Interaction of the Reasons for the Mass Biota Extinctions in the Phanerozoic

Abstract

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.

Full text

ISSN 00014370, Oceanology, 2013, Vol. 53, No. 6, pp. 739–749. © Pleiades Publishing, Inc., 2013.
Original Russian Text © M.S. Barash, 2013, published in Okeanologiya, 2013, Vol. 53, No. 6, pp. 825–837.
739
INTRODUCTION
The geological periods are distinguished on the
basis of greater or lesser changes in the biological com
munities caused by the variations of the conditions.
The organisms partly became extinct and new species
appeared at the boundaries of the geological periods.
Especially catastrophic extinctions, when more than
75% of the Earth’s species disappear in geologically
short periods, are referred to the great mass extinc
tions. Their reasons become rather evident in the
course of the study of these events. Five great extinc
tions are known in the Phanerozoic: the Ordovician,
the Devonian, the Permian, the Triassic, and the Cre
taceous at the Ordovician–Silurian, Devonian–Car
boniferous, Permian–Triassic, Triassic–Jurassic, and
Cretaceous–Tertiary boundaries, respectively.
REASONS FOR THE MASS EXTINCTIONS
Tectonic movements.
The tectonics are undoubt
edly one of the basic abiotic factors that causes the
largescale paleooceanologic evolution of the ocean
and its organisms. The leading effect of the plate tec
tonics and the vertical movements is evident in chang
ing the contours of the continents and oceans, the oro
genesis and volcanism, the relief, the depression
capacity, the variations of the sea level, the relations
between the basins, the circulation of the ocean and
atmosphere, the climate, the onset and degradation of
the continental glaciations, and the biota’s evolution.
However, the tectonic processes last for tens and hun
dreds of millions of years and could not have caused
the geologically short changes in the paleoenviron
ment resulting in mass extinctions.
Climate variations.
Significant climatic variations
occurred in the Phanerozoic. The global cooling may
have been disastrous for marine organisms and the
warmwater organisms disappeared, were reduced,
and moved toward the equator. The cooling intensifies
the oceanic circulation and mixing and enriches the
water in oxygen, which, however, leads to the disap
pearance of fauna that was adapted to life under the
lowoxygen conditions. The productivity increases
and may negatively influence the benthic complexes
formed in oligotrophic conditions. The variation of
the ocean’s hydrodynamics disturbs the ecological
conditions throughout the entire thickness of the
ocean.
The warming periods are determined by the
geochemical and isotopic data, the increase in the
greenhouse gases such as
СО
2
and
NH
4
, and the
spreading of the warmwater organisms into the high
latitudes. Many researchers consider that the fast
Interaction of the Reasons for the Mass Biota Extinctions
in the Phanerozoic
M. S. Barash
Institute of Oceanology, Russian Academy of Sciences, pr. Nakhimovskii 36, Moscow, 117997 Russia
email: barashms@yandex.ru
Received October 10, 2012
Abstract
—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 atmo
sphere by aerosols at volcanism and impact events, etc., had a harmful affect during some periods of time (a
hundred thousand years to millions of 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 pre
vention of photosynthesis, the ocean’s stagnation, and anoxia with the following reduction of the bioproduc
tivity, the destruction of the food chains, and the extinction of a significant part of the biota.
DOI:
10.1134/S0001437013050020
MARINE
GEOLOGY

740
OCEANOLOGY Vol. 53 No. 6 2013
BARASH
warming periods are caused by the emission of green
house gases into the atmosphere at intense volcanic
eruptions. The warming may lead to the dissociation
of gas hydrates and the discharge of methane into the
atmosphere from the bottom sediments and/or per
mafrost in the high latitudinal regions, which should
cause a further increase in the temperature and green
house effect. All the organisms are tolerant to the tem
perature in a certain range; however, the biological
processes and physiological activity beyond this range
are disturbed up to the death of organisms. The global
warming brings about the melting of the continental
glaciers and a corresponding uplift of the sea level,
which is harmful for marine ecosystems. The warming
results in poor ocean circulation, anoxia, the disap
pearance of upwellings, and the decrease in productiv
ity. The lowoxygen or oxygenfree conditions are typ
ically considered as a direct reason for the majority of
the organism extinctions in the geological record.
For the last 500 Ma, all the major extinctions
occurred when the
СО
2
content exceeded 1000 ppm,
which corresponds to the global warming periods [68].
Eustatic variation of the sea level.
The lowering of
the sea level, which is usually combined with periods
of cooling and an increase in the volume of the conti
nental glaciations, is considered to be an important
extinction factor, especially for the shelf communities.
It leads to the reduction of habitats and the violation of
the ecological systems. This is especially ruinous for
organisms inhabiting the epicontinental seas because
of the disturbed connection with the open ocean, the
change in the salinity, and may finally happen to com
plete their drying. In some cases, the transgression also
negatively affects the biodiversity and disturbs the eco
systems.
Volcanism.
