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Early Paleozoic Earth History


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Title: Early Paleozoic Earth History

Chapter 10
Early Paleozoic Earth History
The First Geologic Map
  • William Smith,
  • a canal builder, published the first geologic map
  • on August 1, 1815

The First Geologic Map
  • Measuring more than eight feet high and six feet
  • Smith's hand-painted geologic map of England
  • represented more than 20 years
  • of detailed study of the rocks and fossils of
  • England is a country rich in geologic history
  • Five of the six geologic systems
  • were described and named
  • for rocks exposed in England
  • Cambrian, Ordovician, Silurian, Devonian, and

Fuel for the Industrial Revolution Revolutionized
  • The Carboniferous coal beds of England
  • helped fuel the Industrial Revolution,
  • during the late 1700s and early 1800s
  • William Smith, first began noticing
  • how rocks and fossils repeated themselves
  • in a predicable fashion while mapping various
    coal mines
  • Smith surveyed the English countryside
  • for the most efficient canal routes
  • to bring the coal to market

Understanding Geology Gave Smith an Advantage
  • Much of his success was based on the fact
  • he was able to predict what rocks
  • canal diggers would encounter
  • His observations of the geologic history
  • of England allowed William Smith
  • to make the first geologic map of an entire
  • We will use the same basic geologic principles
  • William Smith used to interpret the geology
  • of the Paleozoic Era

Paleozoic History
  • The Paleozoic history of most continents
  • involves major mountain-building activity along
    their margins
  • and numerous shallow-water marine
  • transgressions and regressions over their
  • These transgressions and regressions
  • were caused by global changes in sea level
  • that most probably were related
  • to plate activity and glaciation

Geologic History of North America
  • We will examine the geologic history of North
  • in terms of major transgressions and regressions
  • rather than a period-by-period chronology
  • and we will place those events in a global

Pangaea-Like Supercontinent
  • During the Precambrian
  • continental accretion
  • and orogenic activity
  • led to the formation of sizable continents
  • At least three large continents
  • existed during the Proterozoic
  • and these landmasses may have later collided
  • to form a single Pangaea-like supercontinent,

Cratons and Mobile Belts
  • This supercontinent began breaking apart
  • sometime during the latest Proterozoic
  • By the beginning of the Paleozoic Era,
  • six major continents were present
  • Each continent can be divided
  • into two major components
  • a craton
  • and one or more mobile belts

Continental Architecture
  • Cratons are the relatively stable
  • and immobile parts of continents
  • and form the foundation upon which
  • Phanerozoic sediments were deposited
  • Cratons typically consist of two parts
  • a shield
  • and a platform

  • Shields are the exposed portion of the
    crystalline basement rocks of a continent
  • and are composed of
  • Precambrian metamorphic
  • and igneous rocks
  • that reveal a history of extensive orogenic
    activity during the Precambrian
  • During the Phanerozoic, however,
  • shields were extremely stable
  • and formed the foundation of the continents

Paleozoic North America
  • The major cratonic structures
  • and mobile belts of North America that formed
    during the Paleozoic Era
  • Shield
  • Mobile belts

  • Extending outward from the shields are buried
    Precambrian rocks
  • that constitute a platform,
  • another part of the craton,
  • the platform is buried by flat-lying or gently
  • Phanerozoic detrital sedimentary rocks
  • and chemical sedimentary rocks
  • The sediments were deposited
  • in widespread shallow seas
  • that transgressed and regressed over the craton

Paleozoic North America
  • Platform

Epeiric Seas
  • The transgressing and regressing shallow seas
  • called epeiric seas
  • were a common feature
  • of most Paleozoic cratonic histories
  • Continental glaciation
  • as well as plate movement
  • caused changes in sea level
  • and were responsible for the advance and retreat
  • of the seas in which the sediments were deposited

Mostly Flat Lying
  • Whereas most of the Paleozoic platform rocks
  • are still essentially flat lying
  • in some places they were gently folded into
    regional arches, domes, and basins
  • In many cases some of the structures stood out
  • as low islands during the Paleozoic Era
  • and supplied sediments to the surrounding epeiric

Mobile Belts
  • Mobile belts are elongated areas of mountain
    building activity
  • They are located along the margins of continents
  • where sediments are deposited in the relatively
    shallow waters of the continental shelf
  • and the deeper waters at the base of the
    continental slope
  • During plate convergence along these margins,
  • the sediments are deformed
  • and intruded by magma
  • creating mountain ranges

