Transcript Chapter 14 - Mesozoic Geology

Chapter
14
Mesozoic Earth history
main points…..
1. Mesozoic breakup of Pangaea profoundly
affected geologic and biologic events
2. Triassic-most N America above sea level
3. Jurassic- seaway flooded interior of
western N America
4. gradual sea level rise resulted in vast
shallow sea covering central and western
N America in Cretaceous
5. 4 related orogenies affected western N
America along oceanic-continental plate
boundary
6. terranes and micro plates affected western N
America
7. major Mesozoic mineral resources- coal,
pertroleum, uranium and copper
Mesozoic Era
• The Mesozoic Era
– 245 to 66 million years ago
– was an important time in Earth history
• The major geologic event
– was the breakup of Pangaea,
– which affected oceanic and climatic circulation
patterns
– and influenced the evolution of the terrestrial and
marine biotas
Paleogeography of the World
• During the Triassic Period
Other Mesozoic Events
• Other important Mesozoic geologic events
– resulting from plate movement
• include
1. the origin of the Atlantic Ocean basin
2. and the Rocky Mountains
3. accumulation of vast salt deposits
• that eventually formed salt domes
• adjacent to which oil and natural gas were trapped
4. and the emplacement of huge batholiths
• accounting for the origin of various mineral resources
The Breakup of Pangaea
• Just as the formation of Pangaea
– influenced geologic and biologic events
• during the Paleozoic,
– the breakup of this supercontinent
– profoundly affected geologic and biologic events
• during the Mesozoic
• The movement of continents
– affected the global climatic and oceanic regimes
– as well as the climates of the individual continents
Effect of the Breakup
• Populations became isolated
– or were brought into contact
– with other populations,
– leading to evolutionary changes in the biota
• So great was the effect of this breakup
– on the world,
– that it forms the central theme of this chapter
Progress of the Breakup
• The breakup of Pangaea
– began with rifting
– between Laurasia and Gondwana during the
Triassic
• By the end of the Triassic,
– the expanding Atlantic Ocean
– separated North America from Africa
• This change was followed
– by the rifting of North America from South
America
• sometime during the Late Triassic and Early Jurassic
Paleogeography of the World
• During the Jurassic Period
Oceans Responded to
Continental Separation
• Separation of the continents
– allowed water from the Tethys Sea
– to flow into the expanding central Atlantic Ocean,
• while Pacific Ocean waters
– flowed into the newly formed Gulf of Mexico,
– which at that time was little more than a restricted
bay
• Evaporites formed in these areas
Early Mesozoic Evaporites
• Water from the
Pacific Ocean
flowed into the
the newly
formed Gulf of
Mexico
• Marine water
from the south
flowed into the
area that would
eventually
become the
southern
Atlantic Ocean
Evaporite Deposits
• During that time, these areas were located
–
–
–
–
–
in the low tropical latitudes
where high temperatures
and high rates of evaporation
were ideal for the formation
of thick evaporite deposits
Further Breakup
• During the Late Triassic and Jurassic periods,
– Antarctica and Australia,
• which remained sutured together,
– began separating from South America and Africa
Also during this time,
– India began rifting from the Gondwana continent
• During the Jurassic,
– South America and Africa began separating
Paleogeography of the World
• During the Jurassic Period
Tethys Sea
• During this time, the western end of the Tethys
Sea – circum equatorial seaway
– began closing toward the east
– as a result of the clockwise rotation
– of Laurasia and the northward movement of Africa
• This narrow Late Jurassic and Cretaceous
seaway
– between Africa and Europe
– was the forerunner
– of the present Mediterranean Sea
End of the Cretaceous
• By the end of the Cretaceous,
–
–
–
–
Australia and Antarctica had separated,
India was nearly to the equator,
South America and Africa were widely separated,
and Greenland was essentially an independent
landmass
Paleogeography of the World
• During the Late Cretaceous Period
Higher Heat Flow Caused
Sea Level Rise
• A global rise in sea level
– during the Cretaceous
– resulted in worldwide transgressions
– onto the continents
• These transgressions were caused
– by higher heat flow along the oceanic ridges
– due to increased rifting
– and the consequent expansion of oceanic crust
Middle Cretaceous Sea Level
Was High
• By the Middle Cretaceous,
– sea level was probably as high
– as at any time since the Ordovician,
– and approximately one-third of the present land
area
– was inundated by epeiric seas
Paleogeography of the World
• During the Late Cretaceous Period
Final Stage in Pangaea's Breakup
• The final stage in Pangaea's breakup
– occurred during the Cenozoic
• During this time,
– Australia continued moving northward,
• and Greenland completely separated
– from Europe and North America
– and formed a separate landmass
The Effects on Global Climates
and Ocean Circulation Patterns
• By the end of the Permian Period,
– Pangaea extended from pole to pole,
– covered about one-fourth of Earth's surface,
– and was surrounded by Panthalassa,
• a global ocean that encompassed about 300 degrees of
longitude
• Such a configuration exerted tremendous
influence
– on the world's climate
– and resulted in generally arid conditions
– over large parts of Pangaea's interior
Paleogeography of the World
• For the Late Permian Period
Ocean Currents and Continents
• The world's climates result from the complex
interaction between
– wind and ocean currents
– and the location and topography of the continents
• In general, dry climates occur
–
–
–
–
on large landmasses
in areas remote from sources of moisture
and where barriers to moist air exist,
such as mountain ranges
• Wet climates occur
– near large bodies of water
– or where winds can carry moist air over land
Climate-Sensitive Deposits
• Past climatic conditions can be inferred from
– the distribution of climate-sensitive deposits
• Evaporites are deposited
– where evaporation exceeds precipitation
• While dunes and red beds
– may form locally in humid regions,
– they are characteristic of arid regions
