Transcript Acadian orogeny

Chapter 11
Late Paleozoic Earth History
Tully Monster
• Tullimonstrum gregarium, also known as the Tully
Monster, is Illinois’s official state fossil
– Specimen from Pennsylvanian rocks, Mazon Creek
Locality,
Illinois
– Reconstruction
of the Tully
Monster
• about 30 cm
long
Mazon Creek Fossils
• Approximately 300 million years ago
– in the region of present-day Illinois,
– sluggish rivers flowed southwestward through
swamps,
– and built large deltas that extended outward into a
subtropical shallow sea
• These rivers deposited high quantities of mud
– that entombed many of the plants and animals
living in the area
• Rapid burial
– and the formation of ironstone concretions
– preserved many of the plants and animals of the
area
Exceptional Preservation
• The resulting fossils,
– known as the Mazon Creek fossils
• for the area in northeastern Illinois
• where most specimens are found,
– provide us with significant insights about the softpart anatomy of the region's biota
• Because of the exceptional preservation of this
ancient biota,
– Mazon Creek fossils are known throughout the
world
– and many museums have extensive collections
from the area
Pennsylvanian Delta Organisms
• During Pennsylvanian time, two major habitats
existed in northeastern Illinois
– One was a swampy forested lowland of the
subaerial delta,
– and the other was the shallow marine environment
of the actively prograding delta
• Living in the warm, shallow waters
– of the delta front were numerous
• cnidarians,
• mollusks,
• echinoderms,
• arthropods,
• worms,
• and fish
Swampy Lowlands
• The swampy lowlands surrounding the delta
were home to more than 400 plant species,
– numerous insects and spiders,
– and other animals such as
• scorpions and amphibians
– In the ponds, lakes, and rivers were many
• fish, shrimp, and ostracods
– Almost all of the plants were
• seedless vascular plants,
• typical of the kinds that lived in the coal-forming
swamps
• during the Pennsylvanian Period
Tully Monster
• One of the more interesting Mazon Creek
fossils is the Tully Monster,
– which is not only unique to Illinois,
– but also is its official state fossil
• Named for Francis Tully,
– who first discovered it in 1958,
– Tullimonstrum gregarium
– was a small
• up to 30 cm long
– soft-bodied animal that lived in the warm, shallow
seas
– covering Illinois about 300 million years ago
Tully Monster
• The Tully Monster had a relatively long
proboscis
–
–
–
–
–
that contained a "claw" with small teeth in it
The round-to-oval shaped body was segmented
and contained a cross-bar,
whose ends were swollen,
and are interpreted by some to be the animal’s
sense organs
– The tail had two horizontal fins
• It probably swam like an eel
– with most of the undulatory movement occurring
behind the two sense organs
Tully Monster
• There presently is no consensus
– as to what phylum the Tully Monster belongs
– or to what animals it might be related
Late Paleozoic Paleogeography
• The Late Paleozoic was a time of
–
–
–
–
–
evolutionary innovations,
continental collisions,
mountain building,
fluctuating seas levels,
and varied climates
• Coals, evaporites, and tillites
– testify to the variety of climatic conditions
– experienced by the different continents during the Late
Paleozoic
Gondwana Continental Glaciers
• Major glacial-interglacial intervals
– occurred throughout much of Gondwana
– as it continued moving over the South Pole
• during the Late Mississippian to Early Permian
• The growth and retreat of continental glaciers
– during this time
– profoundly affected the world's biota
– as well as contributing to global sea level changes
Continental Collisions
• Collisions between continents
– not only led to the formation of the supercontinent
Pangaea
– by the end of the Permian,
– but resulted in mountain building
– that strongly influenced oceanic and atmospheric
circulation patterns
• By the end of the Paleozoic,
– widespread arid and semiarid conditions governed
much of Pangaea
The Devonian Period
• During the Silurian,
– Laurentia and Avalonia-Baltica collided along a
convergent plate boundary
– to form the larger continent of Laurasia
• This collision,
– which closed the northern Iapetus Ocean,
– is marked by the Caledonian orogeny
• During the Devonian,
– as the southern Iapetus Ocean narrowed
– between Laurasia and Gondwana,
– mountain building continued along the eastern
margin of Laurasia
– with the Acadian orogeny
Paleogeography of the World
• For the Late Devonian Period
Paleogeography of the World
• For the Early Carboniferous Period
Paleogeography of the World
• For the Late Carboniferous Period
Paleogeography of the World
• For the Late Permian Period
Reddish Fluvial Sediments
• The erosion of the resulting highlands
– provided vast amounts of reddish fluvial sediments
– that covered large areas of northern Europe
• Old Red Sandstone
– and eastern North America
• the Catskill Delta
Collision of Laurentia and Baltica
• Other Devonian tectonic events include,
– the Cordilleran Antler orogeny,
– the Ellesmere orogeny along the northern margin of
Laurentia