Four Mobile Belts
  • Four mobile belts formed
  • around the margin
  • of the North American craton during the Paleozoic
  • Franklin mobile belt
  • Cordilleran mobile belt
  • Ouachita mobile belt
  • Appalachian mobile belt
  • Each was the site of mountain building
  • in response to compressional forces
  • along a convergent plate boundary
  • and formed such mountain ranges
  • as the Appalachians and Ouachitas

Paleozoic North America
  • Mobile belts

  • Because of plate tectonics,
  • the present-day configuration of the continents
    and ocean basins is merely a snapshot in time
  • As the plates move about, the location of
    continents and ocean basins constantly changes
  • Historical geology provides past geologic and
    paleogeographic reconstruction of the world
  • Paleogeographic maps show
  • the distribution of land and sea
  • possible climate regimes
  • and such geographic features as mountain ranges,
    swamps, and glaciers

Paleogeographic Maps
  • Geologists use
  • paleoclimatic data
  • paleomagnetic data
  • paleontologic data
  • sedimentologic data
  • stratigraphic data
  • tectonic data
  • to construct paleogeographic maps
  • which are interpretations of the geography of an
    area for a particular time in the geologic past

Paleozoic paleogeography
  • The paleogeographic history
  • of the Paleozoic Era is not as precisely known
  • as for the Mesozoic and Cenozoic eras
  • in part because the magnetic anomaly patterns
  • preserved in the oceanic crust
  • was subducted during the formation of Pangaea
  • Paleozoic paleogeographic reconstructions
  • are therefore based primarily on
  • structural relationships
  • climate-sensitive sediments such as red beds,
    evaporites, and coals
  • as well as the distribution of plants and animals

Six Major Paleozoic Continents
  • At the beginning of the Paleozoic, six major
    continents were present
  • Baltica - Russia west of the Ural Mountains and
    the major part of northern Europe
  • China - a complex area consisting of at least
    three Paleozoic continents that were not widely
    separated and are here considered to include
    China, Indochina, and the Malay Peninsula
  • Gondwana - Africa, Antarctica, Australia,
    Florida, India, Madagascar, and parts of the
    Middle East and southern Europe

Six Major Paleozoic Continents
  • Kazakhstan - a triangular continent centered on
    Kazakhstan, but considered by some to be an
    extension of the Paleozoic Siberian continent
  • Laurentia - most of present North America,
    Greenland, northwestern Ireland, and Scotland
  • and Siberia - Russia east of the Ural Mountains
    and Asia north of Kazakhstan and south Mongolia
  • Besides these large landmasses, geologists have
    also identified
  • numerous small microcontinents
  • and island arcs associated with various

Paleogeography of the World
  • For the Late Cambrian Period

Paleogeography of the World
  • For the Late Ordovician Period

Paleogeography of the World
  • For the Middle Silurian Period

Early Paleozoic Global History
  • In contrast to today's global geography,
  • the Cambrian world consisted
  • of six major continents
  • dispersed around the globe at low tropical
  • Water circulated freely among ocean basins,
  • and the polar regions were mostly ice free
  • By the Late Cambrian,
  • epeiric seas had covered areas of
  • Laurentia, Baltica, Siberia, Kazakhstania, China
  • while highlands were present in
  • northeastern Gondwana, eastern Siberia, and
    central Kazakhstania

Ordovician and Silurian Periods
  • Plate movements played a major role
  • in the changing global geography
  • Gondwana moved southward during the Ordovician
    and began to cross the South Pole
  • as indicated by Upper Ordovician tillites found
    today in the Sahara Desert
  • In contrast to Laurentias passive margin in the
  • an active convergent plate boundary existed along
    its eastern margin during the Ordovician
  • as indicated by the Late Ordovician Taconic
    orogeny that occurred in New England

Silurian Period
  • Baltica moved northwestward relative
  • to Laurentia and collided with it
  • to form the larger continent of Laurasia
  • This collision, which closed the northern Iapetus
  • is marked by the Caledonian orogeny
  • The southern part of the Iapetus Ocean
  • still remained open between Laurentia and
  • Siberia and Kazakhstania moved from
  • a southern equatorial position during the
  • to north temperate latitudes
  • by the end of the Silurian Period

Early Paleozoic Evolution of North America
  • The geologic history of the North American craton
    may be divide into two parts
  • the first dealing with the relatively stable
    continental interior over which epeiric seas
    transgressed and regressed,
  • and the other dealing with the mobile belts where
    mountain building occurred
  • In 1963 American geologist Laurence Sloss
  • that the sedimentary-rock record of North America
  • could be subdivided into six cratonic sequences

