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| Japan during the
Early Miocene. |
Neogene
The Neogene ( /ˈniː.əˌdʒiːn, ˈniː.oʊ-/ NEE-ə-jeen,
NEE-oh-) (informally Upper Tertiary or Late Tertiary) is
a geologic period and system that spans 20.45 million
years from the end of the Paleogene Period 23.03 million
years ago (Mya) to the beginning of the present
Quaternary Period 2.58 Mya. The Neogene is sub-divided
into two epochs, the earlier Miocene and the later
Pliocene. Some geologists[who?] assert that the Neogene
cannot be clearly delineated from the modern geological
period, the Quaternary. The term "Neogene" was coined in
1853 by the Austrian palaeontologist Moritz Hörnes
(1815–1868).
During this period, mammals and birds continued to
evolve into modern forms, while other groups of life
remained relatively unchanged. Early hominids, the
ancestors of humans, appeared in Africa near the end of
the period.[citation needed] Some continental movement
took place, the most significant event being the
connection of North and South America at the Isthmus of
Panama, late in the Pliocene. This cut off the warm
ocean currents from the Pacific to the Atlantic Ocean,
leaving only the Gulf Stream to transfer heat to the
Arctic Ocean. The global climate cooled considerably
over the course of the Neogene, culminating in a series
of continental glaciations in the Quaternary Period that
follows. |
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Divisions
In ICS terminology, from upper (later, more recent) to
lower (earlier):
The Pliocene Epoch is subdivided into two ages: |
- Piacenzian Age, preceded by
- Zanclean Age
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The Miocene Epoch is subdivided into six ages: |
- Messinian Age, preceded by
- Tortonian Age
- Serravallian Age
- Langhian Age
- Burdigalian Age
- Aquitanian Age
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In different geophysical regions of the world, other
regional names are also used for the same or overlapping
ages and other timeline subdivisions.
The terms Neogene System (formal) and Upper Tertiary System
(informal) describe the rocks deposited during the Neogene
Period. |
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Geography
The continents in the Neogene were very close to their
current positions. The Isthmus of Panama formed,
connecting North and South America. The Indian
subcontinent continued to collide with Asia, forming the
Himalayas. Sea levels fell, creating land bridges
between Africa and Eurasia and between Eurasia and North
America.
Climate
The global climate became seasonal and continued an
overall drying and cooling trend which began at the
start of the Paleogene. The ice caps on both poles began
to grow and thicken, and by the end of the period the
first of a series of glaciations of the current Ice Age
began.
Flora and fauna
Marine and continental flora and fauna have a modern
appearance. The reptile group Choristodera became
extinct in the early part of the period, while the
amphibians known as Allocaudata disappeared at the end.
Mammals and birds continued to be the dominant
terrestrial vertebrates, and took many forms as they
adapted to various habitats. The first hominins, the
ancestors of humans, may have appeared in southern
Europe and migrated into Africa.
In response to the cooler, seasonal climate, tropical
plant species gave way to deciduous ones and grasslands
replaced many forests. Grasses therefore greatly
diversified, and herbivorous mammals evolved alongside
it, creating the many grazing animals of today such as
horses, antelope, and bison. Eucalyptus fossil leaves
occur in the Miocene of New Zealand, where the genus is
not native today, but have been introduced from
Australia. |
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Disagreements
The Neogene traditionally ended at the end of the
Pliocene Epoch, just before the older definition of the
beginning of the Quaternary Period; many time scales
show this division.
However, there was a movement amongst geologists
(particularly marine geologists) to also include ongoing
geological time (Quaternary) in the Neogene, while
others (particularly terrestrial geologists) insist the
Quaternary to be a separate period of distinctly
different record. The somewhat confusing terminology and
disagreement amongst geologists on where to draw what
hierarchical boundaries is due to the comparatively fine
divisibility of time units as time approaches the
present, and due to geological preservation that causes
the youngest sedimentary geological record to be
preserved over a much larger area and to reflect many
more environments than the older geological record. By
dividing the Cenozoic Era into three (arguably two)
periods (Paleogene, Neogene, Quaternary) instead of
seven epochs, the periods are more closely comparable to
the duration of periods in the Mesozoic and Paleozoic
eras.
The International Commission on Stratigraphy (ICS) once
proposed that the Quaternary be considered a sub-era
(sub-erathem) of the Neogene, with a beginning date of
2.58 Ma, namely the start of the Gelasian Stage. In the
2004 proposal of the ICS, the Neogene would have
consisted of the Miocene and Pliocene epochs. The
International Union for Quaternary Research (INQUA)
counterproposed that the Neogene and the Pliocene end at
2.58 Ma, that the Gelasian be transferred to the
Pleistocene, and the Quaternary be recognized as the
third period in the Cenozoic, citing key changes in
Earth's climate, oceans, and biota that occurred 2.58 Ma
and its correspondence to the Gauss-Matuyama
magnetostratigraphic boundary. In 2006 ICS and INQUA
reached a compromise that made Quaternary a subera,
subdividing Cenozoic into the old classical Tertiary and
Quaternary, a compromise that was rejected by
International Union of Geological Sciences because it
split both Neogene and Pliocene in two.
Following formal discussions at the 2008 International
Geological Congress in Oslo, Norway, the ICS decided in
May 2009 to make the Quaternary the youngest period of
the Cenozoic Era with its base at 2.58 Mya and including
the Gelasian age, which was formerly considered part of
the Neogene Period and Pliocene Epoch. Thus the Neogene
Period ends bounding the succeeding Quaternary Period at
2.58 Mya. |
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 Kiddle: Neogene
Wikipedia: Neogene |
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