Late Paleozoic Earth History

Chapter 11

• Tullimonstrum gregarium, also known as the Tully Monster, is Illinois’s official state fossil– Specimen from Pennsylvanian rocks, Mazon Creek

Locality, Illinois

Tully Monster

– Reconstruction of the Tully

Monster• about 30 cm

long

• 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

Mazon Creek Fossils

• 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 soft-part 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

Exceptional Preservation

• 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,

Pennsylvanian Delta Organisms

• arthropods, • worms, • and fish

• 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

Swampy Lowlands

• 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

Tully Monster

• 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

Late Paleozoic Paleogeography

• 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

Gondwana Continental Glaciers

• 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

Continental Collisions

• 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

The Devonian Period

• 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

Paleogeography of the World

• 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

Reddish Fluvial Sediments

• 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

Collision of Laurentia and Baltica

• 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

Uniform Global Climate

• 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

The Carboniferous Period

• 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

Gondwana/Laurasia Collision

• 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

Pangaea Began Taking Shape

• 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

Coal Basins in Equatorial Zone

• 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

Fossil Plants of Siberia

• 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

Continental Ice Sheets

• 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

The Permian Period

• 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

Pangaea Surrounded

• 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

Climatic Consequences

• 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

Mountains Influenced Climate

• 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

Late Paleozoic History of North America

• 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

Mountain Building

• 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

The Kaskaskia Sequence

• 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

Oriskany Sandstone

• Extent of the basal units of the Kaskaskia sequence in the eastern and north-central United States

Basal Kaskaskia Sandstones

• 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

Source Areas

• Paleogeography of North America during the Devonian Period

Devonian Period

• 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

Sediment Sources

• 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

Kaskaskian Rocks

• 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

Other Parts of the World

• 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

Reef Development in Western Canada

• 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

Middle Devonian Reefs and Evaporites

• Reconstruction of the extensive Devonian Reef complex of western Canada

Devonian Reef Complex

• These reefs controlled the regional facies of the Devonian epeiric seas

• 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

Potash from Evaporites

• In North America, many areas of carbonate-evaporite 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

Black Shales

• Deposition of black shales

• is associated with the Acadian orogeny

Increased Detrital Deposition

• 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

Widespread 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

Extent of Black Shales

• Upper Devonian New Albany Shale,

• Button Mold Knob Quarry, Kentucky

New Albany Shale

• 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

Dating Black Shales

• 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 sediment-

water interface

Origin Debated

• 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

Puzzling Origin

• 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

The Late Kaskaskia

• Paleogeography of North America during the Mississippian Period

Mississippian Period

• 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 present-

day Bahama Banks• In addition, numerous small organic reefs

– occurred throughout the craton during the Mississippian

– These were all much smaller than the large barrier-reef complexes

• that dominated the earlier Paleozoic seas

Mississippian Carbonates

• 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

Regression of the Kaskaskia Sea

• 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

Cratonwide Unconformity

• 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

The Absaroka Sequence

• The Mississippian and Pennsylvanian systems of North America – are equivalent to the European Lower and Upper

Carboniferous systems:• Mississippian = Lower Carboniferous • Pennsylvanian = Upper Carboniferous

Mississippian and Pennsylvanian Versus Carboniferous

• 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

Absaroka Rocks

• 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

Lowermost Absaroka

• Paleogeography of North America during the Pennsylvanian Period

Pennsylvanian Period

• 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

What Are Cyclothems?

• 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

Delicate Interplay

• 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

Nonmarine Units of a Cyclothem

• Columnar section of a complete cyclothem

Cyclothem

• Pennsylvanian coal bed, West Virginia

• part of a cyclothem

Pennsylvanian Coal Bed

• Reconstruction of the environment of a Pennsylvanian coal-forming swamp

Coal-Forming Swamp

The Okefenokee Swamp• in Georgia, is a modern coal-forming environment,

similar to those occurring during the Pennsylvanian Period

• 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

Marine Units of a Cyclothem

Cyclothem

• 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

Why Are Cyclothems Important?