Cratonic Sequences of N. America
  • White areas represent sequences of rocks
  • That are separated by large-scale uncon-formities
    shown in brown
  • Appa-lachian oro-genies
  • Cordilleran orogenies

Cratonic Sequence
  • A cratonic sequence is
  • a large-scale lithostratigraphic unit
  • greater than supergroup
  • representing a major transgressive-regressive
  • bounded by cratonwide unconformities
  • The six unconformities
  • extend across the various sedimentary basins of
    the North American craton
  • and into the mobile belts along the cratonic

Global Transgressive and Regressive Cycles
  • Geologists have also recognized
  • major unconformity bounded sequences
  • in cratonic areas outside North America
  • Such global transgressive and regressive cycles
  • are caused by sea-level changes
  • and are thought to result
  • from major tectonic and glacial events

High-Resolution Stratigraphic Analysis
  • The subdivision and correlation of cratonic
  • provides the foundation for an important concept
    in geology
  • sequence stratigraphy
  • that allows high-resolution analysis
  • within sedimentary rocks of
  • time and facies relationships

Sequence Stratigraphy
  • Sequence stratigraphy is the study of rock
  • within a time-stratigraphic framework of related
  • bounded by erosional or nondepositional surfaces
  • The basic unit of sequence stratigraphy is the
  • which is a succession of rocks bounded by
  • and their equivalent conformable strata

Sequence Stratigraphy
  • Sequence boundaries form
  • as a result of a relative drop in sea level
  • Sequence stratigraphy is an important tool in
  • because it allows geologists to subdivide
    sedimentary rocks
  • into related units
  • that are bounded
  • by time-stratigraphically significant boundaries
  • Geologists use sequence stratigraphy
  • for high-resolution correlation and mapping,
  • as well as interpreting and predicting
    depositional environments

The Sauk Sequence
  • Rocks of the Sauk Sequence
  • during the Neoproterozoic-Early Ordovician
  • record the first major transgression onto the
    North American craton
  • Deposition of marine sediments
  • during the Late Proterozoic and Early Cambrian
  • was limited to the passive shelf areas of the
  • Appalachian and Cordilleran borders of the craton
  • The craton itself was above sea level
  • and experiencing extensive weathering and erosion

Cratonic Sequences of N. America
  • White areas sequences of rocks
  • Brown areas large-scale uncon-formities
  • Sauk sequence

The Sauk Sequence
  • Because North America was located
  • in a tropical climate at this time
  • and there is no evidence of any terrestrial
  • weathering and erosion of the exposed
  • Precambrian basement rocks must have proceeded
  • During the Middle Cambrian,
  • the transgressive phase of the Sauk
  • began with epeiric seas encroaching over the

Transcontinental Arch
  • By the Late Cambrian,
  • the epeiric seas had covered most of North
  • leaving above sea level only
  • a portion of the Canadian Shield
  • and a few large islands
  • These islands,
  • collectively named the Transcontinental Arch,
  • extended from New Mexico
  • to Minnesota and the Lake Superior region

Cambrian Paleogeography of North America
  • During this time North America straddled the
  • Trans-continental Arch

The Sauk Sediments
  • The sediments deposited
  • on both the craton
  • and along the shelf area of the craton margin
  • show abundant evidence of shallow-water
  • The only difference
  • between the shelf and craton deposits
  • is that the shelf deposits are thicker
  • In both areas,
  • the sands are generally clean and well sorted
  • and commonly contain ripple marks
  • and small-scale cross-bedding

Sauk Carbonates
  • Many of the carbonates are
  • bioclastic
  • composed of fragments of organic remains
  • contain stromatolites,
  • or have oolitic textures
  • contain small, spherical calcium carbonate grains
  • Such sedimentary structures and textures
  • indicate shallow-water deposition

A Transgressive Facies Model
  • Sediments become increasingly finer
  • the farther away from land one goes
  • Where sea level remains the same, in a stable
  • coarse detrital sediments are typically deposited
    in the nearshore environment,
  • and finer-grained sediments are deposited in the
    offshore environment
  • Carbonates form farthest from land in the area
    beyond the reach of detrital sediments

A Transgressive Facies Model
  • Recall that facies are sediments
  • that represent a particular environment
  • During a transgression, the coarse (sandstone),
  • fine (shale) and carbonate (limestone) facies
  • migrate in a landward direction

