Download Science Affiliates Workshop NY Geology Powerpoint

New York's
Geologic Past
Science Affiliates Teacher Workshop
April 10, 2010
Instructor: Di Keller
Complete
Geologic Time
Scale
Hadean
to
Recent
88%
Surficial
Glacial
Deposits
A few rocks
Most Rocks in
New York are
mid-Proterozoic to
Devonian in age
88%
Complete
Geologic Time
Scale
Hadean
to
Recent
Pre-Cambrian
pre-“visible life”
88%
Geologic Time Scale
for the first 3.8 Billion Years of Earth's Existence
Proterozoic - "Earlier life" - 'modern' tectonic processes established
Archean – "Archaic," 'ancient,' - origin of continents, oceans, life
Hadean – "Hades-like," - hot, hellish
Early in the Hadean - 4.6 - 4.2 Billion Years Ago
Earth was Hot, Barren, Waterless
• Shortly after accretion, Earth was
•
•
•
•
a rapidly rotating, hot, barren, waterless planet
bombarded by comets, meteorites & intense cosmic radiation
with no continents
widespread volcanism
Oldest Rocks & Minerals
• The oldest known rocks on Earth
• The 3.96-billion-year-old Acasta Gneiss in Canada
+ other rocks in Montana
• indicate that some continental crust had evolved by about 4
billion years ago
• The oldest known minerals on Earth
• Sedimentary rocks in Australia contain detrital
zircons dated at 4.2 billion years old
• These minerals indicate that some kind of Hadean crust
was present but its distribution is unknown
The Archean
3.8 to 2.5 Billion Years Ago
Origin of:
Protocontinents,
Oceans & Life
http://spacebio.net/modules/lu_resource/ArcheanLandscape.jpeg
Cratons
a continent’s ancient
nucleus and its
foundations
Craton = Shield + Platform
•Along the margins of cratons:
more continental crust was later
added as the continents took their
present sizes and shapes
http://www.salemstate.edu/~lhanson/gls210/gls210_Tectonic.htm
Distribution of Precambrian Rocks
• Precambrian shields
– consist of vast areas of exposed ancient rocks
– found on all continents
• Broad platforms extend off shields
– buried Precambrian rocks
– underlie much of each continent
The craton in North America
is the Canadian Shield
"Shield"
- subdued
topography
• occupies:
- most of northeastern Canada
- a large part of Greenland
- some of the Lake Superior region
(Minnesota, Wisconsin and Michigan)
- the Adirondack Mountains of New York
The Origin of Cratons
By the end of the Archean, 30-40% of the
present volume of continental crust existed
Continental Growth
Through Time
100%
Determined
through dating
lots of rocks on
the continents
50%
4.0
3.0
2.0
1.0
Billion yrs
• Several small cratons existed by the beginning of the Archean
• They grew by periodic continental accretion during the rest of
that eon
(& amalgamated into larger units during the Early Proterozoic)
Growth of Continents by Accretion
Most geologists are
convinced that some
kind of plate tectonics
took place during the
Archean
– but it differed in
detail from today
Plates likely moved faster
because the Earth was hotter:
– more residual heat from Earth’s origin
– more radiogenic heat,
– magma was generated more rapidly
Two Main Types of Rocks Formed in Archean
Superior Province 3.2-2.7 Ga
Greenstones (metamorphosed mafic rocks from volcanic arcs)
Graywackes (sedimentary rocks composed of materials eroded
from arcs; texturally & compositionally immature)
The Archean
3.8 to 2.5 Billion Years Ago
Origin of:
Protocontinents
Oceans & Life
3.5-3.4 Bya
1st fossil evidence:
in Apex Chert, Australia
Only: • simplest, prokaryotic life forms
• restricted to ocean
• no terrestrial life yet
Stromatolites
Mounded structures formed when sediment grains are
trapped on sticky mats of photosynthesizing blue-green
algae (cyanobacteria)
The oldest known
undisputed stromatolites
are found in rocks in
South Africa that are
3.0 billion years old
• but probable ones are also
known from the Warrawoona
Group in Australia which is
3.3 to 3.5 billion years old
Modern Stromatolites, Shark Bay, Australia
http://www.mlssa.asn.au/journals/1999Journal.htm
Evidence for Increased Oxygen in Atmosphere
BIFs and Red Beds
~3 - 2 Bya
After ~1.8 Bya
Oxidized Iron
appears in rock record
BIFs - Banded Iron Formations
Most formed ~ 2.5 BYA
Thin alternating bands of oxygen-rich
and oxygen-poor minerals indicate
Oxygen levels in Atmosphere
are shifting between high & low
After 1.8 Bya - no banding oxygen levels remain steadily high
The Proterozoic
2.5 Billion to 544 Million Years Ago
'Modern' Tectonics
Established
-similar processes & rates
Appearance of
Multicellular Life
Tectonics
Proterozoic Accretions
These geologic
provinces form the
core of the North
American craton, the
stable nucleus of the
continent.