• Coal forms in both warm and cool humid
climates
– Vegetation that is eventually converted into coal
– requires at least a good seasonal water supply
• Thus, coal deposits are indicative of humid
conditions
Evaporites, Red Beds, Dunes, Coal
• Widespread Triassic evaporites, red beds, and
desert dunes
– in the low and middle latitudes
– of North and South America, Europe, and Africa
– indicate dry climates in those regions,
• while coal deposits
– are found mainly in the middle-high latitudes,
– indicating humid conditions
• These high-latitude coals are analogous to
– today's Scottish peat bogs
– or Canadian muskeg
Global Temperature Gradient
• The breakup of Pangaea
–
–
–
–
–
during the Late Triassic
caused the global temperature gradient to increase
because the Northern Hemisphere continents
moved farther northward,
displacing higher-latitude ocean waters
• Decrease in temperature in the high latitudes
– and the changing positions of the continents,
– caused the steeper global temperature gradient
• Thus, oceanic and atmospheric circulation
patterns
– greatly accelerated during the Mesozoic
Oceanic Circulation Evolved
• From a simple pattern in a single ocean
(Panthalassa) with a single continent (Pangaea)
Oceanic Circulation Evolved
• to a more complex pattern in the newly formed
oceans of the Cretaceous Period
Faster Circulation
• The temperature gradient
– between the tropics and the poles
– also affects oceanic and atmospheric circulation
• The greater the temperature difference
– between the tropics and the poles,
– the steeper the temperature gradient
– and the faster the circulation of the oceans and
atmosphere
Areas Dominated by Seas
Are Warmer
• Oceans absorb about 90% of the solar radiation
they receive,
– while continents absorb only about 50%,
– even less if they are snow covered
• The rest of the solar radiation is reflected back
into space
• Therefore, areas dominated by seas are warmer
– than those dominated by continents
Equable Worldwide Climate
• Higher-latitude oceans remained warm
– because warm waters from the Tethys Sea
– were circulating to the higher latitudes
• The result was a relatively equable worldwide
climate
– through the end of the Cretaceous
The Mesozoic History
of North America
• In North America, the beginning of the
Mesozoic Era
– was essentially the same in terms of tectonism and
sedimentation
– as the preceding Permian Period
• Terrestrial sedimentation continued over much
of the craton,
– while block faulting and igneous activity
– began in the Appalachian region
– as North America and Africa began separating
Triassic Fault Basins
• During the Late Triassic,
– the first stage in the
breakup of Pangaea
began
– with North America
separating from
Africa
• Fault-block basins
developed
– in response to
upwelling magma
– beneath Pangaea
– in a zone stretching
– from present-day
Nova Scotia to North
Carolina
Newark Group
• Erosion of the adjacent fault-block mountains
– filled these basins with great quantities
• up to 6000 m
– of poorly sorted red nonmarine detrital sediments
– known as the Newark Group
Down-dropped valleys
accumulated sediments
• Down-dropped valleys accumulated
tremendous thickness of sediments
– and were themselves broken
– by a complex of normal faults during rifting
Reptile Footprints
• Reptiles roamed along the margins
–
–
–
–
of the various lakes and streams
that formed in these basins,
leaving their footprints and trackways
in the soft sediments
• Although the Newark rocks contain numerous
dinosaur footprints,
– they are almost completely devoid of dinosaur
bones!
• The Newark Group is mostly Late Triassic,
– but in some areas deposition began in the Early
Jurassic
Reptile Tracks
Igneous Activity
• Concurrent with sedimentation
–
–
–
–
in the fault-block basins
were extensive lava flows
that blanketed the basin floors
as well as intrusions of numerous dikes and sills
• The most famous intrusion
– is the prominent Palisades sill
– along the Hudson River
– in the New York-New Jersey area
Palisades Sill of the Hudson River
• This sill was one of many that were intruded
into the Newark sediments
– during the Late Triassic rifting
– that marked the separation
– of North America from Africa
Passive Continental Margin
• As the Atlantic Ocean grew,
–
–
–
–
rifting ceased along the eastern margin
of North America,
and this once active plate margin
became a passive, trailing continental margin
• The fault-block mountains
– that were produced by this rifting
– continued eroding
• during the Jurassic and Early Cretaceous
– until all that was left was a large low-relief area
Gulf Coastal Region
• The Gulf
Coastal
region was
above sea
level until the
Late Triassic
- Paleogeographic
Map of North
America during
the Triassic
Period
Evaporites in Gulf of Mexico
• As North America separated from South
America
– during the Late Triassic and Early Jurassic,
– the Gulf of Mexico began to form
• With oceanic waters flowing into
– this newly formed, shallow, restricted basin,
– conditions were ideal for evaporite formation
• These Jurassic evaporites
– are thought to be the source
– for the Tertiary salt domes
– found today in the Gulf of Mexico and southern
Louisiana
Jurassic Period
• Paleogeographic
reconstruction
for the Jurassic
Period
• The Gulf of
Mexico began
to form
• Evaporites
precipitates
Evaporite Deposition Ended
• The history of the Tertiary salt domes
– and their associated petroleum accumulations
– will be discussed with the Cenozoic
• By the Late Jurassic,
– circulation in the Gulf of Mexico
– was less restricted,
– and evaporite deposition ended
Normal Marine Conditions
• Normal marine conditions
– returned to the area
– with alternating transgressing and regressing seas
• The resulting sediments were
– covered and buried by thousands of meters
– of Cretaceous and Cenozoic sediments
• During the Cretaceous,
– the Gulf Coastal region,
– like the rest of the continental margin,
– was inundated by northward-transgressing seas
Transgressions and Regression
• As a result of the transgression,
– nearshore sandstones
– are overlain by finer sediments
– characteristic of deeper waters
• Following an extensive regression
–
–
–
–
at the end of the Early Cretaceous,
a major transgression began
during which a wide seaway extended
