Environmental Changes in the Neogene and the Biotic Response

Abstract

Among the abiotic factors that determined via the paleoceanographic processes development and evolution of the oceanic biota
in the Neogene, noteworthy are the tectonic, volcanic, climatic and extraterrestrial events. The most important tectonic events
of such kind include the subsidence of the Faroe-Iceland Threshold 14–13 Ma ago, the closure of the Tethys Ocean in the east
19–12 Ma ago, the orogenesis in the western Mediterranean region and closure of the Mediterranean Sea (Messinian Crisis) 5.59–5.33
Ma ago, the formation of the Central American Isthmus 6.0–3.5 Ma ago, and the opening of the Bering Strait that occurred (according
to different data) in the period of 7.4 to 3.1 Ma ago. The most significant climatic consequence resulted from the formation
of the Circum-Antarctic Current, the irregular growth of the Antarctic ice shield, the cooling in the Arctic region 3.2–3.1
Ma ago, and the development of continental glaciations in the Northern Hemisphere approximately 2.5 Ma ago. The variations
in the atmospheric CO2 content are correlative with the climatic fluctuations. The entire Cenozoic climatic record reflects the influence of the
orbital parameters of the Earth. The Neogene was marked by several significant extraterrestrial events: the fireball falling
in southwestern Germany in the middle Miocene 14.8–14.5 Ma ago probably accompanied by enhanced volcanic activity particularly
in the rift valley of eastern Africa; the drastically increased influx of interplanetary dust due to the disruption caused
by a large asteroid in the late Miocene 8.3 ± 0.5 Ma ago, the fall of a large (>1 km in diameter) asteroid in the Eltanin
Fault zone of the Southern Ocean in the terminal Pliocene 2.15 Ma ago; and the explosion of a supernova star, which was probably
responsible for the partial extinction of marine organisms at the Pliocene-Pleistocene transition approximately 2 Ma ago.

Full text

ISSN 00014370, Oceanology, 2011, Vol. 51, No. 2, pp. 306–314. © Pleiades Publishing, Inc., 2011.
Original Russian Text © M.S. Barash, 2011, published in Okeanologiya, 2011, Vol. 51, No. 2, pp. 319–328.
306
According to the resolution of the International
Commission on Stratigraphy, the Neogene as a geo
logical period and system commenced
23.03
±
0.05
Ma
ago and terminated 2.588 Ma ago to be followed by the
Quaternary Period. The Neogene is divided into geo
logical epochs: the Miocene (23.0–5.33 Ma ago) and
Pliocene (5.33–2.588 or 5.33–1.806 Ma ago, accord
ing to the other standpoint) [28]. The Miocene is sub
divided into the early (23.03–15.97 Ma ago), middle
(15.97–11.608 Ma ago), and late (11.608–5.332 Ma
ago) subepochs.
In the Miocene, the continents continued moving
to their presentday positions, although North and
South America remained separated. The collision of
the Indian Plate with Asia was in progress and respon
sible for orogenic processes. In the period of 19 to
12 Ma ago, the Tethys Ocean was closing in the east
owing to the joining of Africa and Eurasia in the Turk
ish–Arabian region. The subsequent orogenic pro
cesses in the western Mediterranean region and the sea
level fall in the terminal Miocene resulted in the tem
poral desiccation of the Mediterranean Sea (Messin
ian salinity crisis). By the onset of the Neogene, the
deep strait was formed between Tasmania and Antarc
tica and simultaneously the Drake Passage was
opened. This stimulated the further development of
the CircumAntarctic Current and the thermal isola
tion of Antarctica, which resulted in the temperature
falling and the growth of the continental ice shield. In
the Tortonian approximately 9 Ma ago, the water
exchange between the Pacific and Indian oceans in the
tropical zone was weakening due to the rise of the
Malay Archipelago, and this process was in progress
also through the Pliocene and Pleistocene. This
resulted in the formation of a warmwater pool in the
western Pacific and cooling in the adjacent Indian
Ocean [13].
Tectonic movements in the western and eastern
part of the Mediterranean region (Terminal Tethyan
event) led to the separation of the Pacific and Atlantic
realms and the initiation of the Indian Ocean and
Mediterranean Sea. In the period of the Eocene to
early Oligocene, the similarity between the faunas of
Europe and North Africa in the west and East Africa
and western India in the east started decreasing. Most
researchers believe that, by the beginning of the mid
dle Miocene, the biota of these regions was developing
autonomously [35].
