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Abiotic Causes of the Great Mass Extinction of Marine Biota at the Triassic–Jurassic Boundary
Abstract
In the interval of the Triassic–Jurassic boundary up to 80% of marine species became extinct. The
main hypotheses on the causes of this mass extinction are reviewed. The extinction was triggered by a power�
ful eruption of basalts in the Central Atlantic Magmatic Province. In addition, several impact craters have
been found. Extraterrestrial factors resulted in two main sequences of events: terrestrial, leading to strong vol�
canism, and extraterrestrial (impact events). They produced similar effects: emissions of harmful chemical
compounds and aerosols. Consequences included the greenhouse effect, darkening of the atmosphere (which
prevented photosynthesis), stagnation of the oceans, and anoxia. Biological productivity decreased; food
chains collapsed. As a result, all vital processes were disturbed, and a large portion of the biota went extinct.
... The Triassic-Jurassic transition (Tr-J, 201.36 ± 0.17 Ma, Wotzlaw et al., 2014) is marked by the end-Triassic mass extinction, one of the "Big Five" extinction events of the Phanerozoic (Benton, 1995;Raup & Sepkoski, 1982;Sepkoski, 1981). The biotic turnover, ecological crisis, and environmental background across the Tr-J transition have drawn significant attention over the last decades (Barash, 2015;Hesselbo et al., 2007). The impact of the end-Triassic mass extinction on marine organisms has been extensively documented (e.g., radiolarians, Hallam, 2002;foraminifera, Michalík et al., 2007;ammonites and brachiopods, Tomašových & Siblík, 2007;corals and calcisponges, Stanley Jr. et al., 2018; bivalves, Atkinson et al., 2019). ...
The end‐Triassic mass extinction is considered one of the “Big Five” extinction events in the Phanerozoic. However, whether the terrestrial ecosystem began to deteriorate or even collapse prior to the Triassic–Jurassic (Tr‐J) transition remains controversial. Compared with the documented data from the western Tethyan region, evidence from the eastern Tethyan realm is limited. We undertake a fitting analysis of the sedimentary system, floral community successions and major geological events of the Xujiahe Formation as reflected by the Qilixia Section, Xuanhan area, northeast Sichuan Basin, China. Our results reveal an oscillating fluvial‐lacustrine depositional system during the Late Triassic, with the dominant sedimentary processes mainly controlled by the Indosinian Movement. Beside the sedimentary influence on the Xujiahe Flora, climate changes played a more important role. Fluctuating conditions to cooler and dryer climates at this time promoted diversification of gymnosperms under an overall warm and humid climate setting in the Late Triassic in the Xuanhan area. Superimposed on this oscillating long‐term climate state, ecosystem destabilization occurred over 1 million years prior to the Tr–J interval in the Xuanhan study area, possibly in response to the intensified storm and wildfire activity and the following environmental changes. Although the Xujiahe Flora always recovered from the interruption of the tectonic movement, it ultimately collapsed under extreme climatic events and ecological pressures induced by the Late Triassic Central Atlantic Magmatic Province event. An oscillating fluvial‐lacustrine system occurred prior to the end‐Triassic, and the sedimentary processes influenced the floral community successions of the Xujiahe flora in the northeastern Sichuan Basin, China. The Xujiahe flora ultimately collapsed under extreme climatic events and ecological pressures induced by the Late Triassic CAMP event.