• which may reflect the collision of Laurentia with Siberia
– and the change from a passive continental margin
to an active convergent plate boundary
• in the Uralian mobile belt of eastern Baltica
Uniform Global Climate
• The distribution of
• reefs,
• evaporites,
• and red beds,
– as well as the existence of similar floras throughout
the world,
– suggests a rather uniform global climate during the
Devonian Period
The Carboniferous Period
• During the Carboniferous Period
– southern Gondwana moved over the South Pole,
– resulting in extensive continental glaciation
• The advance and retreat of these glaciers
– produced global changes in sea level
– that affected sedimentation pattern on the cratons
• As Gondwana continued moving northward,
– it first collided with Laurasia
• during the Early Carboniferous
– and continued suturing with it during the rest of the
Carboniferous
Gondwana/Laurasia Collision
• Because Gondwana rotated clockwise relative to
Laurasia,
– deformation of the two continents generally
progressed in a northeast-to-southwest direction
along
• the Hercynian,
• Appalachian,
• and Ouachita mobile belts
• The final phase of collision between Gondwana
and Laurasia
– is indicated by the Ouachita Mountains of Oklahoma
– which were formed by thrusting
– during the Late Carboniferous and Early Permian
Pangaea Began Taking Shape
• Elsewhere, Siberia collided with Kazakhstania
– and moved toward the Uralian margin of Laurasia
(Baltica),
– colliding with it during the Early Permian
• By the end of the Carboniferous,
– the various continental landmasses were fairly
close together
– as Pangaea began taking shape
Coal Basins in Equatorial Zone
• The Carboniferous coal basins of
– eastern North America,
– western Europe,
– and the Donets Basin of Ukraine
• all lay in the equatorial zone,
– where rainfall was high and temperatures were
consistently warm
• The absence of strong seasonal growth rings
– in fossil plants from these coal basins
– is indicative of such a climate
Fossil Plants of Siberia
• The fossil plants found in the coals of Siberia,
– however, show well-developed growth rings,
– signifying seasonal growth
– with abundant rainfall
– and distinct seasons
– such as occur in the temperate zones
• at latitudes 40 degrees to 60 degrees north
Continental Ice Sheets
• Glacial condition
–
–
–
–
and the movement of large continental ice sheets
in the high southern latitudes
are indicated by widespread tillites
and glacial striations in southern Gondwana
• These ice sheets spread toward the equator and,
• at their maximum growth,
– extended well into the middle temperate latitudes
The Permian Period
• The assembly of Pangaea
– was essentially completed during the Permian
– as a result of the many continental collisions
• that began during the Carboniferous
• Although geologists generally agree
– on the configuration and locations
– of the western half of the supercontinent,
• no consensus exists
– on the number or configuration of the various
terranes
– and continental blocks that composed the eastern
half of Pangaea
Pangaea Surrounded
• Regardless of the exact configuration
–
–
–
–
of the eastern portion of Pangaea,
geologists know that the supercontinent
was surrounded by various subduction zones
and moved steadily northward during the Permian
• Furthermore, an enormous single ocean,
– Panthalassa,
– surrounded Pangaea and
– spanned Earth from pole to pole
Climatic Consequences
• The formation of a single large landmass
– had climatic consequences for the continent
– Terrestrial Permian sediments indicate
– that arid and semiarid conditions were widespread
over Pangaea
• The mountain ranges produced by
– the Hercynian, Alleghenian, and Ouachita
orogenies
– were high enough to create rain shadows
– that blocked the moist, subtropical, easterly winds
• much as the southern Andes Mountains do in western
South America today
Mountains Influenced Climate
• The mountains’ influence produced very dry
conditions in North America and Europe,
– as evident from the extensive
– Permian red beds and evaporites
– found in western North America, central Europe,
and parts of Russia
• Permian coals,
• indicative of abundant rainfall,
– were mostly limited to the northern temperate belts
• latitude 40 degrees to 60 degrees north
– while the last remnants of the Carboniferous ice
sheets retreated
Late Paleozoic History of
North America
• The Late Paleozoic cratonic history of North
America included periods
– of extensive shallow-marine carbonate deposition
– and large coal-forming swamps
– as well as dry, evaporite-forming terrestrial
conditions
• Cratonic events largely resulted from changes
in sea level because of
– Gondwanan glaciation
– and tectonic events related to the joining of
Pangaea
Mountain Building
• Mountain building
– that began with the Ordovician Taconic orogeny
– continued with the
•
•
•
•
Caledonian,
Acadian,
Alleghenian,
and Ouachita orogenies
• These orogenies were part of the global
tectonic process
– that resulted in the formation of Pangaea
The Kaskaskia Sequence
• The boundary between
– the Tippecanoe sequence
– and the overlying Kaskaskia sequence
