Transcript 5 Cenozoic Geology n

The Geology of the
Cenozoic Era
Introduction
• The Cenozoic began
~65 mya and
continues until the
present
– Cenozoic rocks are
more easily accessible
and less deformed than
older rocks
– divided into the Tertiary
and Quaternary
Early Work on the Cenozoic
• Charles Lyell England’s foremost geologist
of his day.
• Author of Principles of Geology (1830)
• Supported James Hutton's concepts of
Uniformitarianism
• Teacher of Charles Darwin
Charles Lyell studied the Tertiary and Quaternary fossils of
France
Defined the Eocene, Miocene, Pliocene, Pleistocene, and
Holocene
Paleocene and Oligocene were added later
Geologic Events Cenozoic
Mantle upwelling
Colorado Plateau
Washington
Laramide uplifts eroded away
(Longest Tertiary Epoch)
Rockies
• Cenozoic Tectonic activity concentrated in two areas
– Alpine-Himalayan belt deformation began in the Mesozoic
and remains geologically active.
Isolation of Tethys to form the modern Mediterranean Sea
– circum-Pacific belt deformation occurred throughout the
Cenozoic
Cenozoic Pacific realm
1. Subduction of the Farallon Plate and its Mid Ocean Ridge
San Andreas forms
2. Formation of Andean Cordillera
Geologic Events Cenozoic
Mantle upwelling
Colorado Plateau
Washington
, Basin & Range
San Andreas Fault
(Longest Tertiary Epoch)
Rockies
Cordillera
• Circum-Pacific Orogenic belt
–Laramide Lt. Jur - E Tertiary
–further inland than most - CLUE
–deformation was vertical uplift, with
little volcanism
–shallow subduction angle
–“buoyant subduction”
Laramide Orogeny K to T
Buoyant Subduction
• One possible result of shallow angle of
subduction and the drag that it causes with
overlying lithosphere is uplift - Rocky
Mountain formation.
• Renewed normal subduction would restore
normal volcanism within the western part
of the mountains – Basin and Range
Uplift of the Rocky Mountains
Rockies
shear stress
Basin and Range
Teton Range Laramide uplifts eroded away
in Oligocene, renewed uplifts Late Mio – Pleist.
Basin and Range of Cordillera
Columbia River Basalts
Basin and Range
Beginning in the Miocene, 2 mechanisms
1. lessening of the subduction angle allows dewatering
volcanism further west.
2. Farallon pieces under the lithosphere cause uplift,
lithosphere cracking and buoyant decompression
Basin and Range terminology
DISCUSSION, SHIP HULLS
Extensional Feature
w/ Normal Faults
Geologic Events Cenozoic
Mantle upwelling
Colorado Plateau
Washington
San Andreas Fault, Basin & Range
(Longest Tertiary Epoch)
Rockies
San Andreas transform
Ridges Change Orientation
15 mya SAF forms
The Interior Lowlands
• Sediments eroded from the Laramide
highlands were deposited in the
Cannonball Sea Early Paleocene
south to North Dakota.
– Terrestrial deposits are also found, but
much of this area was experiencing erosion
– Igneous activity was significant in some
areas - New Mexico, Colorado, Wyoming,
and others
– East of the Great Plains, deposits other than
glacial are rare until the eastern coastal
plain.
The Gulf Coastal Plain •
The Tejas
epeiric sea
transgressed
briefly over the
southeastern
coastal plains
E. Tertiary
– eight minor
transgressiveregressive
sequences are
recognized as
sea level fell in
general –
reduced rifting
East Coast
• Passive margin sedimentation dominates
– rocks form a seaward thickening wedge that
dips gently seaward
– Cenozoic uplift and erosion produced the
present topography of the Appalachians
– Coastal Plain a thick clastic wedge
– Florida Carbonates Pliocene - Recent
Eastern North America
Allegheny Orogeny still high
Erosion due Transgression
Coastal Plain streams and marshes
Appalachians rejuvenated recently, probably glacial rebound
1.Alpine Orogen
2. Eocene to Miocene
Apennine Balkan Carpathian Caucasus Pyrenees Atlas
4.Closing of the Tethys Sea
3. Vocabulary:
Isolation of the Mediterranean Basin: Evaporites
Nappe Large recumbent folds in thrust-fault zones where orogenic belts impinge craton margins
Flysch alternating thin shales and sandstones. Sandstones turbidites prior orogenic collision.
Molasse non-marine deposits accompanying the uplift of a mountain belt.
Nappe-folded mountains
New Orogen, Nappes still visible
http://www.geol-alp.com/chartreuse/3_tecto_chartreuse/1_ch_occ.html
source
1. The underside of Europe collided with
numerous microplates rifted from Africa
Closing of the Tethys Sea between late
Mesozoic and early Cenozoic time
3. Messinian Salinity Crisis ~ 5.5 mya 4. Thrusts not Subduction
Arabian-African Rift
2. Pliocene three way rift.
3. Arabia Microcontinent collision -> Zagros Mts
Himalayan Orogeny
Thin-skinned tectonics
Subduction
Partly subducted so under AW
Himalayan Orogeny
Zoomed-in Views
AW
FAB
Generalized Cross-Section
South
North
Décollement
• Décollement (from the French 'to detach
from') is a gliding plane between two rock
masses, also known as a basal
detachment fault.
• Décollements result in independent styles
of deformation in the rocks above and
below the fault.
• Both compressional settings (involving
folding and overthrusting) and extensional
settings.