During the Miocene, the climate experienced sig
nificant fluctuations. The Miocene climatic events
Environmental Changes in the Neogene
and the Biotic Response
M. S. Barash
Shirshov Institute of Oceanology, Russian Academy of Sciences (IO RAN), pr. Nakhimovskii 36, Moscow, 117997 Russia
Email: barashms@yandex.ru
Received May 5, 2009
Abstract
—Among the abiotic factors that determined via the paleoceanographic processes development and
evolution of the oceanic biota in the Neogene, noteworthy are the tectonic, volcanic, climatic and extrater
restrial events. The most important tectonic events of such kind include the subsidence of the Faroe–Iceland
Threshold 14–13 Ma ago, the closure of the Tethys Ocean in the east 19–12 Ma ago, the orogenesis in the
western Mediterranean region and closure of the Mediterranean Sea (Messinian Crisis) 5.59–5.33 Ma ago,
the formation of the Central American Isthmus 6.0–3.5 Ma ago, and the opening of the Bering Strait that
occurred (according to different data) in the period of 7.4 to 3.1 Ma ago. The most significant climatic con
sequence resulted from the formation of the CircumAntarctic Current, the irregular growth of the Antarctic
ice shield, the cooling in the Arctic region 3.2–3.1 Ma ago, and the development of continental glaciations
in the Northern Hemisphere approximately 2.5 Ma ago. The variations in the atmospheric CO
2
content are
correlative with the climatic fluctuations. The entire Cenozoic climatic record reflects the influence of the
orbital parameters of the Earth. The Neogene was marked by several significant extraterrestrial events: the
fireball falling in southwestern Germany in the middle Miocene 14.8–14.5 Ma ago probably accompanied by
enhanced volcanic activity particularly in the rift valley of eastern Africa; the drastically increased influx of
interplanetary dust due to the disruption caused by a large asteroid in the late Miocene 8.3 ± 0.5 Ma ago, the
fall of a large (>1 km in diameter) asteroid in the Eltanin Fault zone of the Southern Ocean in the terminal
Pliocene 2.15 Ma ago; and the explosion of a supernova star, which was probably responsible for the partial
extinction of marine organisms at the Pliocene–Pleistocene transition approximately 2 Ma ago.
DOI:
10.1134/S0001437011020019
MARINE
GEOLOGY

OCEANOLOGY Vol. 51 No. 2 2011
ENVIRONMENTAL CHANGES IN THE NEOGENE 307
were responsible for the Late Cenozoic cooling, which
stimulated the formation of the presentday biota. The
main driving forces of these processes were the varia
tions in the atmospheric
СО
2
contents (Fig. 1). Their
measurements in many wood samples revealed strong
fluctuations (Fig. 1). The periods of low
СО
2
concen
trations correspond to the phases of continental glaci
ations in Antarctica, while their increase up to
500 ppmv coincides with the Miocene climatic opti
mum.
The paleotemperatures derived from the
δ
18
О
vari
ations in the CaCO
3
of the benthic foraminiferal tests
[10] indicate warming (Miocene optimum) in the ter
minal early–initial middle Miocene; cooling in the
terminal middle–initial late Miocene; warm climatic
conditions likely through most of the late Miocene,
early Pliocene, and in the Eopleistocene; and an
unstable climate with alternating short warming and
cooling periods in the terminal late Miocene (Messin
ian), late Pliocene, and glacial Pleistocene.
The climatic fluctuations of the Pliocene affected
the distribution of microfossils in all the sedimentary
sections of the World Ocean. For example, according
to the deepsea drilling data [31], a moderately cold
climate in the early Miocene was characteristic of the
Australian region, which is reflected in the develop
ment of the foraminiferal species
Globoturborotalia
woodi.
In the terminal early Miocene, it was replaced
by warm (up to subtropical in the initial middle
Miocene) conditions evident from the occurrence of
abundant
Globigerinoides, Orbulina
, and
Globorotalia
representatives. These events correspond to the global
warming during the Miocene climatic optimum.