• Middle Devonian-Late Mississippian
– is marked by a major unconformity
• As the Kaskaskia Sea transgressed
– over the low-relief landscape of the craton,
– the majority of the basal beds deposited
• consisted of clean, well-sorted quartz sandstones
Oriskany Sandstone
• A good example is the Oriskany Sandstone
– of New York and Pennsylvania
– and its lateral equivalents
• The Oriskany Sandstone,
– like the basal Tippecanoe St. Peter Sandstone,
– is an important glass sand
– as well as a good gas-reservoir rock
Basal Kaskaskia Sandstones
• Extent of the basal units of the Kaskaskia
sequence
in the
eastern
and
northcentral
United
States
Source Areas
• The source areas for the basal Kaskaskia
sandstones
– were primarily the eroding highlands of the
Appalachian mobile belt area,
– exhumed Cambrian and Ordovician sandstones
cropping out along the flanks of the Ozark Dome,
– and exposures of the Canadian Shield in the
Wisconsin area
Devonian Period
• Paleogeography
of North
America during
the Devonian
Period
Sediment Sources
• The earlier Silurian carbonate beds
• below the Tippecanoe-Kaskaskia unconformity
– lacked Kaskaskia-like sands
• The absence of such sands indicates
– that the source areas for the basal Kaskaskia
– were submerged when the Tippecanoe sequence
was deposited
• Stratigraphic studies indicate
– that these source areas were uplifted
– and the Tippecanoe carbonates removed by erosion
– prior to the Kaskaskia transgression
Kaskaskian Rocks
• Kaskaskian basal rocks
–
–
–
–
–
elsewhere on the craton
consist of carbonates
that are frequently difficult to differentiate
from the underlying Tippecanoe carbonates
unless they are fossiliferous
• The majority of Kaskaskian rocks are
– carbonates, including reefs, and associated
evaporite deposits
– except for widespread Upper Devonian and Lower
Mississippian black shales
Other Parts of the World
• In many other parts of the world, such as
•
•
•
•
•
southern England,
Belgium,
Central Europe,
Australia,
and Russia,
– the Middle and early Late Devonian epochs were
times of major reef building
Reef Development in
Western Canada
• The Middle and Late Devonian-age reefs of
western Canada
– contain large reserves of petroleum
– and have been widely studied from outcrops and in
the subsurface
• These reefs began forming
– as the Kaskaskia Sea transgressed southward
– into western Canada
Middle Devonian
Reefs and Evaporites
• By the end of the Middle Devonian,
– the reefs had coalesced into a large barrier-reef
system
– that restricted the flow of oceanic water into the
back-reef platform,
– thus creating conditions for evaporite precipitation
• In the back-reef area, up to 300 m of evaporites
– were precipitated in much the same way as in the
Michigan Basin during the Silurian
Devonian Reef Complex
• Reconstruction of
the extensive
Devonian Reef
complex of western
Canada
• These reefs
controlled the
regional facies of the
Devonian epeiric
seas
Potash from Evaporites
• More than half of the world's potash,
– which is used in fertilizers,
– comes from these Devonian evaporites
• By the middle of the Late Devonian,
– reef growth stopped in the western Canada region,
– although nonreef carbonate deposition continued
Black Shales
• In North America, many areas of carbonateevaporite deposition
– gave way to a greater proportion of shales
– and coarser detrital rocks
• beginning in the Middle Devonian and continuing into
the Late Devonian
• This change to detrital deposition
– resulted from the formation of new source areas
– brought on by the mountain-building activity
– associated with the Acadian orogeny in North
America
Increased Detrital Deposition
• Deposition of
black shales
• is associated
with the
Acadian
orogeny
Widespread Black Shales
• As the Devonian Period ended,
– a conspicuous change in sedimentation took place
over the North American craton
– with the appearance of widespread black shales
• These Upper Devonian-Lower Mississippian
black shales are typically
– noncalcareous,
– thinly bedded,
– and usually less than 10 m thick
Extent of Black Shales
• The extent of
the upper
Devonian and
Lower
Mississippian
Chattanooga
Shale and its
equivalent units
• such as the
Antrim Shale and
the Albany Shale
New Albany Shale
• Upper Devonian
New Albany
Shale,
• Button Mold
Knob Quarry,
Kentucky
Dating Black Shales
• Because most black shales lack body fossils,
– they are difficult to date and correlate
• However, microfossils, such as
– conodonts
• microscopic animals
– acritarchs
• microscopic algae
– or plant spores
– indicate that the lower beds are Late Devonian,
– and the upper beds are Early Mississippian in age
Origin Debated
• Although the origin of these extensive black
shales is still being debated,
– the essential features required to produced them
include
• undisturbed anaerobic bottom water,
• a reduced supply of coarser detrital sediment,
• and high organic productivity in the overlying
oxygenated waters
• High productivity in the surface waters leads to
a shower of organic material,
– which decomposes on the undisturbed seafloor
– and depletes the dissolved oxygen at the sedimentwater interface
