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Changes in Environmental Conditions as the Cause of the Marine Biota Great Mass Extinction at the Triassic–Jurassic Boundary



In the interval of the Triassic–Jurassic boundary, 80% of the marine species became extinct. Four main hypotheses about the causes of this mass extinction are considered: volcanism, climatic oscillations, sea level variations accompanied by anoxia, and asteroid impact events. The extinction was triggered by an extensive flooding of basalts in the Central Atlantic Magmatic Province. Furthermore, a number of meteoritic craters have been found. Under the effect of cosmic causes, two main sequences of events developed on the Earth: terrestrial ones, leading to intensive volcanism, and cosmic ones (asteroid impacts). Their aftermaths, however, were similar in terms of the chemical compounds and aerosols released. As a consequence, the greenhouse effect, dimming of the atmosphere (impeding photosynthesis), ocean stagnation, and anoxia emerged. Then, biological productivity decreased and food chains were destroyed. Thus, the entire ecosystem was disturbed and a considerable part of the biota became extinct.
ISSN 1028334X, Doklady Earth Sciences, 2016, Vol. 466, Part 2, pp. 119–122. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © M.S. Barash, 2016, published in Doklady Akademii Nauk, 2016, Vol. 466, No. 6, pp. 688–691.
The Triassic period (251–199.6 Ma) was a time
when marine biota recovered and developed after the
Great Mass Extinction at the Paleozoic–Mesozoic
boundary. However, one of the five great Phanerozoic
mass extinctions occurred at the end of the Triassic
and involved both marine and terrestrial assemblages.
It is supposed that 47% of genera and 80% of species
became extinct within the interval of 600 ka to 8.3 Ma
[1, 2]. The major tectonic background events for these
processes were the breakup and rifting of Pangaea dur
ing opening of the preAtlantic Ocean.
At the end of the Rhaetian, at the Triassic–Jurassic
boundary (TJB), 48% of invertebrate species (mainly
cephalopods, bivalves, gastropods, brachiopods)
became extinct [3]. Within the limits of presentday
Europe, the territory of which is the most well studied,
92% of species and 42% of genera of marine organisms
went extinct in the Late Triassic. In some local terres
trial ecosystems, about 50% of tetrapods and up to
95% of plant species died off (see overview in [4]).
At the end of the Triassic, global extinction of many
reefforming organisms (first of all, scleractinial corals
and sponges) occurred: 50 genera became extinct,
while 11 survived. Coral reefs and almost all (16 of
18 families) calcareous sponges disappeared. Thus,
reef ecosystems were completely destroyed. Mass
extinction also involved ostracods, foraminifera, coc
colithofora, radiolaria, and dinoflagellates.
The Late Triassic mass extinction was not a single
event. Detailed stratigraphic data have shown that the
extinction of ammonites, brachiopods, and conodonts
was extended in time. Particular events are distin
guished, with higher extinction rates with approaching
the end of the Triassic: in the Middle and Late Norian
and at the end of the Rhaetian.