from the Arctic Ocean to the Gulf of Mexico
• Sediments that were deposited in the Gulf
Coastal region
– formed a seaward-thickening wedge
Cretaceous Period
• Paleogeography
of North America
during the
Cretaceous
Period
• Cretaceous
interior seaway
Cretaceous Bivalve Reefs
• Reefs were also widespread
– in the Gulf Coastal region during the Cretaceous
• Bivalves called rudists
– were the main constituent of many of these reefs
– Rudists are excellent guide fossils
• Because of their high porosity and permeability,
– rudistoid reefs make excellent petroleum reservoirs
– A good example of a Cretaceous reef complex occurs in
Texas
Gulf Shelf-Margin Facies
• Early Cretaceous
shelf-margin
facies around the
Gulf of Mexico
Basin
• The reef trend
shows as a black
line
Reef Environments
• Depositional environment and facies changes
across the Stuart City reef trend, South Texas
• Mesozoic orogenies- 4
– occurring in the
Cordilleran mobile belt
– Start with the first
one….Sonoma
Orogeny
Triassic Period
• Paleogeography
of North
America during
the Triassic
Period
– with a
volcanic
island arc in
the west
1. Sonoma Orogeny
• During the Permian, however,
–
–
–
–
–
–
–
an island arc and ocean basin formed
off the western North American craton
followed by subduction of an oceanic plate
beneath the island arc
and the thrusting of oceanic
and island arc rocks
eastward against the craton margin
• This event, known as the Sonoma orogeny,
– occurred at or near the Permian-Triassic boundary
Steeply Dipping Subduction Zone
• During the Late Triassic,
–
–
–
–
a steeply dipping subduction zone developed
along the western margin of North America
in response to the westward movement
of North America over the Farallon plate
• This newly created oceanic-continental plate
boundary
–
–
–
–
–
controlled Cordilleran tectonics
for the rest of the Mesozoic Era
and for most of the Cenozoic Era
this subduction zone marks the beginning
of the modern circum-Pacific orogenic system
Steeply Dipping Subduction Zone
• Interpretation of the tectonic setting
– of western North America
– during the Late Triassic to Early Jurassic
• Plutons of the Sierra Nevada began forming
2 Distinctive deposits-Franciscan Complex
• The Franciscan Complex, California,
– which is up to 7000 m thick,
– is an unusual rock unit
– consisting of a chaotic mixture of
rocks
– that accumulated during the Late
Jurassic and Cretaceous
• The various rock types include
– graywacke, volcanic breccia,
siltstone, black shale,
– chert, pillow-basalt, and blueschist
• a low temperature, high pressure
metamorphic rock
Depositional Environment
• Reconstruction of the depositional environment
– of the Franciscan Complex
– during the Late Jurassic and Cretaceous periods
Franciscan Complex
• Exposures of the Franciscan Complex along
the central California coast
Great Valley Group
• East of the Franciscan Complex
– and currently separated from it
– by a major thrust fault
– is the Great Valley Group
• It consists of more than 16,000 m
– of Cretaceous conglomerates, sandstones,
siltstones, and shales
• These sediments were deposited
– on the continental shelf and slope
– at the same time the Franciscan deposits
– were accumulating in the submarine trench
Great Valley Group Environment
• Environments of the Great Valley Group
– in relation to the Franciscan Complex
Cordilleran Orogeny
• The general term Cordilleran orogeny
– is applied to the mountain-building activity
– that began during the Jurassic
– and continued into the Cenozoic
• The Cordilleran orogeny
– consisted of a series
– of individual mountain-building events
– that occurred in different regions at different
times
• Most of this Cordilleran orogenic activity
– is related to the continued westward movement of the North
American plate
2. Nevadan Orogeny
• The first phase of the Cordilleran orogeny,
–
–
–
–
–
–
the Nevadan orogeny,
began during the Late Jurassic
and continued into the Cretaceous
as large volumes of granitic magma
were generated at depth
beneath the western edge of North America
• These granitic masses
– ascended as huge batholiths
– that are now recognized as
– the Sierra Nevada, Southern California, Idaho, and
Coast Range batholiths
Batholiths
• Location of Jurassic and
Cretaceous batholiths
– in western North
America
Plutonic Activity
Migrated Eastward
• By the Late Cretaceous,
– most of the volcanic and plutonic activity
– had migrated eastward into Nevada and Idaho
• This migration was probably caused
– by a change from high-angle to low-angle
subduction,
– resulting in the subducting oceanic plate
– reaching its melting depth farther east
Eastward Migrating
• A possible
cause
– for the
eastward
migration
– of Cordilleran
igneous
activity
– during the
Cretaceous
– was a change
from high
angle
subduction to
Lower-Angle Subduction
• to low-angle
subduction
• As the
subducting
plate
– moved
downward
– at a lower
angle,
– its melting
depth
– moved farther
to the east
3. Sevier Orogeny
• Thrusting occurred progressively farther east
– so that by the Late Cretaceous,
– it extended all the way
– to the Idaho-Washington border
• The second phase of the Cordilleran orogeny,
– the Sevier orogeny,
– was mostly a Cretaceous event
Thrust Faults
• Subduction of the Farallon plate
– beneath the North American plate continued during
this time,
– resulting in numerous overlapping,
– low-angle thrust faults
– in which blocks of older strata
– were thrust eastward
– on top of younger strata
• This deformation produced
– generally north-south-trending mountain ranges
– that stretch from Montana to western Canada
Sevier Orogeny
• Associated tectonic features
– of the Late
Cretaceous
Sevier orogeny
– due to
subduction of
the Farallon
plate
– under the North
American plate
Keystone Thrust Fault
• The Keystone thrust fault is a major fault
in the Sevier overthrust belt
– It is exposed west of Las Vagas, Nevada
• The sharp boundary
– between the light-colored Mesozoic rocks
– and the overlying dark-colored Paleozoic
rocks
• marks the trace of the Keystone thrust
fault
Keystone Thrust Fault
4. Laramide orogeny
• During the Late Cretaceous to Early Cenozoic,
– the final pulse of the Cordilleran orogeny
occurred
• The Laramide orogeny
– developed east of the Sevier orogenic belt
