Mass Extinction of Ocean Organisms at the Paleozoic–Mesozoic Boundary: Effects and Causes

Abstract

238 At the end of the Permian, at the boundary between the Paleozoic and Mesozoic (~251 Ma), the largest mass mortality of organisms in the Earth's history occurred. Up to 96% of the marine invertebrates became extinct. The biodiversity decreased from ~250 thousand species to less than 10 thousand. In addition, ~70% of the species of terrestrial vertebrates died off. The scale, specifics, and the time structure of this disaster and the reasons for it can be determined from various paleontological, lithological, petroo graphic, chemical, isotopic, and other types of data generated when examining the sediments of the Perr mian–Triassic boundary (PTB) interval. A specific feature of the Permian paleogeography was the existence of the supercontinent Pangea stretching from one pole to the other and of two oceans—Panthalassa and Thetys. The bed of the Perr mian–Triassic Superocean Panthalassa occupying twoothirds of the Earth's surface was almost comm pletely absorbed as a result of subduction. Fragments of middoceanic rocks were preserved as accretionary blocks near active continental margins. Sediments of the PTB interval in the central parts of the ocean are represented by shallowwwater carbonates of paleoaa tolls, and sediments of deeppwater regions, by silii ceous deposits. Sediments of peripheral and shelf seas were encountered in many parts of the presenttday continents.

Full text

ISSN 00014370, Oceanology, 2012, Vol. 52, No. 2, pp. 238–248. © Pleiades Publishing, Inc., 2012.
Original Russian Text © M.S. Barash, 2012, published in Okeanologiya, 2012, Vol. 52, No. 2, pp. 258–269.
238
At the end of the Permian, at the boundary between
the Paleozoic and Mesozoic (~251 Ma), the largest
mass mortality of organisms in the Earth’s history
occurred. Up to 96% of the marine invertebrates
became extinct. The biodiversity decreased from
~250 thousand species to less than 10 thousand. In
addition, ~70% of the species of terrestrial vertebrates
died off. The scale, specifics, and the time structure of
this disaster and the reasons for it can be determined
from various paleontological, lithological, petro
graphic, chemical, isotopic, and other types of data
generated when examining the sediments of the Per
mian–Triassic boundary (PTB) interval.
A specific feature of the Permian paleogeography
was the existence of the supercontinent Pangea
stretching from one pole to the other and of two
oceans—Panthalassa and Thetys. The bed of the Per
mian–Triassic Superocean Panthalassa occupying
twothirds of the Earth’s surface was almost com
pletely absorbed as a result of subduction. Fragments
of midoceanic rocks were preserved as accretionary
blocks near active continental margins. Sediments of
the PTB interval in the central parts of the ocean are
represented by shallowwater carbonates of paleoa
tolls, and sediments of deepwater regions, by sili
ceous deposits. Sediments of peripheral and shelf seas
were encountered in many parts of the presentday
continents.
During the disastrous events of the PTB interval,
archaic Paleozoic fishes (acanthodians and placo
derms) died off, as did trilobites, sea scorpions
(Eurypterida), graptolites, and fusulinids (bottom for
aminifera). Others survived the disaster with an abrupt
reduction in their biodiversity. 97% of the foraminifera
(Foraminifera), 99% of the radiolarians (Radiolaria),
79% of the bryozoans (Bryozoa), and 96% of the bra
chiopods (Brachipoda) became extinct with produc
tids characteristic of the Paleozoic completely disap
pearing. 59% of the bivalves (Bivalvia), 98% of the gas
tropods (Gastropoda), 97% of the ammonites
(Ammonoidea), 98% of the echinoderms (Echinoder
mata), and 59% of the ostracods (Ostracoda) also died
off [12, 16, 33–35].
The extinction of organisms occupying different
environmental niches was not simultaneous. Both the
extinction of biota and the global changes in the ambi
ent conditions occurred during two phases: the first
one at the boundary between the Middle and Late Per
mian (
Р
2
/Р
3
, 260 Ma) and the second at the PTB
(251–252 Ma) (Fig. 1).