There are four main hypotheses about the causes of
the Late Triassic mass extinction: intensive volcanism
with the accompanying events, climatic variations, sea
level oscillations with the accompanying anoxia, and
impact events (asteroid impacts). It is supposed that
the extinctions of both marine and terrestrial biota
were triggered by some global event. The extensive
flood basalts within the Central Atlantic Magmatic
Province (CAMP), with the maximum estimated to be
at 199.0 ± 2.4 Ma fits in time with the TJB (~200 Ma)
mass extinction. This flood basalt effusion was the
greatest, at least in area: it covers more than 7000 000
, spanning from France to Southern Brazil, with a
volume of more than 2.5
The evidence for intensive tectonic events accom
panied by the volcanic activity is found in the eastern
margin of North America, in South America, in
northwestern Africa, and in southeastern Europe. This
is attributed to the main phase of rifting, which pre
ceded the opening of the preAtlantic Ocean. Erup
tions were characterized by the release of ashes and
Changes in Environmental Conditions
as the Cause of the Marine Biota Great Mass Extinction
at the Triassic–Jurassic Boundary
M. S. Barash
Presented by Academician A.P. Lisitsyn February 28, 2014
Received March 11, 2014
—In the interval of the Triassic–Jurassic boundary, 80% of the marine species became extinct. Four
main hypotheses about the causes of this mass extinction are considered: volcanism, climatic oscillations, sea
level variations accompanied by anoxia, and asteroid impact events. The extinction was triggered by an exten
sive flooding of basalts in the Central Atlantic Magmatic Province. Furthermore, a number of meteoritic cra
ters have been found. Under the effect of cosmic causes, two main sequences of events developed on the
Earth: terrestrial ones, leading to intensive volcanism, and cosmic ones (asteroid impacts). Their aftermaths,
however, were similar in terms of the chemical compounds and aerosols released. As a consequence, the
greenhouse effect, dimming of the atmosphere (impeding photosynthesis), ocean stagnation, and anoxia
emerged. Then, biological productivity decreased and food chains were destroyed. Thus, the entire ecosystem
was disturbed and a considerable part of the biota became extinct.
Shirshov Institute of Oceanology, Russian Academy
of Sciences, Nakhimovskii pr. 36, Moscow, 117213 Russia
considerable amounts of CO
and SO
during degas
sing of basalts, so this should have affected the compo
sitions of both the atmosphere and the ocean.
The new highprecision U/Pb geochronological
technique on volcanic ashes from independent marine
stratigraphic crosssections has shown that the TJB
biological crisis correlates with the beginning of effu
sive volcanic activity on land within the CAMP in a
period of less than 150 ka [6]. It was shown that the
accompanying sea level drop and the negative
peak at the very end of the Triassic occurred over less
than 290 ka. These rapid sea level fluctuations on a
global scale suggest that the global cooling was closely
related to the TJB extinction and potentially caused by
volcanism in the CAMP.
Mineralogical study of the uppermost Rhaetian
layer in the northern Austrian Alps [7] revealed that
ash layer traces that had been interpreted as direct evi
dence for volcanism in the CAMP coincided with or
immediately preceded the mass extinction and the ini
tial negative carbon isotope anomaly. Above the ash
boundary, the clay mineral composition indicates the
intensive erosion under the hot and humid greenhouse
climate conditions. This supports the idea that volca
nism in the CAMP caused the climatic and other envi
ronmental changes, which, in turn, is reflected in the
carbon isotope anomalies and led to the mass extinc
The evidence for the significant influence of volca
nic activity in the CAMP on the change in environ
mental conditions at the TJB in the marine environ
ment is the shift in the ratio between osmium isotopes
and the increase in the rhenium and osmium concen
trations [8].
It is believed that both Late Triassic and Early
Jurassic climates were warm. In the Late Triassic,
greenhouse conditions expanded over the entire Earth
so that humid forests reached polar zones. This was the
only period during the Phanerozoic for which no signs
of glacier activity have been revealed. Some data, how
ever, indicate temperature variations at the boundary
of epochs.
The significant variations in the ratio between car
bon isotopes in carbonates and organic matter verify
the considerable changes in the global carbon cycle at
the TJB [9]. This ratio in marine limestones of North
ern Italy showed a negative peak coinciding with the
disappearance of benthic fauna and the subsequent
positive shift started above the TJB.This ratio in
marine limestones of Northern Italy showed a negative
peak coinciding with the disappearance of benthic
fauna and the subsequent positive shift started above
the TJB. The negative peak could have been caused by
the release of gas hydrates.
The great negative isotope carbon shift defined on
marine carbonates, organic matter, and terrestrial
wood is explained by the fact that degassing of volcan
ogenic CO
caused the release of a significant amount
of CH
from gas hydrates in marine deposits into the
atmosphere. Oxidation of CH
must have additionally
of the atmosphere up to 2500 ppmv by
the beginning of the Jurassic [10].
