habitats, from deep-ocean to shallow-shelf waters. Because of their great abundance, worldwide distribution, strong resistance to rock metamorphism, and mineralogical composition that makes them reliable tools for biostratigraphic and geochemical studies, conodonts have proven to be important tools in defining the Geological Time Scale (GTS) and Global Stratotype Section and Points (GSSPs). We present here an original Upper Triassic conodont biozonation for the Tethyan Realm integrated, where possible, with ammonoid and radiolarian zones, providing also numerical ages for stages and substages. Based on the most recent conodont biostratigraphic and systematic studies, we propose a subdivision of the Upper Triassic interval into 22 conodont zones (nine for the Carnian, ten for the Norian, and three for the Rhaetian), correlated, where possible, with the most recent North American conodont zonations. Discussions on the most biostratigraphically important conodont taxa are also provided, in particular for the stratigraphic intervals around the base of the Norian and Rhaetian stages, the GSSPs of which have yet to be defined. In this view, we provide data supporting the validity of conodonts as reliable tools for global correlations, recommending two conodont biovents as possible primary biomarkers: the FAD (First Appearance Datum) of Metapolygnathus parvus for the base of the Norian and the FAD of Misikella posthernsteini for the base of the Rhaetian. The conodont species Norigondolella carlae n. sp. from the upper Tuvalian (Carnian) is also defined.

Late Triassic Terrestrial Tetrapods: Biostratigraphy, Biochronology and Biotic Events

Chapter

Nov 2018

Spencer G. Lucas

The fossil record of Late Triassic tetrapods can be organized biostratigraphically and biochronologically into five, temporally successive land-vertebrate faunachrons (LVFs) that encompass Late Triassic time (in ascending order): Berdyankian, Otischalkian, Adamanian, Revueltian and Apachean. An up-to-date review of the age constraints on Late Triassic tetrapod fossil assemblages and correlation within the framework of the LVFs is presented. This makes possible a much more accurate evaluation of the timing of biotic events of Late Triassic tetrapod evolution, including: (1) Otischalkian, HO (highest occurrence) of almasaurids and chroniosuchians?, LOs (lowest occurrences) of crocodylomorphs and dinosaurs; (2) Adamanian, HO of mastodonsaurids and trematosaurids, LO of mammals; (3) Revueltian, HOs of capitosaurids, rhynchosaurs and dicynodonts; and (4) Apachean, HOs of metoposaurids, plagiosaurids and aetosaurs. The LO of turtles is Early Triassic or older, and the HO of phytosaurs is an Early Jurassic record. There is no compelling evidence of tetrapod mass extinctions at either the Carnian-Norian or the Triassic-Jurassic boundaries.

A new correlation of Triassic–Jurassic boundary successions in NW Europe, Nevada and Peru, and the Central Atlantic Magmatic Province: A time-line for the end-Triassic mass extinction

Article

Dec 2016
PALAEOGEOGR PALAEOCL

Understanding the end-Triassic mass extinction event (201.36 Ma) requires a clear insight into the stratigraphy of boundary sections, which allows for long-distance correlations and correct distinction of the sequence of events. However, even after the ratification of a Global Stratotype Section and Point, global correlations of TJB successions are hampered by the fact that many of the traditionally used fossil groups were severely affected by the crisis. Here, a new correlation of key TJB successions in Europe, U.S.A. and Peru, based on a combination of biotic (palynology and ammonites), geochemical (δ¹³Corg) and radiometric (U/Pb ages) constraints, is presented. This new correlation has an impact on the causality and temporal development during the end-Triassic event. It challenges the hitherto used standard correlation, which has formed the basis for a hypothesis that the extinction was caused by more or less instantaneous release of large quantities of light carbon (methane) to the atmosphere, with catastrophic global warming as a consequence. The new correlation instead advocates a more prolonged scenario with a series of feedback mechanisms, as it indicates that the bulk of the hitherto dated, high-titanium, quartz normalized volcanism of the Central Atlantic Magmatic Province (CAMP) preceded or was contemporaneous to the onset of the mass extinction. In addition, the maximum phase of the mass extinction, which affected both the terrestrial and marine ecosystems, was associated with a major regression and repeated, enhanced earthquake activity in Europe. A subsequent transgression resulted in the formation of hiati or condensed successions in many areas in Europe. Later phases of volcanic activity of the CAMP, producing low titanium, quartz normalized and high-iron, quartz normalized basaltic rocks, continued close to the first occurrence of Jurassic ammonites and the defined TJB. During this time the terrestrial ecosystem had begun to recover, but the marine ecosystem remained disturbed.