The marine biota responded to the global climatic
fluctuations by the migration of biogeographic prov
inces and changes in the abundance of different organ
isms. At the beginning of the early Miocene, the tem
peratures of the surface waters in the high and middle
latitudes were higher as compared with their present
day values, being maximal for the entire Miocene. The
gradient between the equatorial and polar latitudes
was as high as 8–13
°
C. Judging from the oxygeniso
tope ratios in the planktonic foraminifers that popu
lated different depths, the equatorial divergence zone
was practically missing at that time [4]. The pale
oceanographic reorganization in the initial Neogene
provoked the development of latitudinal biogeo
graphic communities with progressively increasing
taxonomic differences. It stimulated the evolutionary
radiation of planktonic foraminifers and radiolarians
as well. The period of 22.5 to 21.0 Ma ago was charac
terized by the advance of thermophilic thanato
coenoses to high latitudes of both hemispheres and
their low differentiation. Based on the deepsea drill
(а) (b)
Miocene
Oligocene
LateEarly Middle
8
12
16
20
24
Ma
Expansion of the
East Antarctic
ice shield
Climatic
optimum
Glaciation
4200 300 400 500 600 700 –1 0 1 2 3 4
CO
2
, ppmv
Δ
T
,
°
C
Late
Fig. 1.
Variations in the atmospheric CO
2
concentration (a) and the global average air temperature (b) through the Miocene (after
[30], reduced).

308
OCEANOLOGY Vol. 51 No. 2 2011
BARASH
ing materials, the following assemblages of planktonic
foraminifers were defined for the Neogene biostrati
graphic foraminiferal zones N4–N21 and different
biogeographic zones: equatorial (E), equatorial–trop
ical (ET), tropical (T) subtropical (ST), temperate
(TM), and subpolar (SP). The assemblages made it
possible, in turn, to reconstruct these zones [1]. Figure 2
illustrates the migration of their boundaries. In this
work, reconstructions based on other microfossil
groups (calcareous nannoplankton, diatoms, radiolar
ians) are presented. The reconstructed positions of the
biogeographic zones based on the study of microfossils
in deepsea drilling cores are consistent with the pale
oclimatic estimates obtained by other methods.
The comprehensive paleoclimatic investigations
based on the distribution of the planktonic foramin
iferal assemblages in deepsea drill cores (interval of
the upper Oligocene Zone P21 to the lower Miocene
Zone N5) were also carried out in the Atlantic, Indian,
and southern Pacific oceans [37].
Defining the groups of species as biogeographic
indices, the authors compiled paleoclimatic curves,
outlined the positions of the biogeographic provinces,
and established pulses in the upwelling development.
They revealed also cooling and strong climatic insta
bility at the terminal Oligocene (Zone P22)–initial
Miocene (Zone N4) transition and warming in the
early Miocene (the upper part of Zone N4 and Zone
N5). The species
Paragloborotalia kugleri, Globorota
loides hexagonus, Globorotaloides stainforthi
, and
proten
tellids
were accepted to play the role of upwelling indi
cators. The abundances of these species combined
with radiolarians, diatoms, and sponge spicules,
allowed the upwelling pulses to be defined for the ini
tial Miocene.
Among the abiotic factors affecting the biota’s
development via the climate, noteworthy are the
Milankovitch orbital variations, which are observable
through the entire Cenozoic. In the oceanic sedi
ments, the latter are reflected by the periodic accumu
lation of carbonates and organic matter, which is
determined by the migrations of climatic belts and
corresponding variations in the paleohydrologic char
acteristics and bioproductivity.
The presentday thermohaline circulation appeared
13.2 Ma ago, when the Scotland–Faeroe–Iceland–
Greenland threshold subsided to a depth sufficient for
penetration of the Arctic Bottom Water into the Atlan
tic. During the Messinian, the formation of this bot
tom water in the North Atlantic terminated due to the
salt deficit after the closure of the Mediterranean Sea.
The presentday deepwater circulation was restored
when the Mediterranean Sea opened again at the
beginning of the Pliocene [14].
In the terminal early–middle Miocene, the situa
tion in the deepwater North Atlantic was subjected to
substantial transformation: the biogenic siliceous sed
imentation was almost completely replaced by the car
bonate and terrigenous one, presentday communities
of benthic foraminifers occupied the oceanic bottom,
and the deep waters became enriched in
13
C, which
indicates their young age [12]. All these processes are
related to the tectonic subsidence of the Faeroe–Ice
land Ridge and the significant flow of cold bottom
waters from the Norwegian–Greenland basin 14–
13 Ma ago [15].
The influx of surface Atlantic waters to the Norwe
gian Sea in the middle Miocene is reflected in the
occurrence of subtropical diatom taxa in this basin [7].