– in the present-day Rocky Mountain areas
– of New Mexico, Colorado, and Wyoming
Present-Day Rocky Mountains
• Most of the features
– of the present-day Rocky Mountains
– resulted from the Cenozoic phase
– of the Laramide orogeny,
– and for that reason,
– we will discuss it with Cenozoic tectonics
Mesozoic Sedimentation
• Concurrent with the tectonism
– in the Cordilleran mobile belt,
• Early Triassic sedimentation
– on the western continental shelf
– consisted of shallow-water marine
– sandstones, shales, and limestones
• During the Middle and Late Triassic,
– the western shallow seas
– regressed farther west,
– exposing large areas of former seafloor to erosion
Stratigraphic section of Triassic formations in the
western United States
• Kayenta: fluvial, lake
• Wingate: desert dune
• Chinle: petrified wood,
amphibians; fluvial
deltaic sediments
• (Petrified Forest)
• Shinarump:
conglomerate
• Moenkopi: shale, red
beds…non marine
Early Jurassic Sandstones
• Early Jurassic deposits
– in a large part of the western region
– consist mostly of clean, cross-bedded sandstones
– indicative of windblown deposits
• The thickest and most prominent of these is the
Navajo Sandstone,
– a widespread cross-bedded sandstone
– that accumulated in a coastal dune environment
– along the southwestern margin of the craton
Navajo Sandstone, Zion Canyon
• View of East Entrance of Zion Canyon, Zion
National Park, Utah
• The light-colored massive rocks
– are the Jurassic Navajo Sandstone
• while the slope-forming rocks below the
Navajo
– are the Upper Triassic Kayenta Formation
• The Navajo Sandstone's most distinguishing feature-is
its large-scale cross-beds indicative of Sand Dunes,
some of which are more than 25 m high, in Zion
National Park, Utah
Sundance Sea
• The upper part of the Navajo
– contains smaller cross-beds
– as well as dinosaur and crocodilian fossils
• Marine conditions returned to the region
– during the Middle Jurassic
– when a seaway called the Sundance Sea
– twice flooded the interior of western North America
Sundance Sea Retreated Northward
• These highlands
– resulted from intrusive igneous activity
– and associated volcanism
– that began during the Triassic
• During the Late Jurassic,
–
–
–
–
a mountain chain formed
in Nevada, Utah, and Idaho
as a result of the deformation
produced by the Nevadan orogeny
• As the mountain chain grew
– and shed sediments eastward,
– the Sundance Sea began retreating northward
Morrison Formation
• A large part of the area
– formerly occupied by the Sundance Sea
– was then covered
– by multicolored sandstones, mudstones, shales, and
occasional lenses of conglomerates
– that comprise the world-famous Morrison
Formation
• The Morrison Formation
– contains the world's richest assemblage
– of Jurassic dinosaur remains
Morrison Formation
• View of the Jurassic Morrison Formation
– from the Visitors’ center
– at Dinosaur National Monument, Utah
Skeletons Deposited on Sandbars
• Although most of the dinosaur skeletons
– are broken up,
– as many as 50 individuals
– have been found together in a small area
• Such a concentration indicates
– that the skeletons were brought together
– during times of flooding and deposited on sandbars
• in stream channels
• Soils in the Morrison indicate
– that the climate was seasonably dry
Dinosaur National
Monument
• Although most major
museums have either
– complete dinosaur skeletons
– or at least bones from the Morrison Formation,
– the best place to see the bones still embedded in the rocks
– is the visitors' center at Dinosaur National Monument near
Vernal, Utah
• The north wall of the visitors’ center
– shows dinosaur bones in bas relief
– just as they were deposited 140 million years ago
Mid-Cretaceous Transgressions
• Shortly before the end of the Early Cretaceous,
– Arctic waters spread southward
– over the craton, forming a large inland sea
– in the Cordilleran foreland basin area
• Mid-Cretaceous transgressions
–
–
–
–
–
also occurred on other continents,
and all were part of the global mid-Cretaceous
rise in sea level
that resulted from accelerated seafloor spreading
as Pangaea continued to fragment
Cretaceous Interior Seaway
• By the beginning of the Late
Cretaceous,
– this incursion
– joined the northward-transgressing
waters from the Gulf area
– to create an enormous
Cretaceous Interior Seaway
– that occupied the area east of the
Sevier orogenic belt
Cretaceous deposits
• Cretaceous deposits
– less than 100 m thick indicate
– that the eastern margin of the Cretaceous Interior
Seaway
– subsided slowly
– and received little sediment
– from the emergent, low-relief craton to the east
• The western shoreline, however,
–
–
–
–
shifted back and forth,
primarily in response to fluctuations
in the supply of sediment
from the Cordilleran Sevier orogenic belt to the
west
Facies Relationships
• The facies relationships
– show lateral changes
– from conglomerate and coarse sandstone adjacent
to the mountain belt
– through finer sandstones, siltstones, shales,
– and even limestones and chalks in the east
• During times of particularly active mountain
building,
– these coarse clastic wedges of gravel and sand
– prograded even further east
Cretaceous Facies Related to Sevier
• This restored west-east cross section
– of Cretaceous facies of the western Cretaceous
Interior Seaway
– shows the facies relationship to the Sevier orogenic
belt
Exotic Terranes-along W coast
• Geologists now know that portions of many
mountain systems
– are composed of small accreted lithospheric blocks
– that are clearly of foreign origin
• These terranes
–
–
–
–
–
–
differ completely in their fossil content,
stratigraphy, structural trends,
and paleomagnetic properties
from the rocks
of the surrounding mountain system
and adjacent craton
Accreting Terranes Scraped off
• The accreting terranes
–
–
–
–
–
–
are composed of volcanic island arcs,
oceanic ridges,
seamounts,
volcanic plateaus,
hot spot tracks,
and small fragments of continents
• that were scraped off and accreted
– to the continent's margin
– as the oceanic plate with which they were carried
– was subducted under the continent
Terranes of Western
North America
• Some of the accreted lithospheric
blocks
– called terranes
– that form the western margin
– of the North American Craton