Puzzling Origin
• The wide extent in North America
– of such apparently shallow-water black shales
– remains puzzling
• Nonetheless, these shales
– are rich in uranium
– and are an important source rock of oil and gas
– in the Appalachian region
The Late Kaskaskia
• Following deposition of the black shales,
– carbonate sedimentation on the craton dominated
the remainder of the Mississippian Period
• During this time, a variety of carbonate
sediments was deposited in the epeiric seas
– as indicated by the extensive deposits of
– crinoidal limestones
• rich in crinoid fragments
– oolitic limestones,
– and various other limestones and dolostones
Mississippian Period
• Paleogeography
of North
America during
the
Mississippian
Period
Mississippian Carbonates
• These Mississippian carbonates display
• cross-bedding, ripple marks, and well-sorted fossil
fragments,
– all of which are indicative of a shallow-water
environment
– Analogous features can be observed on the presentday Bahama Banks
• In addition, numerous small organic reefs
– occurred throughout the craton during the
Mississippian
– These were all much smaller than the large barrierreef complexes
• that dominated the earlier Paleozoic seas
Regression of the Kaskaskia Sea
• During the Late Mississippian regression
– of the Kaskaskia Sea from the craton,
– carbonate deposition was replaced
– by vast quantities of detrital sediments
• The resulting sandstones,
• particularly in the Illinois Basin,
– have been studied in great detail
– because they are excellent petroleum reservoirs
Cratonwide Unconformity
• Prior to the end of the Mississippian,
– the epeiric sea had retreated
• to the craton margin,
– once again exposing the craton
– to widespread weathering and erosion
• This resulted in a craton-wide unconformity
– at the end of the Kaskaskia Sequence
The Absaroka Sequence
• The Absaroka sequence
– includes rocks deposited
• during the Pennsylvanian
• through Early Jurassic
– At this point, we will only discuss the Paleozoic
rocks of the Absaroka sequence
• The extensive unconformity
–
–
–
–
separating the Kaskaskia and Absaroka sequences
essentially divides the strata
into the North American
Mississippian and Pennsylvanian systems
Mississippian and Pennsylvanian
Versus Carboniferous
• The Mississippian and Pennsylvanian systems
of North America
– are equivalent to the European Lower and Upper
Carboniferous systems:
• Mississippian = Lower Carboniferous
• Pennsylvanian = Upper Carboniferous
Absaroka Rocks
• The rocks of the Absaroka sequence
– are not only different from those of the Kaskaskia
sequence,
– but they are also the result of different tectonic
regimes
• The lowermost sediments of the Absaroka
sequence
– are confined to the margins of the craton
Lowermost Absaroka
• These lowermost deposits
– are generally thickest in the east and southeast,
• near the emerging highlands of the Appalachian and
Ouachita mobile belts,
– and thin westward onto the craton
• The rocks also reveal lateral changes
– from nonmarine detrital rocks and coals in the east,
– through transitional marine-nonmarine beds,
– to largely marine detrital rocks and limestones
farther west
Pennsylvanian Period
• Paleogeography
of North
America
during the
Pennsylvanian
Period
What Are Cyclothems?
• A cyclical pattern of alternating marine and
nonmarine strata
– is one of the characteristic features of
Pennsylvanian rocks
• Such rhythmically repetitive sedimentary
sequences are known as cyclothems
• They result from repeated alternations
– of marine
– and nonmarine environments,
– usually in areas of low relief
Delicate Interplay
• Though seemingly simple,
• cyclothems reflect a delicate interplay between
– nonmarine deltaic environments
– shallow-marine interdeltaic environments
– and shelf environments
• For example,
– a typical coal-bearing cyclothem from the Illinois
Basin contains
• nonmarine units,
• capped by a coal unit
• and overlain by marine units
Nonmarine Units of a Cyclothem
• The initial units represent
– deltaic deposits
– and fluvial deposits
• Above them is an underclay
– that frequently contains roots from the plants and
trees
– that comprise the overlying coal
• The coal bed
– results from accumulations of plant material
– and is overlain by marine units
Cyclothem
• Columnar section of a complete cyclothem
Pennsylvanian
Coal Bed
• Pennsylvanian coal
bed, West Virginia
• part of a cyclothem
Coal-Forming Swamp
• Reconstruction of the environment of a
Pennsylvanian coal-forming swamp
The Okefenokee Swamp
• in Georgia, is a modern coal-forming environment,
similar to those occurring
during the Pennsylvanian
Period
Marine Units of a Cyclothem
• Next the marine units consist of alternating
– limestones and shales,
– usually with an abundant marine invertebrate fauna
• The marine cycle ends with an erosion surface
• A new cyclothem begins with a nonmarine
deltaic sandstone
• All the beds illustrated in the idealized
cyclothems are not always preserved because of
– abrupt changes from marine to nonmarine conditions
– or removal of some units by erosion
Cyclothem
Why Are Cyclothems Important?