A specific feature of the first phase is the predomi
nant deaths of benthos organisms (rugose coral,
fusulinids, brachiopods, bryozoans, etc) explained by
the beginning of oceanic anoxia. During the second
phase (PTB), the biodiversity decreased primarily due
to nekton and plankton. At both levels of the Per
mian–Triassic extinction, the ratios of the biomarkers
Mass Extinction of Ocean Organisms at the Paleozoic–Mesozoic
Boundary: Effects and Causes
M. S. Barash
Shirshov Institute of Oceanology, Russian Academy of Sciences, pr. Nakhimovskii 36, Moscow, 117218 Russia
email: barashms@yandex.ru
Received June 8, 2011
Abstract
—At the end of the Permian, at the boundary between the Paleozoic and Mesozoic (251.0 ± 0.4 Ma),
the largest mass extinction of organisms on the Earth occurred. Up to 96% of the species of marine inverte
brates and ~70% of the terrestrial vertebrates died off. A lot of factors were suggested and substantiated to
explain this mass mortality, such as the disappearance of environmental niches in the course of the amalgam
ation of the continental plates into Pangea, sea level fluctuations, anoxia, an elevated CO
2
content, H
2
S
intoxication, volcanism, methane discharge from gashydrates, climate changes, impact events (collisions
with large asteroids), or combinations of many of these reasons. Some of these factors are in subordination to
others, while others are independent. Almost all of these factors developed relatively slowly and could not
cause the sudden mass mortality of organisms globally. It could have happened when large asteroids, whose
craters have been discovered lately, fell to the Earth. It is suggested that the impact events “finished off” the
already suppressed biota. A simultaneous change in many of the factors responsible for the biodiversity,
including those not connected in a causeandeffect relationship, proves the existence of a common extrater
restrial cause that affected both the changes in the internal and external geospheres and the activation of
asteroid attacks (the Sun’s transit of spiral arms of our galaxy, the Sun’s oscillations perpendicularly to the
galactic plane, etc).
DOI:
10.1134/S000143701201002X
MARINE
GEOLOGY

OCEANOLOGY Vol. 52 No. 2 2012
MASS EXTINCTION OF OCEAN ORGANISMS AT THE PALEOZOIC–MESOZOIC 239
Radiolarians
Fishes/
Ammonoids
Rugoses
Calcarean
sponges
Bryozoans
Large
foraminifera
Small
foraminiferans
Articulate
brachiopods
Echinoderms
Gastropods
Bivalves
Stages MAOKOUAN WUJIAPINGIAN CHANGXINGIAN SCYTHIAN ANISIAN LADIN
260
Ma
Permian Triassic
250
Ma
Marine
reptiles
Scleractinia
NEKTON AND PLANKTON BENTHOS
conodonts
Fig. 1.
Development of some plankton, nekton, and benthos representatives during the Late Permian to Early Triassic (after [16],
with modifications). The dashed lines denote the “temporarily disappeared” taxa.
manifest values normally associated with anoxic con
ditions [50]. At first (
Р
2
/Р
3
), the anoxic conditions
developed in the deepwater environment, but they
later (PTB) spread to the shelves dragging the
chemocline to the ocean’s surface. Lowoxygen or
anoxic conditions embraced almost the entire mass of
the ocean waters (superanoxia).
During the Late Permian, large reef constructions
developed, while the end of the Permian was charac
terized by the termination of the longterm develop
ment of rugose and tabulate corals. The development
of reefs ceased for a period of 7–8 Myr. The environ
mental characteristics of the reefs at the PTB interval
correspond to the pattern of a reduction in the quan
tity of the atmospheric oxygen during the Permian [20].
After almost complete extinction at the PTB, there are
practically no radiolarians in the sediments for ~1 Myr.
The mass mortality of the radiolarians is explained by
the global collapse of the bioproductivity. The degra
dation of fusulinids and, equally, the simultaneous
similar development of bivalves and rugose corals
could also have been caused by the extinction of sym
biotic algae, which, in turn, was probably due to the
reduced insolation [42]. The quantitative examination
of the morphology of brachiopods indicated a consid
erable reduction in their shell sizes before, during, and
after the PTB interval [19]. The authors explain this by
a reduction in and the collapse of the primary produc
tion confirming the data on other organisms.
A detailed stratigraphic analysis of the rock
sequence from the Middle to Late Permian boundary
to the Lower Triassic was conducted in Chaotian,
China [22]. Two considerable mass disappearance
horizons were identified, one at the
Р
2
/Р
3
boundary,
and the other at the PTB. At each of the boundaries,
the biodiversity abruptly reduces, and later new fauna

240
OCEANOLOGY Vol. 52 No. 2 2012
BARASH
appears. Acid tuff layers are present at these disappear
ance horizons. Thus, the Late Permian biosphere
underwent the effect of strong explosive volcanism
twice. Both of the tuff layers were traced at the same
stratigraphic levels in South China and Japan, thus
confirming the largescale association between the
explosive volcanism and mass extinctions.
The rock sequences of the PTB interval in the
Meishan prefecture in South China were examined in
the greatest detail [24] (Fig. 2). A statistical analysis of
the distribution of 162 genera and 333 species from 15
different groups of marine organisms was conducted.