The Cambrian of the Grand Canyon Region
  • This region provides an excellent example
  • of sedimentation patterns of a transgressing sea
  • The region of the Grand Canyon occupied
  • the western margin of the craton during Sauk
  • a passive shelf
  • During Neoproterozoic and Early Cambrian time,
  • most of the craton was above sea level
  • deposition of marine sediments
  • was mainly restricted to the margins of the
  • on continental shelves and slopes

  • A transgression covered
  • the Grand Canyon region.
  • The Tapeats Sandstone represents
  • the basal transgressive shoreline deposits
  • that accumulated as marine waters
  • transgressed across the shelf
  • and just onto the western margin
  • of the craton during the Early Cambrian

Cambrian Transgression
  • Cambrian strata exposed in the Grand Canyon
  • The three formations exposed
  • along the Bright Angel Trail, Grand Canyon Arizona

  • The Tapeats sediments
  • are clean, well-sorted sands
  • of the type one would find on a beach today
  • As the transgression continued into the Middle
  • muds of the Bright Angle Shale
  • were deposited over the Tapeats Sandstone

Continued Transgression
  • The Sauk Sea had transgressed so far onto the
  • by the Late Cambrian that
  • in the Grand Canyon region
  • carbonates of the Muav Limestone were being
    deposited over the Bright Angel Shale
  • This vertical succession of
  • sandstone (Tapeats)
  • shale (Bright Angel)
  • and limestone (Muav)
  • forms a typical transgressive sequence
  • and represents a progressive migration
  • of offshore facies toward the craton through time

Time Transgressive Formations
  • Cambrian rocks of the Grand Canyon region
  • also illustrate how many formations are time
  • that is, their age is not the same every place
    they are found
  • Mapping and correlations based on faunal evidence
  • indicate that deposition of the Mauv Limestone
  • had already started on the shelf
  • before deposition of the Tapeats Sandstone
  • was completed on the craton

Time Transgressive Formations
  • Faunal analysis of the Bright Angel Shale
  • that it is Early Cambrian in age in California
  • and Middle Cambrian in age in the Grand Canyon
  • thus illustrating the time-
    transgressive nature of formations and

younger shale
older shale
Cambrian Transgression
  • Cambrian strata exposed in the Grand Canyon
  • Observe the time transgressive nature of the
    three formations
  • The three formations exposed
  • along the Bright Angel Trail, Grand Canyon Arizona

Same Facies Relationship
  • This same facies relationship also occurred
    elsewhere on the craton
  • as the seas encroached from the Appalachian and
    Ouachita mobile belts onto the craton interior
  • Carbonate deposition dominated on the craton as
    the Sauk transgression continued
  • during the early Ordovician,
  • and the islands of the Transcontinental Arch were
    soon covered by the advancing Sauk Sea
  • By the end of Sauk time, much of the craton
  • was submerged beneath a warm, equatorial epeiric

Cambrian Facies
  • Block diagram from the craton interior to the
    Appalachian mobile belt margin
  • showing 3 major Cambrian facies
  • and the time transgressive nature of the units
  • The carbonate facies developed progressively
  • because of submergence of the detrital source
    areas by the advancing Sauk Sea

Upper Cambrian Sandstone
  • Outcrop of cross-bedded Upper Cambrian sandstone
    in the Dells area of Wisconsin

Regression and Unconformity
  • As the Sauk Sea regressed
  • from the craton during the Early Ordovician,
  • it revealed a landscape of low relief
  • The rocks exposed were predominately
  • limestones and dolostones
  • that experienced deep and extensive erosion
  • because North America was still located in a
    tropical environment
  • The resulting cratonwide unconformity
  • marks the boundary between the Sauk
  • and Tippecanoe sequences

Ordovician Period
  • Paleo-geography of North America
  • showing change in the position of the the equator
  • The continent
  • was rotating counter-clockwise

Cratonic Sequences of N. America
  • White areas sequences of rocks
  • brown areas large-scale uncon-formities
  • Regression
  • Tippecanoe sequence

The Tippecanoe Sequence
  • A transgressing sea deposited the Tippecanoe
    sequence over most of the craton
  • Middle Ordovician-Early Devonian
  • Like the Sauk sequence, this major transgression
    deposited clean, well-sorted quartz sands
  • The Tippecanoe basal rock is the St. Peter
  • an almost pure quartz sandstone used in
    manufacturing glass
  • that occurs throughout much of the midcontinent
  • and resulted from numerous cycles of weathering
  • and erosion of Proterozoic and Cambrian
  • deposited during the Sauk transgression

Transgression of the Tippecanoe Sea
  • Resulted in deposition of
  • the St. Peter Sandstone
  • Middle Ordovician
  • over a large area of the craton