• The dark brown blocks
– probably originated as terranes
– and were accreted to North America
• The light green blocks
– are possibly displaced parts of
North America
• Dark green
– represents the North American
craton
Mesozoic Mineral Resources
• Although much of the coal in North America
– is Pennsylvanian or Tertiary in age,
– important Mesozoic coals
– occur in the Rocky Mountains states
• These are mostly lignite and bituminous coals,
– but some local anthracites are present as well
• Particularly widespread in western North
American
– are coals of Cretaceous age
• Mesozoic coals are also known
– from Alberta and British Columbia, Canada,
– as well as from Australia, Russia, and China
Petroleum in Gulf
• Large concentrations of petroleum
– occur in many areas of the world,
– but more than 50% of all proven reserves
– are in the Persian Gulf region
• During the Mesozoic Era,
– what is now the Gulf region
– was a broad passive continental margin
– conducive for the formation of petroleum
• Similar conditions existed in what is now the
Gulf Coast region
– of the United States and Central America
Gulf Coast Region
• Here, petroleum and natural gas
– also formed on a broad shelf
– over which transgressions and
regressions occurred
• In this region, the hydrocarbons
– are largely in reservoir rocks
– that were deposited
– as distributary channels on deltas
– and as barrier-island and beach sands
• Some of these hydrocarbons are associated
– with structures formed adjacent to rising salt domes
Louann Salt
• Salt
deposits
in the
Gulf of
Mexico
• formed
during the
initial
opening
of the
Atlantic
Uranium Ores
• The richest uranium ores in the United States
– are widespread in Mesozoic rocks
– of the Colorado Plateau area of Colorado
– and adjoining parts of Wyoming, Utah, Arizona, and
New Mexico
• These ores, consisting of fairly pure masses
– of a complex potassium-, uranium-, vanadiumbearing mineral
• called carnotite,
– are associated with plant remains in sandstones
– that were deposited in ancient stream channels
Mesozoic Iron Ores
• Proterozoic banded iron formations
– are the main sources of iron ores
• Exceptions exist such as
– the Jurassic-age "Minette" iron ores of Western
Europe,
– which are composed of oolitic limonite and hematite,
– and are important ores in France, Germany, Belgium,
and Luxembourg
• In Great Britain, low-grade Jurassic iron ores
– consist of oolitic siderite, which is an iron carbonate
• In Spain, Cretaceous rocks are the host rocks for
iron minerals
Kimberlite Pipes
• South Africa,
• the world's leading producer
• of gem quality diamonds
• and among the leaders in industrial diamond production,
– mines these minerals from conical igneous
intrusions
• called kimberlite pipes
• Kimberlite pipes
– are composed of dark gray or blue igneous rock
known as kimberlite
Mother Lode
• Emplacement of Triassic and Jurassic
– diamond-bearing kimberlites
– also occurred in Siberia
• The mother lode
• or source for the placer deposits mined during the
California gold rush
– is in Jurassic-age intrusive rocks of the Sierra
Nevada
• Gold placers are also known in Cretaceous-age
conglomerates
– of the Klamath Mountains of California and
Oregon
Porphyry Copper
• Porphyry copper was originally named
– for copper deposits in the western United States
– mined from porphyritic granodiorite,
– but the term now applies to large, low-grade copper
deposits
– disseminated in a variety of rocks
• These porphyry copper deposits
– are an excellent example of the relationship
– between convergent plate boundaries
– and the distribution, concentration, and exploitation
of valuable metallic ores
Plate Tectonics and the
Distribution of Natural Resources
• Magma generated by subduction can create
this activity
– Bingham Mine in Utah is a
– Example: copper
deposits in
western Americas
huge open-pit copper mine
Summary
• Summary of the breakup of Pangaea
a. During the Late Triassic,
• North America began separating from Africa
• This was followed by the rifting
• of North America from South America
b. During the Late Triassic and Jurassic periods,
• Antarctica and Australia,
– which remained sutured together
• began separating from South America and Africa,
• while India began rifting from Gondwana
Summary
c. South America and Africa
•
•
•
•
began separating
during the Jurassic
and Europe and Africa
began converging during this time
d. The final stage in Pangaea's breakup
• occurred during the Cenozoic
• when Greenland separated
• from Europe and North America
Summary
• The breakup of Pangaea influenced
– global climatic
– and atmospheric circulation patterns
• While the temperature gradient
– from the tropics to the poles
– gradually increased during the Mesozoic
– overall global temperatures remained equable
• An increased rate of seafloor spreading
– during the Cretaceous Period
– caused sea level to rise
– and transgressions to occur
Summary
• Except for incursions along the continental
margin and two major transgressions
– the Sundance Sea and the Cretaceous Interior
Seaway
– the North American craton was above sea level
during the Mesozoic Era
• The Eastern Coastal Plain
– was the initial site of the separation of North
America from Africa
– that began during the Late Triassic
Summary
• During the Cretaceous Period,
– the Coastal Plain was inundated by marine
transgressions
• The Gulf Coastal region
– was the site of major evaporite accumulation
– during the Jurassic
– as North America rifted from South America
• During the Cretaceous, it was inundated
– by a transgressing sea, which, at its maximum,
– connected with a sea transgression from the
north
– to create the Cretaceous Interior Seaway
Summary
• Mesozoic rocks of the western region of
North America
– were deposited in a variety of continental and
marine environments
– One of the major controls of sediment
distribution patterns was tectonism
• Western North America was affected by
four interrelated orogenies
– the Sonoma, Nevadan, Sevier, and Laramide
– Each involved igneous intrusions,
– as well as eastward thrust faulting and folding
Summary
• The cause of the Sonoma, Nevadan, Sevier,
and Laramide orogenies
– was the changing angle of subduction of the
oceanic Pacific plate
– under the continental North American plate