• Cyclothems represent
– transgressive
– and regressive sequences
– with an erosional surface separating one cyclothem
from another
• Thus, an idealized cyclothem
–
–
–
–
passes upward from fluvial-deltaic deposits,
through coals,
to detrital shallow-water marine sediments,
and finally to limestones typical of an open marine
environment
Modern Analogues
• Such places as
• the Mississippi delta,
• the Florida Everglades,
• and the Dutch lowlands
– represent modern coal forming environments
– similar to those that existed during the
Pennsylvanian Period
• By studying these modern analogues,
– geologists can make reasonable deductions
– about conditions existing in the geologic past
Sea Level Changes
• The Pennsylvanian coal swamps
– must have been large lowland areas neighboring
the sea
• In such cases,
– a very slight rise in sea level
• would have flooded large areas,
– while slight drops
• would have exposed large areas,
– resulting in alternating marine and nonmarine
environments
• The same result could have been caused by
– rising sea level and progradation of a large delta,
such as occurs today in Louisiana
Explaining Cyclicity
• Such regularity and cyclicity in sedimentation
– over a large area requires an explanation
• In most cases, local cyclothems of limited
extent can be explained
– by rapid but slight changes in sea level
– in a swamp-delta complex of low relief near the sea
– such as progradation or by localized crustal
movement
• Explaining widespread cyclothems is more
difficult
Favored Hypothesis
• The hypothesis currently favored
• by most geologists
• for explaining widespread cyclothems
– is a rise and fall of sea level
– related to advances and retreats of Gondwanan
continental glaciers
• When the Gondwanan ice sheets advanced,
• sea level dropped,
– and when they melted,
• sea level rose
• Late Paleozoic cyclothem activity on all cratons
– closely corresponds to Gondwana glacialinterglacial cycles
Cratonic Uplift
• Recall that cratons are stable areas,
– and when they do experience deformation, it is
usually mild
• The Pennsylvanian Period, however, was a time
of unusually severe cratonic deformation,
– resulting in uplifts of sufficient magnitude to expose
Precambrian basement rocks
• In addition to newly formed highlands and
basins,
– many previously formed arches and domes,
– such as the Cincinnati Arch, Nashville Dome, and
Ozark Dome,
– were also reactivated
Ancestral Rockies
• During the Pennsylvanian Period,
– the area of greatest deformation occurred in the
southwestern part of the North American craton
– where a series of fault-bounded uplifted blocks
formed the Ancestral Rockies
• Uplift of these mountains,
– some of which were elevated more than 2 km along
near-vertical faults,
– resulted in the erosion of the overlying Paleozoic
sediments
– and exposure of the Precambrian igneous and
metamorphic basement rocks
Pennsylvanian Highlands
• Location of the principal Pennsylvanian highland areas
and basins of the southwestern part of the craton
Ancestral Rockies
• Block diagram of the Ancestral Rockies, which were
elevated by faulting during the Pennsylvanian Period
• Erosion of
these
mountains
produced
• coarse red
sediments
• that were
deposited
in the
adjacent
basins
Red Basin Sediment
• As the Ancestral Rocky mountains eroded,
– tremendous quantities of
– coarse, red arkosic sand and conglomerate
– were deposited in the surrounding basins
• These sediments are preserved in many areas
– including the rocks of the Garden of the Gods near
Colorado Springs
– and at the Red Rocks Amphitheater near Morrison,
Colorado
Garden of the Gods
• Storm-sky view of Garden of the Gods from
Near Hidden Inn, Colorado Springs, Colorado
Intracratonic Mountain Ranges
• Intracratonic mountain ranges are unusual,
– and their cause has long been debated
– It is thought that the collision of Gondwana with
Laurasia along the Ouachita mobile belt
– generated great stresses in the southwestern region
of the North American craton
• These crustal stresses were relieved by faulting
– that resulted in uplift of cratonic blocks
– and downwarp of adjacent basins,
– forming a series of ranges and basins
The Middle Absaroka
More Evaporite Deposits and Reefs
• While the various intracratonic basins
– were filling with sediment
• during the Late Pennsylvanian,
– the epeiric sea slowly began retreating from the
craton
• During the Early Permian,
– the Absaroka Sea occupied a narrow region
– from Nebraska through west Texas
Permian Period
• Paleogeography
of North
America during
the Permian
Period
Middle Permian Absaroka Sea
• By the Middle Permian,
– the sea had retreated to west Texas
– and southern New Mexico
• The thick evaporite deposits
– in Kansas and Oklahoma
– show the restricted nature of the Absaroka Sea
• during the Early and Middle Permian
– and its southwestward retreat from the central
craton
Restricted Absaroka Sea
• During the Middle and Late Permian,
– the Absaroka Sea was restricted to
– west Texas and southern New Mexico,
– forming an interrelated complex of
• lagoonal environments,
• reef environments,
• and open-shelf environments
• Three basins separated by two submerged
platforms
– formed in this area during the Permian
Permian Reefs and Basins
• Location of
the west
Texas
Permian
basins and
surrounding
reefs
Massive Reefs
• Massive reefs grew around the basin margins
– while limestones, evaporites, and red beds were
deposited
• in the lagoonal areas behind the reefs
• As the barrier reefs grew and the passageways
between the basins became more restricted,
– Late Permian evaporites gradually filled the
individual basins
Capitan Limestone
Reef Reconstruction
• Reconstruction of
the Middle
Permian Capitan
Limestone reef
environment
• Shown are
brachiopods,
corals, bryozoans
and large glass
sponges
Capitan Limestone
• Spectacular deposits representing the geologic
history of this region
– can be seen today in the Guadalupe Mountains of
Texas and New Mexico
– where the Capitan Limestone forms the caprock of
these mountains
• These reefs have been extensively studied
– because of the tremendous oil production that
comes from this region
• By the end of the Permian Period,
– the Absaroka Sea had retreated from the craton
– exposing continental red beds
– over most of the southwestern and eastern region
Guadalupe
Mountains, Texas
• The prominent
Capitan
Limestone
• forms the
caprock of the
Guadalupe
mountains
• It is rich in fossil
corals and reef
organisms.