Cenozoic Climates, Currents, and
Volcanism
• Ocean current flow changes due to
tectonics in Antarctic-Australian and
Central American regions
• Dramatic changes in climate
• Major plume under North America
• Continuous cooling, culminating in
on-going Ice Age
Cenozoic Cooling
Australia separates
Central
America
construction
Starts see
Monterey Fm.
(Northern
Hemisphere)
Geologic Events Cenozoic
Panama Closes
Mediterranean Dries Out
Circumpolar Current
Antarctica
(Longest Tertiary Epoch)
High CO2
Rockies
Antarctic Circumpolar Current
Paleocene to Mid-Eocene
WARM Currents from Tropics
Early Eocene Warm
Green River Formation
Oil Shales
Green River Formation
Lake (lacustrine) silts
Organic-rich (oil) shales w/ fossils
Green River Formation
Tropical Plants to High Latitudes
Antarctic Circumpolar Current
2. Late Eocene
Sudden Antarctic cooling as warm currents barred
3.
5. Longest continuous Ice Sheets
4. Fauna changes. Example: Penguin relationships
from S. American bird following current rich in fish.
1. Australia pulls away
Fossils in volcanic tuff deposit
Cooler
Tree stumps, insects in Oligocene Ash, Florissant, Colorado
Extensive Volcanism Late Eocene to Oligocene
Pre Gulf Stream Current
Isthmus of Panama
open, same salinity
Atlantic and Pacific
Early Pliocene
Modern Gulf Stream Current
1. Terranes, Subduction, Volcanic Arc,
Isthmus of Panama closed, North Atlantic isol.,
higher salinity, dense cool water sinks before it
reaches Arctic, polar sea freezes
Late Pliocene
Mediterranean Dried Out
2. Caused Formation of the present Gulf Stream Current in the Atlantic
3. Dramatic Cooling
Late Pliocene 5.96 to 5.33 mya
Messinian Salinity Crisis
– recall salt buoyancy, low competence
Evaporites, Gorges, Faunal Exchanges
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The Great Exchange
Bears
Camels
Cats
Dogs
Elephants
Horses
Peccaries
Rabbits
Raccoons
Skunks
Tapirs
Weasels
North America
Anteaters
Armadillos
Capybaras
Glyptodonts
Monkeys
South America
Opossums
Porcupines
Sloths
Late Pliocene,
Toxodonts
Isthmus of Panama
closed, migrations
North and South
With cooling comes drought. Grasses replaced forests, mammals
adapted for a diet of grass, grew larger, faster as predators
pursued.
Geologic Events Cenozoic
Mantle upwelling
Colorado Plateau
Washington
Laramide uplifts eroded away
(Longest Tertiary Epoch)
Rockies
Pliocene 2000 m uplift of Colorado Plateau
(Grand Canyon - Colorado River incised )
Evidence,
Incised meanders
The Yellowstone Plume
• Miocene to Recent
• Starts with flood basalts in Columbia
Plateau Washington and Oregon 15 mya
• Continues into Snake River Basin
• Then to Yellowstone in Holocene
Basalt flows - Columbia Plateau
Miocene 15 – 12 mya
Start of Plume forming Snake River Plateau
and recently Yellowstone
Just like the Watchungs
Craters of the Moon Monument
Migration of Snake River Basin over the plume 10 mya
Migration of Yellowstone Park over the plume 2 mya to recent
Geologic Events Cenozoic
(Longest Tertiary Epoch)
Rockies
Pleistocene Glaciation
• The Pleistocene began about 1.8 – 1.6 mya and
ended about 10,000 years ago
– several intervals of widespread glaciation took place,
separated by warmer intervals
Causes of Ice Ages
• Plate Tectonics
Moves Continents to Poles
Raises mountains above snowline
• Orbit distance, Axis Tilt and Wobble
– Moderates solar radiation north of 65 N
– Milankovitch Cycles ~ 100,000 years
– Low summertime radiation 65 N, glaciers expand
Milankovitch Cycles
Discussion: cool summers and wet winters
Moisture content of air masses
100,000 years
Warm Wet Winter
Cool Summer
Cold Dry Winter Hot
Summer
41,000 years
Discussion: Perihelion and Aphelion
25,700 years
Louis Agassiz
• Swiss Geologist
• Eventually Professor of Geology at
Harvard
• Familiar with Alpine Glaciers
• Recognized Moraines, erratic boulders,
and scoured bedrock in Europe and N.Am
• Proposed huge glaciations Europe and N.
America
Glacial and Interglacial Stages
C-14 works here
Medieval warm 900-1300
Little Ice Age 1300 -1850
65 (ongoing)
50
140
35
135
65
(Many)
Glacial advances named for states
Foraminifera
tests
Ice
Age
Warm
Cold
Wisconsinan
Illinoian
About 30 pulses in
4 or so major
groups
Kansan
Nebraskan
3. Also spiral direction &
diversity depends on Temp.
1. Evap. water and CO2
removes 16O from oceans
18O left in oceans
used to make shells
2. Ice traps CO2
and water with light
oxygen
The Effects of Glaciation
• The effects of glacial erosion and
deposition are evident worldwide
– lowering of sea level affected
base level of streams
– pluvial lakes
– proglacial lakes
– Compression of the Crust
Pleistocene Lakes - West
Pluvial Lakes
Remnant of Bonneville
Lake Bonneville terraces
Much deeper that GSL
(melting)