Gawlick et al (2009) - Jurassic tectonostratigraphy of the Austroalpine domain

Data

Full-text available

Dec 2016

Upper Carnian to Rhaetian (Upper Triassic) conodont and carbon-isotope stratigraphy of the Csővár borehole succession, Hungary

Article

Sep 2023
PALAEOGEOGR PALAEOCL

Weathering trends in the Norian through geochemical and rock magnetic analyses from the Pignola-Abriola Section (Lagonegro Basin, Italy)

Preprint

Full-text available

Aug 2023

We investigated the geochemical and rock magnetic properties of the magnetostratigraphically-calibrated Pignola-Abriola section (Italy) in order to understand the climatic perturbations that characterize the late Norian–early Rhaetian interval (Late Triassic). We performed experiments on anhysteretic and isothermal remanence (ARM, IRM), and on magnetic susceptibility (χ), to obtain the rock magnetic parameters necessary for our paleoclimatic investigation. An episode of increase in relative quantity of hematite, suggesting enhanced subaerial oxidation of iron minerals, was identified in the Norian from ~217 Ma in the Alaunian up to ~211 Ma in the early Sevatian, followed by a decline up to 207–206 Ma at the end of the Norian (late Sevatian). The results of geochemical and multivariate statistical analyses support a long-term increase and reduction in rock weathering, confirming and extending previous 87Sr/86Sr data from the Pizzo Mondello section (Italy). Possible causes of these long-term weathering trends are the multiphase uplifting of the Cimmerian orogen, occurring at mid northern latitudes along the southern margin of Asia in the Late Triassic, and/or the northward motion of Pangea across the equatorial humid belt. Rapid excursions in oxidized iron minerals have also been observed across the Norian/Rhaetian boundary, the origin of which has still to be determined.

Biological extinction and photic-zone anoxia across the Triassic-Jurassic transition: Insights from the Qiangtang Basin, eastern Tethys

Article

Full-text available

Aug 2023

The end-Triassic mass extinction (ETME) is one of the five catastrophic extinction events. However, the driving mechanisms of biodiversity loss during this interval remain controversial. In this study, we investigate the marine sediment geochemistry and fauna across the Triassic-Jurassic boundary in the Wenquan section of Qiangtang Basin, and the triggering mechanism of the Late Triassic extinction in the eastern Tethys Ocean. Our study shows that the main pulse of the ETME occurred in Bed 8, manifesting as the disappearance of four brachiopod species, a significant decrease of other faunas, and the “Lilliput Effect” on bivalves. Analyses of pyrite framboids and redox-sensitive trace elements, suggest the development of photic zone anoxia near the T/J boundary and coincident with the Late Triassic extinction. Thus, the development of abrupt and intense photic-zone anoxia could play an important role in the end-Triassic extinction. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6771606

Did changes in terrigenous components of deep-sea cherts across the end-Triassic extinction relate to Central Atlantic magmatic province volcanism?

Article

Full-text available

Jul 2023

The end-Triassic mass extinction event (ETE) is considered to be linked with the emplacement of the Central Atlantic magmatic province (CAMP), yet their temporal relation and underlying nature of global environmental and biotic changes remain controversial. A drastic radiolarian faunal turnover was associated with deep-sea acidification and changes in the chemical composition of pelagic terrigenous components, which were interpreted as the results of increased CAMP-derived materials, such as Fe2O3/Al2O3, MgO/Al2O3, and SiO2/Al2O3, without statistical tests. Here, we re-examined these CAMP-like signatures in terms of changes in the chemical composition of the Triassic–Jurassic pelagic deep-sea chert succession in Japan. Our newly compiled dataset suggests that changes in Fe2O3/Al2O3 and MgO/Al2O3 across the ETE were not significant, and thus, they may not be appropriate proxies for CAMP-derived material, potentially due to the dissolution of iron by ocean acidification and the formation of chlorite during diagenesis, respectively. Decreased SiO2/Al2O3 was also considered to have been reflected in increased CAMP-related dust flux and/or decreased biosiliceous productivity, but a slight increase in the Al2O3/TiO2 ratio (a biosiliceous productivity proxy) and an increase in shale bed thickness (dust flux proxy) across the radiolarian ETE imply increased eolian dust flux rather than decreased productivity. Furthermore, statistically significant Na enrichment at the radiolarian ETE level might be related to CAMP volcanism and/or associated changes in the source areas of eolian dust.