Late Paleozoic Mobile Belts
• Having examined the Kaskaskia and
Absarokian history of the craton,
– we now turn our attention to the orogenic activity
in the mobile belts
• The mountain building that occurred during
this time
– profoundly influenced the climatic and sedimentary
history of the craton
• In addition it was part
– of the global tectonic regime that formed Pangaea
Cordilleran Mobile Belt
• During the Neoproterozoic and Early
Paleozoic,
– the Cordilleran area was a passive continental
margin
– along which extensive continental shelf sediments
were deposited
• Thick sections of marine sediments
– graded laterally into thin cratonic units
– as the Sauk Sea transgressed onto the craton
• Beginning in the Middle Paleozoic,
– an island arc formed off the western margin of the
craton
Antler orogeny
• A collision between
– this eastward-moving island arc
– and the western border of the craton
– took place during the Late Devonian and Early
Mississippian,
– resulting in a highland area
• This orogenic event,
– the Antler orogeny,
– was caused by subduction
– and resulted in the closing of the narrow ocean
basin
• that separated the island arc from the craton
Antler Highlands
• Reconstruction of the Cordilleran mobile belt
during the Early Mississippian
– in which deep-water continental slope deposits
– were thrust
eastward
– over
shallowwater
continental
shelf
carbonates
– forming the
Antler
Highlands
Erosion of the
Antler Highlands
• Erosion of the resulting Antler Highlands
– produced large quantities of sediment
– that were deposited to the east in the epeiric sea
covering the craton
– and to the west in the deep sea
Major Tectonic Activity
• The Antler orogeny was the first in a series
– of orogenic events to affect the Cordilleran mobile
belt
• During the Mesozoic and Cenozoic,
– this area was the site of major tectonic activity
– caused by oceanic-continental convergence
– and accretion of various terranes
Ouachita Mobile Belt
• The Ouachita mobile belt
– extends for approximately 2100 km
– from the subsurface of Mississippi
– to the Marathon region of Texas
• Approximately 80% of the former mobile belt
– is buried beneath a Mesozoic and Cenozoic
sedimentary cover
• The two major exposed areas in this region are
– the Ouachita Mountains of Oklahoma and Arkansas
– and the Marathon Mountains of Texas
Beginning of the Ouachita Orogeny
• During the Neoproterozoic to Early
Mississippian,
– shallow-water detrital and carbonate sediments
– were deposited on a broad continental shelf,
– while in the deeper-water portion of the adjoining
mobile belt,
– bedded cherts and shales were accumulating
• Beginning in the Mississippian Period,
– the rate of sedimentation increased dramatically
– as the region changed from a passive continental
margin to an active convergent plate boundary,
– marking the beginning of the Ouachita orogeny
Ouachita Mobile Belt
• Plate Tectonic model for the deformation of the
Ouachita mobile belt
• Depositional environment prior to the
beginning of orogenic activity
Ouachita Mobile Belt
• Incipient continental collision between
North America and Gondwana began during
the Mississippian Period.
Ouachita Mobile Belt
• Continental collision continued during the
Pennsylvanian and Permian periods
Gondwana/Laurasia Collision
• Thrusting of sediments continued
–
–
–
–
throughout the Pennsylvanian and Early Permian
as a result of the compressive forces generated
along the zone of subduction
as Gondwana collided with Laurasia
• The collision of Gondwana and Laurasia
– is marked by the formation of a large mountain
range,
– most of which was eroded during the Mesozoic Era
• Only the rejuvenated Ouachita and Marathon
Mountains remain of this once lofty mountain
range
Three Continuous Mobile Belts
• The Ouachita deformation
– was part of the general worldwide tectonic activity
– that occurred when Gondwana united with Laurasia
• Three mobile belts
• the Hercynian,
• Appalachian,
• and Ouachita
– were continuous, and marked the southern
boundary of Laurasia
Complex Tectonic Activity
• The tectonic activity that resulted in the uplift
– in the Ouachita mobile belt was very complex
• and involved not only the collision of Laurasia and
Gondwana
• but also several microplates and terranes between the
continents
• that eventually became part of Central America
• The compressive forces impinging on the
Ouachita mobile belt
– also affected the craton
– by broadly uplifting the southwestern part of North
America
Appalachian Mobile Belt
Caledonian Orogeny
• The Caledonian mobile belt extends
– along the western border of Baltica
– and includes the present-day countries of Scotland,
Ireland, and Norway
• During the Middle Ordovician,
– subduction along the boundary
– between the Iapetus plate and Baltica began,
– forming a mirror image of the convergent plate
boundary
– off the east coast of Laurentia (North America)
Caledonian Orogeny
• The culmination of the Caledonian orogeny
– occurred during the Late Silurian and Early
Devonian
– with the formation of a mountain range
– along the western margin of Baltica
• Red-colored sediments deposited along the
front of the Caledonian Highlands
– formed a large clastic wedge
– the Old Red Sandstone
Acadian Orogeny
• The third Paleozoic orogeny to affect Laurentia