Based on the paleobotanic data, the TJB was char
acterized by a fourfold increase in the atmospheric
concentration and 3–4°C increase in tempera
ture and by settling of greenhouse conditions. Tempera
tures exceeded the living ranges for many plants, leading
to the extinction of 95% of megaflora species [11].
In the ocean, wind circulation and meridional
water exchange must have decreased (the latter, four
fold), whereas stratification must have increased, on
the contrary. With respect to an increase in tempera
ture, oxygen solubility (and hence its concentration in
water) decreased, causing anoxia that led to extinction
of marine fauna.
The sea level oscillations at the end of the Triassic
are well supported by the geological data on Europe
and North America. The large regression was rapidly
replaced by the transgression in the Early Jurassic. For
example, deposits of the western Tethys Ocean in the
Iberian Craton demonstrate a regression–transgres
sion cycle of about 12 Ma long: it started in the Late
Triassic and finished in the Early Jurassic. The sea level
drop was accompanied by reduction of the shelf seas.
Transgressions of lowoxygen or deoxygenated waters
into shelf zones and subsequent regressions destroyed
the environments of bivalves and caused their mass
extinction. Relatively small sea level drops at the TJB
were defined by tectonic movements, because no
traces of continental glaciations were found. However,
sea level oscillations could have intensified the deteri
orating effect of the main causes.
The Jurassic basal layers in Europe and the Ameri
cas are rich in organic matter and contain no benthic
organisms, or contain impoverished assemblages indi
cating the stagnation conditions. The well proved oce
anic anoxia can explain the mass extinction of marine
biota; however, the decline of the terrestrial fauna and
flora suggests that more universal causes took place.
The relationship between the Late Triassic mass
extinction and the impact events has certain evidence.
The impact time for the Manicouagan crater, Quebec,
is defined at 214
1 Ma (an alternative estimate is
4 Ma; hereinafter, the ages of impact structures
are after [12]).
Impact craters of the same age have also been found
in France (Rochechouart) and England (near Bristol).
In the latter case, chromium isotopes have indicated the
cosmic origin of the impactites formed after the event.
According to the Armethod, the age of these impac
tites is 214
8 Ma. This time precedes the period of
stepwise extinction in the Middle Norian.
It was reported in [13] that there is a stratum of Late
Triassic deformed deposits (seismites) of 2–4 m thick,
occupying several thousand square kilometers, in
England. These deposits were produced by a seismic
event of extraordinary magnitude. M.J. Simms thinks
that they indicate an impact of a fireball of several kilo
meters in crosswidth: it produced a crater of several
tens of kilometers in diameter and triggered intensive
seismic waves. The epicentral position is supposed to
be more than 500 km westnorthwest of central Brit
ain, on the shelf west of Ireland, where the possible
crater is buried beneath young deposits of 23 km
There are a number of craters on the Earth’s sur
face with an age of about 214 Ma: Rochechouart
(France), Manicouagan and Saint Martin (eastern
and western Canada, respectively), Obolon (Ukraine),
and Red Wing (western United States). These five
impact structures were probably formed during a mul
tiple impact event due to the Earth’s collision with a
fragmented comet or asteroid [14].
The Rochechouart crater in France is hosted in the
Hercynian rocks of the Central Massif and not
reflected in the topography (its diameter is about
25 km). The Manicouagan crater is about 100 km in
diameter. The Saint Martin crater is about 40 km in
diameter and was revealed from gravimetric and mag
netic data, with subsequent verification by drilling.
The Obolon and Red Wing craters are about 15 and
9 km in diameter, respectively, with the latter having
an age of 200
25 Ma (based on the stratigraphic
data). In the United States (Tennessee), the Wells
Creek crater has also been found: its diameter is
13.7 km and the approximate age is 200 Ma. The mass
extinction at the TJB in Italy is associated with the
shale horizons containing the impact quartz; in the
Newark Basin, eastern United States, it is linked with
the iridium anomaly.
