Transcript Chapter 11 - HCC Learning Web

Chapter 11
Late Paleozoic Events
Paleozoic
overview
Paleozoic Era
Paleozoic can be divided into:
• Early Paleozoic = Cambrian, Ordovician
and Silurian
• Late Paleozoic = Devonian, Mississippian,
Pennsylvanian, and Permian
Carboniferous
• Mississippian and Pennsylvanian Periods are
also referred to with one name - Carboniferous
Period.
• Large plants (including spore-bearing trees and
seed ferns) colonized the land during Late
Paleozoic. Accumulation of plant remains in
swamps produced the vast coal deposits for
which Carboniferous was named.
Late Paleozoic
plate geography
• The supercontinent
Pangea assembled
as the continents
collided during Late
Paleozoic.
• Larger continents
grew by addition of
island arcs and
microcontinents
around their edges.
Late Paleozoic Orogenies of
eastern North America
Continental collisions caused several
orogenies or mountain-building events in
eastern North America.
1. Acadian orogeny and Caledonian
orogeny
2. Alleghanian orogeny in eastern North
America and Hercynian orogeny in
central Europe
Late Paleozoic Orogenies of
eastern North America
1. Acadian orogeny and Caledonian
orogeny
– Middle Silurian to Middle Devonian.
– Laurentia (North America) and Baltica
(Europe) collide to form Laurasia.
– A volcanic island arc (Avalon terrane or
Carolina terrane) collides with eastern North
America.
Late Paleozoic Orogenies in
eastern North America
2. Alleghanian orogeny in eastern North
America and Hercynian orogeny in
central Europe
– Late Carboniferous
– Gondwana (the southern continents, Africa,
South America, India, Australia, Antarctica)
and Laurasia collide.
– Southern Appalachian mountains form as
Laurasia collides with northwestern Africa
(part of Gondwana).
Late Paleozoic Orogenies in
eastern North America
• The Acadian and Alleghanian orogenies
were the result of the closure of the
Iapetus Ocean and continental collisions
which resulted in the formation of the
supercontinent Pangea.
Physiographic
provinces of the
Appalachian
region in
eastern North
America.
The Alleghanian orogeny
The Alleghanian orogeny produced folds in the
Appalachian Valley and Ridge province, and
large thrust faults in the southern
Appalachians.
Many folds are asymmetrically overturned to
the northwest, and surfaces of thrust faults dip
to the southeast.
The Alleghanian orogeny
Blue Ridge and Piedmont metamorphic and
igneous rocks form a sheet ranging from 6-15 km
thick, overlying relatively flat-lying lower Paleozoic
sedimentary rocks. This type of tectonic
deformation is called "thin-skinned tectonics."
Late Paleozoic Orogenies of
western North America
• In the western part of North America, the
Antler orogeny began during Devonian
with the subduction of oceanic lithosphere
beneath the western margin of the
continent.
• The Antler Orogeny continued into
Mississippian and Pennsylvanian.
Late Paleozoic Orogenies of
western North America
• A volcanic island arc collided with the western
margin of North America, crushing sediments
and causing thrust faulting (Roberts Mountains
Thrust Fault of Nevada).
• Continental rise and slope deposits were thrust
as much as 80 km over shallow water sediments
of the former continental shelf.
Late Paleozoic Sedimentary
Sequences
• Shallow epicontinental seas transgressed
and regressed across Laurasia (North
America) during Late Paleozoic as the
glaciers melted and enlarged.
• These sequences are bounded by (or
separated by) unconformities.
Late Paleozoic Sedimentary
Sequences
• Two major transgressions occurred in North
America during Late Paleozoic:
– Kaskaskia (Devonian-Mississippian)
– Absaroka (Pennsylvanian-Permian)
• During regressions, such as the one between
Mississippian and Pennsylvanian, the former
seafloor was exposed to erosion, creating one of
the most widespread regional unconformities in
the world.
North
American
cratonic
sequences
Green =
sedimentary
deposits
Yellow = missing
strata associated
with
unconformities
Devonian Paleogeography
• As Late Paleozoic began, the continents
were fairly fragmented and separate,
particularly in the Northern Hemisphere.
Devonian Paleogeography
• There is an extensive sedimentary record
for Devonian.
• Note that North America sat on the
equator, with warm, tropical climatic
conditions.
Devonian Paleogeography
• A large continental landmass named
Gondwana (composed of South America,
Africa, India, Antarctica, and Australia)
was present in the southern hemisphere,
on or near the South Pole.