The basaltic eruptions are also consid
ered as a potential reason for the mass extinctions in
the Phanerozoic. The eruptions release significant
amounts of
СО
2
and
SO
2
, which affects the composi
tion of the atmosphere and ocean. A statistical analysis
was applied to reveal the relation between the extinc
tions from the end of the Permian until the present and
between the possible reasons (such as volcanism, great
lowering of the sea level, and impact events). Scenarios
of the influence of individual reasons were also consid
ered [48]. The author has found only one statistically
significant link between the extinction peaks and the
volcanism. In his opinion, the impact events play a
role when they initiate volcanism. However, these
conclusions may hardly be referred to the volcanism of
the Central Atlantic igneous province caused by the
main rifting phase during Gondwana’s breakup at the
Triassic–Jurassic boundary. In this case, the tectonic
evolution of the lithosphere is the initial reason for the
crisis.
Impact events.
The impacts of large cosmic bodies
(asteroids and comets) are considered as one of the
major reasons for the mass extinctions of organisms.
Alvares et al. first attracted attention to this idea [5]. It
is suggested that a large impact event could bring about
prolonged global dimming because of the dust and
small detritus vented into the atmosphere. The dim
ming prevented photosynthesis and led to the stopping
of the primary production. Correspondingly, the food
chains were violated and the foodchainrelated com
munities of organisms perished. In addition, the dust
clouds reflected the sun’s rays and caused a strong
decrease in the temperature. The broad fires harmfully
affecting the land biota were one more result of the
impact events. Charcoal fragments as evidence of
these fires were found in the sedimentary rocks at the
CretaceousTertiary periods, although they may have
been caused by other reasons. The impact events also
could have produce giant tsunami, which could have
an adverse effect on shallowwater ecosystems; caused
the formation of acid rains harmful for the land and
subsurface marine biota, caused an increase in the
level of the cosmic radiation, and caused a poisonous
increase in the content of the rare elements. The cal
culations show that a giant asteroid could penetrate
the lithosphere and cause a volcanic eruption [19].
The idea concerning the strong influence of cosmic
factors, in particular, impact events, on the evolution
of the Earth’s biota attracts much more interest as
events are studied and new information is obtained.
New evidence of the catastrophic collision of the
Earth with large asteroids and comets is being found.
This partially returns us to the catastrophic ideas of
Cuvier yielding to the ideas of the gradualism or evo
lutionism of Ch. Lyell and Ch. Darwin in the middle
of the 19th century.
GREAT MASS EXTINCTIONS
The Ordovician extinction
at the Ordovician–Sil
urian boundary (OSB) lasted for 3.3–1.9 Ma, ended
about 443 Ma ago, and led to the extinction of 49–
57% of the genera and 86% of the species [6, 60]. The
general paleogeographical extinction conditions were
the result of Gondwana’s movement toward the South
Pole, which caused the global cooling and continental
glaciation in the Southern Hemisphere. After the
greenhouse period typical of the Ordovician, the cool
ing, as many researchers believe, led to the mass biota
extinction along with the lowering of the ocean’s level.
Based on the isotope paleothermometry, the tempera
ture in the tropical ocean in the end of the Ordovician
is estimated as
32–37
°
C
, excluding the shortterm
cooling by
~5
°
C
. The continental glaciation exceeded
the Late Pleistocene maximum, the carbon cycle
greatly changed, and mass extinction occurred [20].
The lowering of the ocean’s level reduced the areas
of the most inhabited coastal ecological niches. The
warming (the increase in the level) and cooling (the
increase in the glaciation and the lowering of the level)
episodes alternated several times, which consequently
reduced the biodiversity. Periodic anoxia is suggested.

OCEANOLOGY Vol. 53 No. 6 2013
INTERACTION OF THE REASONS FOR THE MASS BIOTA EXTINCTIONS 741
The noticeable
δ
13
С
excursion 444 Ma ago [10]
reflects the bioproductivity’s oscillation.
The cooling could have been provided by the first
onland plants, which extracted a great amount of Ca,
Mg, P, and Fe from the soil. As a result of the Ca and
Mg removal, new minerals were formed, in particular,
carbonates, which bound the atmospheric carbon
dioxide. In turn, the ingress of P and Fe into the seas
provoked the impetuous growth of the live organisms,
which also began to extract the carbon dioxide from the
atmosphere. As a result, the planetary carbon cycle sig
nificantly changed, which finally led to a decrease in the
CO
2
content in the atmosphere. The temperature
dropped and consistently came several ice ages [42].
The abundant organic matter and the variations in
the
δ
13
С
org
and
δ
34
S
sulf
in the South China OSB sec
tions have shown great climatic oscillations, a change
in the sea level, and multiple anoxia in the water col
umn, which could have caused a biological crisis [74].
The OSB volcanic activity could also have triggered
the mass extinction [32]. The bentonite clays wide
spread in South China, North America, and Europe
contain minerals typical of felsic volcanic ashes and
are their submarine diagenetic metamorphism prod
ucts. Because these data indicate the global character
of the volcanic eruptions, they should have strongly
affected the atmosphere and biosphere.