• 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

Modern Analogues

• 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

Sea Level Changes

• 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

Explaining Cyclicity

• 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 glacial-interglacial cycles

Favored Hypothesis

• 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

Cratonic Uplift

• 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

Ancestral Rockies

• Location of the principal Pennsylvanian highland areas and basins of the southwestern part of the craton

Pennsylvanian Highlands

• Block diagram of the Ancestral Rockies, which were elevated by faulting during the Pennsylvanian Period

Ancestral Rockies

• Erosion of these mountains produced

• coarse red sediments

• that were deposited in the adjacent basins

• 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

Red Basin Sediment

Garden of the Gods• Storm-sky view of Garden of the Gods from Near Hidden Inn, Colorado Springs, Colorado

• 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

Intracratonic Mountain Ranges

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

The Middle Absaroka

• Paleogeography of North America during the Permian Period

Permian Period

• 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

Middle Permian 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

Restricted Absaroka Sea

• Location of the west Texas Permian basins and surrounding reefs

Permian Reefs and Basins

• 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

Massive Reefs

• Reconstruction of the Middle Permian Capitan Limestone reef environment

• Shown are brachiopods, corals, bryozoans and large glass sponges

Capitan Limestone Reef Reconstruction

• 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

Capitan Limestone

• The prominent Capitan Limestone

• forms the caprock of the Guadalupe mountains

• It is rich in fossil corals and reef organisms.

Guadalupe Mountains, Texas

• 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

Late Paleozoic Mobile Belts

• 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

Cordilleran Mobile Belt

• 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 orogeny

• Reconstruction of the Cordilleran mobile belt during the Early Mississippian

Antler Highlands

– in which deep-water continental slope deposits– were thrust

eastward – over

shallow-water continental shelf carbonates

– forming 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

Erosion of the Antler Highlands

• 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

Major Tectonic Activity

• 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

Ouachita Mobile Belt

• 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

Beginning of the Ouachita Orogeny

• 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

Ouachita Mobile Belt

• 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

Gondwana/Laurasia Collision

• 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

Three Continuous Mobile Belts

• 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

Complex Tectonic Activity

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)

Appalachian Mobile Belt

• 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

Caledonian 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 Orogeny

• 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

Acadian Zone of Collision

• 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

Increased Metamorphic and Igneous Activity

• Just as with the Taconic orogeny, – deep-water sediments

– were folded and thrust northwestward,

– producing angular unconformities

– separating Upper Silurian from Mississippian rocks

Folding and Thrusting

• 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

• Area of collision between Laurentia and Baltica

Catskill Delta Clastic Wedge

– The Catskill Delta clastic wedge – and the Old

Red Sand-stone

– are bilaterally symmetrical

– and derived their sediments

– from the Acadian and Caledonian Highlands

• 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

Devonian Rocks of New York

• 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

Catskill Delta Red Beds

• 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

The Old Red Sandstone

• The Old Red Sandstone

Old Red Sandstone

– is the counterpart to the Catskill Delta clastic wedge

• 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

Red Beds Traced North

• 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

Closing of the Iapetus Ocean

• 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

Hercynian-Alleghenian Orogeny

• 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

Eastern Laurasia Collided with Gondwana

• These three Late Paleozoic orogenies • Hercynian, • Alleghenian, • and Ouachita

– represent the final joining of Laurasia and Gondwana

– into the supercontinent Pangaea – during the Permian

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

The Role of Microplates and Terranes in the Formation of Pangaea

• 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

Terranes or Microplates

• 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

Avalonia

• 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

A Separate Continent

• 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

Numerous Microplates

• 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

The Basic History Remains the Same

• 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

Late Paleozoic Mineral Resources

• 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

Hydrocarbons

• 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

Permian-Age Coal Beds

• The age of the coals in the midwestern states and the

U.S. Coal Deposits

Appalachian region are mostly Pennsyl-vanian

• whereas those in the west are mostly Cretaceous and Cenozoic

• 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

Bituminous Coal

• 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

Anthracite

• 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

Evaporite and Gas

• 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

More Nonmetal Resources

• 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

Limestones

• 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

Silica Sand

• 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

Metallic Minerals