The extinction at the PTB occurred for 3 Myr both
before and after it. However, the extinction was the
most intense and sudden (for a period of less than 500
years) 251.4 Myr ago. The event coincides with an
abrupt reduction in the
δ
13
С
carb
and a ~100 times
increase in the number of presumably volcanic micro
spherules compared with the overlying and underlying
sediments. In the PTB region, interbeds of pyrite (evi
dence of anoxia) and volcanic ash are observed.
Finally, a rapid transgression occurred at the PTB (a
cosmopolitan conodont species
H. parvus
appeared).
An elevated Ir content was discovered, which is an
order of magnitude higher than the background con
centration in the Upper Permian and Lower Triassic
sediments [51]. This rock sequence and equally a
number of others are characterized by abundant fungi
spores, which is an indicator of a strong disturbance in
the land ecosystems.
The examination of the distribution of a number of
chemical components and the relationship between
the isotopes allows defining the ambient conditions
and the processes of their change during the Permian.
Siliceous midoceanic sediments in Japan and British
Columbia (Canada) reflect superanoxic conditions
(pyretic alteration, the sulfur isotope ratio, the
geochemistry of the organic matter, rare elements, and
dolomite concretions). The anoxia lasted for ~20 Myr
from the Late Permian to the Middle Triassic [20]. For
50 Myr before and after that interval, oxygensatu
rated waters dominated near the deepwater portion of
the seabed. The oxygen concentration in the atmo
sphere also reduced at the end of the Permian,
whereas, at the Carboniferous–Permian boundary, it
reached the maximum level of 35%. At the end of the
Permian, it decreased to 15% [45].
According to Hallam and Wignall [16], the princi
pal episode of global warming at the end of the Per
mian was caused by a strong increase in the
CO
2
con
tent in the atmosphere as a result of strong volcanism.
The level of atmospheric
CO
2
expressed as parts per
million by volume (
μ
L L
–1
) increased from 1500 to
3000 pCO
2
(
μ
L L
–1
)
during the period of 260–250 Ma
[41]. In combination with the reduced oxygen con
centration in the water, this created conditions for
δ
13
C, ‰
–2 012345
250
251
252
253
Permian Triassic
Ma
(PDB)
Species
Fig. 2.
Stratigraphic distribution of species in Meishan rock sequences and
δ
13
С
fluctuations (after [24], simplified).

OCEANOLOGY Vol. 52 No. 2 2012
MASS EXTINCTION OF OCEAN ORGANISMS AT THE PALEOZOIC–MESOZOIC 241
anoxia. Most scientists consider anoxia as a direct rea
son for the mass mortality of organisms, but others
believe that hypercapnia—CO
2
intoxication—was
more harmful [30]. Under the anoxic conditions of the
end of the Permian, the sulfatereducing bacteria
Chlorobiaceae could become dominant in the oceanic
ecosystems by discharging hydrogen sulfide, which
was deleterious for terrestrial and marine animals and
made the ozone layer of the atmosphere thinner. As a
result, organisms were exposed to increased deleteri
ous ultraviolet radiation [31]. In addition, hydrogen
sulfide intoxication by itself could be one of the rea
sons for the extinction [14].
During the Phanerozoic, the Mg/Ca ratio in the
sea water varied from 1.0 to 5.2, which was caused by
the predominant accumulation of either aragonite and
highmagnesium calcite (mMg/Ca > 2; “aragonite
seas”) or lowmagnesium calcite (mMg/Ca < 2; “cal
cite seas”). This ratio is governed by the mixing of the
hydrothermal waters of middle ridges and river waters
and is traced in the geological record (fluid inclusions
in primary marine halite, the Mg content in fossil sea
urchins and mollusks, and the primary mineralogy of
sediments of abiotic carbonates and marine evapor
ites). The Mg/Ca ratio in sea water varies in inverse
proportion to the global rate of growth of the oceanic
crust [40]. The end of the Paleozoic to the beginning
of Mesozoic was a period of predominantly aragonite
sedimentation. The rate of global rifting was therefore
minimal.
At the PTB, some isotope ratios changed abruptly.