and Baltica
– began during the Late Silurian
– and concluded at the end of the Devonian Period
• The Acadian orogeny affected the Appalachian
mobile belt
– from Newfoundland to Pennsylvania
– as sedimentary rocks
– were folded and thrust against the craton
Acadian Zone of Collision
• As with the preceding Taconic and Caledonian
orogenies,
– the Acadian orogeny occurred along
– an oceanic-continental convergent plate boundary
• As the northern Iapetus Ocean continued to
close during the Devonian,
– the plate carrying Baltica
– finally collided with Laurentia,
– forming a continental-continental convergent plate
boundary along the zone of collision
Increased Metamorphic and
Igneous Activity
• As the increased metamorphic and igneous
activity indicates,
– the Acadian orogeny was more intense
– and of longer duration
– than the Taconic orogeny
• Radiometric dates
– from the metamorphic and igneous rocks
• associated with the Acadian orogeny
– cluster between 360 and 410 million years ago
Folding and Thrusting
• Just as with the Taconic orogeny,
– deep-water sediments
– were folded and thrust northwestward,
– producing angular unconformities
– separating Upper Silurian from Mississippian rocks
Catskill Delta
• Weathering and erosion of the Acadian
Highlands
– produced the Catskill Delta,
– a thick clastic wedge
• named for the Catskill Mountains
• in upstate New York
• where it is well exposed
• The Catskill Delta, composed of
– red, coarse conglomerates, sandstones, and shales,
– contains nearly three times as much sediment as the
Queenston Delta
Catskill Delta Clastic Wedge
• Area of collision between Laurentia and Baltica
– The Catskill Delta clastic wedge
– and the Old
Red Sandstone
– are bilaterally
symmetrical
– and derived
their sediments
– from the
Acadian and
Caledonian
Highlands
Devonian Rocks of New York
• The Devonian rocks of New York are among
the best studied on the continent
• A cross section of the Devonian strata
– clearly reflects an eastern source for the Catskill
facies
• from the Acadian Highlands
• These detrital rocks can be traced
– from eastern Pennsylvania,
• where the coarse clastics are approximately 3 km thick,
– to Ohio,
• where the deltaic facies are only about 100 m thick
• and consist of cratonic shales and carbonates
Catskill Delta Red Beds
• The red beds of the Catskill Delta
– derive their color from the hematite found in the
sediments
• Plant fossils and oxidation of the hematite
indicate
– that the beds were deposited in a continental
environment
The Old Red Sandstone
• The red beds of the Catskill Delta
– have a European counterpart
– in the Devonian Old Red Sandstone
• of the British Isles
• The Old Red Sandstone,
– just like its North American Catskill counterpart,
– contains numerous fossils of
• freshwater fish,
• early amphibians,
• and land plants
Old Red Sandstone
• The Old Red Sandstone
– is the counterpart to the Catskill Delta clastic wedge
Red Beds Traced North
• By the end of the Devonian Period,
– Baltica and Laurentia were sutured together,
– forming Laurasia
• The red beds of the Catskill Delta
–
–
–
–
can be traced north,
through Canada and Greenland,
to the Old Red Sandstone of the British Isles
and into Northern Europe
• These beds were deposited
– in similar environments
– along the flanks of developing mountain chains
– formed at convergent plate boundaries
Closing of the Iapetus Ocean
• The Taconic, Caledonian, and Acadian
orogenies
– were all part of the same orogenic event
– related to the closing of the Iapetus Ocean
• This event began
– with paired oceanic-continental convergent plate
boundaries
– during the Taconic and Caledonian orogenies
• and culminated
– along a continental-continental plate boundary
– during the Acadian orogeny
– as Laurentia and Baltica became sutured
Hercynian-Alleghenian Orogeny
• Following this,
– the Hercynian-Alleghenian orogeny began,
– followed by orogenic activity
– in the Ouachita mobile belt
• The Hercynian mobile belt
• of southern Europe
– and the Appalachian and Ouachita mobile belts
• of North America
– mark the zone along which Europe
• as part of Laurasia
– collided with Gondwana
Eastern Laurasia Collided
with Gondwana
• While Gondwana and southern Laurasia
collided
– during the Pennsylvanian and Permian
– in the area of the Ouachita mobile belt,
– eastern Laurasia
• Europe and southeastern North America
– joined together with Gondwana
• Africa
– as part of the Hercynian-Alleghenian orogeny
Pangaea
• These three Late Paleozoic orogenies
• Hercynian,
• Alleghenian,
• and Ouachita
– represent the final joining of Laurasia and
Gondwana
– into the supercontinent Pangaea
– during the Permian
The Role of Microplates and Terranes in
the Formation of Pangaea
• We have discussed the geologic history
– of the mobile belts
– bordering the Paleozoic continents
– in terms of subduction along convergent plate
boundaries
• However, accretion along the continental
margins
– is more complicated than the somewhat simple,
– large-scale plate interactions discussed here
Terranes or Microplates
• Geologists now recognize
–
–
–
–
that numerous terranes or microplates existed
during the Paleozoic
and were involved in the orogenic events
that occurred during the time
• We have been concerned only
– with the six major Paleozoic continents