Some researchers emphasize the greater or lesser
gaps between volcanism, impact events, and mass
extinctions. In the author’s opinion [15], these gaps
are insignificant because events of cosmic origin trig
ger the occurrence of unfavorable conditions lasting
millions of years. Mass extinctions occur within these
intervals, when some combination of hostile environ
mental conditions reaches the level that makes exist
ence of certain organisms or their assemblages impos
Under the effect of causes that are likely induced by
orbital movement of the Solar System around the cen
ter of the Milky Way, two sequences of events develop
on the Earth: the terrestrial ones that lead to intensive
volcanism and the cosmic ones that are related to
impacts of large asteroids and comets (Fig. 1). How
Orbital movement of the Sun around the galaxy's center
Intersection of the galaxy's branches Oscillations relative to the plane
Tectonics Mantle
Asteroids Comets
Impact events
Ash, aerosolsСО
, SO
, Cl, F, CH
Dimming of the atmosphere,
reduction of the UV radiation
Greenhouse effect
Ocean stagnation Reduction of photosynthesis
and bioproductivity
Anoxia Destruction of the food chains
Mass extinction
Sea level
Processes that led to the mass extinction at the TJB.
ever, mass extinctions may occur in the presence of
effects from only one sequence of these two, either
volcanismrelated or that related to large impact
events. In this case, extinctions are probably less
As is shown from the scheme in Fig. 1, volcanism
and impact events produce similar effects. In both
cases, poisonous chemical compounds and aerosols
are released into the atmosphere. The greenhouse
effect settles followed by global warming and dimming
of the atmosphere; in turn, dimming impedes penetra
tion of UVradiation and thus reduces photosynthesis,
ocean stagnation, and anoxia. Bioproductivity
reduced and food chains were destroyed. In the end,
all important lifesupporting processes stop for most
of the fauna and mass extinction occurs.
This work was supported by the Presidium of the
Russian Academy of Sciences (Program no. 28 enti
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Translated by N. Astafiev
... In addition, there is a second hypothesis about the occurrence of ETE, the hypothesis that multiple bolide events lead to ETE 24 , serious environmental disasters caused by giant impacts, like massive volcanic activities, can also lead to the extinction of biological clusters [24][25][26][27][28] . However, compared with ETE, the existing impact craters are either too early in time or too small in scale 35 . ...
... Secondly, it can organically link the several important events at the End-Triassic with each other, instead of the vague understanding of "accidental coincidence" between volcanic eruptions and bolide events in time. Four of the five mass extinctions have caused controversy 13,25,27,28,[59][60][61] over the origin of impact and volcano, and the interpretation of impact based on the discovery of C5 structure, will help to clarify the primary causes of the other three mass extinctions. ...
... Based on the GI-GR hypothesis and the discovery of the Bermuda Impact Crater, we proposed an improved version of Bolide Extinction Theorythe Giant Impact and Large Igneous Provinces (GI-LIPs) model, which using in the End-Triassic Extinction can be called GI-CAMP model. Referring to the charts of Bond & Wignall (2014) 13 and Barash (2016) 28 , use GI-LIPs model to explain the process of ETE as shown in Fig.5. The diagram shows various structures, clues, evidences, factors and events, which associated with Bermuda Impact Event (BIC).The model points out that the direct killings by BIC and CAMP were primary causes of ETE, that the Climatic Disturbances as a result were the secondary causes, and that the Food -Chain Breaks were the third, they together led to the occurrence of ETE. ...