The abrupt decrease in
δ
18
O
observed at the PTB
interval was caused by warming [16]. Negative devia
tions of the
δ
13
C
values were observed for both extinc
tion phases (P
2
/P
3
and PTB). At P
2
/P
3
, a 2–4‰ neg
ative shift in the
δ
13
C
values in the carbonates and
organic matter was discovered in marine (including
midoceanic) and terrestrial sediments in South
China, Japan, British Columbia (Canada), Greece,
and Armenia [20, 21, 24]. An unusually high positive
shift in
δ
13
C
(
5–7‰
) was observed before this negative
shift. The interval of positive deviations that lasted 3–
4 Myr was called the Kamura event. It may represent a
high bioproductivity interval caused by the activation
of vertical circulation. The following processes are
suggested to explain the rapid decrease in
δ
13
C
at the
PTB: a reduction in the supply of biogenic elements in
the euphotic zone, a decrease in the bioproductivity,
the effects of volcanism, weathering, gashydrate dis
charge, and biomass oxidation [16].
The negative shift in the
δ
13
C
in the rock sequences
of the PTB interval in South China might have been
caused by eruptions of the Siberian Traps, a change in
the supply ratio between the terrestrial and marine
organic carbon, or a change in the dominant commu
nities of marine organisms due to the changing envi
ronment. Thus, a transition from cyanobacteria to
phototrophic sulfuroxidizing bacteria is assumed for
the shelf environment due to the rise of euxinic water
to the photic zone. The diagenetic processes led to a
change in the isotope ratios [38, 39]. At both levels of
the Permian–Triassic extinction, the ratios of the
biomarkers manifest values normally associated with
anoxic conditions [50]. At first (
Р
2
/Р
3
), the anoxic
conditions developed in a deepwater environment,
but they later (PTB) spread to the shelves dragging the
chemocline to the ocean’s surface.
D. Erwin [12] believes that the only process that
can quantitatively correspond to the total global
decrease in the
13
C/
12
C
ratio of
~10‰
is methane dis
charge from gashydrates of marine sediments. This
occurs in the case of a rapid increase in the tempera
ture or a pressure decrease. Such a process might, for
instance, take place during the eruption of the lavas of
the Siberian Traps onto the beds of the neighboring
Arctic seas.
The reduction in the
87
Sr/
86
Sr
ratio at the end of the
Permian to the Phanerozoic minimum is explained by
the change in the weathering pattern during the land
aridization [20]. The aridization was caused by the
appearance of the giant supercontinent Pangea,
warming, and the formation of the atmospheric circu
lation system in which the supply of moisture in the
central parts of the continent was minimal.
A shift in the
δ
34
S
values was also observed at the
PTB interval. The following factors are suggested to
explain it: (1) the predominant withdrawal of
32
S
dur
ing the pyrite burial via the bacterial sulfate reduction
must have increased the
δ
34
S
in the evaporites [16];
(2) the formation of framboidal pyrite with wide
spread euxinic conditions [49]; (3) sulfur discharge
from the mantle during the impact event [25].
A number of hypotheses were suggested to explain
the extinction of organisms: the disappearance of
environmental niches in the course of the integration
of the continental plates into Pangea; a fall in the sea
level to the minimum value during the Phanerozoic;
transgressions; climatic fluctuations (in particular,
warming and acid rainfalls as a result of volcanism and
methane discharge from gashydrates); hypersalinity;
anoxia; elevated
СО
2
and
H
2
S
contents; volcanism. A
shift in the facies as a result of any changes (tempera
ture, sea level, etc) had an adverse impact, particularly
in the marginal and shallowwater regions. All these
factors that reduced the biodiversity are substantiated
by paleontological, geological, geochemical, isotopic,
and other types of data. Some of these factors are in
subordination to others, while obvious relations
between others are lacking or unknown. Why did dif
ferent processes harmful for the biota proceed simul
taneously within a limited time interval from the geo
logical viewpoint? Did asteroid impacts play any role
65 Myr ago at the Mesozoic–Cenozoic boundary and
during a number of other events of mass mortality of
organisms [1, 2]?
During the Permian, the sea level lowered to the
Phanerozoic minimum, which is associated with Pan
gea’s integration. This happened ~260 Myr ago [18].

242
OCEANOLOGY Vol. 52 No. 2 2012
BARASH
At the same time, a shortterm cooling probably took
place, which was determined from the Late Guade
loupean limestone from the lowlatitude regions of the
Panthalassa Ocean [21] and from the glacial tillite in
the high latitudes. A transgression followed it in the
Thetys region. A regression occurred again at the end
of the Permian (PTB). For a long time, rapid changes
in the sea level were considered as one of the major
reasons for the mass extinction of marine organisms.
However, the examination of a number of rock
sequences at the PTB interval in combination with an
improved conodont biostratigraphy cast doubt on the
importance of the transgression–regression patterns.
Although the end of the Permian is normally consid
ered to be a period of the low standing of the sea level,
new data indicate that mass extinction occurred dur
ing the phases of a rapid rise and expansion of the low
oxygen or anoxic deep waters in shallowwater envi
ronments [17]. Shelf communities suffered the most.