Based on the similarity of the generic composition of
the diatom assemblages, A.P. Jousé also assumed the
water exchange with the North Pacific.
Since the middle Miocene until recently, the biodi
versity grew both in the tropical and temperate lati
tudes, although this process was more rapid in the
tropical zone [19]. Its growth was probably explained
by the progressively increasing temperature differenti
ation. The tropical–subtropical province of plank
tonic foraminifers in the Atlantic was significantly
reduced, and coldresistant assemblages of calcareous
nannoplankton became distributed up to the tropical
latitudes [26]. The tropical zone of the Pacific Ocean was
populated approximately 15 Ma ago by the most thermo
philic silicoflagellate community, and its water tempera
tures were maximal for the entire Neogene [18].
The middle Miocene (14.8–14.5 Ma ago) was
marked by an extinction episode among the terrestrial
and aqueous organisms [8]. According to the maximal
estimates, up to 30% of the mammal genera became
extinct at that time. One of the possible causes respon
sible for this phenomenon is a fireball falling, which is
reflected in the formation of a crater in southwestern
Germany (Nördlinger Ries crater). It is also conceiv
able that it was related to the elevated volcanic activity:
ash ejections particularly in the rift valley of eastern
Africa, which presumably caused global cooling and
the advance of the East Antarctic ice shield, were max
imal at that time.
The cooling in the terminal middle Miocene
affected the distribution of the diatom assemblages:
ArctoBoreal and Antarctic provinces were formed in
the Pacific approximately 11 Ma ago. In the Norwe
gian Sea, coldresistant species became a permanent
element of the radiolarian communities [5]. Thanato
coenoses of planktonic foraminifers in the World
Ocean retreated to the low latitudes, particularly in the
Southern Hemisphere.
Despite the climatic fluctuations, the late Miocene
was marked by a general tendency for cooling. Ice
fields were developed in the Norwegian Sea and near
Alaska. According to [16], the Miocene–Pliocene
transition was marked by the formation of the Malvi
nas Current, which significantly reduced the tempera
tures on the Argentine shelf and pushed the biogeo
graphic boundaries northward. The West Antarctic ice
shield and shelf glaciers were presumably formed at
that time as well. The growth of the global temperature
gradients stimulated the further intensification of the

OCEANOLOGY Vol. 51 No. 2 2011
ENVIRONMENTAL CHANGES IN THE NEOGENE 309
N70
°
60
°
50
°
40
°
20
°
10
°
0
°
S
0
Ma
1.8
3.0
4.0
5.0
6.0
10.5
11.7
15.0
17.0
21.0
22.5
N21
N20
N19
N18
N17
N14
N13
N8
N4
60
°
50
°
40
°
30
°
10
°
30
°
20
°
early middle late
Miocene Pliocene
SP T
SPTM
?
E
ET
early
late
ST SP
ST
ST
ST
ST
ST
ST
ST
ST
ST
ST ST ST
STST
TM
TM
T
T
TT
T
T
T
T
T
TT
TT
T
ET
ET
ET ET
ET
ET
ET
TETTET
TET TET
N10
°
0
°
S
0
Ma
1.8
3.0
4.0
5.0
6.0
10.5
11.7
15.0
17.0
21.0
22.5
N21
N20
N19
N18
N17
N14
N13
N8
N4
60
°
50
°
40
°
30
°
10
°
20
°
early middle late
Miocene Pliocene
SP
T
late
ST
ST
ST
T
T
ST
T
ST
ST
ST
ST SP
SP
SPT
T
T
T
?
??
?
ET
ET
ET
ET
ET
ET P
E
E
E
E
E
E
ET
(a)
(b)
Fig. 2.