• However, microplates of varying size
– were present during the Paleozoic
– and participated in the formation of Pangaea
Avalonia
• For example, the microcontinent of Avalonia
–
–
–
–
–
–
–
–
–
is composed of
some coastal parts of New England,
southern New Brunswick,
much of Nova Scotia,
the Avalon Peninsula of eastern Newfoundland,
southeastern Ireland,
Wales,
England,
and parts of Belgium and Northern France
A Separate Continent
• The Avalon microcontinent
– existed as a separate continent
– during the Ordovician
– and began to collide with Baltica
• during the Late Ordovician-Early Silurian
– and then with Laurentia
• as part of Baltica
• during the Silurian
Numerous Microplates
• Other terranes and microplates include
– Iberia-Armorica (southern France, Sardinia, Iberian
peninsula)
– Perunica (Bohemia)
– numerous Alpine fragments (especially in Austria)
• Microplates usually developed their own
unique faunal and floral assemblages
The Basic History
Remains the Same
• Thus, while the basic history
– of the formation of Pangaea during the Paleozoic
remains the same,
– geologists now realize that microplates and terranes
also played an important role
• Furthermore, the recognition of terranes
– within mobile belts helps explain
– some previously anomalous geologic situations
Late Paleozoic
Mineral Resources
• Late Paleozoic-age rocks contain
– a variety of important mineral resources
– including energy resources
– and metallic and nonmetallic mineral deposits
• Petroleum and natural gas
– are recovered in commercial quantities
– from rocks ranging
– from the Devonian through Permian
Hydrocarbons
• Devonian-age rocks in
– the Michigan Basin,
– Illinois Basin,
– and the Williston Basin of Montana, South Dakota,
and adjacent parts of Alberta, Canada,
– have yielded considerable amounts of
hydrocarbons
• Permian reefs and other strata in the western
United States, particularly Texas,
– have also been prolific producers
Permian-Age Coal Beds
• Although Permian-age coal beds
– are known from several areas including Asia,
Africa, and Australia,
– much of the coal in North America and Europe
comes from Pennsylvanian deposits
• Upper Carboniferous
• Large areas in the Appalachian region and the
midwestern United States
– are underlain by vast coal deposits
– formed from the lush vegetation
– that flourished in Pennsylvanian coal-forming
swamps
U.S. Coal Deposits
• The age of the coals in the midwestern states and the
Appalachian
region are
mostly
Pennsylvanian
• whereas those
in the west are
mostly
Cretaceous
and Cenozoic
Bituminous Coal
• Much of the coal is characterized as
bituminous coal
– which contains about 80% carbon
• It is a dense, black coal
– that has been so thoroughly altered
– that plant remains can be seen only rarely
• Bituminous coal is used to make coke,
– a hard gray substance made up of the fused ash
• Coke is used to fire blast furnaces during the
production of steel
Anthracite
• Some of the Pennsylvanian coal from North
America is anthracite,
– a metamorphic type of coal
– containing up to 98% carbon
• Most anthracite is in the Appalachian region
• It is an especially desirable type of coal
– because it burns with a smokeless flame
– and it yields more heat per unit volume
– than other types of coal
• Unfortunately, it is the least common type
– so that much of the coal used in the U.S. is
bituminous
Evaporite and Gas
• A variety of Late Paleozoic-age evaporite
deposits are important nonmetallic mineral
resources
• The Zechstein evaporites of Europe extend
– from Great Britain across the North Sea and into
Denmark, the Netherlands, Germany and eastern
Poland and Lithuania
• Besides the evaporites themselves,
– Zechstein deposits form the caprock
– for the large reservoirs of the gas fields of the
Netherlands
– and parts of the North Sea region
More Nonmetal Resources
• Other important evaporite mineral resources
include
– those of the Permian Delaware Basin of West Texas
and New Mexico
– and Devonian evaporites in the Elk Point basin of
Canada
• In Michigan, gypsum is mined and used in the
construction of sheetrock
Limestones
• Late Paleozoic-age limestones
– from many areas in North America
– are used in the manufacture of cement
• Limestone
– is also mined and used
– in blast furnaces
– when steel is produced
Silica Sand
• The majority of the silica sand
– mined in the United States comes from east of the Mississippi
River
– and much of this comes from Late Paleozoic-age rocks
• Silica sand from
– the Devonian Ridgely Formation is mined in West Virginia,
Maryland, and Pennsylvania
– and the Devonian Sylvania Sandstone is mined near Toledo,
Ohio
• Recall that silica sand is used
–
–
–
–
in the manufacture of glass
for refractory bricks in blast furnaces
for molds for casting aluminum, iron, and copper alloys
and for a variety of other uses
Metallic Minerals
• Metallic mineral resources including
– tin, copper, gold, and silver
– are also known from Late Paleozoic-age rocks
– especially those that have been deformed during
mountain building
• Although the precise origin of the Missouri
lead and zinc deposits remains unresolved
– much of the ores of these metals come from
Mississippian-age rocks
• In fact, mines in Missouri account for a
substantial amount of all domestic production
of lead ores