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Transcript
Chapter 10
Early Paleozoic Earth History
New York State
Most surface rocks are from the Paleozoic
Paleozoic History of North America
• Major mountain-building activity
• Shallow-water marine transgressions
and regressions over the interiors
Causes:
global changes in sea level
• plate activity along continental margins
• glaciation
Continental Architecture
• Cratons are stable and “immobile”
a shield and a platform (granite-gneiss)
form the foundation upon which
Phanerozoic sediments were deposited
Mobile Belts
• Areas of mountain building activity –
– “orogenic activity” along the margins of
continents
– sediment are deposits in shallow waters
• continental shelf
– and the deeper waters at the base of the
continental slope
During plate convergence along margins,
the sediments are deformed
– intruded by magma
– mountain ranges are formed from subduction volcanoes
• Or continental collision
Epeiric Seas
• The transgressing and regressing shallow seas
– common feature of Paleozoic
as evidenced by sediments deposited
now forming the surface rock
in New York State
Marcellus
Shale
Devonian Age
Conglomerate
Mt. Marion
Saugerties NY (exit 20 I-87
Oriskany
Sandstone
Near Utica NY
How old are the
Herkimer “diamond”
source rocks?
Paleogeographic Maps
• Geologists use
– paleoclimatic data: (glacial, rock types,
coal)
– paleomagnetic data: (preserved in igneous
rocks) tells latitude and magnetic pole
directions
– paleontologic data: pollens, plants, animals
– sedimentologic data: structures,
environments
– Stratigraphic: data rock relationships and
age
– tectonic data : evidence of plate
boundaries
Six Major Paleozoic Continents
• At the beginning of the Paleozoic:
– 1. Baltica - Russia west of the Ural Mountains
and the major part of northern Europe
– 2. Gondwana - Africa, Antarctica, Australia,
Florida, India, Madagascar, and parts of the
Middle East and southern Europe
– 3. Laurentia - most of present North
America, Greenland, northwestern Ireland,
and Scotland
Six Major Paleozoic Continents
– 4. China - include China, Indochina, and the
Malay Peninsula
– 5. Kazakhstan - a triangular continent
centered on Kazakhstan,
– 6. Siberia - Russia east of the Ural Mountains
and Asia north of Kazakhstan and south
Mongolia
• AND numerous small microcontinents
• and island arcs associated with various
microplates
Paleogeography of the World
• For the Late Cambrian Period
Paleogeography of the World
• For the Late Ordovician Period
Paleogeography of the World
• For the Middle Silurian Period
Early Paleozoic Evolution of North
America
– epeiric seas transgressed and regressed
Over the stable continental interior
– mobile belts where mountain building
occurred
Cratonic Sequences of N. America
• White areas represent sequences of rocks That are separated by
large-scale unconformities shown in brown
Cordillera
orogenies
Appalachia
orogenies
Cratonic Sequence
• A cratonic sequence is
– a large-scale lithostratigraphic unit
representing a major transgressiveregressive cycle
bounded by cratonwide unconformities
Regressing Sea
• White areas = sequences of rocks
• Sauk
sequence
The Sauk Sequence
• Rocks of the Sauk Sequence
– Late Proterozoic-Early Ordovician (long, slow process)
– first major transgression onto the North American
craton
• Deposition of marine sediments :
• passive shelf areas of the East and West borders of craton
•
Many of the Sauk carbonates (limestones) contain fragments of organic
remains – bioclastic rock
• The craton was above sea level
– and experiencing extensive weathering & erosion
SHALLOW WATER DEPOISITION!
The Sauk Sequence:
Middle Cambrian Period
• North America was located in a tropical climate at
this time
– there is no evidence of any terrestrial vegetation,
NO plants!
– Rapid weathering and erosion of the exposed
Precambrian basement rocks
= widespread unconformity
Highlands:
Transcontinental Arch
• By the Late Cambrian,
– the epeiric seas covered most of North America,
• Above the sea:
• a portion of the Canadian Shield
• and a few large islands
• “Transcontinental Arch”
Cambrian Paleogeography of North America
Sauk Transgression
• During this
time North
America
straddled
the equator
• Transcontinental
Arch
A Transgressive Facies Model
• Facies are sediments
that represent a particular environment
• During a transgression:
the coarse (sandstone),
fine (shale) and
carbonate (limestone) facies
migrate in a landward direction
The Cambrian of
the Grand Canyon Region
• Grand Canyon
at western margin of the
craton during Sauk time,
a passive shelf
– most of the craton was still
above sea level
– deposition of marine
sediments
• was at the margins of the
craton
• on continental shelves and
slopes
Evidence of Transgression
– The Tapeats Sandstone represents the shoreline
deposits
are clean, well-sorted sands
– of the type one would find on a beach today
• By Middle Cambrian,
– muds of the Bright Angle Shale
– were deposited over the Tapeats Sandstone
By Late Cambrian
– carbonates of the Muav Limestone were being
deposited over the Bright Angel Shale
Cambrian Transgression
• Cambrian strata in the Grand Canyon
• The three formations exposed
– along the Bright Angel Trail, Grand Canyon
Arizona
Cambrian Transgression
– Observe the time transgressive nature of the
three formations
Regression and Unconformity
• The Sauk Sea regressed
• rocks exposed were predominately
– Limestones: deep extensive erosion
– North America was still located in a tropical
environment – increased weathering
• The resulting cratonwide unconformity
– marks the boundary between the Sauk
– and the NEXT Cratonic sequence
Tippecanoe
Cratonic Sequences of N. America
• White areas = sequences of rocks
Brown
areas =
large-scale”
uncon-formities
• Regression
• Tippecanoe
sequence
Ordovician Period
• Paleogeography of
North America
– showing
change in the
position of
the the
equator
• The continent
– was rotating
counterclockwise
Transgression of the
Tippecanoe Sea
Resulted in
deposition
of the St.