The Triassic–Jurassic transition – A review of environmental change at the dawn of modern life

Article

Jul 2022
EARTH-SCI REV

The Triassic–Jurassic transition, which is here broadly defined as extending from the Late Triassic through the Early Jurassic (~237 Ma to 174 Ma), was an important interval in Earth history. The end-Triassic mass extinction (ETME), at ~201 Ma, ranks among the ‘Big Five’ Phanerozoic mass extinctions. It largely completed the shift from the ‘Paleozoic Evolutionary Fauna’ to the ‘Modern Evolutionary Fauna’ that had been initiated by the end-Permian mass extinction, and may have contributed to the ‘Mesozoic Marine Revolution’ and rise of dinosaurs to dominance in terrestrial environments. In addition, the Triassic–Jurassic transition encompasses a second-order mass extinction during the early Toarcian oceanic anoxic event (T-OAE), at ~181 Ma. The ETME was triggered by Central Atlantic Magmatic Province (CAMP) magmatism, and the T-OAE by Karoo-Ferrar Large Igneous Province (KFLIP) magmatism, both associated with the stepwise disintegration of the Pangean supercontinent. These events led to major changes in continental and marine habitats, including climatic warming, ocean acidification, and widespread watermass anoxia, that produced a cascade of lethal environmental stresses. This article undertakes a review of the ETME and T-OAE mass extinctions, the large igneous province eruptions that triggered those biotic events, and the web of environmental changes that linked them together.

Paleoenvironmental Interpretation of the Late Triassic Norian – Rhaetian Boundary Interval in the Whitehorse Trough (Stikine Terrane, Northern Canadian Cordillera)

Article

Jan 2022

The End-Triassic Extinction as Recorded in the Deep-Sea Archive of the Budva Basin, Dinarides, Montenegro

Article

Jan 2022

Body size changes in bivalves of the family Limidae in the aftermath of the end-Triassic mass extinction: the Brobdingnag effect

Article

Jan 2019

Reduction in body size of organisms following mass extinctions is well‐known and often ascribed to the Lilliput effect. This phenomenon is expressed as a temporary body size reduction within surviving species. Despite its wide usage the term is often loosely applied to any small post‐extinction taxa. Here we assess the size of bivalves of the family Limidae (Rafineque) prior to, and in the aftermath of, the end‐Triassic mass extinction event. Of the species studied only one occurs prior to the extinction event, though is too scarce to test for the Lilliput effect. Instead, newly evolved species originate at small body sizes and undergo a within‐species size increase, most dramatically demonstrated by Plagiostoma giganteum (Sowerby) which, over two million years, increases in size by 179%. This trend is seen in both field and museum collections. We term this within‐species size increase of newly originated species in the aftermath of mass extinction, the Brobdingnag effect, after the giants that were contemporary with the Lilliputians in Swift's Gulliver's Travels. The size increase results from greater longevity and faster growth rates. The cause of the effect is unclear, although it probably relates to improved environmental conditions. Oxygen‐poor conditions in the Early Jurassic are associated with populations of smaller body size caused by elevated juvenile mortality but these are local/regional effects that do not alter the long‐term, size increase. Although temperature‐size relationships exist for many organisms (Temperature‐Size Rule and Bergmann's Rule), the importance of this is unclear here because of a poorly known Early Jurassic temperature record.