The Triassic-Jurassic (Tr-J) boundary marks one of the five largest mass extinctions in the past 0.5 b.y. In many of the exposed rift basins of the Atlantic passive margin of eastern North America and Morocco, the boundary is identified as an interval of stratigraphically abrupt floral and faunal change within cyclical lacustrine sequences. A comparatively thin interval of Jurassic strata separates the boundary from extensive overlying basalt flows, the best dates of which (ca. 202 Ma) are practically indistinguishable from recent dates on tuffs from marine Tr-J boundary sequences. The pattern and magnitude of the Tr-J boundary at many sections spanning more than 10° of paleolatitude in eastern North America and Morocco are remarkably similar to those at the Cretaceous-Tertiary boundary, sparking much debate on the cause of the end-Triassic extinctions, hypotheses focusing on bolide impacts and climatic changes associated with flood basalt volcanism. Four prior attempts at finding evidence of impacts at the Tr-J boundary in these rift basin localities were unsuccessful. However, after more detailed sampling, a modest Ir anomaly has been reported (up to 285 ppt, 0.29 ng/g) in the Newark rift basin (New York, New Jersey, Pennsylvania, United States), and this anomaly is directly associated with a fern spike. A search for shocked quartz in these rift basins has thus far been fruitless. Although both the microstratigraphy and the biotic pattern of the boundary are very similar to continental Cretaceous-Tertiary boundary sections in the western United States, we cannot completely rule out a volcanic, or other nonimpact, hypothesis using data currently available.
The consideration of the conditions during the mass extinctions has shown that a series of factors, including mutually independent tectonic movements, variations in the sea level and climate, volcanism, asteroid impacts, changes in the composition of the atmosphere and hydrosphere, the dimming of the atmosphere by aerosols at volcanism and impact events, etc., had a harmful affect during some periods of time (a hundred thousand years to a millions years). Some of the listed events occurred for a long period of time and could not have caused the abrupt catastrophic death of organisms on a global scale. The examination of the hierarchy of the major events allows us to distinguish the primary terrestrial (volcanism) and cosmic (impact events) reasons for the mass extinctions. The coeval mutually independent events testify to the common external reasons for the higher order beyond the solar system. These events are suggested to be related with the orbital movement of the solar system around the galaxy’s center, the intersection of the galactic branches, and the oscillations of the solar system’s position relative to the galactic plane. These reasons influence the processes on the Earth, including the internal and external geospheres, and activate the impacts of asteroids and comets. Under their effect, two main subsequences of events are developed: terrestrial, leading to intense volcanism, and cosmic impact events. In both cases, harmful chemical elements and aerosols are vented to the atmosphere, thus resulting in the greenhouse effect, warming, the dimming of the atmosphere, the prevention of photosynthesis, the ocean’s stagnation, and anoxia with the following reduction of the bioproductivity, the destruction of the food chains, and the extinction of a significant part of the biota.
New high-precision U/Pb geochronology from volcanic ashes shows that the Triassic-Jurassic boundary and end-Triassic biological crisis from two independent marine stratigraphic sections correlate with the onset of terrestrial flood volcanism in the Central Atlantic Magmatic Province to <150 ka. This narrows the correlation between volcanism and mass extinction by an order of magnitude for any such catastrophe in Earth history. We also show that a concomitant drop and rise in sea level and negative δ13C spike in the very latest Triassic occurred locally in <290 ka. Such rapid sea-level fluctuations on a global scale require that global cooling and glaciation were closely associated with the end-Triassic extinction and potentially driven by Central Atlantic Magmatic Province volcanism.
The evolution of life on Earth is marked by catastrophic extinction events, one of which occurred ca. 200 Ma at the transition from the Triassic Period to the Jurassic Period (Tr-J boundary), apparently contemporaneous with the eruption of the world's largest known continental igneous province, the Central Atlantic magmatic province. The temporal relationship of the Tr-J boundary and the province's volcanism is clarified by new multidisciplinary (stratigraphic, palynologic, geochronologic, paleomagnetic, geochemical) data that demonstrate that development of the Central Atlantic magmatic province straddled the Tr-J boundary and thus may have had a causal relationship with the climatic crisis and biotic turnover demarcating the boundary.
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.