Several meteorite craters indicate the Late Ordovi
cian impact events: the Kyardla crater 7 km in diameter
in Estonia (~455 Ma), the Lockne crater 7.5–13.5 km in
diameter in Sweden (455 Ma), and the Rock Elm Dis
turbance crater 6 km in diameter in Wisconsin in the
United States. The diameter of the latter meteorite is
estimated as 170 m, and its age is determined as 455–
430 Ma (from the Middle Ordovician to the Early
Silurian), which includes the period of the mass
extinction. One more, the Pilot crater
445
±
2
Ma in
age and 6 km in diameter, is located in northern Can
ada [18]. The Slate Islands in Ontario, Canada repre
sent the central uplift of the impact crater 32 km in
diameter [61]. Their age is estimated as 450 Ma; how
ever, based on other determinations, this event could
have occurred in the Proterozoic or Early Paleozoic.
Thus, although several craters are known in the Late
Ordovician, the age of only the Pilot crater corre
sponds to the mass extinction period. This relatively
small impact event could not have affected the worsen
ing of the ecological environment, and the influence
of the asteroid impacts on the great Ordovician extinc
tion has not been proven yet.
The Devonian extinction
at the Devonian–Carbon
iferous boundary (DCB) finished about 359 Ma ago
and lasted for 29–3 Ma, resulting in the extinction of
35% of the genera and 75% of the species [6, 60]. This
extinction affected both the marine and onland hab
itats and included two stages: (1) about 372 Ma at the
Fransian–Famenian boundary (FFB) and (2) ~359 Ma
at the DCB. The alternation of the greenhouse and
glacial conditions (the Gondwana ice sheet), the fluc
tuations of the sea level and the CO
2
content, the abys
sal anoxia, its spreading at shallow depths at transgres
sions, and the impact events are usually considered as
the reasons.
The Late Devonian is characterized by the rise of
the sea level with the Fransian maximum and the great
Famenian lowering complicated by a series of fluctua
tions. The lowering of the level was related to the
Gondwana ice sheet, which is evident from the South
America glacial deposits. It suggested that the FFB
extinction pulse was associated with a sharp drop in
global temperature after the abnormally warm interval
caused by impact events [49]. This period interrupted
the general cooling trend from the Middle Devonian
greenhouse climate to the Early Carboniferous glacial
climate.
Buggish has suggested a closed cyclic model with
variations of the climate and sea level [12]. The rise of
the sea level causes the flooding of the shelves and an
increase in the productivity. The increasing organic
matter provides oxygenfree conditions and the mass
death of organisms. The flooding of the tropic shelves
leads to the formation of highly saline water, which
submerged to the depth of the Late Devonian Ocean
and stratified the water column, thus preventing the
vertical water circulation and ventilation. A significant
amount of sedimentburied organic carbon decreases
the CO
2
content in the atmosphere, which brings
about cooling, the formation of continental ice, and
regression. Next are the drainage of the shelves, the
productivity’s reduction, the oxidation of black shales,
an increase in the CO
2
content in the atmosphere,
warming, transgression, etc. Thus, the Buggish model
envisages the alternation of the Late Devonian green
house and icehouse conditions.
According to the Becker–House model, the FFB
mass extinction was caused by the oceanic volcanism
[7]. The intense basaltic volcanism in the rifting zones
along eastern Laurasia and northern Gondwana in the
middle of the Late Devonian played a role in the global
warming, the methane release, and the rise of the sea
level. The volcanism stimulated the increase in the
СО
2
content in the atmosphere, the formation of the
highly saline deep waters, the increased vertical strati
fication, the anoxia, and the death of organisms. The
detail geochemical and sedimentological data show
the influence of the liberation of gas hydrates [22]. The
period of the elevated accumulation of the organic
carbon in Iran, South China, and the Subpolar Urals
corresponds to the short negative
δ
13
C
excursion of
3.5‰
at the FFB. The oxygen isotopic ratio in these
sedimentary rocks demonstrates a rapid increase in the
temperature of the ocean and atmosphere, which,
according to the author’s opinion, was caused by the
methane released from gas hydrates.
The content of REE and other elements indicates
that the Late Devonian hydrothermal activity pro
voked the seawater’s acidation, pollution in heavy
metals, and eutrophication, which could have

742
OCEANOLOGY Vol. 53 No. 6 2013
BARASH
destroyed the nerithic ecosystems and lead to the FFB
mass extinction [75].
The Late Devonian (FFB) Ir peak (0.24 ppb) was
detected in China, which is interpreted as evidence of
an impact event or reduction processes [67]. A high Ir
content (4 ppb) is found in Canada; it is 85 cm below
the FFB relative to China [44]. Several interlayers with
increased Ir contents and microtektites are located
both below and above the FFB in South China [47].
Microtektites and impact craters of the same age
were found in Sweden. The clearest evidence of the
asteroid impact in the Early Fransian (~380 Ma) was
identified in the North America [52]. The Alamo cra
ter 44–150 km in diameter in Nevada in the United
States is 367 Ma (382.1 Ma by other data) in age [64].
The corresponding rocks contain shocked quartz and
an Ir anomaly [43]. Here is the Alamo impact breccia,
which is a layer 1–135 m thick of Late Devonian shal
low coarseclastic limestone [69]. The total volume of
the deformed, partially melted, or displaces rocks is
about 1000 km
3
.
The same age was determined for the Sweden Siljan
crater 52–80 km in diameter [57; 64] and the Flynn
Creek crater 3.8 km in diameter and 150 m deep in
Texas in the United States. The latter has all the fea
tures typical of an impact structure: a central uplift,
deformed frame layers, a breccia lens 40 m thick, etc.