Learning from past climatic changes

Article

Jun 2018

Christophe Lécuyer

66 million years ago, sea temperatures rose rapidly as a result of environmental perturbations

Planets and Life

Article

May 2018

Cambridge Core - Computational Science and Modelling - Planets and Life - edited by Woodruff T. Sullivan, III

An examination of the impact of Olson’s extinction on tetrapods from Texas

Article

Full-text available

May 2018

Neil Brocklehurst

It has been suggested that a transition between a pelycosaurian-grade synapsid dominated fauna of the Cisuralian (early Permian) and the therapsid dominated fauna of the Guadalupian (middle Permian) was accompanied by, and possibly driven by, a mass extinction dubbed Olson's Extinction. However, this interpretation of the record has recently been criticised as being a result of inappropriate time-binning strategies: calculating species richness within international stages or substages combines extinctions occurring throughout the late Kungurian stage into a single event. To address this criticism, I examine the best record available for the time of the extinction, the tetrapod-bearing formations of Texas, at a finer stratigraphic scale than those previously employed. Species richness is calculated using four different time-binning schemes: the traditional Land Vertebrate Faunachrons (LVFs); a re-definition of the LVFs using constrained cluster analysis; individual formations treated as time bins; and a stochastic approach assigning specimens to half-million-year bins. Diversity is calculated at the genus and species level, both with and without subsampling, and extinction rates are also inferred. Under all time-binning schemes, both at the genus and species level, a substantial drop in diversity occurs during the Redtankian LVF. Extinction rates are raised above background rates throughout this time, but the biggest peak occurs in the Choza Formation (uppermost Redtankian), coinciding with the disappearance from the fossil record of several of amphibian clades. This study, carried out at a finer stratigraphic scale than previous examinations, indicates that Olson's Extinction is not an artefact of the method used to bin data by time in previous analyses. Subjects Evolutionary Studies, Paleontology

The Missing Mass Extinction at the Triassic-Jurassic Boundary

Chapter

Nov 2018

The Late Triassic was a prolonged episode characterized by high rates of biotic turnover and discrete extinction events due to elevated extinction rates for some biotic groups and low origination rates for many. An end-Triassic mass extinction continues to be cited as one of the “big five” mass extinctions of the Phanerozoic. However, a detailed examination of the fossil record, especially by best-sections analysis, indicates that many of the groups usually claimed to have suffered catastrophic extinction at the end of the Triassic, such as ammonoids, marine bivalves, conodonts and tetrapod vertebrates, experienced multiple extinctions throughout the Late Triassic, not a single mass extinction at the end of the Period. Many other groups were relatively unaffected, whereas some other groups, such as reef communities, were subject to only regional effects. Indeed, the lack of evidence of a collapse of trophic networks in the sea and on land makes the case for an end-Triassic mass extinction untenable. Still, marked evolutionary turnover of radiolarians and ammonoids did occur across the Triassic-Jurassic boundary. The end of the Triassic encompassed temporary disruptions of the marine and terrestrial ecosystems, driven by the environmental effects of the eruption of the flood basalts of the Circum-Atlantic Magmatic Province (CAMP), through outgassing in particular, but these disruptions did not produce a global mass extinction.

Calcareous nannofossils at the Triassic/Jurassic boundary: Stratigraphic and paleoceanographic characterization

Article

Full-text available

Nov 2016

In this work, calcareous nannofossils are identified for the first time in the uppermost Triassic sequence of the Lombardy Basin (Southern Calcareous Alps, Italy). Two zones are recognized, namely the NT2b (latest Triassic) and the NJT1 (earliest Jurassic). Two species resulted to be good markers to constrain the TJB interval: Prinsiosphaera triassica and Schizosphaerella punctulata. Nannofossil data are calibrated with C isotopic chemostratigraphy obtained for carbonate and organic matter. Size reduction of P. triassica and a decline in the abundance of Triassic nannofossils are detected soon after the “precursor Carbon Isotope Excursion (CIE) and culminated during the “initial negative CIE” characterized by lowest nannofossil abundances and small-sized P. triassica. The extinction of Triassic nannofossils occurred in distinctive steps within the “initial negative CIE”, while the Jurassic S. punctulata is first observed at the base of the “main negative CIE”. The latest Triassic nannofossil decline in abundance, size reduction and extinctions, represent a progressive deterioration associated to the Central Atlantic Magmatic Province (CAMP) volcanism. Our findings are consistent with nannofossil changes at supraregional scale and indicate that the massive CAMP flood basalts were preceded by initial volcanic pulses. We speculate that a combination of climate change, fertilization and ocean acidification started to influence the calcification process prior to the “initial negative CIE”. Nannoplankton extinctions were not simultaneous and might imply limited capacity for adaptation in the early stages of evolutionary history. However, originations of new taxa soon after the disappearance of Triassic forms suggest the ability to rapidly overcame extreme stressing conditions.