Devonian Paleogeography
• Laurentia and Baltica collided to form
Laurasia in the Caledonian orogeny
affecting northeastern Canada, Greenland,
and Europe).
Devonian Paleogeography
• A volcanic island arc or exotic terrane,
called the Avalon terrane (or Carolina
terrane), collided with Eastern North
America in the Acadian orogeny.
Acadian Orogeny
• The effects of the Acadian orogeny are
seen in a belt extending from
Newfoundland to West Virginia, where
thick sequences of sedimentary rocks are
interbedded with rhyolitic volcanic rocks
and granitic intrusions.
Devonian
Paleogeography
• The Acadian highlands
in eastern North
America (orange), form
a continuous belt with
the Caledonian
Mountains adjacent to
Greenland and Europe.
• Erosion of these
mountains resulted in
the deposition of the
Catskill Red beds in
the Appalachian area,
and the Old Red
Sandstone in Europe.
Devonian
Paleogeography
• Sea levels were high
worldwide during
Devonian (indicating
that there were no
glaciers).
• Much of the North
American continent
was flooded by shallow
seas.
Devonian Sedimentary Deposits
• The seas regressed from the continents at
the end of Early Paleozoic as a result of
the Ordovician-Silurian glaciation.
• Gradual flooding of the North American
craton occurred during Late Paleozoic,
reaching its maximum extent during
Mississippian Period. This new inland sea
was called the Kaskaskia sea.
Devonian Sedimentary Deposits
• In eastern North America, initial deposits of the
Kaskaskia sea were clean quartz sands, such as
the Devonian Oriskany Sandstone, used for
glass making because of its purity.
• As the sea continued to transgress, shales, and
then limestones with reef-forming coral were
deposited over the sands.
• In areas where water circulation was more
restricted, evaporites were deposited.
• Reefs and carbonates indicate a warm climate.
• Evaporites suggest dry conditions.
Devonian Sedimentary Deposits
• After the Acadian orogeny, carbonate
sedimentation was followed by deposition of
clastic sediments.
• Clastic sediments are thicker and coarser to the
east, nearer their source area in the Acadian
highlands.
• Primarily continental red beds (stream deposits).
• Wedge-shaped deposit called the Catskill clastic
wedge or Catskill delta (although these are not
deltaic deposits).
Devonian Sedimentary Deposits
• Similar Devonian red beds are also
present in Europe, such as the Old Red
Sandstone.
• The red color of the sandstone indicates
deposition under oxidizing conditions in
continental or non-marine environments.
Catskill clastic wedge deposits
Catskill clastic wedge deposits
East-west cross-section across the Devonian
Catskill clastic wedge in New York.
• Isopach (sediment
thickness) and
lithofacies map of
Upper Devonian in the
eastern U.S.
• The Catskill clastic
wedge sediments are
thicker and coarser in
the east.
• The sediments become
finer-grained westward,
away from the Acadian
highland source area.
Chattanooga Shale
• Farther west, black shales were deposited in a
thin unit (less than about 10-20 m thick) over a
wide area (Chattanooga Shale) during Late
Devonian and Early Mississippian.
• Offshore equivalent of the 3000 m thick Catskill
clastic wedge.
• An important marker bed for regional correlation.
• High organic carbon content, along with finely
disseminated pyrite, and uranium.
• Chattanooga Shale was deposited in stagnant,
oxygen-deficient water.
Williston Basin
• In the Williston Basin area (South Dakota,
Montana, and adjacent Canada),
extensive reefs formed.
• Restricted circulation within the reefencircled basin led to the deposition of
thick evaporite deposits.
• The reefs of the Williston Basin provided
permeable structures into which petroleum
migrated, forming rich oil fields.
Carboniferous
In North America, Carboniferous consists
of two periods: Mississippian and
Pennsylvanian.
– Mississippian is Early Carboniferous.
– Pennsylvanian is Late Carboniferous.
Mississippian
• The name "Mississippian" is derived from
exposures of rock in the valley region of
the Mississippi River.
• Mississippian sedimentary deposits
contain abundant limestone with fossils of
crinoids, blastoids, bryozoans, and
fusulinid foraminifera.
Pennsylvanian
• Pennsylvanian rocks are dominated by
coal-rich sediments that were deposited in
swamps and deltas.
• Coal deposits are particularly well
developed in Pennsylvania.
Mississippian
Paleogeography
Landmass in eastern
North America and
Europe (yellow),
formed as the
mountains (orange)
eroded after
Caledonian and
Acadian orogenies.