Its age is estimated as
360
±
20
Ma [18]. The large bur
ied Woodleigh meteorite crater in Western Australia is
40 to 120 km in diameter based on different estima
tions [53]. The drilling in its central uplift has exposed
shocked quartz and other impact features of the bolide
6–12 km in diameter. If the higher size estimation is
true, then this is the fourth largest crater on the Earth.
Its age is
364
±
8
Ma [18]. Thus, numerous impact
events in the end of the Devonian played an important
role concerning the harmful conditions leading to the
mass extinction of organisms.
The profound changes of the conditions ~359 Ma
ago are confirmed by the geochemical data, including
the variations in the
δ
13
С
values [37]. Abundant biom
arkers from the algae and bacteria were distinguished
in the FFB’s basal fractions in South China. The
molecular stratigraphic parameters, the micron gyp
sum crystals, and the pyrite framboids show that supersa
linity and anoxia were dominant for 1.2 Ma at the FFB
and could be the reason for the gradual degradation of the
ecosystems from the Middle Devonian [25].
The Permian extinction
at the Permian–Triassic
boundary (PTB) lasted no more than several tens of
thousands of years during the giant eruption of the
Siberian traps and finished 252.28 Ma ago, thus lead
ing to the extinction of 56% of the genera and 96% of
the species of organisms [6, 38, 60]. The following rea
sons are considered: the disappearance of the ecologi
cal niches after Pangea’s formation, the lowering of
the sea level up to the Phanerozoic minimum, the
transgressions, the shortterm cooling episodes, the
volcanism, the warming, the acid rains as a result of
the methane released from the gas hydrates, the deep
water anoxia, the supersalinity, the increase in the
H
2
S
and
CO
2
contents in aquatic and terrestrial environ
ments, and the impacts of large asteroids.
Taking into account the sea level oscillations, the
variable masses of the isotope parameters and the lipid
biomarkers in a 241m PTBintersected stratigraphic
section show the clear shifts of the conditions and fun
damental changes in the plankton’s ecology for 1.5 Ma
prior to and during the main phase of the mass extinc
tion [13]. The authors relate the global development of
euxinic conditions in the photic zone in the end of the
Permian with Pangea’s aggregation, intense weather
ing, and an increase in the biogenic runoff into the
ocean.
The PTB sections in China show an abrupt
decrease in the
δ
13
C and an increase in the amount of
presumably volcanic microspherules by ~100 times in
comparison with the overlapping and underlying
rocks. Interlayers of pyrite (evidence of anoxia) and
volcanic ash are observed. The Ir content exceeds by
an order of magnitude its background concentration
in the Upper Permian and Lower Triassic sedimentary
rocks [73]. The midoceanic siliceous rocks in Japan
and British Columbia (Canada) reflect the supeanoxia
conditions (the pyritization, the sulfur isotope ratio,
the geochemistry of the organic matter, the rare ele
ments, and the dolomite concretions). The anoxia
lasted about 20 Ma from the Late Permian to the Mid
dle Triassic [34].
The following processes may explain the rapid
δ
13
C
decrease at the PTB: the reduction of the input of the
biogenic elements in the euphotic zone and the
decrease in the bioproductivity, the influence of volca
nism, the weathering, the extractions from the gas
hydrates, and the oxidation of the biomass [28].
The complex modeling of the climate conditions
for the end of the Permian has shown that the surface
temperatures in the tropical ocean zone are similar to
the modern ones; however, they are higher by 8–10
°
C
in the high latitudes [39]. The sea level lowered by
~230 and 280 m during the Permian and from the
Middle Carboniferous, respectively, which is related to
Pangea’s integration 260 Ma ago [27, 30]. The mass
death occurred under the rapid uplift and spreading of
the lowoxygen or oxygenfree deep waters into the
shallow areas [29].
The volcanic initiation of the Late Permian extinc
tion is beyond question. Both midoceanic basaltic
and intraplate magmatism occurred. The greatest
eruption of the Siberian traps for the entire Earth’s
record created ruinous conditions for the biota [35].
The eruption began
251.7
±
0.4
Ma ago and became
weaker
251.1
±
0.3
Ma ago. Its coincidence with the
PTB age confirms that it was the most important rea
son for the mass extinction of organisms in the end of
the Permian. The eruption of up to
4
×
10
6
km
3
of vol
canic material during a short period (about 0.6 Ma)
could have rapidly released a great amount of
CO
2
,

OCEANOLOGY Vol. 53 No. 6 2013
INTERACTION OF THE REASONS FOR THE MASS BIOTA EXTINCTIONS 743
SO
2
, F, and Cl leading to the destruction of the atmo
spheric and biospheric systems [36].
The ecological conditions may also have been
changed under the impacts of large asteroids or com
ets. Their influence has been proved only in the last
years. Typical impact material was observed in several
PTB sections: shocked quartz in Antarctica and Aus
tralia, Fe–Ni–Si and Fe–Ni fragments and spherules,
and fullerenes with nonterrestrial gases (
3
He) in China
and Japan. Cosmic CrNi spinel microspherules were
found in several PTB sections in Eastern Europe and
the Caucasus region [65].