Meridional migrations of the boundaries between the biogeographic zones of the planktonic foraminifers in the Atlantic
(a) and Indian (b) oceans. Reconstruction by Os’kina and Ivanova [1]. (N4–N21) biostratigraphic zones. Biogeographic zones:
(ET) equatorial–tropical, (T) tropical, (ST) subtropical, (TM) temperate, (SP) subpolar, and (P) polar.
early
TM
TM
TM
TM TM
TM
TM
TM
TM
TM
TM
TM
TM

310
OCEANOLOGY Vol. 51 No. 2 2011
BARASH
oceanic and atmospheric circulation, which was
responsible for the enhanced biogenic siliceous accu
mulation both in the Southern Ocean and equatorial
realm as well as along the periphery of the Pacific
Ocean. Simultaneously, a stable upwelling zone
appeared near Southwest Africa. Under conditions of
intensified upwellings and increased bioproductivity,
many shallow areas such as, for example, the south
eastern Australia shelf, the Campbell and Chatham
plateaus, the Agulhas Bank, the Florida shelf, and the
Yamato Bank in the Sea of Japan [2] accumulated
phosphatebearing sediments, which subsequently
were transformed into phosphorites during the
Messinian regression.
The growth of the Antarctic ice shield was accom
panied by regression and the sealevel fall by 40 to 70 m
according to different estimates. This sealevel fall and
closure of the Bethic Strait (Spain) interrupted the
water exchange between the ocean and Mediterranean
Sea, which turned in the Messinian into a system of
large inner lakes (5.59–5.33 Ma ago). The thick
evaporite sequences accumulated in these basins (ca
10
6
km
3
) with salt reserves 40 times exceeding its con
tent in the Mediterranean Sea water under salinity
close to the normal one [36] implies that the eposodic
or permanent influx of oceanic waters and their evap
oration lasted for a relatively long period (several ten
thousands of years). The corresponding salinity
decrease in the ocean by 6‰ raised the water’s freez
ing temperature, which should have intensified the ice
formation in the ocean and increased the albedo. Sim
ilar processes also occurred in the deeps of the Persian
Gulf and Red Sea, where comparable evaporate
sequences were deposited [3]. The cessation of the
highsaline water flow from the Mediterranean Sea to
the northeast Atlantic resulted in the transformation
of the benthic foraminiferal assemblages.
The growth of the temperature gradients between
the high latitudes and the equatorial zone stimulated
the development of latitudinal biogeographic assem
blages. Judging from the distribution of the planktonic
foraminifers, the migrations of the biogeographic
boundaries in the terminal Miocene reflect the com
plex sometime differently directed climatic changes.
The most significant feature in common was the
enhanced biogeographic differentiation in response to
the global growth of the temperature gradients
between the high and low latitudes.
In the late Miocene (
8.3
±
0.5
Ma ago), the destruc
tion of a 150km cosmic body produced the Veritas
group of asteroids. The flow of interplanetary dust to
the Earth’s surface increased four times to die off
1.5 Ma later [23]. The peaks of the cosmic
3
He con
tents that reflect this event approximately 8 Ma ago
correspond in ODP Holes 757 (Indian Ocean) and
926 (West Equatorial Atlantic). In the last hole, this
level is marked by the replacement of illite by kaolin
ite, which reflects the climatic changes. The latter nat
urally affected the development of the marine biota.
The Pliocene (5.332–1.806 Ma ago) is subdivided
into three stages: the Zanclean (5.332–3.600 Ma ago),
Piacenzian (3.600–2.588 Ma ago), and Gelasian
(2.558–1.806 Ma ago) [28]. In the Pliocene, the cool
ing that started in the Miocene was in progress to form
continental ice shields, particularly in Antarctica
(although, judging from palynological data, vegetation
still existed in this region at that time). Subtropical
biogeoprovinces were displaced toward the equator.
The formation of the Antarctic ice shield is reflected in
the significant shift of the oxygenisotope ratio and the
appearance of icerafted material (gravel and pebbles)
in the sediments of the North Atlantic and North
Pacific [40]. The Pliocene was marked by the transi
tion of the warm climate to a cold one, which was
dominant in the Pleistocene and provoked cyclic gla
ciation in the Northern Hemisphere.
