Last Time
UNIVERSITY OF SOUTH ALABAMA
Submarine Fans
MAS 603: Geological Oceanography
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Definition and morphology
Transport mechanisms (density currents)
Submarine fan facies/sedimentary sequences
Lecture 16:
Greenhouse vs. Icehouse Earths
Submarine Canyons and Fans
Submarine canyons: major conduits
of siliciclastic sediment from the
continental shelf to the abyssal plain
Submarine fans: accumulations of
siliciclastic sediment from the shelf
break onto the base of the
continental slope
Submarine Fans: Transport Mechanisms
Mass movement is particularly important as a sediment
transport mechanism on submarine fans.
Increase in water:sediment ratio
http://www.dkimages.com/discover/previews/851/20117924.JPG
From Walker, R.G. (1980). Facies Models. Geological Association of Canada.
Submarine Fans: Transport Mechanisms
Turbidites
On the distal fan, the flow has a high water:sediment ratio
and moves as a density current.
Turbidites are formed
as a result of waning
flow.
A classic Bouma sequence
http://faculty.gg.uwyo.edu/heller/Sed%20Strat%20Class/SedStrat%208/bouma.jpg
http://serc.carleton.edu/
http://instruct.uwo.ca/earth-sci/200a-001/07turbidity.jpg
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The Submarine Fan Model
This is the best (and
simplest) model we have
of a submarine fan
depositional facies.
Today’s Agenda
Greenhouse vs Icehouse Earths
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Paleozoic-Mesozoic Paleogeography
Cenozoic Paleogeography
Plio-Pleistocene climatic oscillations
From Walker, R.G. (1980). Facies Models. Geological Association of Canada.
Paleoclimate Phases
Paleoclimate Phases
We now recognize three major climatic phases
We now recognize three major climatic phases
1) Snowball Earth
(no continental glaciers present)
Paleoclimate Phases
Paleoclimate Phases
We now recognize three major climatic phases
We now recognize three major climatic phases
1) Snowball Earth
1) Snowball Earth
(no continental glaciers present)
(no continental glaciers present)
2) Icehouse Earth
2) Icehouse Earth
(continental glaciers present)
(continental glaciers present)
a) Glacial stage (18 KA)
b) Interglacial stage (Today)
http://www.snowballearth.org/end.html
http://www.snowballearth.org/end.html
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Paleoclimate Phases
Proterozoic Paleogeography
We now recognize three major climatic phases
1) Snowball Earth
(no continental glaciers present)
Insert greenhouse
2) Icehouse Earth
(continental glaciers present)
3) Greenhouse Earth
(no continental glaciers present)
Icehouse Earth
Early Paleozoic Paleogeography
Greenhouse Earth
Early Mesozoic Paleogeography
Greenhouse Earth
Late Paleozoic Paleogeography
Icehouse Earth
Middle Mesozoic Paleogeography
Greenhouse Earth
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Late Mesozoic Paleogeography
Mesozoic Greenhouse Earth
• High latitudes were
warm
– 50°F / 10°C
– Dinosaurs near south
pole
• Wind belt
– Evaporite deposition
Greenhouse Earth
Mesozoic Greenhouse Earth
• Most continents were
isolated
• Seas opened:
– South Atlantic; Gulf of
Mexico; Caribbean Sea
Mesozoic Greenhouse Earth
•Leading to
High Sea Level
Mesozoic Greenhouse Earth
•Increased volume of
mid-oceanic ridges
due to rapid sea floor
spreading
•Long period without
a magnetic reversal
Mesozoic Greenhouse Earth
•Increased sedimentation
•Thick cratonic sequences
•Epicontinental
sea ways
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Mesozoic Climate
• Oceans stagnated
– Epicontinental black
muds when seas spilled
over
– Normally thin oxygen
poor zone expanded
Cenozoic Climate
• Oxygen isotopes from
deep sea foraminifera
suggest Late Eocene
cooling
This situation will change
in the early Cenozoic
(Late Eocene)
Cenozoic Climate
• The temperature
change is also
recorded by terrestrial
fossils (e.g., leaf
margins)
Cenozoic
Icehouse Earth
Paleocene-Middle Eocene:
•No circumpolar current
Late Eocene-today:
•Circumpolar current
–Permitted development of glaciers
on Antarctica
Cenozoic Icehouse Earth
Plio-Pleistocene
Is most notable for rapid, short
duration shifts in temperature and
ice volume.
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Plio-Pleistocene
Is most notable for rapid, short
duration shifts in temperature and
ice volume.
Plio-Pleistocene
• Glaciations started around
5 million years ago.
• Isthmus of Panama
– Emplaced 3.5–3 M years
ago
– Started modern circulation
• Gulf stream carries salty
Atlantic north
• Cools, sinks
– Oceanic conveyor belt
• High latitudes cool
Milankovitch Cycles
Three major changes in
Earth’s orbit are linked to
glacial oscillations
Milankovitch Cycles
When taken together, the 3 cycles are capable of dropping
temperatures globally
•Eccentricity
•Obliquity
•Precession
Milankovitch Cycles
The Present Icehouse Earth
These cycles have been confirmed via stable isotope analysis
of deep sea foraminifera (ice volume).
Glacial/
interglacial
stage
Name of stage
interglacial
Holocene
0 - 10 KA
glacial
Wisconsinian
10 – 75 KA
interglacial
Sangamon
75 – 125 KA
glacial
Illinoisan
125 – 265 KA
interglacial
Yarmouth
265 – 300 KA
glacial
Kansan
300 – 435 KA
interglacial
Aftonian
435 – 500 KA
glacial
Nebraskan
> 500 KA
Time frame
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The Present Icehouse Earth
The Present Icehouse Earth
• Lowering of sea level
• And permitted
migrations
– Exposed continental
shelves
The Present
Icehouse Earth
• Ocean circulation
changed during
glaciation
Holocene Sea Level Change
• Transgression
– Lagoonal complexes transgress over coastal plain
sediments
• Regression
– High sediment supply causes coast to move offshore
– Mammals crossed
Bering Strait on land
corridors
– Vegetation changed in
response to global
changes
The Present Icehouse
Earth
• Glaciers began to retreat
around 15,000 years ago
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Waters drained to lakes
Sea level rose
Tundra shifted northward
Deciduous trees migrated
northward
Holocene Sea Level Change
•In southern Alabama,
regressions caused the
shoreline to shift 100
miles south. Base level
of rivers dropped by
300 feet.
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Holocene Sea Level Change
Holocene Sea Level Change
•The Mobile River
carved a canyon, the
remnants of which are
still exposed along the
Eastern Shore
Next Week
SLEEP!
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