• Although a large
mountain range was
present in the
Appalachian area,
another orogeny was
soon to occur, as
indicated by the
arrows and the
words "Africa
approaching" along
the right side of the
map.
• Much of North
America was
covered by a shallow
epicontinental sea.
• North America sat on
the equator, so
temperatures were
warm.
• Note the Antler
highlands in the
western U.S.
Mississippian Sedimentary
Deposits
• By Mississippian, the Acadian highlands were
reduced in size by erosion, and were no longer
releasing large quantities of sediment.
• In the east, near the remaining highlands, nonmarine shales, sandstones, and conglomerates
were deposited.
• These sediments belong to the Pocono Group.
Mississippian Sedimentary
Deposits
• As muddy sediment from the eroding highlands
decreased, carbonate deposition became
widespread in the warm, shallow Kaskaskia sea.
• Mississippian limestones contain abundant
crinoids, blastoids, bryozoans, and fusulinid
foraminifera.
• The widespread blanket of carbonate rocks
deposited during this time is called the great
Mississippian lime bank.
• In places, Mississippian limestones are more
than 700 m thick.
Crinoids
Mississippian Sedimentary
Deposits
• Sands, clays, and thin layers of
carbonates were deposited during Late
Mississippian time as the Kaskaskia sea
regressed.
• These rocks are a source of petroleum in
Illinois.
• They appear to have been deposited in
stream valleys developed on the former
seafloor.
Mississippian Sedimentary
Deposits
• Farther west, extensive reefs developed
around the Williston basin (South Dakota,
Montana, and part of Canada).
• Arid climatic conditions and restricted
circulation resulted in the deposition of
thick units of gypsum and salt.
• Petroleum migrated into the permeable
reef deposits, forming rich oil fields.
Mississippian Sedimentary
Deposits
• In the Gulf Coast area, slow deposition continued
from Early Devonian to Late Mississippian.
• Carbonates predominated in the more northerly
shelf zone.
• Cherty rocks called novaculites were deposited in
deeper waters to the south. Novaculites are
composed of microcrystalline quartz, which has
been subjected to heat and pressure.
• Arkansas novaculite is used as a whetstone to
sharpen steel knives and tools.
Mississippian Sedimentary
Deposits
• Graywackes and shales spread into the
depositional basin near the end of Mississippian,
forming a clastic wedge more than 8000 m thick,
that thickened and coarsened to the south,
where a new mountain range had formed and
was eroding.
• The remnants of this mountain range are the
Ouachita Mountains of Arkansas and Oklahoma,
and the Marathon Mountains of southwestern
Texas.
Mississippian Sedimentary
Deposits
• The Kaskaskia sea retreated from the
craton at the end of Mississippian.
• This event is marked by one of the most
widespread unconformities in the world.
This unconformity separates Mississippian
from Pennsylvanian.
• The overlying Pennsylvanian rocks were
deposited under very different conditions.
Alleghanian orogeny
• During Late Paleozoic, northwestern Africa
collided with southeastern North America,
causing the Alleghanian orogeny, and building
the Appalachian mountains.
• The orogeny began during Mississippian and
continued through Pennsylvanian and Permian.
Alleghanian orogeny
• South America collided with the Gulf Coast
region of North America, forming the
Ouachita Mountains, a southwestern
continuation of the Alleghanian orogenic
belt.
Plate tectonics model for the
continental collisions during
Late Paleozoic
Pangea
• By Late Carboniferous, a large continental
landmass called Pangea, had formed by
the collision of Laurasia (North America
plus Europe) with Gondwana (the
southern continents of Africa, South
America, Australia, Antarctica, and India).
Pangea on the South Pole
• The supercontinent, Pangea, sat over the
South Pole. When a continent is over a
pole, conditions are right for a glaciation, if
the climate is cold and if sufficient
moisture is present.
Iapetus Ocean closed
• The Iapetus Ocean (or Proto-Atlantic),
completely closed by Late Carboniferous.
• Closure of the Iapetus Ocean disrupted global
ocean circulation and caused currents to be
diverted from the tropics to more polar areas,
contributing to glaciation.
Late Paleozoic Evaporites
• The presence of evaporites (E) indicates
that the climate was at least locally dry.
• This was probably due in part to changes
in global oceanic and atmospheric
circulation induced by the closure of the
Iapetus, as well as by orogeny.
Late Paleozoic Glacial Deposits
• Glacial deposits are present in the
southern hemisphere, indicating that a
glaciation occurred during Carboniferous
and Permian.
Pennsylvanian
Paleogeography
• Large landmass in
the east, with
extensive lowlands
(yellow).