Peter
Sandstone
– Middle
Ordovician
over a large
area of the
craton
St. Peter Sandstone
Outcrop of St. Peter Sandstone in
Governor Dodge State Park, Wisconsin
The Tippecanoe Sequence
• The Tippecanoe basal sandstones were
followed by widespread carbonate
deposition
• The limestones were generally the result of
deposition
– by
calcium carbonatesecreting organisms
such as
•
•
•
•
corals,
brachiopods,
stromatoporoids,
and bryozoans
Tippecanoe Reefs and Evaporites
• Organic reefs
limestone structures constructed by living organisms,
• Today, corals, and calcareous algae
– are the most prominent reef builders,
– but in the geologic past other organisms
– played a major role in reef building
• Reefs appear to have occupied
– the same ecological niche in the geological
past as today
Present-day reefs are
30 degrees north and south of the equator
• Corals require warm, clear, shallow water
– of normal salinity for optimal growth
Present-Day Reef Community
• with reef-building organisms
Reef Environments
• Block diagram of a reef showing the
various environments within the reef
complex
Michigan Basin Evaporites
• significant structure in the region
a broad, circular basin surrounded by large
barrier reefs
• reefs contributed to restricted circulation
– and the precipitation of Upper Silurian
evaporites within the basin
– Evaporites form when water evaporates
and leaves salts and brines behind
halite, gypsum, sylvite
Silurian Period
• Paleogeography
of North America
Silurian Period
• Reefs developed
in the Michigan,
Ohio, and
Indiana-IllinoisKentucky areas
Origin of Thick Evaporites – 1500 m
(Gypsum, Halite)
1. When sea level dropped, the tops of the barrier reefs
were as high as or above sea level,
2. Preventing influx of new seawater into the basin
Evaporation of the basin seawater would result in the
precipitation of salts
2. Alternatively, the reefs grew upward so close to sea
level
– that they formed a sill or barrier that eliminated interior
circulation
Silled Basin Model
• Silled Basin
Model for
evaporite
sedimentatio
n by direct
precipitation
from
seawater
Basin Brines
• Because North America was still near the
equator during the Silurian Period,
– temperatures were probably high
The Appalachian Mobile Belt
– Phanerozoic orogeny – mountain building
Iapetus Ocean was widening as a divergent
plate boundary caused movement
• Beginning with the subduction of the
Iapetus plate beneath Laurentia
– which was an oceanic-continent convergent
plate boundary
• the Appalachian mobile belt was born
The Taconic Orogeny
• The resulting Taconic orogeny,
– Today’s Taconic Mountains
• eastern New York,
• central Massachusetts,
• and Vermont
– First of 3 to form Appalachians
Appalachian Mobile Belt
• Transition to convergence resulted in
orogenic activity
Queenston Delta Clastic Wedge
• Evidence for the Taconic orogeny
• The remnants of the mountains
The remains of a large clastic wedge,
• detrital sediments adjacent to an uplifted area
• thinner and finer grained away from the source area,
• eventually grading into the carbonate cratonic facies
• The clastic wedge resulting from the erosion
of the Taconic Highlands is referred to
as the Queenston Delta
• Queenston Delta clastic
wedge
– coarsegrained
detrital
sediments
near the
highlands
– thins
laterally
into finergrained
sediments
on the
craton
• Taconic
Highland
s
Caledonian Orogeny
• The Caledonian orogeny was a mirror
image of Taconic orogeny
• Caledonians are similar age in Europe
today.
Caledonian Orogeny
• The transition to convergence resulted in
orogenic activity in North America and
Europe
– Caledonian
Orogeny
– was a
mirror
image of
the Taconic
Orogeny
Resources of Early Paleozoic
Sandstone, Salts, Gypsum, natural gas
Igneous minerals during orogeny