St. Peter Sandstone
  • Outcrop of St. Peter Sandstone in Governor Dodge
    State Park, Wisconsin

The Tippecanoe Sequence
  • The Tippecanoe basal sandstones were followed by
    widespread carbonate deposition
  • The limestones were generally the result of
  • by calcium carbonate-secreting organisms such
  • corals,
  • brachiopods,
  • stromatoporoids,
  • and bryozoans

Dolostones and Shales
  • Besides the limestones, there were also many
  • Most of the dolostones formed as a result of
    magnesium replacing calcium in calcite,
  • thus converting limestones into dolostones
  • In the eastern portion of the craton, the
    carbonates grade laterally into shales
  • These shales mark the farthest extent
  • of detrital sediments derived from
  • weathering and erosion of the Taconic Highlands
  • a tectonic event in the Appalachian mobile belt

Tippecanoe Reefs and Evaporites
  • Organic reefs are limestone structures
  • constructed by living organisms,
  • some of which contribute skeletal materials to
    the reef framework
  • Today, corals, and calcareous algae
  • are the most prominent reef builders,
  • but in the geologic past other organisms
  • played a major role in reef building
  • Reefs appear to have occupied
  • the same ecological niche in the geological past
  • that they do today regardless of the organisms

Modern Reef Requirements
  • Because of the ecological requirements
  • of reef-building organisms,
  • present-day reefs are confined
  • to a narrow latitudinal belt
  • between 30 degrees north and south of the equator
  • Corals,
  • the major reef-building organisms today,
  • require warm, clear, shallow water
  • of normal salinity for optimal growth

Present-Day Reef Community
  • with reef-building organisms

Reef Environments
  • Block diagram of a reef showing the various
    environments within the reef complex

Size and Shape of Reefs
  • The size and shape of a reef
  • are largely the result of the interaction between
  • the reef-building organisms,
  • the bottom topography,
  • wind and wave action,
  • and subsidence of the seafloor
  • Reefs also alter the area around them
  • by forming barriers to water circulation
  • or wave action

Barrier Reefs
  • Reefs typically are long,
  • linear masses forming a barrier between
  • a shallow platform on one side
  • and a comparatively deep marine basin
  • on the other side
  • Such reefs are known as barrier reefs
  • Reefs create and maintain a steep seaward front
  • that absorbs incoming wave energy
  • As skeletal material breaks off
  • from the reef front,
  • it accumulates as talus along a fore-reef slope

Barrier Reef
  • Barrier Reef
  • Fore-reef slope

The Lagoon
  • The reef barrier itself is porous
  • and composed of reef-building organisms
  • The lagoon area is a low-energy,
  • quiet water zone where fragile,
  • sediment-trapping organisms thrive
  • The lagoon area can also become the site
  • of evaporitic deposits
  • when circulation to the open sea is cut off
  • Modern examples of barrier reefs
  • are the Florida Keys, Bahama Islands,
  • and Great Barrier Reef of Australia

Ancient Reefs
  • Reefs have been common features since the
  • and have been built by a variety of organisms
  • The first skeletal builders of reeflike
  • were archaeocyathids
  • These conical-shaped organisms lived
  • during the Cambrian and had double,
  • perforated, calcareous shell walls
  • Archaeocyathids built small mounds
  • that have been found on all continents
  • except South America

Stromatoporoid-Coral Reefs
  • Beginning in the Middle Ordovician,
  • stromatoporoid coral reefs
  • became common in the low latitudes,
  • and similar reefs remained so throughout the rest
    of the Phanerozoic Eon
  • The burst of reef building seen in the Late
    Ordovician through Devonian
  • probably occurred in response to evolutionary
  • triggered by the appearance
  • of extensive carbonate seafloors and platforms
  • beyond the influence of detrital sediments

Michigan Basin Evaporites
  • The Middle Silurian rocks of the present-day
    Great Lakes region
  • Tippecanoe sequence
  • are famous for their reef and evaporite deposits
  • The most significant structure in the region
  • the Michigan Basin
  • is a broad, circular basin surrounded by large
    barrier reefs
  • These reefs contributed to increasingly
    restricted circulation
  • and the precipitation of Upper Silurian
    evaporites within the basin

Silurian Period
  • Paleogeography of North America during the
    Silurian Period
  • Reefs developed in the Michigan, Ohio, and
    Indiana-Illinois-Kentucky areas