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Today, the causal link between the End-Triassic Mass Extinction and the 200-million-year-old volcanisms of the Central Atlantic Magmatic Province (CAMP) has been widely recognized,but what dynamical mechanism led to the instantaneous eruptions of CAMP and the rapid fracture of Pangaea′s lithosphere are still not clear. Here we report a huge potential impact crater: C5, with a diameter of 2000 km on the Triassic/Jurassic boundary, the rupture of Pangaea and the formation of CAMP may be related to C5. Different from varieties of endogenesis theories that were lack of enough power, our Giant Impact-Great Rift hypothesis suggests that: at end-Triassic, an asteroid with a 293km-diameter named Bermuda violently hit the Pangaea Supercontinent, formed the Bermuda Impact Crater (i.e.C5) and a main great rift within the lithosphere, then the melts in situ and the spewing lavas by decompression effect quickly start to create the CAMP′s volcanisms from inside through out of this rift; Later, the Great Impact Rift that evolved into the Mid-Atlantic Ridge, made new plates and became the starting line of new oceanic crust, seafloor spreading and continental drift, due to the long-term mantle plume activities beneath it. So nowaday′s continental shelf arc of the east coast of North America exists as the remnant of the edge of Bermuda Impact Crater.
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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.
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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.
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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.
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Evidence for the collision of fragmented comets or asteroids with some of the larger (jovian) planets and their moons is now well established following the dramatic impact of the disrupted comet Shoemaker-Levy 9 with Jupiter in 1994 (ref. 1). Collisions by fragmented objects result in multiple impacts that can lead to the formation of linear crater chains, or catenae, on planetary surfaces. Here we present evidence for a multiple impact event that occurred on Earth. Five terrestrial impact structures have been found to possess comparable ages (~214 Myr), coincident with the Norian stage of the Triassic period. These craters are Rochechouart (France), Manicouagan and Saint Martin (Canada), Obolon' (Ukraine) and Red Wing (USA). When these impact structures are plotted on a tectonic reconstruction of the North American and Eurasian plates for 214 Myr before present, the three largest structures (Rochechouart, Manicouagan and Saint Martin) are co-latitudinal at 22.8°(within 1.2°, ~ 110 km), and span 43.5°of palaeolongitude. These structures may thus represent the remains of a crater chain at least 4,462 km long. The Obolon' and Red Wing craters, on the other hand, lie on great circles of identical declination with Rochechouart and Saint Martin, respectively. We therefore suggest that the five impact structures were formed at the same time (within hours) during a multiple impact event caused by a fragmented comet or asteroid colliding with Earth.
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The lower part of the Cotham Member in the Penarth Group (latest Triassic, Rhaetian) of the UK incorporates a uniquely extensive metre-scale horizon of soft-sediment deformation. Interpreted as a seismite, it shows evidence for only a single seismic event even at its thickest development. It is recorded from more than forty sites across at least eight discrete sedimentary basins covering > 250,000 km2, and originally must have covered a still larger area. Such a widespread horizon of soft-sediment deformation, unique for the UK Phanerozoic and implying a seismic event of exceptional magnitude, is difficult to account for by conventional terrestrial mechanisms. Contemporaneous volcanism in the Central Atlantic Magmatic Province (CAMP) was too far distant to cause the deformation, and the tectonic setting of the region was not conducive to earthquakes on this scale. Slump fold long axes suggest an epicentre broadly in the southern Irish Sea or St. George's Channel. Impact of a km-scale asteroid here potentially could produce the observed sedimentological effects across the UK, but any late Triassic impact structure would now be concealed by a km or more of younger strata. At its thickest development, in Northern Ireland, the seismite is succeeded by a rip-up breccia and hummocky- and wave-rippled cross stratification. These facies, and their position immediately above the seismite, are consistent with the effects of a tsunami arising directly from the seismic event. Tentative evidence for a tsunamite of this age has also been reported from southern France. The putative tsunamite in Northern Ireland is succeeded by a desiccation-cracked hiatus which may correlate with a similar hiatus truncating the seismite at sites in southern England. The hiatus in southern England correlates closely with a δ13C isotope excursion that has been traced from eastern Europe across to western North America and is associated with significant biotic changes. The ultimate cause of the seismite and associated tsunamite remains unclear. No impact crater of appropriate age or location is currently known and other evidence for impact at this time is at best equivocal. It is considered here that impact of a km-scale asteroid may have caused the observed sedimentological effects in the Lilstock Formation across the UK area, but was not necessarily a significant contributory factor in the generation of either the isotope excursion or of the biotic changes through the Triassic–Jurassic boundary interval.