D. Kidder and T. Worsley [27] described the
changes in the climate system at the end of the Per
mian to the beginning of the Triassic and the associ
ated processes. During the Permian, the Hercynian
orogenesis gradually stopped, which weakened the
chemical weathering of silicates. The supply of bio
genic components in the biosphere was reduced
accordingly; it decreased even more as a result of the
increased
СО
2
content and warming. The polar ice
melting reduced the submersion of cold sea waters rich
in
О
2
and biogenic elements. The pole–equator tem
perature gradient decreased, upwellings relaxed, and
the productivity and carbonate sedimentation reduced
even more. As the climate became warmer, arid condi
tions embraced the middle latitudes causing a latitudi
nal expansion of the midlatitude atmospheric circu
lation Ferrel cells, while the polar cells reduced. The
increased coastal evaporation led to the submersion of
warm surface waters deficient in
О
2
and biogenic water
elements and to the formation of poorly circulated
bottom waters. These waters transported heat to the
high latitudes and rose in upwelling zones. When the
submersion of subpolar waters stopped, the ocean was
rapidly filled in with warm lowoxygen water. Trans
gressions brought anoxic conditions to the shelf
regions. Anoxia or hypoxia was a reason for the mass
extinctions, which is proved for the end of the Permian
by the investigations of the facies, geochemistry, and
biomarkers [14, 49]. Shortterm cold events are also
known for the end of the Permian; these periods
caused a shift in the facies and had an adverse effect on
the shelf ecosystems.
The comprehensive modeling of the climate condi
tions for the end of the Permian [29] indicated that the
sea surface temperatures (SST) in the tropical zone
were comparable to the presentday temperatures, but
those in the high latitudes were 8–10
°
C higher. The
salinity also increased. The modeling of the tempera
ture at the PTB interval for the inland parts of the
supercontinent Pangea manifested very high average
annual values (over 40
°
C) [28].
The most popular hypothesis tries to explain the
Late Permian extinction by largescale volcanism pri
marily due to the fact that the time ranges of these two
events coincide. Both basalt magmatism of midoce
anic ridges and withinplate magmatism existed. Fel
sic volcanism also made its contribution to the sup
pression of the Permian biosphere in a few large igne
ous rock provinces in East Pangea. Temporal
coincidence was noted between the basalt eruptions in
South China and the first phase of the biota’s extinc
tion at the end of the Permian, and also between the
largest eruptions of the Siberian Traps and the second,
principal phase of extinction.
Volcanism at the PTB, felsic and medium, was
widespread along the western edge of Panthalassa, in
South Primorye [48], South China [53], and Gond
wana [46]. It could have been associated with plate
convergence or rifting. The subsequent subduction hid
the sources of the eruptions. However, in South China
alone, the volcanoclastic rock layer covers over 1 mil
lion km
2
. The volcanism had an explosive nature. In
the case of such volcanism, enormous masses of gases
and ashes are discharged. The volcanism took place in
the carbonate sediment area, which led to a discharge
of large volumes of CH
4
and CO
2
supplementing the
effect of the Siberian Traps.
The Siberian Traps are a result of the largest volca
nic eruption in the Earth’s history (Fig. 3). Traps are
widespread on the entire East Siberian Platform, in
the Khatanga downfold, and in the Minusinsk depres
sion; there is a magmatic zone on the bed of the Kara
Sea as well. Apart from trap fields and interstratal lava
intrusions (sills), enormous regions within this volca
nic province are covered with volcanic tuffs—a result
of explosive eruptions. The trap province encompasses
~2 million km
2
; its initial size is estimated at 7 million
km
2
; and the volume of the lavas, at 1–4
×
10
6
km
3
[5].
The thickness of the volcanic rocks is occasionally
considerable, e.g., 3.5 km in the vicinity of Norilsk.
Siberian trap volcanism began
251.7
±
0.4
Myr ago and
relaxed
251.1
±
0.3
Myr ago. It was most intense
250.2
±
0.3
Myr ago. The coincidence of the time
interval of this eruption and the age of the PTB con
firms that this was the principal cause of the mass
extinction of organisms at the end of the Permian.