• The timing, rate, and, to some degree, the
direction of plate movement
– were related to seafloor spreading
– and the opening of the Atlantic Ocean
Summary
• Orogenic activity
– associated with the oceanic-continental
convergent plate boundary
– in the Cordilleran mobile belt
– explains the structural features
– of the western margin of North American
• It is thought, however,
– that more than 25% of the North American
western margin
– originated from accretion of terranes
Summary
• Mesozoic rocks
– contain a variety of mineral resources,
– including
•
•
•
•
•
coal,
petroleum,
uranium,
gold
and copper
Nevadan Orogeny and Gold
• Approximately 150 to 210 million years after
– the emplacement of massive plutons created the
Sierra Nevada
• in the Nevadan orogeny
– gold was discovered at Sutter's Mill
• on the South Fork of the American River at Coloma,
California
• On January 24, 1848, James Marshall,
– a carpenter building a sawmill for John Sutter,
– found bits of the glittering metal in the mill's
tailrace
Gold Rush
• Soon, settlements throughout the state
– were completely abandoned as word
– of the chance for instant riches
– spread throughout California
• Within a year after
– the news of the gold discovery reached the East
Coast,
– the Sutter's Mill area was swarming with more than
80,000 prospectors,
– all hoping to make their fortune
Gold Mining
• By 1852,
– mining
operations were
well underway
– on the
American
River near
Sacramento
Prospecting Was Very Hard Work
• In all, at least 250,000 gold seekers
– prospected the Sutter's Mill area,
• and though most were Americans,
– they came from all over the world,
• even as far away as China
• Most of them thought
– the gold was simply waiting to be taken,
– and didn't realize that prospecting
– was very hard work
Shopowners Made More Money
• Of course, no one gave any thought
– to the consequences of so many people converging
on the Sutter's Mill area,
– all intent on making easy money
• In fact, life in the mining camps
– was extremely hard and expensive
• Frequently, the shopowners and traders
– made more money than the prospectors
Abandoning Their Dream
• In reality, only a small percentage of
prospectors
– ever hit it big
– or were even moderately successful
• The rest barely eked out a living
– until they eventually abandoned their dream and
went home
Placer Gold
• The gold these prospectors sought was mostly
in the form of placer deposits
• Placer deposits form
– when gold-bearing igneous rocks weather
– Stream transport mechanically separates minerals
• by density
• Although many prospectors searched for the
mother lode,
– all of the gold recovered during the gold rush came
from placers
Gold Panning
• Panning is a common method of mining placer
deposits
• In this method,
– a shallow pan is dipped into a streambed,
– the material is swirled around
– and the lighter material is poured off
• Gold, being about six times heavier
– than most sand grains and rock chips,
– concentrates on the bottom of the pan
– and can then be picked out
$200 million in gold
• Although some prospectors
–
–
–
–
–
dug $30,000 worth of gold dust a week
out of a single claim
and gold was found practically on the surface
most of this easy gold was recovered
very early during the gold rush
• Most prospectors made only a living wage
working their claims
• Nevertheless, during the five years
• from 1848 to 1853
– that constituted the gold rush proper,
– miners extracted more than $200 million in gold
Navajo Sandstone, Zion Canyon
Navajo Sandstone, Zion Canyon
Bordering the Tethys Sea
• The lands bordering the Tethys Sea
– were probably dominated by seasonal monsoon
rains
– resulting from the warm moist winds
– and warm oceanic currents
– impinging against the east-facing coast of
Pangaea
Reptile Tracks
•
•
Reptile tracks in the Triassic Newark Group
– were uncovered during the excavation
– for a new state building in Hartford, Connecticut
Because the tracks were so spectacular,
– the building side was moved
– and the excavation was designated as a state park
Cretaceous Period
• Paleogeography
of North America
during the
Cretaceous
Period
– with its
northwardtransgressing
seas
Cordilleran
Mobile Belt
• Mesozoic orogenies
– occurring in the
Cordilleran mobile belt
Keystone Thrust Fault
Microplate Tectonics—Growth of
Western North America
• As we have seen, convergent plate boundaries
– resulted in continental accretion
• Much of the material accreted to continents
– during such events is simply eroded older
continental crust,
• but a significant amount of new material
– is added to continents
– such as igneous rocks that formed as a consequence
– of subduction and partial melting
Accretion of Microplates
• While subduction
– is the predominant influence
– on the tectonic history
– in many regions of orogenesis,
• other processes are also involved
– in mountain building
– and continental accretion,
– especially the accretion of microplates
More Than 25% Accreted Terranes
• In fact, terranes are so different from adjacent
rocks
–
–
–
–
–
that most geologists think they formed elsewhere
and were carried great distances
as parts of other plates
until they collided
with other microplates or continents
• Geologic evidence indicates
–
–
–
–
that more than 25%
of the entire Pacific Coast
from Alaska to Baja California
consists of accreted terranes
Maastrichtian Period
Thick Southern Ocean Evaporites
• Marine
water
flowed into
the
southern
Atlantic
Ocean
from the
south
Cratonic Sequences of N. America
• Zuni
sequence
• Absaroka sequence
Gulf of Mexico
• The newly forming Gulf of Mexico
– experienced extensive evaporite deposition
– during the Late Triassic and Jurassic
– as North America separated from South America
Eastern Continental Shelf
• The sediments produced
– by this erosion
– contributed to the growing eastern continental shelf
• During the Cretaceous Period,
–
–
–
–
–
–
the Appalachian region was uplifted
and once again shed sediments
onto the continental shelf,
forming a gently dipping,
seaward-thickening wedge of rocks
up to 3000 m thick
Seaward-Thickening Wedge
• The seaward-thickening wedge of rocks
–
–
–
–
is currently exposed
in a belt extending from
Long Island, New York,
to Georgia
Rudist Reef Facies Patterns
• Here the reef trend