Ascent of dinosaurs linked to an iridium anomaly at the Triassic-Jurassic boundary

Article

Full-text available

May 2002
SCIENCE

Analysis of tetrapod footprints and skeletal material from more than 70 lo- calities in eastern North America shows that large theropod dinosaurs appeared less than 10,000 years after the Triassic-Jurassic boundary and less than 30,000 years after the last Triassic taxa, synchronous with a terrestrial mass extinction. This extraordinary turnover is associated with an iridium anomaly (up to 285 parts per trillion, with an average maximum of 141 parts per trillion) and a fern spore spike, suggesting that a bolide impact was the cause. Eastern North American dinosaurian diversity reached a stable maximum less than 100,000 years after the boundary, marking the establishment of dinosaur-dominated communities that prevailed for the next 135 million years.

Carbon isotope anomaly and other geochemical changes at the Triassic-Jurassic boundary from a marine section in Hungary

Article

Full-text available

Nov 2001
GEOLOGY

Most mass extinctions are linked with carbon isotope excursions, implying that biotic crises are coupled with changes in the global carbon cycle. The isotopic evolution during the end-Triassic extinction is far less documented than that for the other major Phanerozoic extinctions. Here we report a sharp and short-lived -3.50/00 excursion in carbon isotope values for carbonate (delta13Ccarb) corresponding to a -20/00 excursion in the isotopic composition of marine organic matter (delta13Corg) and other geochemical changes from the topmost Triassic in the Csovár section in Hungary. The Triassic- Jurassic boundary is defined by ammonoid and conodont biostratigraphy in a marine limestone sequence. A decline in primary productivity, release of methane through dissociation of gas hydrates, or a combination of the two may account for the correlative biotic and isotopic events.

Fades and geochemical evidence bearing on the end-Triassic disappearance of the Alpine reef ecosystem

Article

Full-text available

Jan 1990

A carbon and oxygen isotope profile is presented across the Triassic‐Jurassic boundary at the classic locality of Kendelbach, Austria. In conjunction with faciès data it lends no support to the claim that the spectacular disappearance of the reef ecosystem at the end of the Triassic was due to a sharp fall of seawater temperature. A model relating mass extinction to sea‐level change is preferred.

Timing the end-Triassic mass extinction: First on land, then in the sea?

Article

Full-text available

Jan 2000
GEOLOGY

The end-Triassic marks one of the five biggest mass extinctions, but current geologic time scales are inadequate for understanding its dynamics. A tuff layer in marine sedimentary rocks encompassing the Triassic-Jurassic transition yielded a U-Pb zircon age of 199.6 ± 0.3 Ma. The dated level is immediately below a prominent change in radiolarian faunas and the last occurrence of conodonts. Additional recently obtained U-Pb ages integrated with ammonoid biochronology confirm that the Triassic Period ended ca. 200 Ma, several million years later than suggested by previous time scales. Published dating of continental sections suggests that the extinction peak of terrestrial plants and vertebrates occurred before 200.6 Ma. The end-Triassic biotic crisis on land therefore appears to have preceded that in the sea by at least several hundred thousand years.

Carbon and nitrogen isotope disturbances and an end-Norian (Late Triassic) extinction event

Article

Full-text available

Dec 2002
GEOLOGY

Major perturbations of organic carbon and nitrogen isotope ratios from a Norian-Rhaetian (Late Triassic) boundary section in British Columbia coincide with an extinction of the dominant, deep-water invertebrate fauna of the Late Triassic (monotids and most ammonoids). The carbon isotope excursion is attributed to the development of widespread oceanic stagnation that favored organic-rich shale deposition. The coincident nitrogen isotope excursion suggests that progressively more nitrate-limited productivity forced a change to nitrogen-fixing cyanobacteria populations as ocean stagnation created nutrient-starved conditions. The biotic crisis and geochemical events of the Norian-Rhaetian boundary predate the latest Rhaetian (end-Triassic) mass extinction. Thus, the Late Triassic interval was marked by more than one extinction event.

Biochronology and paleontology of uppermost Triassic (Rhaetian) radiolarians, Queen Charlotte Islands, British Columbia, Canada

Article

Full-text available

Jan 1993

Elizabeth S. Carter

Spine title: Uppermost Triassic radiolarians, Queen Charlotte Islands (Canada). At head of title: Université de Lausanne. Faculté des sciences. Institut de géologie et de paléontologie. Text in English; summaries in English and French. Thesis (Ph. D.)--Université de Lausanne. Includes bibliographical references (p. 120-126).