When up to
4
×
10
6
km
3
of volcanic material was
erupted within a short time (~0.6 Myr), large quanti
ties of
CO
2
, SO
2
, fluorine, and chlorine must have
been released quite rapidly to destroy the atmospheric
and biosphere systems [26]. These components of vol
canic outbursts to the atmosphere could affect the
ambient conditions. The discharge of
СО
2
led to glo
bal warming, and the release of
SO
2
and sulfate aero
sols resulted in global cooling. Halogens and their
compounds caused a reduction in the ozone content
and an increase in the deleterious ultraviolet radiation
[37]. Where the eruptions of the Siberian Traps

OCEANOLOGY Vol. 52 No. 2 2012
MASS EXTINCTION OF OCEAN ORGANISMS AT THE PALEOZOIC–MESOZOIC 243
occurred in the areas with coal fields and oil shales,
enormous volumes of
СО
2
and methane must have
been emitted into the atmosphere in the case of ther
mal metamorphism. This strengthened the green
house effect [43]. The marine sediments of the end of
the Permian that deposited immediately before the
mass mortality contain noticeable quantities of free car
bon that formed when coal and oil shales burned and
then spread wide. These carbon particles were similar to
the presentday products of coal burning and could have
poisoned the aquatic environment [13].
Thus, the eruptions caused a “volcanic winter” with
global cooling due to the aerosol screening of the
atmosphere with cinder particles, gas discharge, and
acid rainfalls poisonous to plants. The main basalt
eruption was followed by a “volcanic summer,” which
delayed the recovery of the biodiversity and enhanced
the ocean’s stratification. The decomposition of the
gas hydrates led to the emission of enormous quanti
ties of
СО
2
and methane into the atmosphere and a
very strong deleterious greenhouse effect. The rapid
global warming caused environmental changes harm
ful to the biosphere: weakening of upwellings, ocean
stagnation, and a decrease in the productivity. This
occurred twice, during the first and the second phases
of the Late Permian extinction.
Although the factors considered had an adverse
effect on the biodiversity, they developed relatively
slowly and could not have caused the sudden mass
mortality of organisms globally. The abrupt changes in
the environmental conditions could have possibly
been triggered by impacts of large asteroids or comets.
In is only in the recent years that the effect of impact
events has been proved. Material typical of impact
events was encountered at the PTB in a number of
rock sequences: shocked quartz in Antarctica and
Australia and Fe–Ni–Si and Fe–Ni fragments and
spherules and fullerenes with indicators of extraterres
trial gases (
3
He) in China and Japan (the latter possi
bly formed somewhat earlier). According to Kaiho
et al. [25], noticeable variations in the values of
34
S/
32
S
and
87
Sr/
86
Sr
in Chinese rock sequences of the end of
the Permian, along with high concentrations of impact
minerals and a considerable reduction in the contents
40
°
60
°
80
°
100
°
120
°
140
°
70
°
60
°
05001000
km
Kara
Sea
Laptev
Sea
Lake Baikal
Trap province Lava Tuff and tuffite
Fig. 3.
Siberian Trap Province (after [5, 23]).

244
OCEANOLOGY Vol. 52 No. 2 2012
BARASH
of Mn, P, Ca, and microfossils, prove the fall of an
asteroid or a comet to the ocean, which caused a mas
sive discharge of sulfur from the mantle to the ocean–
atmosphere system. This led to a considerable
decrease in the oxygen concentration, acid rainfalls,
and a biotic crisis. J. Théry et al. [44] present data on
the microspherules of a Cr/Nispinel of cosmic origin
in a number of rock sequences at the PTB, which was
exactly determined based on micropaleontological
data in Eastern Europe and the Caucasus region.
However, it is only in the recent years that actual
craters have been discovered (Fig. 4). Thus, evidence
of the sedimentburied Bedout (Bedoo) impact struc
ture was found on the northwestern continental mar
gin of Australia 25 km away from the coast (
18.18
°
S,
119.25
°
E) [9, 10]. Seismic and gravity surveys were
conducted there, and two holes were drilled to the
3000 m depth. An impact breccia was discovered a few
hundred meters thick with almost pure glass and disin
tegrated plagioclase grains. Just like in the Chicxulub
crater, there is a central uplift typical of large astrob
lemes in the center of the crater 180–200 km in diam
eter. Based on the plagioclase, the Ar/Ar age was esti
mated at
250.1
±
4.5
and
253
±
5
Ma, which corre
sponds to the PTB.
There are other known craters formed at the PTB
[11]. The Araguainha crater was discovered in Brazil
(
16.77
°
S,
52.98
°
W; 40 km in diameter) with an age of
~250 Ma according to [32] and
244.4
±
3.25
Ma
according to [11]. The 40 km wide Araguainha struc
ture is the largest crater in South America. The crater
penetrates horizontally lying sediments of the basin of
the Parana River in Central Brazil. The asteroid fell
~250 Myr ago. It had a diameter of 2–3 km and broke
through the 2 km thick sediments exposing crystalline
rocks of the basement on a 4 km wide territory. The
central uplift 6–7 km wide and the circular trough are
welldefined topographically. The impact melt has a
granite composition. During the Jurassic, the crater
was filled in with sediments and basaltic lavas.