– had a strong influence
– on the carbonate platform deposition of the region
• The facies patterns of these carbonate rocks
– are as complex as those found
– in the major barrier-reef systems
– of the Paleozoic Era
Western Region—
Mesozoic Tectonics
• The Mesozoic geologic history
–
–
–
–
–
of the North American Cordilleran mobile belt
is very complex,
involving the eastward subduction
of the oceanic Farallon plate
under the continental North American plate
• Activity along this oceanic-continental
convergent plate boundary,
– resulted in an eastward movement of deformation
Cordilleran Orogenic Activity
• This orogenic activity
– progressively affected
– the trench and continental slope, the continental
shelf, and the cratonic margin,
– causing a thickening of the continental crust
• Except for the Late Devonian-Early
Mississippian Antler orogeny,
– the Cordilleran region of North America
experienced little tectonism during the Paleozoic
Two Subduction Zones
• Two subduction zones,
– dipping in opposite directions from each other,
– formed off the west coast of North America
– during the Middle and early Late Jurassic
The North American Overrode
the Farallon Plate
• The more westerly subduction zone
– was eliminated
– by the westward-moving North American plate,
– which overrode the oceanic Farallon plate
Petrified Wood and Plants Fossils
• Whereas fossil ferns are found here,
–
–
–
–
the park is best known for
its abundant and beautifully preserved logs
of gymnosperms especially conifers
and plants called cycads
• Fossilization resulted from the silicification of
the plant tissues
• Weathering of volcanic ash beds
– interbedded with fluvial and deltaic Chinle
sediments
– provided most of the silica for silicification
Cycads
Fossilization
• Some trees were preserved in place,
– but most were transported during floods
– and deposited on sandbars
– and on floodplains,
– where fossilization took place
• After burial, silica-rich groundwater
– percolated through the sediments
– and silicified the wood
Other Fossils
• Though best known for its petrified wood,
– the Chinle Formation has also yielded fossils of
• labyrinthodont amphibians,
• phytosaurs,
• and small dinosaurs
• The section on Mesozoic life will cover the
latter two animal groups
Upward in the Stratigraphy
• The Wingate Sandstone,
–
–
–
–
a desert dune deposit,
and the Kayenta Formation,
a stream and lake deposit,
overlie the Chinle Formation
• These two formations are well exposed
– in southwestern Utah and complete the Triassic
stratigraphic succession
– in the Southwest
Triassic Formations
• Stratigraphic
section of Triassic
formations in the
western United
States
Sedimentary Structures
• Such sedimentary structures
– as desiccation cracks and ripple marks,
• as well as fossil amphibians and reptiles and their tracks,
– indicate deposition in a variety of continental
environments,
• including stream channels, floodplains, and fresh and
brackish water ponds
• Thin tongues of marine limestones
– indicate brief incursions of the sea,
– while local beds with gypsum and halite crystal
casts
– attest to a rather arid climate
Shinarump and Chinle
• Unconformably overlying the Moenkopi
– is the Upper Triassic Shinarump Conglomerate,
– a widespread unit generally less than 50 m thick
• Above the Shinarump
– are the multicolored shales, siltstones, and
sandstones
– of the Upper Triassic Chinle Formation
• This formation is widely exposed
– throughout the Colorado Plateau
– and is probably most famous for its petrified wood,
– spectacularly exposed in Petrified Forest National
Park, Arizona
Triassic Formations
• Stratigraphic
section of Triassic
formations in the
western United
States
Cretaceous Interior Seaway
• Extending from the Gulf of Mexico
– to the Arctic Ocean
– and more than 1500 km wide at its maximum
extent,
• this seaway
– effectively divided North America
– into two large landmasses
– until just before the end of the Late Cretaceous
New Additions
• Furthermore, these accreted microplates
– are often new additions to a continent,
– rather than reworked older continental material
• So far, most microplates
–
–
–
–
have been identified in mountains
of the North American Pacific Coast region,
but a number of such plates are suspected
to be present in other mountain systems as well
• They are more difficult to recognize in older
mountain systems,
– such as the Appalachians, however,
– because of greater deformation and erosion
Microplate Tectonics Provides
• Thus, microplate tectonics
–
–
–
–
provides another way
of viewing Earth
and gaining a better understanding
of the geologic history of the continents
Franciscan Complex
• The rock types suggest
– that continental shelf, slope, and deep-sea
environments
– were brought together
– in a submarine trench
– when North America overrode the subducting
Farallon plate
Continued Tectonic Evolution
Thick Evaporites from the
Southern Ocean
• The subsequent separation of South America
and Africa
–
–
–
–
formed a narrow basin
where thick evaporite deposits
accumulated from the evaporation
of southern ocean waters
Early Mesozoic Evaporites
• Evaporites
accumulated in
shallow basins
– as Pangaea
broke apart
during the Early
Mesozoic
– Water from the
Tethys Sea
flowed into the
Central Atlantic
Ocean
Growth along Active Margins
• The basic plate tectonic reconstruction
– of orogenies and continental accretion
– remains unchanged,
• but the details of such reconstructions
– are decidedly different
– in view of microplate tectonics
• For example, growth along active continental
margins
– is faster than along passive continental margins
– because of the accretion of microplates
Sonoma Orogeny
• Tectonic activity that culminated
– in the Permian-Triassic Sonoma orogeny
• in western
North
America
– was the result
of a collision
– between the
southwestern
margin of
North America
– and an island
arc system
Oceanic-Continental Convergent
Plate Boundary
• Following
– destruction of the volcanic island arc
– during the Late Paleozoic-Early Mesozoic Sonoma
orogeny,
– the western margin of North America
– became an oceanic-continental convergent plate
boundary
Paleogeography of the World
• During the Late Cretaceous Period
Fault-Block Basins
• After the Appalachians were eroded to a lowlying plain