• Appalachian
Mountains (orange)
have formed as a
result of the
Alleghanian orogeny.
Pennsylvanian Paleogeography
• Sediment eroding from the Appalachian
Mountains was transported to the west
into the epicontinental sea that covered
much of North America during
Mississippian.
• These sedimentary deposits have built a
broad plain to the west, with alternating
non-marine and marine deposits, as the
sea transgressed and regressed.
Pennsylvanian
Paleogeography
• Coal swamps
formed along the
western edge of
the Appalachian
Mountains, in what
was basically a
tropical rainforest
setting.
Pennsylvanian
Paleogeography
• Uplifts in the
southern and
southwestern North
America
(Uncompahgre
mountains or
ancestral Rockies,
and others), and the
Antler Mountains in
the western U.S.
Pennsylvanian Sedimentary Deposits
• The erosion of the Antler Mountains
provided detrital sediment that was
transported into adjacent basins.
• Thick sequences of Pennsylvanian and
Permian shelf sediments accumulated in
the area now occupied by the Wasatch
and Oquirrh Mountains in Utah.
Pennsylvanian Sedimentary
Deposits
• The Absaroka sea began to transgress upon the
North American craton near the beginning of
Middle Pennsylvanian.
• The rocks in the eastern half of the U.S. are
predominantly interbedded marine and
nonmarine sediments, indicating the advance
and retreat of the sea.
• Each nonmarine-marine sequence is called a
cyclothem.
Pennsylvanian cyclothem
• A typical Pennsylvanian
cyclothem contains 10
units.
• The lower half consist of
nonmarine sediments,
topped by a coal deposit.
• The coal is overlain by
marine deposits,
indicating the advance of
the sea into the swampy,
vegetated area.
Marine and Non-marine deposits
• The repetitious interbedding of non-marine
and marine sedimentary deposits indicates
either:
– Episodic regional subsidence and uplift
OR
– Eustatic (worldwide) sea level changes
related to Carboniferous-Permian glaciation in
Gondwana.
Coal and Plant Fossils
• Pennsylvanian coal deposits are mined
extensively in the Appalachian area, the
Illinois basin, and in Europe.
• They are commonly associated with rocks
containing plant fossils.
Southwestern North America
• SW part of the North American craton experienced
mountain building during Pennsylvanian.
• The highlands are called the Uncompahgre
Mountains (or ancestral Rockies) in southwestern
Colorado, and the Oklahoma Mountains of
western Oklahoma.
• These mountains and related uplifts resulted from
movement along large, nearly vertical faults.
Colorado Front Range
• The Colorado Front Range-Pedernal
uplifts extending north-south through
central Colorado formed at this time.
• Precambrian igneous and metamorphic
rocks are now exposed in the cores of
these eroded mountain ranges.
Pennsylvanian and Permian
sandstone deposits
• Erosion produced great wedge-shaped deposits
of red arkosic sandstone during Pennsylvanian
and Permian, some of which is exposed in
Colorado as:
– The "flatirons" near Boulder
– The rocks at Red Rocks Amphitheatre near Morrison,
west of Denver
– The Garden of the Gods, near Colorado Springs
Deposition of Pennsylvanian clastic
sediments in eastern Colorado and New
Mexico. Note the accumulation of coarse
arkosic sandstones east of the
Uncompahgre Mountains.
The Flatirons, near Boulder, Colorado. Steeply
dipping red arkosic sandstones, conglomerates,
and mudstones of Upper Pennsylvanian and Lower
Permian Fountain Formation.
Sediments were derived from the erosion of the
ancestral Rocky Mountains to the west.
The beds were tilted during the orogeny that
produced the modern Rocky Mountains.
Other Uplifts
• Other uplifts also formed, including the
Zuni-Fort Defiance uplift, the Amarillo
mountains, and the Oklahoma mountains
(represented today by the Arbuckle and
Wichita mountains).
• The origin of these mountains may be
related to the collision of Gondwana along
the southern edge of the North American
craton in the Ouachita orogenic belt.
Other Uplifts
Crustal adjustments to relieve stress may
have resulted in the deformation that
produced the highlands and associated
basins (such as the Early Pennsylvanian
Paradox basin, which contains evaporites
and petroleum deposits).
Paradox
Basin
• The Paradox basin lies southwest of the
Uncompahgre mountains.
• Clastic sediments from the mountains were
deposited along the northeastern side of the basin.
Paradox
Basin
• The Paradox basin was flooded by the Absaroka
sea during Early Pennsylvanian.
• Shales were deposited over Mississippian
limestone.