However, the real craters have been found only
recently. Thus, evidence for the sedimentburied Bed
out (Bedoo) impact structure was found in northwest
ern continental margin of Australia 25 km from the
coast [8, 9]. The Ar–Ar age of the plagioclase of
250.1
±
4.5
and
253
±
5
Ma corresponds to the PTB.
The Araguainha crater 40 km in diameter in Brazil has
an age of 250 Ma [41] and
244.4
±
3.25
Ma [64]. A
500km crater located under the East Antarctic ice
sheet was revealed after the surface radar mapping of
Wilkes Land in Antarctica. It is suggested that this is a
consequence of the impact of a 55km asteroid. Based
on the gravitation data, this event occurred 250 Ma
ago [66]. The Arganaty crater in Kazakhstan found on
the basis of a cosmic photosurvey has also been estab
lished for sure [40]. However, its PTB age is based only
on an assemblage of geological–geophysical data. The
probable Falkland crater 300 km in diameter near
Argentina is dated at 250 Ma. Some small craters on
the East Siberian platform are less reliable.
The study of the facies, geochemistry, and biomar
kes has proved that anoxia or hypoxy were the direct
reasons for the mass extinction in the end of the Per
mian, as well as others [26, 71].
The Triassic extinction
at the Triassic–Jurassic
boundary (TJB) included several stages, lasted for
8.3 Ma–160 ka, and finished ~200 Ma ago with the
extinction of 47–48% of the genera and 80% of the
species [6, 60]. Four events are distinguished with an
increased extinction rate up to the TJB: the middle,
late, and end of the Norian (~216.5–203.6 Ma) and
the end of the Rhaetian (about 200 Ma) [46]. The
main hypotheses concerning them are related to the
climate oscillations and the changes in the sea level
accompanying by anoxy, volcanism, and impact
events. In the end of the Triassic, the greenhouse con
ditions were global and humid forests grew at the
poles. This is the only Phanerozoic period devoid of
glaciation. Nonetheless, the temperature oscillations
at the boundary of the epochs are confirmed by some
materials. The following trends are identified on the
basis of the palinological data from the sections of the
northern Alps: abrupt warming changed by short cool
ing followed by more prolonged warming [40]. It is
suggested that the initial warming phase led to the dis
sociation of gas hydrates, methane’s release into the
atmosphere, and a further increase in the temperature,
(probably by
10
°
С
) [54].
The sharp changes in the sea level in the end of the
Triassic are well geologically substantiated in Europe
and North America. In the Late Rhaetian, the pulse of
the rise of the sea level changed with its global lowering
at the TJB in various regions of the Northern Hemi
sphere [24, 45]. The large regression was rapidly
replaced by the transgression in the beginning of the
Jurassic.
According to the U–Pb age, the mass extinction in
the end of Triassic correlates with the volcanism in the
Central Atlantic Magmatic Province (CAMP) within
less than 150 ka and the oscillations of the sea level and
the negative
δ
13
С
deviation within less than 290 ka
[59]. The Sr and Os isotope ratios changed in the Rha
etian, which is related to the weathering of the CAMP
basalts [15]. The degassing of the basalts should release
a significant amount of
СО
2
and
SO
2
, which could
have affected the composition of the atmosphere and
ocean. The considerable variations of the carbon iso
tope ratio in the carbonates and organic matter con
firm the significant changes in the global carbon cycle
at the periods boundary [63]. This ratio in marine
limestones from northern Italy has shown a negative
pulse and a following positive shift after the boundary.
The negative pulse may have been caused by the
decomposition of gas hydrates [21].
The modeling shows the possibility of the harmful
influence of the rapid
СО
2
release on the marine and
terrestrial biota in the end of the Triassic [32]. On land,
the increase in the
CO
2
content exceeding by 2–
8 times the modern preindustrial values should have
increased the duration of the hot and dry seasons and
the seasonal contrasts. In the ocean, the windy circu
lation and longitudinal waterexchange (by 4 times)
should decrease, and the stratification should inten
sify. The solubility of the oxygen and its content in the
water decreased with the increase in temperature.
Anoxia developed. The marine fauna was deprived of
oxygen.
The relation between this extinction and the
impact events is certainly substantiated by the craters
with ages of ~214 Ma (the Norian Stage of the Late
Triassic) [17]: the Rochechouart in France, the Mani
couagan 100 km in diameter and the Saint Martin in
Canada, the Obolon in Ukraine, the Red Wing in the
United States, and the crater near Bristol in the
United Kindgom. Probably, the impact structures
were formed simultaneously at multiple impacts
caused by the Earth’s collision with a fragmented
comet or asteroid.
Simms [62] reported on a 2 to 4m thick sequence
of deformed rocks (seismites) in the end of the Triassic
(Rhaetian Stage) widely spread in the United King
dom. The author suggests that they may testify to the
impact of a bolide several kilometers in diameter,
which excited seismic waves. The epicenter’s location
is suggested to be on a shelf westward of Ireland, where

744
OCEANOLOGY Vol. 53 No. 6 2013
BARASH
the possible crater is buried under a 2 to 3km
sequence of young sedimentary rocks.