Terrestrial and marine extinction at the Triassic-Jurassic boundary synchronized with major carbon-cycle perturbation: A link to initiation of massive volcanism?

Article

Full-text available

Mar 2002
GEOLOGY

Mass extinction at the Triassic-Jurassic (Tr-J) boundary occurred about the same time (200 Ma) as one of the largest volcanic eruptive events known, that which characterized the Central Atlantic magmatic province. Organic carbon isotope data from the UK and Greenland demonstrate that changes in flora and fauna from terrestrial and marine environments occurred synchronously with a light carbon isotope excursion, and that this happened earlier than the Tr-J boundary marked by ammonites in the UK. The results also point toward synchronicity between extinctions and eruption of the first Central Atlantic magmatic province lavas, suggesting a causal link between loss of taxa and the very earliest eruptive phases. The initial isotopic excursion potentially provides a widely correlatable marker for the base of the Jurassic. A temporary return to heavier values followed, but relatively light carbon dominated the shallow oceanic and atmospheric reservoirs for at least 600 k.y.

Fossil Plants and Global Warming at the Triassic-Jurassic Boundary

Article

Full-text available

Aug 1999
SCIENCE

The Triassic-Jurassic boundary marks a major faunal mass extinction, but records of accompanying environmental changes are limited. Paleobotanical evidence indicates a fourfold increase in atmospheric carbon dioxide concentration and suggests an associated 3° to 4°C “greenhouse” warming across the boundary. These environmental conditions are calculated to have raised leaf temperatures above a highly conserved lethal limit, perhaps contributing to the >95 percent species-level turnover of Triassic-Jurassic megaflora.

Sudden Productivity Collapse Associated with the Triassic-Jurassic Boundary Mass Extinction

Article

Full-text available

Jun 2001

The end-Triassic mass extinction is one of the five most catastrophic in Phanerozoic Earth history. Here we report carbon isotope evidence of a pronounced productivity collapse at the boundary, coincident with a sudden extinction among marine plankton, from stratigraphic sections on the Queen Charlotte Islands, British Columbia, Canada. This signal is similar to (though smaller than) the carbon isotope excursions associated with the Permian-Triassic and Cretaceous-Tertiary events.

The Triassic-Jurassic transition at Kunga Island, Queen Charlotte Islands, British Columbia, Canada

Article

Jul 2007

Procedures of organic geochemical analysis

Article

Jan 1983

Carbon-isotope anomalies at era boundaries; Global catastrophes and their ultimate cause

Article

Jan 1990

In modern oceans, the calcareous skeletons of plankton are characterized by positive δ13C values because the dissolved bicarbonate in surface seawater is relatively depleted in carbon-12, a consequence of the preferential utilization of the lighter isotope during photosynthesis. At the K/T boundary, the gradient collapsed to zero, or a reversed gradient was temporarily established. The breakdown of the gradient is a manifestation of greatly reduced biomass production in the strangelove ocean after the terminal Cretaceous catastrophe (Hsu and McKenzie, 1985). In addition, we propose that the reversed gradient is possibly characteristic of an ocean in which a bacterial respiration control on the surface-water δ13C dominated over photosynthesis (McKenzie and others, 1989). We further suggest that the very large negative δ13C values across the K/T, Permian/Triassic, and Precambrian/Cambrian boundaries are evidence of "respiring oceans" after global catastrophes at era boundaries. The origins of strangelove (zero-gradient) and respiring (negative gradient) oceans are related to reduced biomass productions after global catastrophes. Either an impact by a very large bolide or by explosive volcanism could be the ultimate cause of such catastrophes. From what we know now, however, the latter happened too frequently in geologic history to account for the rare era-boundary events.