Other Types of Reefs
  • Within the rapidly subsiding interior
  • of the basin, other types of reefs are found
  • Pinnacle reefs are tall,
  • spindly structures up to 100 m high
  • They reflect the rapid upward growth
  • needed to maintain themselves near sea level
  • during subsidence of the basin
  • Besides the pinnacle reefs,
  • bedded carbonates and thick sequences of salt
  • and anhydrite are also found in the Michigan Basin

Northern Michigan Basin
  • Northern Michigan Basin sediments during the
    Silurian Period

Stromatoporoid Reef Facies
  • Stromato-poroid barrier-reef facies of the
    Michigan Basin

  • Evaporite facies

Carbonate Facies
  • Carbonate Facies

Tippecanoe Regression and Evaporites
  • As the Tippecanoe Sea gradually regressed
  • from the craton during the Late Silurian,
  • precipitation of evaporite minerals occurred in
  • Appalachian Basin,
  • Ohio Basin,
  • and Michigan Basin
  • In the Michigan Basin alone,
  • approximately 1500 m of sediments were deposited,
  • nearly half of which are halite and anhydrite

Origin of Thick Evaporites
  • How did such thick sequences of evaporites
  • 1. When sea level dropped, the tops of the
    barrier reefs were as high as or above sea level,
  • thus preventing the influx of new seawater into
    the basin
  • Evaporation of the basinal seawater would result
    in the precipitation of salts
  • 2. Alternatively, the reefs grew upward so close
    to sea level
  • that they formed a sill or barrier that
    eliminated interior circulation

Silled Basin Model
  • Silled Basin Model for evaporite sedimentation by
    direct precipitation from seawater
  • Vertical scale is greatly exaggerated

Basin Brines
  • Because North America was still near the equator
    during the Silurian Period,
  • temperatures were probably high

Basin Brines
  • As circulation to the Michigan Basin was
  • seawater within the basin evaporated,
  • forming a brine
  • Because the brine was heavy,
  • it concentrated near the bottom,
  • and minerals precipitated on the basin floor

Replenishment of Salt
  • Some seawater flowed in over the sill
  • and through channels cut in the barrier reefs,
  • but this only added new seawater that later
    became concentrated as brine
  • In this way, the brine in the basin became
    increasingly concentrated
  • until the salts could no longer stay in solution,
  • thus precipitating to form evaporite minerals

Order of Precipitation
  • The order and type of salts precipitating from
    seawater depends on
  • their solubility,
  • the original concentration of seawater,
  • and local conditions of the basin
  • Salts generally precipitate in order beginning
    with the least soluble
  • and ending with the most soluble
  • Therefore, the order of precipitation is
  • calcium carbonate first,
  • followed by gypsum
  • and lastly halite

  • Gypsum is the common sulfate precipitated from
  • but when deeply buried,
  • gypsum loses its water and is converted to
  • Many lateral shifts and interfingering
  • of the limestone, anhydrite, and halite facies
  • may occur, however, because of
  • variations in the amount of seawater entering the
  • and changing geologic conditions

Problems with the Model
  • Thus, the periodic evaporation or seawater
    proposed by this model
  • could account for the observed vertical and
    lateral distribution
  • of evaporites in the Michigan Basin
  • However, associated with those evaporites
  • are pinnacle reefs,
  • and the organisms constructing those reefs
  • could not have lived in such a highly saline

Reefs in a Highly Saline Environ-ment?
  • Organisms constructing reefs could not have lived
    in such a highly saline environ-ment

No Model Is Perfect
  • How then, can such contradictory features be
  • Numerous models have been proposed, ranging from
  • cessation of reef growth followed by evaporite
  • to alternation of reef growth and evaporite
  • Although the Michigan Basin has been studied
    extensively for years,
  • no model yet proposed completely explains
  • the genesis and relationship of its various reef,
    carbonate, and evaporite facies

The End of the Tippecanoe Sequence
  • By the Early Devonian,
  • the regressing Tippecanoe Sea
  • had retreated to the craton margin
  • exposing an extensive lowland topography
  • During this regression,
  • marine deposition was initially restricted to
  • a few interconnected cratonic basins and
  • by the end of the Tippecanoe
  • to only the mobile belts surrounding the craton

Domes and Basins
  • As the Tippecanoe Sea regressed
  • during the Early Devonian,
  • the craton experienced mild deformation
  • resulting in the formation of many domes, arches,
    and basins
  • These structures were mostly eroded
  • during the time the craton was exposed
  • so that they were eventually covered by deposits
  • from the encroaching Kaskaskia Sea