According to various data, the global climate of the
early and middle Pliocene was generally warmer as
compared with that in the late Miocene and late
Pliocene. The Antarctic glaciations became reduced
to cause transgression. In the Labrador Sea, the
assemblage of planktonic foraminifers includes tropi
cal species, which is explained by the penetration of
the Gulf Stream jet into this region until the middle
Pliocene, when the northern continental glaciations
commenced [11]. According to V.V. Mukhina and
G.Kh. Kazarina [1], the tropical diatom assemblage in
the North Pacific was located 4.3 Ma ago
30
°
–40
°
to
the north of its middle Miocene position (11 Ma ago)
and the ArctoBoreal community was replaced by the
Boreal one. The cooling 4–3 Ma ago was responsible
for the displacement of the planktonic foraminiferal
thanatocoenoses in the bottom sediments: equatorial
thanatocoenoses disappeared from the Pacific and
Atlantic oceans, while, in the Indian Ocean, their dis
tribution areas became reduced, the boundaries of the
biogeographic zones retreated toward the equator, and
the Polar thanatocoenosis that existed in the late
Miocene appeared again near Antarctica. The surface
circulation was intensified.
The tectonic event that happened by the beginning
of the late Pliocene significantly affected both the
paleoceanographic situation and the climatic system.
The Central America Isthmus, which appeared 3.5–
3.1 Ma ago [29], blocked the water exchange between
the Atlantic and Pacific oceans in the tropical lati
tudes, which resulted in the intensification of the Gulf
Stream and the North Atlantic Current. These pro
cesses affected the width and intensity of the equato
rial current and the associated upwelling, the balance
of nutrients, the biological productivity, and the devel
opment of the oceanic flora and fauna. They also stim
ulated the formation of the continental ice shields in the
Northern Hemisphere and the appearance of ice in the
Arctic region. This was accompanied by the significant
expansion of the Antarctic polar waters. In both hemi
spheres, numerous climatic fluctuations resulted in sea
level oscillations, opening/closure of straits, flood

OCEANOLOGY Vol. 51 No. 2 2011
ENVIRONMENTAL CHANGES IN THE NEOGENE 311
ing/drainage of shelves, and increases/decreases in the
sizes of the epicontinental seas. The complex feedbacks
determined the global paleoceanographic, climatic,
and biogeographic changes.
The oxygenisotope ratios in the marine microfos
sils demonstrate that the cooling in the high and mid
dle altitudes of the Northern Hemisphere initiated
suddenly 3.2–3.1 Ma ago and large ice shield started
forming approximately 2.5 Ma ago. Glaciations until
ca 0.9 Ma ago reflected the orbital cycles with a peri
odicity of approximately 41 ka and subsequently with
a periodicity of ca 100 ka. The longperiod climatic
changes in the North Atlantic through the Neogene
were likely caused by tectonic processes: closure of the
Panama Seaway and rise of the Tibet Plateau [38].
The cooling in the South Atlantic approximately
3.5 Ma ago affected the composition of the benthic
foraminiferal assemblages on the Rio Grande Rise and
in the Vema Channel [27]. The cooling in the terminal
Pliocene was preceded by the warm period lasting
from 3.15 to 2.85 Ma ago. It is reflected in the surface
temperatures derived from the microfossil assemblages
in deep cores as well as in the compositions of the
palynological spectra and greenhouse gases. Accord
ing to the modeling, this warming is related to the
increased transfer of heat by the oceanic currents [20].
For example, the temperatures along the Arctic coast
increased by
10
°
C
. The subsequent cooling in the
Northern Hemisphere was accompanied by the south
ward migration of marine invertebrate organisms: Arc
tic species first appeared in Britain and, then, in the
Mediterranean region.
Many areas demonstrate the complete transforma
tion of molluscan communities, which was frequently
related to migrations due to climate fluctuations,
rather than to extinction. This phenomenon is readily
observable along the North America coast. Neverthe
less, some researchers [39] who investigated the devel
opment of postlate Miocene (12 Ma ago) molluscan
assemblages in the Caribbean basin established that
the gradual decrease in the concentration of nutrients
due to the appearance of the Central America Isthmus
and the isolation of the basin from the Pacific (not the
temperature) was the main responsible factor. In this
case, the tectonics were a principal driving force.