Ocean acidification associated with emplacement of the Central Atlantic Magmatic Province (CAMP) has been hypothesized as a kill mechanism for the end-Triassic mass extinction, but few direct proxies for ancient ocean acidity are available. This paper describes a new proxy that uses the presence of fossil corals and coral reefs to determine aragonite saturation state (ΩArag). Modern scleractinian corals struggle to biomineralize a skeleton below an ΩArag of 2 and modern shallow water coral reefs are typically only found in areas with source water of ΩArag > 3; so when corals or coral reefs are preserved in the fossil record, these ocean saturation states can be inferred. Atmospheric pCO2 reconstructions are combined with the coral ΩArag limitations to calculate the total dissolved inorganic carbon (DIC) in the Late Triassic ocean, which is a measure of the buffering capacity or ocean sensitivity to acidification. Once DIC is known, the severity of an acidification due to a carbon dioxide injection can be determined, for example the Triassic–Jurassic (T–J) event. Our results suggest that if Late Triassic DIC values were low to moderate (2000–3000 μmol/kg), the T–J pCO2 increases would have depressed saturation state to the point where coral biomineralization would have been extremely challenging (ΩArag < 2), resulting in the observed coral and coral reef gap in the fossil record. While the average pCO2 elevations recorded in stomatal and pedogenic proxies are not sufficient to cause complete carbonate undersaturation, modeled scenarios for CAMP-related T–J pCO2 increases (within error of pedogenic pCO2 proxies) suggest that aragonite undersaturation is plausible and in extreme cases calcite undersaturation is achievable. Thus, a short but extreme acidification event could occur and would satisfactorily explain the significant extinction of calcareous organisms, the Early Hettangian coral gap, and the T–J carbonate crisis.
While demonstrating ocean acidification in the modern is relatively straightforward (measure increase in atmospheric CO2 and corresponding ocean chemistry change), identifying palaeo-ocean acidification is problematic. The crux of this problem is that the rock record is a constructive archive while ocean acidification is essentially a destructive (and/or inhibitory) phenomenon. This is exacerbated in deep time without the benefit of a deep ocean record. Here, we discuss the feasibility of, and potential criteria for, identifying an acidification event in deep time. Furthermore, we investigate the evidence for ocean acidification during the Triassic-Jurassic (T-J) boundary interval, an excellent test case because 1) it occurs in deep time, beyond the reach of deep sea drilling coverage; 2) a potential trigger for acidification is known; and 3) it is associated with one of the ‘Big Five’ mass extinctions which disproportionately affected modern-style invertebrates.
The end-Triassic extinction (ETE), one of the five largest Phanerozoic mass extinctions, is associated with rapid and severe environmental change, but existing data permit alternative models of causation. Volcanism in the Central Atlantic Magmatic Province (CAMP) has been proposed as the main trigger, but direct evidence for this linkage is scarce. To help constrain scenarios for the ETE and other Triassic–Jurassic boundary (TJB) events, we obtained a temporally highly resolved, multidisciplinary dataset from the Kendlbachgraben section in the Northern Calcareous Alps in Austria. The section belongs to the same paleogeographic unit (Eiberg Basin) and share similar stratigraphy with the recently selected base Jurassic Global Stratotype Section and Point at Kuhjoch.
The mass extinction at the Triassic-Jurassic (Tr-J) boundary at 200 Ma ranks amongst the five most extreme in the Phanerozoic and occurred approximately at the same time as one of the largest volcanic episodes known from the geological record, that which characterized the Central Atlantic Magmatic Province (CAMP). Interpretations of climate change across the boundary are contradictory, whilst changes in the carbon cycle are poorly constrained. Here we present new organic carbon isotope data that demonstrate that changes in flora and fauna from both terrestrial and marine environments occurred synchronously with a transient light-carbon-isotope excursion and that this happened significantly earlier than the conventionally established marine Tr-J boundary. A second negative carbon-isotope excursion dominated the shallow-marine and atmospheric reservoirs for at least 600 k.y. These data suggest that a major perturbation occurred in the global carbon cycle at the Tr-J boundary which resulted in a significant increase in atmospheric pCO2 in less than a million years. Our results indicate synchroneity between the carbon-isotope excursion, the extinction event, the eruption of the first CAMP lavas, suggesting a causal link between loss of terrestrial and marine taxa and the very earliest eruptive phases.