• The basin became restricted and thick beds of
evaporites (salt, gypsum and anhydrite) were
deposited.
Paradox
Basin
• Reef-like algal mounds, associated with
fossiliferous and oolitic limestones, developed
along the western rim of the basin.
• The reefs serve as petroleum reservoirs.
• Near the end of Pennsylvanian, the basin filled with
arkosic sediments eroded from the Uncompahgre
highlands.
Regression of the Absaroka sea
• The Absaroka sea, which began its
transgression at the beginning of
Pennsylvanian, began a slow and irregular
regression before the end of
Pennsylvanian, which continued into
Permian.
Permian Paleogeography
• During Permian, the continents collided and
joined to form the supercontinent, Pangea.
• Pangea was surrounded by a huge ocean called
Panthalassa.
• The oceanic area east of Pangea, and between
Africa and Europe was called the Tethys Sea.
Permian Paleogeography
• Continental collision was accompanied by
orogeny, and the Appalachian mountain
chain reached its peak during the
Alleghanian orogeny.
Permian Paleogeography
• Late Permian was a time of widespread
regression of the seas.
• The global map above indicates that sea levels
were low worldwide.
• The vast epicontinental seas that once covered
North America and parts of other continents
were gone.
Permian Paleogeography
• The Gondwana part of Pangea continued
to sit atop the South Pole, and glaciation
continued into Permian.
Permian Paleoclimatic Indicators
Red circles are coal
deposits (humid climates
during interglacial periods,
possibly associated with
glacial meltwaters).
Blue triangles are glacial
tillites.
Irregular green areas are
evaporites (arid climates).
Permian Glaciation
Distribution of glaciers can
be determined from
Permian glacial tillites, or
striations on bedrock,
caused by the movement
of the glaciers.
Glacial deposits are white.
Arrows indicate direction of
glacial movement as
determined from glacial
striations on the bedrock.
Permian Evaporites
Cold air holds less moisture
than warm air, and the
climate became arid during
Permian.
Evaporite deposits (gypsum
and salt) accumulated in the
green areas on the map.
There are more Permian salt
deposits than any other age.
End of the Coal Swamps
• Drying of climates at low latitudes led to
contraction of coal swamps and
extinctions among spore-bearing plants
and amphibians that required moist
conditions.
• Because of the drying, gymnosperms
(seed plants, including conifers) replaced
many spore-bearing plants, which require
moist conditions.
Orogeny and climate
• Orogenies probably also affected the
climate.
• Locations of mountains can affect climate
and control precipitation (rain-shadow
effect).
• Deserts form on the downwind side of
mountain ranges.
Permian
Paleogeography
• The eastern 2/3 of
North America
consisted of lowlands,
undergoing erosion.
• Continental red beds
were deposited locally.
Permian
Paleogeography
• Appalachian mountains
in the east.
• Ouachita mountains in
the southeast.
• Farther west are the
"Ancestral Rockies."
• Antler Mountains have
been eroded, and are
called uplands.
• Subduction and
volcanism continue in
the far west.
Permian Sedimentary Deposits
• The Absaroka sea continued its regression
during Permian.
• Fossiliferous limestones were deposited in
the Absaroka sea, overlain in places by
shales, red beds, and evaporites.
• The Kaibab Limestone, which forms the
cliffs along the rim of the Grand Canyon, is
a Permian carbonate deposit.
Phosphate Deposits in NW U.S.
• Deep marine basin in the Wyoming, Montana,
and Idaho area filled with cherts, sandstones,
and mudstones of the Phosphoria Formation.
• Formation named for layers of dark phosphatic
sediments and phosphorites.
• Phosphorite = dark gray variety of calcium
phosphate. May have formed by upwelling of
phosphorus-rich sea water from deeper parts of
basin.
• Phosphate is mined for fertilizers and other
products.
• Note phosphate
deposits
• Carbonates and
evaporites were
deposited in marine
basins in the western
U.S., as Permian seas
withdrew, and basins
became restricted.
• Extensive salt beds
were deposited in
Kansas.
Permian basins in west Texas and
New Mexico
• Several irregularly subsiding basins (such
as the Delaware basin) developed
between shallow submerged carbonate
platforms.
Permian basins in west Texas and
New Mexico
• Reefs formed along the basin edges (Capitan
Limestone).
• The ancient reef forms the steep El Capitan
promontory in the Guadalupe Mountains.
Permian basins in west Texas and
New Mexico
• In the shallow water lagoons behind the
reefs, thin limestones, evaporites, and red
beds were deposited.
Paleozoic
review