The Cretaceous extinction
at the Cretaceous–Ter
tiary boundary (KTB) ended about 66 Ma ago, lasted
for less than one year up to 2.5 Ma, and led to the
extinction of 40% of the genera and 76% of the species
[6, 60]. It is assumed that the global catastrophe was
promoted by the large bolide impact in the Yucatan
Peninsula, the greatest volcanic eruption of the Dec
can traps on the Indian plate (probably, beginning
before the impact event), the
CO
2
variations, the glo
bal warming, the tectonic uplifts, the increased ero
sion, the eutrophication and anoxia in the ocean, and
the bioproductivity’s reduction. In addition to the
Chicxulub crater in the Yucatan Peninsula, the great
KTB impact events are confirmed by the Shiva, Bolt
ysh, Silverpit, and other craters (see the review in [3]).
What is the evidence of the natural KTB events?
The identified
δ
13
С
shift was caused by the productiv
ity’s reduction because of the mass extinction of the
plankton organisms. In the western North Atlantic
based on the
δ
18
О
value for the planktonic foraminifers,
the temperature has risen by
6
°
C
during the Maastrich
tian last three million years (~68.5–65.5 Ma). Thus, the
Maastrichtian cooling was replaced by warming with
shortterm variations. The KTB’s
87
Sr/
86
Sr
ratio’s
peak is explained by the intensified weathering of the
continental rocks and the radiogenic Sr runoff to the
oceans as a result of the lowering of the sea level and
the expanded continental area. The other hypothesis
relates it to an impact event and acid rains, which
increased the weathering [28].
Wilf et al. [72] have studied the oceanic (foramini
ferbased) and onland (florabased) evidence of the
temperature fluctuations before the KTB and have
shown the high degree of coincident changes. An
especially clear warming tendency was found begin
ning from 66.0–65.9 Ma with a warming peak at about
65.8–65.6 Ma and consequent cooling directly before
the KTB. The authors interpret these data as a global
climatic shift. These results correspond to the modern
data on the
p
CO
2
from the carbonates of the paleosoils
of Canada, Southern France, and other regions,
which confirm almost the duplication of the
p
CO
2
for
~0.5 Ma before the KTB, the return to the low values
directly before the KTB, the small fluctuations or their
absence at the boundary, and the near duplication after
~1.5 Ma after the boundary. These data corroborate
the close relation of the
p
CO
2
and the temperature.
The volcanism on the Indian plate was probably one of
the
CO
2
sources.
Thus, to explain the KTB crisis, impact events, vol
canism, cooling, warming, regressions, transgressions,
anoxia, and tectonic movements are attractive, and
each of them or their combinations really negatively
affected the evolution of the marine organisms. The
reviews of the evolution of the Mesozoic conditions
and, in particular, the hypotheses of the reasons for the
mass extinction [1, 2] show that almost all of them
could not have caused the abrupt catastrophic change
of the conditions that led to the coeval death of
numerous marine and onland organisms inhabiting
various ecological niches.
Two major hypotheses are currently considered in
the world literature: a meteorite impact and volcanic.
The first hypothesis suggests the fatal change of many
conditions as a result of the intense and numerous
impacts of large asteroids or collisions with comets,
and the second one supposes the pollution of the
atmosphere and ocean by harmful substances at the
eruption of the Deccan traps on the Indian plate and,
probably, the simultaneous volcanism of the Hawaii–
Emperor Ridge in the Pacific Ocean.
The finding of the Ir anomaly at the KTB in Gub
bio (Italy) by Alvares et al. [5] was the most important
geochemical evidence of a large bolide’s impact. This
anomaly at the boundary was found in many drill cores
from the deep oceanic drilling and onland sections.
The other evidence of the impact events include
shocked quartz; glassy spherules; microtektites; tsuna
mites; and, most important, impact craters with typi
cal structures. The Chicxulub crater 180 to 280 km in
diameter with an age of 65 Ma was first found on a
shelf of the Yucatan Peninsula in Mexico [51].
The KTB mass extinction is probably related to
other catastrophic impact events. The giant Shiva cra
ter in the Indian Ocean westward of Mumbai may be
its result [14]. It was identified by the geophysical,
structural, and drilling data at the Indian–Seychelles
plate. This buried elongated crater
600
×
450
km in
size and 12 km deep may represent the largest Phaner
ozoic impact structure. Its age was determined by the
basement of the Deccan lavas, the overlapping Paleo
gene sediments, and the isotope dating (65 Ma). The
sedimentary interlayers between the Deccan trap lavas
contain dinosaur bones and eggs. However, no dino
saur relics were found above the traps. Consequently,
the trap’s eruption by itself did not cause their extinc
tion: it began before the Shiva impact event [11]. The
asteroid impact could have shook the mantle and
strongly intensified the eruption precisely at the KTB,
which reinforced the catastrophic influence on the
biota.
In addition to the above mentioned craters, other
impact craters of this period are also known (see the
review in [3]): the Boltysh crater in the central part of
the Ukrainian shield; the Manson crater (a ring struc
ture) 35 km in diameter in Iowa in the United States;
the Kara crater near the Russian Arctic coast in the
mouth of the Ob River; and the sedimentburied Eagle
Butte crater 10 km in diameter in Alberta, Canada.
Based on the seismic data, the Silverpit impact crater
20 km in diamete r with a possib le age of 60–65 Ma wa s
found in the North Sea near the UK coasts in 2001.