Carbon and nitrogen isotope disturbances and an end-Norian (Late Triassic) extinction event: Comment and Reply: COMMENT

Article

Jan 2003
GEOLOGY

[Sephton et al. (2002)][1] reported a complex isotopic event, marked by a positive δ13Corg excursion and an initially positive δ15Norg excursion, from a Triassic-Jurassic boundary succession at Black Bear Ridge, Williston Lake, northeastern British Columbia, corresponding to the level of

Mass Extinctions and Their Aftermath

Article

Aug 1999

This is a systematic review of the major mass extinctions in the history of life. It covers all groups of organisms - plant, animal, terrestrial, and marine - that have become extinct alongside the geological and sedimentological evidence for environmental changes during the biotic crises. All proposed extinction mechanisms - climate change, meteorite impact, volcanisms - are critically assessed. In this text the demise of the dinosaurs is put into the proper context of other extinction events. This book is intended for undergraduates in Europe and graduate students in the US, studying geology, palaeontology, or evolutionary biology, and their teachers. It should also be of interest to research scientists in adjacent subjects.

Organic carbon isotopic record across the Triassic–Jurassic boundary in Austria and its bearing on the cause of mass extinction

Article

May 1996
GEOLOGY

Carbon isotope analyses of total organic carbon across the Triassic-Jurassic boundary in the classic section of Kendelbach, Austria, show that a positive excursion in delta13C values of organic carbon in the boundary marl correlates with a negative excursion in delta13C values in carbonates. In this section, the change in isotope values is inferred to be the result of diagenesis with no evidence of any primary change that could relate to bioproductivity. This and other evidence do not support the claim that there was a fall in productivity associated with the end-Triassic mass extinction, possibly caused by bolide impact.

Climatic and oceanographic signals from the carbonate rock record and their preservation

Article

Mar 1992
GEOL MAG

Jim Marshall

Stable isotopic data from marine limestones and their constituent fossils and marine cements can provide quantitative evidence for changes in global climate and ocean circulation. Oxygen isotopic data can indicate changes in temperature and ocean composition whereas stratigraphic variation in carbon isotope ratios may reflect changes in the carbon cycle that can be linked to changes in oceanic productivity and atmospheric greenhouse gases. Terrestrial carbonates–meteoric cements, calcretes and speleothems–similarly offer significant potential for understanding the evolution of terrestrial climates by providing evidence for the composition of rainwater and the nature of vegetative cover. Primary environmental isotopic signals may be obscured by the effects of post-depositional diagenetic alteration. Cementation and replacement reactions can take place in a wide range of diagenetic environments; the diagenetic history of an individual limestone is determined by a combination of its mineralogical diagenetic potential and depositional setting, together with subsequent changes in relative sea-level and burial history. Carbon isotopic values are less prone to alteration during diagenesis than oxygen values but shifts can be significant where organogenic carbon is incorporated. Linear covariation of carbon and oxygen values is not a reliable indicator of diagenetic alteration: water-rock interaction and fluid mixing may produce non-linear distributions. Attempts to determine long-term changes in climatic and oceanographie conditions through isotope stratigraphy of shallow-water limestones must include an assessment of the diagenetic history of the materials analysed. Pétrographic examination using conventional microscopy backed up, where appropriate, by cathodoluminescence and scanning electron microscopy together with elemental and strontium isotopic analysis can help to identify the effects of diagenetic alteration. Where material with a range of different degrees of alteration is preserved in the same sediment it may be possible to compare patterns of isotopic and elemental variation and to attempt to unravel the effects of diagenesis in order to determine primary, environmental, isotopic signals. Recent research has shown that these techniques can be successfully employed in both Phanerozoic and Precambrian sediments.

Mass Extinctions and Sea-Level Changes

Article

Dec 1999
EARTH-SCI REV

Review of sea-level changes during the big five mass extinctions and several lesser extinction events reveals that the majority coincide with large eustatic inflexions. The degree of certainty with which these eustatic oscillations are known varies considerably. Thus, the late Ordovician and end Cretaceous extinctions are associated with unequivocal, major regressions demonstrated from numerous, widespread regions. In contrast, the multiple, high frequency sea-level changes Ž . reported for the Frasnian–Famennian crisis based on the supposed depth-preferences of conodont taxa have little support from sequence stratigraphic analyses, which reveals the interval to be one of highstand. The end Permian mass extinction has w long been related to a severe, first order lowstand of sea level Newell, N.D., 1967. Revolutions in the history of life. Geol. x Soc. Am. Spec. Pap. 89, 63–91. based primarily on the widespread absence of latest Permian ammonoid markers, but field evidence reveals that the interval coincides with a major transgression. Newell's hypothesis that marine extinctions are related to shelf habitat loss during severe regression remains tenable for the end Guadalupian and end Triassic extinction events but not for other crises. Rapid high amplitude regressive–transgressive couplets are the most frequently observed eustatic changes at times of mass extinction, with the majority of extinctions occurring during the transgressive pulse when anoxic bottom waters often became extensive. The ultimate cause of the sea-level changes is generally unclear. A glacioeustatic driving mechanism can only be convincingly demonstrated for the end Ordovician and end Devonian events. Ž . At other times, it is speculated that they may relate to the widespread regional doming and subsequent collapse caused by Ž . the impingement of superplumes and ultimate eruption on the base of the lithosphere. q 1999 Elsevier Science B.V. All rights reserved.