The older rocks
probably accreted
about 1.8 - 1.9 Bya.
The Grenville
Province was sutured
about 1.0 Bya.
(Adks)
Fig. 8.11
Supercontinent Rodinia
Late Proterozoic
http://www.ig.utexas.edu/research/projects/umkondo/umkondo.htm
Forms and begins
to rift apart
http://www.nvcc.edu/home/cbentley/shenandoah/
Devonian
Silurian
Ordovician
Proterozoic
Cambrian
Timeline of Continent Positions
Devonian
Silurian
Ordovician
Proterozoic
Cambrian
Timeline of Continent Positions
Complete
Geologic Time
Scale
Cambrian
First period of the
"Phanerozoic"
"Visible life"
Good fossil record
88%
Life in the Cambrian
Simple in structure & low in ecological diversity
Main types:
-
bottom-feeding trilobites
suspension-feeding archeocyathids
(cone-shaped, shelled sponges)
brachiopods
stalked echinoderms
http://www.palaeos.com/Paleozoic/Cambrian/Cambrian.htm
Supercontinent Rodinia
Late Proterozoic
http://www.ig.utexas.edu/research/projects/umkondo/umkondo.htm
Forms and begins
to rift apart
http://www.nvcc.edu/home/cbentley/shenandoah/
Early Cambrian Geography of North America
Passive
Margin
Fig. 13.15
Edge of the North
American continent
remained tectonically
quiet for a period after
the rifting of Rodinia
Tectonically like East
Coast of North America
today except location at
the equator
S. Marshak, “Earth, Portrait of a Planet, 2nd ed.,” W.W. Norton, Fig. 13.16
Cambrian
sedimentary
facies
Geographic variations
in sediment types of ~520
million years old
ls
sh
ss
sh
ss
Rock types common to
Passive Margins:
ls
Quartz sandstones
- mature, reworked
Limestones (Carbonates)
- indicative of warm, shallow seas
where there is low terrestrial input
Copyright ©The McGraw-Hill Companies, Inc
Some Indicators of
Deposition in
Shallow Seas in
the Cambrian
stromatolites
photosynthetic cyanobacteria
that only live in sunlit water so
no deeper than 150-200 meters
Copyright ©The McGraw-Hill Companies, Inc
fossil mud cracks
polygonal network formed by
shrinkage of drying mud
Copyright ©The McGraw-Hill Companies, Inc
Supercontinent Rodinia
A lot of
continents
positioned
at the Pole
Sea Level Fall
Sauk Transgression
With rifting of Rodinia
& shift of continents
off the South Pole
Raised seafloor near rifts
(hot crust is less dense - floats higher)
+
melting of ice sheets
rise
fall
Sea level
Global
Sea Level Rise
Transgression - shoreline moves landward
= Relative sea level rise
Regression - shoreline moves seaward
= Relative sea level fall
http://www.wwnorton.com/college/geo/earth2/content/chapter_7/animations.asp
Layers of sediment build up over time and record
alternating transgressive & regressive sequences
Contacts between layer form zig-zag patterns
Layers of sediment build up over time and record
alternating transgressive & regressive sequences
rise
fall
Sea level
Cambrian
Passive
Margin
Fig. 13.15
Rising
Seas
S. Marshak, “Earth, Portrait of a Planet, 2nd ed.,” W.W. Norton, Fig. 13.16
Complete
Geologic Time
Scale
On to the
Ordovician
88%
Devonian
Silurian
Ordovician
Proterozoic
Cambrian
Timeline of Continent Positions
Ordovician Paleogeography
A Passive Margin NO LONGER
Just of the east coast
of North America…
Oceanic crust is
(farthest from the rift)
Older
new trench
Colder