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.
1] The end-Triassic mass extinctions represent one of the five most severe biotic crises in Earth history, yet remain one of the most enigmatic. Ongoing debate concerns the environmental effects of the Central Atlantic Magmatic Province (CAMP) eruptions and their linkage with the mass extinction event across the Triassic-Jurassic boundary. There is conflicting paleo-evidence for changes in atmospheric pCO 2 during the extrusion of the CAMP basalts. Studies on sediments from European and Pacific localities have, however, identified a substantial negative isotopic anomaly (up to À3.5%) across the TR-J boundary, providing an important indicator of changes in the operation of the ancient global carbon cycle. We sought to explain the paleo-evidence by utilizing a carbon cycle model for the ''hothouse'' world of the end-Triassic that emphasizes the chemical weathering of silicate and carbonate rocks and the ocean carbonate chemistry. We find that volcanic CO 2 outgassing fails to fully account for either a sufficient rise in atmospheric pCO 2 (indicated by the stomata of fossil leaves) or the sedimentary isotopic fingerprint. Instead, the scenario that best fits all of the geologic evidence is a positive feedback loop in which warming, due to a buildup of volcanically derived CO 2 , triggers destabilization of seafloor methane hydrates and the catastrophic release of CH 4 [Pálfy et al., 2001]. We calculate that this carbon cycle perturbation was huge, involving the release of $8000–9000 Gt C as CO 2 during the CAMP basaltic eruptions and $5000 Gt C as CH 4 . In the model the initial isotopic excursion is assumed to take place over $70 kyr, while complete reequilibration of the ocean-atmosphere system with respect to CO 2 is accomplished over 700–1000 kyr. Our results thus provide a preliminary theoretical explanation for the bioevents, estimated pCO 2 changes, and isotopic excursions observed in marine and continental sediments at this time.
The mass extinction at the end-Triassic is one of the five biggest in the Phanerozoic However it is the least well understood among these five events, and only till last decade it became a great academic interesting subject to geologists. The evidences for this event come obviously from bivalves, brachiopods, ammonites, corals, radiolaria, ostracods and foraminifera of marine habitats, and plants and tetrapods of terrestrial realm. By contrast, for some of other groups, such as marine gastropods and marine vertebrates, no mass extinction has been recognized yet. The extinction event is strongly marked at specific level but shown a complicated situation at generic and family levels. Dramatic changing of the environment, such as the temperature raise due to the greenhouse effect, the marine anoxic habitats caused by a sudden transgression after the regression at the end of Triassic, has been claimed to be the main cause of the extinction. Many hypotheses have been suggested to demonstrate the mechanisms of the environment changing, among which two popular ones are the bolide impact and volcanic eruption. The Triassic-Jurassic (Tr-J) boundary mass extinction event is still poorly understood because no enough data have been obtained from the Tr-J boundary successional sections of both marine and terrestrial sediments, and most of these studies were regionally restricted. The basic aspects of the event and its associated environmental conditions remain poorly characterized and the causal mechanism or mechanisms are equivocal. Some authors even doubt its occurrence. China has many successionally developed terrestrial and marine Tr-J sections. Detailed studies of these sections may be important and significant for well understanding of the event.
The hypothesis of periodicity in extinction is an empirical claim that extinction events, while variable in magnitude, are regular in timing and therefore are serially dependent upon some single, ultimate cause with clocklike behavior. This hypothesis is controversal, in part because of questions regarding the identity and timing of certain extinction events and because of speculations concerning possible catastrophic extraterrestrial forcing mechanisms. New data on extinctions of marine animal genera are presented that display a high degree of periodicity in the Mesozoic and Cenozoic as well as a suggestion of nonstationary periodicity in the late Paleozoic. However, no periodicity is evident among the as yet poorly documented extinction events of the early and middle Paleozoic.