The Arganaty crater in Kazakhstan is referred to
observed craters. It was discovered based on the results
of satellite photography [4]. The crater is located
between lakes Balkhash and Sasykkol. The inner circle
60 km in diameter reflects the pediment levee of the
crater. The diameter of the structure is up to 300–
315 km based on external arched faults. The circular
rim is over 700 m high and 7.5–11.5 km wide. The cra
ter and its circular structures are represented by sandy
sediments underlied by granites in the central portion.
The cosmogenic origin of the crater was confirmed by
petrographic studies (shocked quartz) and the exist
ence of circular magnetic and gravity anomalies.
There is an oval massif of leucocratic granites in the
center of the structure under an unconsolidated sedi
ment cover. The author believes that a release of gran
ite magma from a deep focus was initiated by a cos
mogenic explosion. Based on combined geological
and geophysical data, the age of the crater corresponds
to the PTB.
Inferred craters include the Falkland crater near
the coast of Argentina (
51
°
S,
60
°
W, 300 km in diam
eter, age 250 Ma). Less reliable craters are the follow
ing on the Siberian Platform: the Great Kuonamki
(
70
°
N,
111
°
E, diameter not available, age 251 Ma),
the Gulinskii Massif (
70.91
°
N,
101.2
°
E, over 50 km
in diameter, age 251 Ma), the Essei (
68.81
°
N,
102.18
°
E,
4.5 km in diameter, age 251 Ma), as well as the Alpian
crater in Europe (
43
°
N,
8
°
E, age ~250 Ma) and SAR
28 in Canada (56.57
°
N, 110.57
°
W, 7.5 km in diame
ter, age ~250 Ma) [11].
Numerous fragments of chondritic meteorites with
characteristic geochemical indicators, shocked
quartz, and extraterrestrial fullerenes with trapped
3
He
were discovered in argillite breccia of the PTB at
Graphite Peak in the Central TransAntarctic Moun
tains near the Beardmore Glacier in Antarctica [8].
Metallic grains were found similar to those encoun
tered in boundary layers in South China and Japan.
The age was determined from the paleobotanic and
isotopic data. The discovery confirms the occurrence
of a global impact event.
Such an event might be the largest impact event in
the Earth’s history that occurred in Wilkes Land, Ant
arctica [47]. A large negative magnetic anomaly was
discovered there; it coincides with a circular topo
graphic depression 243 km wide having a minimum
depth of 848 m with the center being at 70
°
S, 120
°
E.
In 2006, satellite gravity mapping detected a positive
gravity anomaly reflecting a protuberance of ultrama
fic mantle rocks, which is typical of large impact cra
ters. Subsurface radar mapping by NASA detected a
500 km crater located under the East Antarctic Ice
Sheet. It is assumed to be a consequence of the impact
of a 55 km asteroid that was 4–5 times greater than the
Chicxulub asteroid, which led to the mass extinction
of organisms 65 Myr ago. The impact caused the rise
of a 200 km dome of mantle material. Based on the
gravity data, this impact event occurred ~250 Myr ago.
Along with the large Bedout impact event and others,
this impact event probably was the most important
reason for the sudden mass extinction of organisms at
the PTB. No geological samples have been collected
from under the ice sheet yet, and direct evidence is
required to confirm the occurrence of the impact
event. There are also other hypotheses regarding the
origin of this structure: the formation of a mantle
plume or the manifestation of different largescale
volcanic activity.
The consequences of the impacts of large asteroids
(even more so a number of them occurring within a
short time interval) must have exerted a deleterious
influence on marine and terrestrial organisms [7]. The
lighting intensity reduced and temperature changes,
acid rainfalls, and fires happened. Global expansion of
dust clouds consisting of fragmented rock of the
Earth’s crust thrown out of the crater and the material

OCEANOLOGY Vol. 52 No. 2 2012
MASS EXTINCTION OF OCEAN ORGANISMS AT THE PALEOZOIC–MESOZOIC 245
of the cosmic body weakened the photosynthesis and
disturbed the entire food chain. The effect must have
been strengthened by fires. The outburst of water vapor
to the atmosphere when the asteroid fell to the ocean
must have triggered a greenhouse effect. The impact of
the asteroid on carbonate rocks with high contents of
CaCO
3
and
CaSO
4
resulted in an increase in the con
tents of
CO
2
and sulfurous aerosols in the atmosphere.
This must have led to acid rainfalls and a few degrees
temperature increase.