Several impact structures were identified in Brazil,
e.g., the Vista Alegre crater 9.5 km in diameter in
Parana. The suggested age of the Eagle Butte and Vista

OCEANOLOGY Vol. 53 No. 6 2013
INTERACTION OF THE REASONS FOR THE MASS BIOTA EXTINCTIONS 745
Alegre str uctures i s less tha n 65 Ma (th e Paleoc ene and
earlier), which could be close to the KTB [16].
Thus, the review of the data shows that the Chicx
ulub; Shiva; Boltysh; Silverpit; and, probably, Manson
craters were formed at the KTB. A series of other cra
ters are the results of the impact events either at the
KTB or close to this boundary. Because the area of the
ocean significantly exceeds the continental one, the
majority of the asteroids could have undoubtedly
fallen into the ocean, where finding of craters is diffi
cult. Unambiguously, the Earth’s collided with several
cosmic objects at the Cretaceous–Tertiary boundary.
The ruinous influence of strong volcanic eruptions
and impact events on organisms is partially similar;
however, volcanic rocks, e.g., traps, erupt for a long
period and, consequently, gradually have an effect for
ten to a hundred thousand years. The fluctuations of
the temperature, sea level,
CO
2
content, and other
atmospheric components; the structure and chemistry
of the water column; the tectonic movements; etc.,
also gradually influenced the environment. In the end
of the Cretaceous, these factors, along with the volca
nism and possible relatively weak impact events, pro
voked the gradual or stepwise degradation and even
the extinction of some part of the marine organisms.
In contrast, the intense impact events are very rapid.
The catastrophic KTB events are consequently caused
mainly by the impacts of large asteroids.
Racki [56] casts doubts on the key influence of the
impact events on the mass extinction. He emphasizes
the revealed unsatisfactory correspondence of the
impact ages with the mass extinctions, excluding the
Cretaceous–Paleogene boundary. In addition, the
erroneous identification of the lithological, geochem
ical, and other features of the impact events and the
inaccurate dating of the real astroblems are possible.
This is justified; however, we mainly stand upon the
origin of the unfavorable intervals for the biota, when
impact events could have been one of the reasons
(locally or major) or, probably, triggered the event
chains leading to the mass extinctions. Nobody casts
doubts that all the craters yet have been found: each
year brings new ones. The majority of the astroblems
are sedimentburied in the ocean. At present, only
some of them are known, mostly, in the shelf area.
Thus, we may consider the impact events that were
only part of asteroid attacks.
The study of the mass extinction has revealed their
periodicity, temporal correlation, and casual relation
to the geological events [58]. Periodicity of 25–35 Ma
Tectonic s Mantle
plumes
Volc a n i s m
Asteroids Comets
Impact events
Orbital movement of the sun around the galaxy’s center
Intersection of the galaxy’s branches Oscillations relative to the plane
Emission CO
2
, SO
2
, Cl, F, CH
4
Ash, aerosols
Greenhouse effect Dimming of the atmosphere,
reduction of the UV radiation
Ocean stagnation Reduction of the photosynthesis
and the bioproductivity
Anoxia Destruction of the food chains
Mass extinction
The interrelations between the processes leading to mass biota extinctions.

746
OCEANOLOGY Vol. 53 No. 6 2013
BARASH
(mantle plumes/basaltic eruptions in the large volca
nic provinces and the death of genera of marine organ
isms), 60–62 Ma (the death of genera of marine
organisms, a change in the sea level, basaltic eruptions
in the large volcanic provinces), and 135–145 Ma (the
death of genera of marine organisms, changes in the
paleoclimates based on the oxygen isotopic data, and
glacial epochs) has been established. The longer correla
tions may be outlined with mantle plumes and large igne
ous provinces (160–170, 330, 550–730, and 820 Ma).
CONCLUSIONS
The available data have shown that a series of fac
tors, including independent: tectonic movements,
changes in the sea level and climate, volcanism, aster
oid impacts, variations in the composition of the
atmosphere and hydrosphere, the dimming of the
atmosphere by aerosols at volcanism and impact
events, etc., harmfully affected the organisms in some
periods (from hundreds of thousands of years to the
first million years). The UV rays sharply stopped pen
etrating to the Earth’s surface and the photosynthesis
and primary production were reduced, thus leading to
anoxia in the ocean and atmosphere and mass extinc
tions.
All these factors, which reduced the biodiversity,
are substantiated by paleontological, geological,
geochemical, isotopic, and other data. Some factors
are hierarchal, whereas no visible relations are found
for other factors. In addition, some of the listed events
occurred for a long time and could not have brought
about the abrupt catastrophic death of organisms on a
global scale. The hierarchy of the main events allows
us to distinguish the primary terrestrial (volcanism)
and cosmic (impact event) reasons for the mass
extinctions.
An hypothesis concerning the consequent geo
spheric processes leading to such events was put for
ward using the example of the Late Permian extinction
[33]. After the 50Ma stability of the geomagnetic field
(the superchron of the reverse polarity, 312–264 Ma),
the Earth’s system began to change ~265 Ma ago after
the Illawara polarity change, which reflected the dis
turbance of the stable condition of the Earth’s core
and mantle. The prolonged period of frequent inver
sions of the geomagnetic field began after this event.