– by the Middle Triassic,
• fault-block basins formed
– as a result of Late Triassic rifting
– between North America and Africa
Global Sea-Level Rise
• A global rise in sea level
– during the Cretaceous
– resulted in worldwide transgressions
– onto the continents such that marine deposition
– was continuous over much of the North American
Cordillera
Next, Specific Regions
• Keeping in mind this simplified overview
– of the Mesozoic history of North America,
– we will now examine the specific regions of the
continent
More Than 100 Terranes
• It is estimated that more than 100 differentsized terranes
– have been added to the western margin
– of North America
– during the last 200 million years
• A good example of this
– is the Wrangellian Terranes
– which have been accreted
– to North America's western margin
Permian Period
• Paleogeography
of North
America during
the Permian
Period
Volcanic Island Arc at the
Western Edge of the Craton
• A volcanic island arc system
– that formed off the western edge of the craton
– during the Permian
• was sutured to North America
– sometime later during the Permian or Triassic
• This event is referred to as the Sonoma
orogeny
– and will be discussed later
Triassic Period
• Paleogeography
of North
America during
the Triassic
Period
Cordilleran Area
• During the Jurassic,
–
–
–
–
–
–
the entire Cordilleran area
was involved in a series
of major mountain-building episodes
that result in the formation of the Sierra Nevada,
the Rocky Mountains,
and other lesser mountain ranges
• While each orogenic episode
– has its own name,
– the entire mountain-building event
– is simply called the Cordilleran orogeny
Jurassic Period
• Paleogeography
of North
America during
the Jurassic
Period
Continental Interior
• Recall that the history of the North American
craton
– can be divided into unconformity-bound sequences
– reflecting advances and retreats
– of epeiric seas over the craton
• While these transgressions and regressions
– played a major role in the Paleozoic geologic history
of the continent,
– they were not as numerous during the Mesozoic
Cratonic Sequences of N. America
• White areas represent sequences of rocks
• that are
separated
by largescale
unconformities
• shown in
brown
Continental Interior With Inundation
• Cratonic sequences are less important because
–
–
–
–
most of the continental interior
during the Mesozoic
was well above sea level
and did not experience epeiric sea inundation
• As we examine the Mesozoic history
– of the continental margin regions of North America
• in the next section,
• we will include the two cratonic sequences,
– the Absaroka sequence
• Late Mississippian to Early Jurassic
– and Zuni sequence
• Early Jurassic to Early Paleocene
Eastern Coastal Region
• During the Early and Middle Triassic,
– coarse detrital sediments derived from the erosion
of the recently uplifted Appalachians
• Alleghenian Orogeny
– filled the various inter-montane basins
– and spread over the surrounding areas
• As erosion continued during the Mesozoic,
– this once lofty mountain system was reduced to a
low-lying plain
Navajo Sandstone's
Large-Scale Cross-Beds
• The Navajo Sandstone's most distinguishing
feature
– is its large-scale cross-beds,
– some of which are more than 25 m high
Terranes of Western
North America
• The light green blocks
– are possibly displaced parts of
North America
• Dark green
– represents the North
American craton
Oceans Still Quite Warm
• By knowing the distribution of continents and
ocean basins,
–
–
–
–
geologists can generally estimate
the average annual temperature
for any region on Earth,
as well as determining a temperature gradient
• Though the temperature gradient and
seasonality on land
– were increasing during the Jurassic and Cretaceous,
– the middle- and higher-latitude oceans
– were still quite warm
Fault-block Basins
• During the Late Triassic,
– the first stage in the breakup of Pangaea began
– with North America separating from Africa
• Fault-block basins developed
–
–
–
–
in response to upwelling magma
beneath Pangaea
in a zone stretching
from present-day Nova Scotia to North Carolina
Reef-Building Bivalves
• Two genera of Cretaceous bivalves known as
rudists replaced corals as the main reefbuilding animals of the Mesozoic
Franciscan Complex
• Map showing the
location of the
Franciscan Complex
Cordilleran
Mobile Belt
• Mesozoic orogenies
– occurring in the Cordilleran
mobile belt
– Nevadan orogeny
Cordilleran
Mobile Belt
• Mesozoic orogenies
– occurring in the Cordilleran
mobile belt
– Sevier orogeny
Cordilleran
Mobile Belt
• Mesozoic orogenies
– occurring in the Cordilleran
mobile belt
– Laramide orogeny
Marine and Nonmarine Triassic
Rocks Make Colorful Scenery
• Marginal marine and nonmarine Triassic rocks,
– particularly red beds,
– contribute to the spectacular
– and colorful scenery of the region
• The Lower Triassic Moenkopi Formation
– of the southwestern United States
– consists of a succession of brick-red
– and chocolate-colored mudstones
Sundance Sea
• The resulting
deposits,
– the Sundance
Formation,
– were produced
from erosion
– of tectonic
highlands to
the west
– that paralleled
the shoreline
North Wall
Cretaceous Interior Seaway
• Paleogeography
of North America
during the
Cretaceous
Period
• Cretaceous
Interior Seaway
Louann Salt
• The salt, called the Louann Salt,
– initially formed in a long, narrow sea
– when North America separated from Europe and
North Africa
– during the fragmentation of Pangaea in the Jurassic
Cretaceous Kimberlite Pipes
• Diamonds,
• which form at great depth where pressure and
temperature are high,
– are brought to the surface
• during the explosive volcanism
• that forms kimberlite pipes
• Although kimberlite pipes have formed
throughout geologic time,
–
–
–
–
the most intense episode
of such activity in South Africa
and adjacent countries
was during the Cretaceous Period
Tertiary Salt Domes
Origin of Porphyry Copper
• Magma generated by partial melting
– of a subducting plate
– rises toward the surface,
– and as it cools, it precipitates and concentrates
various metallic ores
• The world's largest copper deposits
– were formed during the Mesozoic and Tertiary
– in a belt along the western margins
– of North and South America