According to Isozaki et al. [20], changes in the geo
systems began ~265 Myr ago, when, after 50 Myr of
the geomagnetic field’s stability, the Illawarra Reversal
occurred. After it, a long period of frequent changes in
the geomagnetic field began. This event caused by
changes in the condition of the Earth’s nucleus and
mantle manifested itself on the Earth’s surface as a
series of the abovelisted events.
Extraterrestrial cosmic causes probably triggered
both changes in the Earth’s spheres and asteroid
attacks. The influence of outer space on earthly pro
cesses was suspected as early as in the first half of the
20th century (V.I. Vernadskii, A.L. Chizhevskii,
M. Milankovich, etc) and has been studied since the
mid20th century. The influence of solar activity fluc
tuations, the interaction of the Earth and the Moon,
the Earth’s orbital revolution, and collisions of cosmic
bodies—asteroids and comets—with the Earth were
considered. In the recent years, studies in this direc
tion have been actively conducted. The reasons for the
geological periodicity normally mentioned are
changes in the gravity potential of the Galaxy at differ
ent distances from its center, variations in the rate of
the Sun’s orbital motion, the Sun’s transit of spiral
arms of the Galaxy, its oscillations perpendicular to
the galactic plane, etc.
The period of the Sun’s orbital motion in the Gal
axy (200–300 Myr) is compared to the duration of the
geological eras. The time required to transit a galactic
arm is 20–30 Myr, and the time during which the
Solar system is exposed to the effect of galactic shock
waves is 4–5 Myr [6]. These periodic intervals are
associated with the boundaries between differentlevel
subdivisions of the stratigraphic scale of the Phanero
zoic. Geological and, primarily, paleontological
changes occurring every 0.1–10 Myr can be explained
either by collisions of large solitary asteroids a few
kilometers in size with the Earth or by asteroid
attacks—the fall of a series of asteroids to the Earth
[36, and others]. A.A. Barenbaum [3] believes that the
mortality of organisms and the activity of tectonic pro
cesses abruptly increase when the Sun is in the regions
of gas condensation and star formation within the
galactic arms.
The estimates of the ages of the impact craters cor
relate with the events of mass extinction of organisms
(Fig. 5). Mass extinctions have a periodicity of 26–
30 Myr, and the series of welldated impact craters has
periodicities of
30
±
0.5
and
35
±
2
Myr [36]. The
abovementioned cosmic phenomena of similar fre
quency are suggested to explain this quasiperiodicity.
As regards mass extinctions of organisms, given that
these events were sudden and shortlived, they can
only be explained by rapid disastrous changes in the
ambient conditions caused by the impacts of large
asteroids.
120
°
60
°
0
°
180
°
30
°
0
°
2
6
9
8
7
1
3
5
I
II
III
120
°
60
°
30
°
30
°
30
°
0
°
60
°
60
°
60
°
10
STP
120
°
60
°
0
°
180
°
120
°
60
°
4
60
°
Fig. 4.
Presentday positions of craters of the PTB interval [11] and Siberian Trap Province (STP). Craters: (
1
) Bedout, (
2
) Ara
guainha, (
3
) Arganaty, (4) Wilkes, (
5
) Falkland, (
6
) Great Kuonamki,
(7
) Gulinskii, (
8
) Essei, (
9
) Alpian, (
10
) SAR 28. Crater
diameters (km): (I) >100, (II) 100–10, (III) <10. Black circles denote observed impact craters, and white circles, inferred or pos
sible craters.

246
OCEANOLOGY Vol. 52 No. 2 2012
BARASH
Fig. 5.
Association between abiotic factors and the mass extinction of organisms at the Permian–Triassic boundary (after [52]; ocean level after [15] with modifications). Cli
mate: W—warmer, C—colder.
Interaction of
internal geospheres Earth surface system
T
2
T
1
P
3
P
2
240
250
260
270
Mz
Pz
T–J
C–P
inverse.
variable
Siberian
Traps
Chinese
basalt
Ocean
level
0+100 m
δ
13
C, ‰ Ocean
chemistry
–+
Aragonite
and Mg/Ca
Anoxia
δ
34
S
Atmosphere
Climate
W C
methane
discharge
Outer
Impact
craters
Biodiversity
Extinction,
Phase 2
Extinction,
Phase 1
–+
Permian Triassic Stratigraphy
Ma
Pangea integration Plate
motions
Geoid
transition
P–T superchron
variable
Geomagnetic
polarity
Volcanism
Evaporites
–2 0 2 4
Evaporites
space

OCEANOLOGY Vol. 52 No. 2 2012
MASS EXTINCTION OF OCEAN ORGANISMS AT THE PALEOZOIC–MESOZOIC 247
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