More dense
Begins to Subduct
Ordovician Paleogeography
Oceanic crust is
(farthest from the rift)
new trench
Older
Colder
More dense
Begins to Subduct
Cambrian into Ordovician Plate Tectonics
• development of a
convergent plate
boundary
• closure of the
Iapetus Ocean
CAMBRIAN
Ordovician -Early Silurian Plate Tectonics
Taconic Orogeny
460 - 440 million years ago
Collision of a volcanic arc
BALTICA
AVALONIA
ORDOVOCIAN
Taconic Orogeny
Ordovician -Early Silurian
Foreland Basin
load weight causes downwarping between
Island Arc
&
Continent
Clastic Wedges
- fan-shaped deposits of
clastic, silicate sediment
http://manhattan.unipv.it/sedgeo/Research/Basin%20Analysis.htm
Active tectonism creates:
• uplifted areas of igneous & metamorphic rocks
• from which silicate-rich sediments are eroded
Complete
Geologic Time
Scale
The
Silurian
88%
Devonian
Silurian
Ordovician
Proterozoic
Cambrian
Timeline of Continent Positions
Sea Level Regression
Gondwana at the South Pole
A lot of
continents
positioned
at the Pole
Sea Level Fall
S. Marshak, “Earth, Portrait of a Planet, 2nd ed.,” W.W. Norton, Fig. 13.15
Shallow Seas
Middle Silurian Paleogeography
(Post-Taconic Orogeny - 430 MYA)
~ Short, quiet period between
orogenies
Large areas of craton
flooded by shallow sea
Warm due to equatorial
paleo-latitude
Development of widespread
carbonate reef deposits
Copyright ©The McGraw-Hill Companies, Inc
WHERE DO CARBONATES FORM?
Marine organisms are most abundant and most diversified
in shallow, clear, well-lighted, agitated, warm seas
Fig. 12.19
*Subtidal carbonate factory
- shallow warm seas, formation of reefs
Deep sea carbonates – particle by particle settling of shells of planktonic
marine organisms – rain of carbonate particles accumulating at sea floor
Late Silurian Paleogeography
Michigan – NY – Ohio evaporite basins
Barrier reefs restricted marine circulation - Evaporites occur in basin centers
EVAPORITE DEPOSITS
Fig. 12.29
Copyright ©The McGraw-Hill Companies, Inc
Extensive deposits in Silurian
(consider that Syracuse is nicknamed “Salt City”)
Life in the Silurian
Some milestones:
Plants on Land!
First Fishes
Eurypterids Fluorish
(New York's State Fossil)
Richard Bizley - [email protected]
Large Eurypterid
Lang Fossil Quarry
Ilion, New York
www.pbs.org
Complete
Geologic Time
Scale
The
Devonian
88%
Tectonics
Late Silurian into Devonian
Acadian Orogeny
410-380 mya
Collision of the
Fig. 12.44
Avalon Terrane
Catskill Mountains
& Catskill Delta
(coincided with Caledonian
Orogeny in Europe)
Copyright ©The McGraw-Hill Companies, Inc
Devonian Geography of North America
Catskill Deltas
Clastic Wedges
shed from newly
uplifted highlands
W. W. Norton. Modified from Dott and
Prothero
These are the
sediments that
form our local
rocks
Deposited into
warm, shallow sea
S. Marshak, “Earth, Portrait of a Planet, 2nd ed.,” W.W. Norton, Fig. 13.21
Sedimentary Rocks of Devonian Age
• Recent tectonic uplift
leads to active erosion
- Clastic Wedges
- Silicate dominated sediments
But are often fossiliferous because
• Deposited into warm, shallow sea
- Good living conditions
- Carbonate fossils preserved
Life in the Devonian
Some milestones:
Age of Fishes
Animals on Land!