Palaeoenvironmental interpretation of a Triassic-Jurassic boundary section from Western Austria based on palaeoecological and geochemical data

Article

Dec 1997
PALAEOGEOGR PALAEOCL

A section spanning the Triassic-Jurassic boundary is described from near the village of Lorüns in the Vorarlberg region of western Austria. At Lorüns, the uppermost Triassic is characterised by bedded carbonates of the Kössen Formation supporting a stenotopic fauna indicative of a shallow sub-tidal environment of normal marine salinity. The Triassic-Jurassic boundary may be represented as a sequence boundary developed on top of a 1.1 m thick red mudstone of the lower Schattwald Shale, which is interpreted to have been deposited in a marginal marine environment, possibly a mud flat. Above the boundary beds, the upper Schattwald Shale is characterised by thin-bedded marl and dark limestone beds with an earliest Hettangian macrofauna dominated by epifaunal filter-feeding bivalves, including ostreids, mytilids and oxytomids, which suggest a shallow, subtidal, salinity-controlled environment typical of an interplatform lagoon. Carbonate production rejuvenated in the later Early Hettangian with development of the Lorüns oolite, a shallow subtidal oolitic and oncolitic unit bearing echinoderms indicative of normal marine conditions.

Field Trip B1: Haida Gwaii (Queen Char-lotte Islands

Jan 1998
127-229

J Jakobs
Pá

Jakobs, J. Pá, Field Trip B1: Haida Gwaii (Queen Char-lotte Islands, in: P.L. Smith (Ed.), Field Trip B1: Haida Gwaii (Queen Charlotte Islands), International Union of Geological Sciences, Vancouver, 1998, pp. 127 – 229.

Carbon-isotope anomalies at era boundaries; global catastrophes and their ultimate cause Global catastrophes in Earth history; an interdisciplinary conference on impacts, volcanism, and mass mortality

Jan 1990
61

Hsü

K.J. Hsü, J.A. Mckenzie, Carbon-isotope anomalies at era boundaries; global catastrophes and their ultimate cause Glo-bal catastrophes in Earth history; an interdisciplinary confer-ence on impacts, volcanism, and mass mortality, in: V.L.

Stratigraphy of Triassic/Jurassic boundary strata, Queen Charlotte Islands, British Columbia: potential global system stratotype boundary

Jan 2001
10-13

J W Haggart
E S Carter
M J Beattie
P S Bown
R J Enkin
D A Kring
M J Johns
V J Mcnicoll
M J Orchard
R Perry
C J Schrö-Adams
P L Smith
L B Suneby
H W Tipper
P D Ward

J.W. Haggart, E.S. Carter, M.J. Beattie, P.S. Bown, R.J. Enkin, D.A. Kring, M.J. Johns, V.J. Mcnicoll, M.J. Orchard, R. Perry, C.J. Schrö-Adams, P.L. Smith, L.B. Suneby, H.W. Tipper, P.D. Ward, Stratigraphy of Triassic/Jurassic boundary strata, Queen Charlotte Islands, British Columbia: potential global system stratotype boundary. IGCP #458 (Triassic – Jurassic Events), Southwest England Field Workshop, 2001, pp. 10 – 13.

Field Trip B1: Haida Gwaii (Queen Charlotte Islands

Jan 1998
127

Tipper

Stratigraphy of Triassic/Jurassic boundary strata, Queen Charlotte Islands, British Columbia: potential global system stratotype boundary. IGCP #458 (Triassic–Jurassic Events)

Jan 2001
10

Haggart

Isotopic evidence bearing on Late Triassic extinction events, Queen Charlotte Islands, British Columbia, and implications for the duration and cause of the Triassic/Jurassic mass extinction

Abstract

No full-text available

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