The response of benthic foraminifers to changes in
the bottom water circulation in the Pliocene is exem
plified by their assemblages from the northern Indian
Ocean [25]. Four periods marked by faunal and climatic
turnovers are definable in the Pliocene and Pleistocene:
5.2–5.1, 3.9–3.2, 3.2–3.1, and 3.1–0.6 Ma ago. The
first of them is characterized by the expansion of the
Antarctic glaciations, the deepwater stratigraphic hia
tuses, the cooling and intensification of the bottom
circulation, the enhanced upwelling, the high sedi
mentation rates, and the maximal abundances of
Uve
gerina
representatives. During the period of 3.9–
3.2 Ma ago, the bottom waters were warmer, which is
reflected in the significant reduction of the
Uvegerina
abundances and the increased role of the
Cibicides
spe
cies. The period of 3.2 to 3.1 Ma ago was marked by
the bottom water temperature drop evident from the
global positive oxygenisotope shift in the benthic for
aminiferal tests. This was accompanied by the growth
of Antarctic ice shield and the initiation of continental
glaciation in the Northern Hemisphere. The terminal
Pliocene and Pleistocene were characterized by dras
tic changes in the composition of the benthic assem
blages, cyclic temperature fluctuations, alternating
glacial–interglacial cycles, and enhanced upwelling.
The oceanographic changes related to the rise of
the Central America Isthmus stimulated the evolution
of reefbuilding corals and benthic foraminifers in the
Caribbean Sea. Particularly intense diversification of
the benthic biota was in the period between 6.0 and
3.5 Ma ago [21]. The isolation of the Caribbean Sea from
the East Pacific resulted in corresponding changes of the
ecological settings and biota in the period of 4.25 to
3.45 Ma ago. This period was also marked by smoothed
seasonal temperature variations, the attenuation of
upwellings, the plankton productivity reduction and, by
the dominant development of mixotrophic reef corals
and calcareous algae instead of the formerly prevalent
heterotrophic mollusks [34]. The extinction of taxa
associated with the high productivity was maximal
approximately 2 Ma ago (Fig. 3).
In the terminal Miocene–early Pliocene, the Arc
tic basin was connected only with the Atlantic and
characterized by a relatively warm climate favorable
for the dwelling of Boreal taxa. The opening of the
Bering Strait 3.4–3.1 Ma ago is reflected in the migra
tion of Pacific endemics via the Arctic basin to the
North Atlantic and vice versa [17]. According to the
data on the molluscan and diatom assemblages, the
Bering Strait opened to permit the biota exchange
with the Arctic basin and the North Atlantic earlier in
the period of 7.3–7.4 to 4.8 Ma ago [32].
The period of alternating continental glaciations
and interglacials was accompanied by transgressive–
regressive cycles and, correspondingly, episodes of the
Bering Strait opening and closing. These events to a
significant extent determined the evolution of the Arc
tic and Subarctic biota, the diatom algae included [6].
In the North Pacific, the climate changes affected
the distribution of diatoms. Cooling led to the progres
sive prevalence of the species
Neodenticula koizumii
over
Neodenticula kamtschatica
, which started approxi
mately 2.7 Ma ago [9] (Fig. 4).
The extinction rate of bryozoans (order Cyclosto
mata) was increasing through the Miocene and
Pliocene to reach maximal values in the Pliocene in
parallel with the extinction of corals and mollusks in
the western Atlantic and Caribbean basin. These
extinction events are thought to be related to the envi
ronmental changes due to the closure of the Panama
Seaway and remote consequences of activated glacia
tions [33].

312
OCEANOLOGY Vol. 51 No. 2 2011
BARASH
The terminal Pliocene (2.15 Ma ago) was marked
by the fall of a large asteroid (>1 km in diameter) into
the Eltanin Fault zone of the Southern Ocean [24].
This event should result in global consequences,
although they are practically unknown so far. There
are grounds to believe that this was followed by the
explosion of a supernova star at the Pliocene–Pleis
tocene transition approximately 2 Ma ago [22]. Cos
mic rays destroyed the ozone layer of the Earth and
hard ultraviolet radiation caused partial extinction of
marine planktonic communities, mollusks, and other
organisms.
CONCLUSIONS
The abiotic (tectonic, volcanic, climatic, and
extraterrestrial) factors controlled the evolution of the
oceanic biota. The tectonic processes were undoubt
edly the leading driving force among these factors.
Horizontal movements of the lithospheric plates
determined the general arrangement patterns of the
continents and oceans on the Earth. Their spatial
combination determined the configuration of the dif
ferent segments of the World Ocean and their relations
between each other. Vertical tectonic movements
opened or closed seaways, which were of importance
for the oceanic circulation. The mutual position of the
oceans, continents, and geographic poles determined
the oceanic and atmospheric circulation and conti
nental glaciations in the Northern and Southern
Hemispheres.