The Appalachian Mobile Belt
  • Having examined the Sauk and Tippecanoe geologic
    history of the craton,
  • we turn our attention to the Appalachian mobile
  • where the first Phanerozoic orogeny
  • began during the Middle Ordovician
  • The mountain building occurring
  • during the Paleozoic Era
  • had a profound influence on
  • the climate
  • and sedimentary history of the craton

Mountain Building
  • Additionally, it was part of the global tectonic
  • that sutured the continents together,
  • forming Pangaea by the end of the Paleozoic
  • The Appalachian region
  • throughout Sauk time,
  • was a broad, passive, continental margin
  • Sedimentation was closely balanced by subsidence
  • as thick, shallow marine sands were succeeded
  • by extensive carbonate deposits

Iapetus Ocean
  • During this time,
  • the Iapetus Ocean was widening
  • as a result of movement
  • along a divergent plate boundary
  • Beginning with the subduction of the Iapetus
    plate beneath Laurentia
  • which was an oceanic-continental convergent plate
  • the Appalachian mobile belt was born

Appalachian Mobile Belt
  • Evolution of the Appalachian mobile belt
  • Neoproterozoic opening of Iapetus Ocean
  • with passive continental margins
  • and large carbonate platforms

The Taconic Orogeny
  • The resulting Taconic orogeny,
  • named after present-day Taconic Mountains of
  • eastern New York,
  • central Massachusetts,
  • and Vermont
  • was the first of several orogenies
  • to affect the Appalachian region

Shallow-Water Deposition
  • The Appalachian mobile belt
  • can be divided into two depositional environments
  • The first is the extensive,
  • shallow-water carbonate platform
  • that formed the broad eastern continental shelf
  • and stretched from Newfoundland to Alabama
  • It formed during the Sauk Sea transgression
  • onto the craton when carbonates
  • were deposited in a vast shallow sea
  • The shallow water depth on the platform
  • is indicated by stromatolites, mud cracks,
  • and other sedimentary structures and fossils

Deep-Water Deposits
  • Carbonate deposition ceased along the East Coast
  • during the Middle Ordovician
  • and was replaced by deepwater deposits
    characterized by
  • thinly bedded black shales,
  • graded beds,
  • coarse sandstones,
  • graywackes,
  • and associated volcanics
  • This suite of sediments marks the onset
  • of mountain building, the Taconic orogeny

Eastern Sediment Source
  • The subduction of the Iapetus plate beneath
  • resulted in volcanism
  • and downwarping of the carbonate platform
  • Throughout the Appalachian mobile belt,
  • indications that these deposits were derived from
    the east, come from
  • facies patterns,
  • paleocurrents,
  • and sedimentary structures
  • The sediment originated where
  • the Taconic Highlands
  • and associated volcanoes were rising

Appalachian Mobile Belt
  • Middle Ordovician transition to convergence
    resulted in orogenic activity

Evidence for Orogeny
  • Evidence for the timing and origin of this
    orogeny comes from
  • additional structural,
  • stratigraphic,
  • petrologic,
  • and sedimentologic information
  • For example,
  • at many locations within the Taconic belt,
  • pronounced angular unconformities occur
  • where steeply dipping Lower Ordovician rocks
  • are overlain by gently dipping or horizontal
    Silurian and younger rocks

Orogeny Timing
  • Other evidence in the area from
  • present-day Georgia to Newfoundland includes
  • volcanic activity in the form of deep-sea lava
  • volcanic ash layers,
  • and intrusive bodies
  • These igneous rocks show a clustering
  • of radiometric ages corresponding to Middle to
    Late Ordovician
  • In addition, regional metamorphism
  • coincides with the radiometric dates

Queenston Delta Clastic Wedge
  • The final piece of evidence
  • for the Taconic orogeny is
  • the development of a large clastic wedge,
  • an extensive accumulation of mostly detrital
  • were deposited adjacent to an uplifted area
  • and become thinner and finer grained away from
    the source area,
  • eventually grading into the carbonate cratonic
  • The clastic wedge resulting from the erosion
  • of the Taconic Highlands is referred
  • to as the Queenston Delta

Queenston Delta Clastic Wedge
  • Queenston Delta clastic wedge
  • Taconic Highlands
  • consists of thick, coarse-grained detrital
    sediments nearest the highlands
  • and thins laterally into finer-grained sediments
    on the craton

A European Orogeny
  • The Taconic orogeny
  • marked the first pulse of mountain building in
    the Appalachian mobile belt
  • and was a response to the subduction taking place
    beneath the east coast of Laurentia
  • As the Iapetus Ocean narrowed and closed,
  • another orogeny occurred in Europe during the

