吾々の時代: 氷河時代
NSA
氷河時代 Ice Ages
Pleistocene 更新世 2.58〜0.0117 M.y. 特に
この時代をここでは。
Permian 250-220 M.y.
Ordovician 450 M.y.
Precambrian
900-650 M.y. (Snowball Earth)
2300 M.y.
中期更新世以降 0.78 Mya〜
更新世の
氷河時代
の始まり
氷河時代の証拠1: 氷礫岩tillite
www.eriding.net/media/photos/geograp/_geo_lpp_007_boulder_clay.jpg
www.scottishgeology.com/gallery/image02.html
boulder
続 Gowganda tillite, Ontario
Rock record of glaciation, this one ~2.3 billion years ago!
氷河時代の証拠1’:
氷河性堆積物の再現
• In the early 1800s Jean de Charpentier observed
the advance and retreat of glaciers in the Alps
and studied the kind of deposits they left behind.
1820s
1850s
Glacial
retreat
en.wikipedia.org/wiki/Image:Johann_von_Charpentier.jpg
氷河時代の証拠2: 氷河地形
www.swisseduc.ch/glaciers/earth_icy_planet/glaciers15-en.html?id=15
Parallel marks show
former level of an
ice-dammed lake
Glen Roy, Scotland
• Agassiz amassed more evidence from landforms and boulder
clays to support his idea of a Great Ice Age in recent times.
www.geo.umn.edu/courses/4703/Spring00/5-NorthShore/images/striations.jpg
氷河時代の証拠2’: 擦痕
• In 1840, Louis Agassiz
observed similar glacial
features in Scotland.
• He found scratches on
a rocky hillside near
Edinburgh like those
made by glaciers.
ice scratches
en.wikipedia.org/wiki/Image:Louis_Agassiz-2.jpg
• He argued that Scotland
had recently been covered
in a thick ice sheet.
氷河時代の証拠3: 化石
www.colby.edu/geology/gifs/M.nelsoni.jpg
• Fossil discoveries also
suggested that climate had
recently been much colder.
Pollen
www.aip.org/history/climate/images/Dryas_octopetala.pollengrain.jpg
en.wikipedia.org/wiki/Image:Mammoth_mg_2791.jpg
Beetles
Mammoth
• Beetles and pollen grains
found in sediments associated
with the boulder clays were
identified as types known only
from the Arctic tundra today.
• Woolly mammoths found
deep frozen in Siberia had
fur adapted to tundra life.
仮説:ミランコヴィッチサイクル
Milankovich Cycles
Cool Summers More Important Than
Cold Winters
自転軸の傾き Tilt of Axis
公転軌道の離心率 Shape of Orbit
自転軸の歳差運動 Precession
ミルティン・ミランコビッチ
Milutin Milanković
 1920年,太陽の放
射による熱現象の
数学理論 Théorie
mathématique des
phénomènes
thermiques
produits par la
radiation solaire
Axis Tilt
 Small Axis Tilt: Mild winters but cool summers.
Favors Ice Age
 Large Axis Tilt: Cold winters but hot summers. Favors
Interglacial
Precession:
26,000 year
cycle
Shape of Orbit + Precession
Summer at Perihelion (Eccentric Orbit)
Cold winters but hot summers. Favors Interglacial
Summer at Aphelion (Eccentric Orbit)
Near-circular Orbit
Mild winters but cool summers. Favors Ice Age
Cause (4): Cycles
en.wikipedia.org/wiki/Image:Milankovitch_Variations.png
• Milanković added up all the orbital wobbles and predicted that
ice ages should occur in regular cycles - probably happening
every hundred thousand years or so.
ミランコビッチサイクルの証明:
安定酸素同位体比:18O/16O
氷河成長・減衰の指標
 16O
 17O
 18O
天然存在比 0.99757
天然存在比 0.00038
天然存在比 0.00205
特に,18O/16O を指標とする。δ18Oで示す。
安定酸素同位体比:18O/16O
蒸発は16Oの方が
容易。
雲の16O量は相対
的に多い。
氷期には,氷河中
の16Oも相対的に多
く,海水中の18Oは
相対的に多くなる。
間氷期には,氷河
中の16Oが相対的
に多い水が海に注
がれて,18Oが希釈
される。
If we collect a shell made out of CaCO3, we can analyze
the O18:O16 ratio by the following formula:
delta O18= [ (O18/O16 sample) / (O18/O16 standard) -1 ] x1000
The standard that your sample is compared to
is either one prepared from ocean water or
from a fossil standard. Positive delta O18
values mean that your sample is enriched in
the heavy O isotope; negative delta O18
values mean it’s depleted in the heavy O18.
Curve of average O18 isotope variation over
the past 2my based on analysis of deep
sea sediment
The curve illustrates changes
in global ice volume in
successive glacial (blue) and
interglacial (green) cycles of the
Quaternary Period.
Note that this graph does not
show fluctuating temperatures,
but changes in the dilution of sea
water as a result of freshwater
influx from melting glacial ice, i.e.,
this is a climate proxy
氷河地形diagram1
氷河進出前の河川による山地斜面:
上に凸
氷河地形diagram2
氷河進出による侵食
氷河地形diagram3
氷河融解後に出現した氷食による山地斜面:
下に凸
U字谷と氷河
Franz Josef Glacier
氷 河2
氷食崖
擦痕
フィヨルドと懸谷
Milford Sound
ホルン
 Ost- und
Nordwand
des
Matterhorn
s, an der
Licht/Schattengr
enze der
Hörnligrat
圏谷,Kar: 穂高岳の涸沢カー
ル
仙丈ケ岳(南アルプス)山頂:
カールとモレーン(堆石)
モレーンの堆積物:
ティル glacial till ←水の礫岩と比較
周氷河地形:
構造土 frost
hexagons
A blockfield
around 4000m on
Mount Kenya
凍結融解作用
一応終了
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