The subsidence of the Faroe–Iceland Ridge and
substantial flow of cold waters from the Norwegian–
Greenland basin 14–13 Ma ago stimulated the forma
tion of the presentday benthic foraminiferal commu
nities. In the period of 19–12 Ma ago, the Tethys
Ocean was closed in the east owing to Africa and Eur
asia joining. The subsequent orogenic processes in the
western Mediterranean region and the sealevel fall in
the terminal Miocene were responsible for the temporal
desiccation of the Mediterranean Sea 5.59–5.33 Ma
ago (Messinian salinity crisis). This led to the inter
ruption of the connections between the biotas in the
low latitudes of the Indian and Atlantic oceans. The
rise of the Central American Isthmus 6.0–3.5 Ma ago
stopped the water exchange in the tropical zone
between the Atlantic and Pacific oceans, which caused
drastic changes in the paleoecological situation. The
first opening of the Bering Sea and initiation of the
water and biota exchange via the latter between the
Corals
Mollusks
0
2
4
6
8
Miocene Pliocene Pleisto
Ma
0.5 0 0.5
Extinction rate
Fig. 3.
Extinction rate of coral species and molluscan genera
and subgenera in the Caribbean Sea (after [34], modified).
0 5 10 15 20 25
T
,
°
C
2.5
2.6
2.7
2.8
2.9
3.0
3.1
3.2
3.3
February August
Age, Ma
Fig. 4.
Pliocene surface temperature (SST) in the North
Pacific derived from the composition of the diatom assem
blages; ODP Hole 1022 (after [9], modified). The present
day temperatures are shown by vertical dotted lines.
cene

OCEANOLOGY Vol. 51 No. 2 2011
ENVIRONMENTAL CHANGES IN THE NEOGENE 313
Pacific and the Arctic and North Atlantic basins
occurred in the period of 7.3–7.4 to 4.8 Ma ago
(according to some data, 3.4–3.1 Ma ago).
Of events the that provided a substantial impact on
the climate, noteworthy was the formation of the Cir
cumAntarctic Current accompanied by the progres
sively growing thermal isolation of Antarctica and the
expansion of the ice shield. Through the Miocene, the
climate was subjected to significant fluctuations. The
Late Cenozoic glaciation in the Northern Hemisphere
was responsible for the formation of the presentday
biota. One of the factors associated with the climate
changes were the variations in the atmospheric
СО
2
concentration. Among the abiotic factors influencing
the development of the biota via the climate changes,
the variations in the orbital parameters traceable
through the entire Cenozoic should be mentioned.
The paleoceanographic reorganization in the ini
tial Neogene led to the formation of latitudinal bio
geographic zones and the growth of taxonomic differ
ences in the corresponding biotic communities. The
climate fluctuations affecting the biota distribution
were reflected in the migration of biogeographic prov
inces, the abundance of various organisms, and the
succession of assemblages through time, which pro
vides grounds for defining stratigraphic units.
The Neogene was marked by several significant
extraterrestrial events. The middle Miocene (14.8–
14.5 Ma ago) biota suffered the mass extinction of
many terrestrial and aqueous taxa. One of the possible
factors responsible for this phenomenon could be the
fireball that fell in southwestern Germany. Volcanic activ
ity cannot be ruled out as well: ash ejections particularly
in the rift valley of eastern Africa, which are thought to be
responsible for global cooling, were maximal at that time.
In the late Miocene (
8.3
±
0.5
Ma ago), the flow of inter
planetary dust to the Earth produced by the disintegra
tion of a large asteroid significantly increased to affect
the climate system. The terminal Pliocene (2.15 Ma
ago) was marked by the fall of a larger (>1 km in diam
eter) asteroid to the Southern Ocean in the Eltanin
Fault zone. This event should have had global conse
quences, which are, however, unknown so far. There
are grounds to believe that the Pliocene–Pleistocene
transition approximately 2 Ma ago coincided with the
explosion of a supernova star: cosmic rays destroyed
the ozone layer of the Earth and hard ultraviolet radi
ation caused the partial extinction of marine plank
tonic communities, mollusks, and other organisms.
The reflection of many abiotic events with
unknown causeandeffect relations between them or
lacking the latter in the sedimentary record provide
grounds for the assumption that largescale environ
mental changes on the Earth, their periodicity
included, are controlled by general extraterrestrial
phenomena.
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