Caledonian Orogeny
  • The Caledonian orogeny was essentially a mirror
    image of
  • the Taconic orogeny and the Acadian orogeny
  • and was part of the global mountain-building
  • that occurred during the Paleozoic Era
  • Even though the Caledonian orogeny
  • occurred during Tippecanoe time,
  • we will discuss it with the Acadian orogeny
  • because the two are intimately related

Caledonian Orogeny
  • The transition to convergence resulted in
    orogenic activity in North America and Europe
  • Caledonian Orogeny
  • was a mirror image of the Taconic Orogeny

Early Paleozoic Mineral Resources
  • Early Paleozoic-age rocks contain a variety
  • of important mineral resources, including
  • sand and gravel for construction,
  • building stone,
  • and limestone used in the manufacture of cement
  • Important sources of industrial or silica sand
  • the Upper Cambrian Jordan Sandstone of Minnesota
    and Wisconsin,
  • the Lower Silurian Tuscarora Sandstone in
    Pennsylvania and Virginia,
  • and the Middle Ordovician St. Peter Sandstone

Silica Sand
  • The St. Peter Sandstone,
  • the basal sandstone of the Tippecanoe sequence,
  • occurs in several states,
  • but the best-known area of production
  • is in La Salle County, Illinois
  • Silica sand has a variety of uses including
  • the manufacture of glass,
  • molds for casting iron, aluminum, and copper
  • and refractory bricks for blast furnaces
  • It is also pumped into oil and gas wells
  • to fracture the source rocks and provide
    permeable zones
  • for the oil or gas to migrate to the well

Salt and Oil
  • Thick deposits of Silurian evaporites,
  • mostly rock salt (NaCl)
  • and rock gypsum (CaSO42H2O) altered to rock
    anhydrite (CaSO4)
  • underlie parts of Michigan, Ohio, New York, and
    adjacent areas in Ontario, Canada
  • and are important sources of various salts
  • In addition, barrier and pinnacle reefs
  • in carbonate rocks
  • associated with these evaporites
  • are the reservoirs for oil and gas in Michigan
    and Ohio

Lead and Zinc
  • The host rocks for deposits of lead and zinc
  • in southeast Missouri are Cambrian dolostones,
  • although some Ordovician rocks contain these
    metals as well
  • These deposits have been mined since 1720
  • but have been largely depleted
  • Now most lead and zinc mined in Missouri
  • come from Mississippian-age sedimentary rocks

  • The Silurian Clinton Formation crops out
  • from Alabama north to New York,
  • and equivalent rocks are found in Newfoundland
  • This formation has been mined for iron in many
  • In the United States, the richest ores
  • and most extensive mining occurred near
    Birmingham, Alabama,
  • but only a small amount of ore is currently
    produced in that area

  • Six major continents existed
  • at the beginning of the Paleozoic Era
  • four of them were located near the paleo-equator
  • During the Early Paleozoic (Cambrian-Silurian)
  • Laurentia was moving northward
  • and Gondwana moved to a south polar location,
  • as indicated by tillite deposits

  • Most continents consisted of two major components
  • a relatively stable craton over which epeiric
    seas transgressed and regressed,
  • surrounded by mobile belts in which mountain
    building took place
  • The geologic history of North America
  • can be divided into cratonic sequences
  • that reflect cratonwide transgressions and

  • The Sauk Sea was the first major transgression
    onto the craton
  • At its maximum, it covered the craton
  • except for parts of the Canadian Shield
  • and the Transcontinental Arch,
  • a series of large northeast-southwest trending
  • The Tippecanoe Sequence began with
  • deposition of an extensive sandstone over
  • the exposed and eroded Sauk landscape

  • During Tippecanoe time,
  • extensive carbonate deposition took place
  • In addition, large barrier reefs
  • enclosed basins,
  • and resulted in evaporite deposition within these
  • The eastern edge of North America
  • was a stable carbonate platform during Sauk time

  • During Tippecanoe time
  • an oceanic-continental convergent plate boundary
  • resulting in the Taconic orogeny,
  • the first of three major orogenies to affect the
    Appalachian mobile belt
  • The newly formed Taconic Highlands
  • shed sediments into the western epeiric sea
  • producing the Queenston Delta, a clastic wedge

  • Early Paleozoic-age rocks contain a variety of
    mineral resources including
  • building stone,
  • limestone for cement,
  • silica sand,
  • hydrocarbons,
  • evaporites,
  • and iron ores
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