Lobe-finned fishes
- fins become walking appendages
Gotta Love
Ray Troll Art
Life in the Devonian
Some common local fossils
Brachiopods
filter feeders
individual shells
are symmetrical
but are not mirror
images of each other
http://www.uky.edu
Life in the Devonian
Corals
Some common local fossils
Order Rugosa (now extinct)
modern scleractiniancoral
Stanley, S., “Earth System History, 2nd ed.,” W.H. Freeman, Fig. 3-25a
Life in the Devonian
Some common local fossils
Crinoids
- often called "Sea lilies"
but actually are animals
Life in the Devonian
Some common local fossils
Pelecypods
- clams & oysters
the two shells are
mirror images of
each other
individual shells
are asymmetrical
http://www.uky.edu
Life in the Devonian
Some common local fossils
Gastropods
- snails
usually
asymmetrically
coiled
with no internal chambers
Life in the Devonian
Some common local fossils
Trilobites
- bodies composed
of 3 sections
glabella (head)
thorax (middle)
often found enrolled
(defensive position)
or in parts (molted shells)
pygidium (tail)
(also 3 sections laterally)
Complete
Geologic Time
Scale
88%
After the
Devonian
Since the Devonian,
New York has been above sea level
MIDDLE PENNSYLVANIAN ~300 MY AGO
• limited deposition
• subject to erosion
MIDDLE PERMIAN ~260 MY AGO
This is why the NY rock record ~stops in the Devonian
Middle Mississippian Paleogeography
Except for a few
small areas still
submerged in
southwestern
New York
no new rocks …
Timeline of Continent Positions
Devonian
Carboniferous
Permian
Triassic
Silurian
Ordovician
Proterozoic
Cambrian
… just metamorphism of existing ones
Tectonics
Late Mississippian - Pennsylvanian - Permian
Alleghanian Orogeny
330-250 mya
Formation of Pangea
Appalachian Mountains
Pangea - Late Carboniferous - 306 Mya
Pennsylvanian Period - Lots of Coal
Scotese Paleomap
Ice covered much of the southern hemisphere and
vast coal swamps formed along the equator.
Proterozoic
Devonian
Carboniferous
Permian
Triassic
Silurian
Ordovician
Cambrian
Timeline of Continent Positions
Pangea Rifts!
Tectonics
Triassic …
Rifting of Pangea
Began ~220 Mya
Opening of the
Altlantic Ocean
Mesozoic Rift Valleys
Newark & Hartford Basins
Red beds & basalt dikes
Dinosaur Footprints
Surficial
Glacial
Deposits
A few rocks
Most Rocks in
New York are
mid-Proterozoic to
Devonian in age
Not many rocks
after areas became
exposed so…
The time since the
Devonian will be
recorded in the rock
record as a gap or
"unconformity"
Under
Water
Most of our
rocks are
sedimentary
Pleistocene Glaciation
Surficial Sediments
Passive Margin
Rifting of Pangea
Red conglomerates, sandstones &
shales + basalt dikes
(Rift Basins)
Alleghanian Orogeny
(Supercontinent Pangea)
For all orogenies metamorphism of rocks in
the eastern mountain belts
(Avalon Terrane)
Catskill Deltas - our local fossil-rich
sandstones & shales
Shales, limestones, evaporites
Taconic Orogeny
Foreland basin - shales, siltstones
Acadian Orogeny
(Volcanic arc)
Passive Margin
Grenville Orogeny
(Supercontinent Rodinia)
Arkosic & quartz sandstones,
limestones
Highly deformed gneisses
What controls the preservation of calcium carbonate deposits in the ocean?
High dissolved carbon dioxide levels = more acidic waters
Low carbon dioxide levels = less acidic waters
carbonates dissolve
carbonates are preserved
So, what controls the level of carbon dioxide in the oceans?
Level of carbon dioxide in the atmosphere:
controlled by rate of sea floor spreading & anthropogenic input
Pressure and temperature
Consider a can of soda…..
Unopened, when the pressure is high, carbon dioxide in solution high
Opened - pressure is released – that noise you hear is the loss of carbon dioxide
Deeper waters are under higher pressure
more dissolved CO2
carbonates dissolve
Cold soda versus the warm soda
Cold soda is fizzy (lots of carbon dioxide), warm soda is flat (not much carbon dioxide)
Colder waters hold more dissolved carbon dioxide
carbonates dissolve
So….MORE CARBONATES PRESERVED IN SHALLOW AND WARM WATERS - TROPICAL