These disturbances activated the movement of the
mantle flows; the plate tectonics; plume volcanism;
and dimming of the atmosphere by ash aerosols,
which hampered the penetration of the UV rays and
photosynthesis and caused acid precipitation and
cooling. Thus, the changes in the core and mantle
resulted in a series of geological, paleogeographical,
and biological events on the Earth’s surface, which led
to the great mass extinction 252–251 Ma ago at the
Permian–Triassic boundary.
A series of the above mentioned large impact events
occurred at the same time (~252–251 Ma), as well as
in the periods of other mass extinctions. The coeval
manifestation of mutually independent events testifies
to the common external reasons of the higherorder
beyond the solar system. The suggested reasons affect
the Earth’s processes; cause the collisions of asteroids
and comets with the Earth and other bodies of the
solar system; and, probably, influence, using the rays
and energy flows, changes in the gravitation and other
fields.
Several hypotheses are suggested. The gamma
radiation lights in our galaxy could have repeatedly
damaged the Earth’s biosphere. It is suggested [50]
that the Late Ordovician mass extinction, at least par
tially, could have been a result of this event. Such a
burst is manifested on the Earth as a powerful energy
impulse 10 s long. The sharp destruction of the ozone
layer results in an increase in the UV radiation, which
may explain some peculiarities of the biota’s extinc
tion and renewal. In addition, a gammaradiation
burst could be a reason for the global cooling and gla
ciation in the end of the Ordovician.
However, among the hypotheses relating the cos
mic processes with the biota’s evolution on the Earth,
Gillman and Ehrenler proposed the most probable
hypothesis [23], which accounts for the temporal
intervals and the periodicity of the cosmic and terres
trial events. This work examines the periods of the
greatest impacts, the carbon isotopic excursions, and
the formation of magmatic provinces, which are com
pared with the intervals of the largest mass extinctions
and changing of geological periods. Using some aver
age age estimations, the authors have identified a cer
tain relation of these events with the orbital movement
of the Solar system around the Milky Way’s center, the
intersection of the galaxy’s branches, and the oscilla
tions of the Solar system’s position relative to the gal
axy’s plane. Based on their data, the repetition of the
extinction events in the same points of different spiral
branches confirm the major (galaxy) source of the
extinctions and affected the geological, solar, and
extrasolar processes.
Three Phanerozoic geomagnetic superchrons are
considered as stable periods when the solar system
moved through the galaxy’s branches [70]: 120–84 Ma
(the positive Cretaceous superchron), 312–264 Ma
(the superchron of the reverse polarity), and ~485–
463 Ma (the Ordovician superchron) [55].
Numerous hypothetical schemes suggested by dif
ferent authors to explain the reasons and interrelations
of the natural events that may lead to mass biota
extinctions include the majority of such events. Most
of them are accompanying but not obligatory mem
bers in the consequent events related by the causal
effect and led to the mass biota extinctions. However,
they are present in the hypothetical schemes because
they occur during the reviewed processes.
These are, in my opinion, geomagnetic inversions,
which have a common reason, along with other events
in the internal geospheres, but they do not bring about

OCEANOLOGY Vol. 53 No. 6 2013
INTERACTION OF THE REASONS FOR THE MASS BIOTA EXTINCTIONS 747
the mass extinctions by themselves. These are also
plate tectonics, orogenesis, and changes in the inten
sity of the weathering and the continental runoff into
the ocean at climate changes and oscillations of the sea
level.
The rate of the processes leading to mass extinc
tions is of great importance. The deepwater anoxia
may develop gradually; however, it may reach the
ocean’s surface and become the reason for the fast
mass extinction of organisms inhabiting the entire
water column. The death of the plankton algae (the
major oxygen producers) results in a decrease in the
oxygen content in the atmosphere, as during the Per
mian–Triassic crisis, and the extinction also embraces
the terrestrial biota.
The intense volcanic eruptions in the magmatic
provinces and all their negative results also developed
for hundreds of thousands of years to millions years.
By themselves, they could not have caused the unex
pected rapid extinction. However, the harmful volca
nic results could have exceeded some tolerable limit.
Thus, terrestrial events leading to intense volcan
ism and cosmic events or the impacts of large asteroids
are probably caused by the orbital movement of the
Solar system around the galaxy’s center (figure). They
could have acted in the same more or less temporal
intervals as recorded for all the great mass extinctions,
except for the Ordovician.
However, mass biota extinctions may also occur
under only one event consequence evolving as a result
of volcanism or a large impact event. In this case, the
extinction probably has a lesser scale.
As seen from the scheme, volcanism and impact
events have similar results. In both cases, harmful
chemical elements and aerosols are ejected into the
atmosphere, which leads to the greenhouse effect,
warming, the dimming of the atmosphere, the ham
pering of the penetration of UV rays and the photosyn
thesis, the ocean’s stagnation, and anoxia. This results
in the bioproductivity’s reduction, the destruction of
the food chains, the violation of all the vital processes,
and the extinction of a significant part of the biota.
ACKNOWLEDGMENTS
This work was supported by program no. 28 of the
Presidium of the Russian Academy of Sciences “The
Origin of the Biosphere and the Evolution of Geobio
logical Systems” (subprogram no. 1).
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