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Chapter 10
Early Paleozoic Earth History
The First
Geologic
Map
• William
Smith,
– a canal
builder,
published
the first
geologic
map
– on August 1,
1815
Paleozoic History
• The Paleozoic history of continents:
– major mountain-building activity along
continental margins
– numerous shallow-water marine
transgressions and regressions over their
interiors
• These transgressions and regressions
– were caused by global changes in sea level
– that most probably were related
– to plate activity and glaciation
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
Epeiric Seas
• The transgressing and regressing
shallow seas
– called epeiric seas
– were a common feature of Paleozoic
• 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
Mobile Belts
• Mobile belts are elongated areas of mountain
building activity – “orogenic activity”
• 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
Paleogeographic Maps
• Geologists use
– paleoclimatic data
– paleomagnetic data
– paleontologic data
– sedimentologic data
– stratigraphic data
– tectonic data
Six Major Paleozoic Continents
• At the beginning of the Paleozoic, six major
continents were present including:
– Baltica - Russia west of the Ural Mountains
and the major part of northern Europe
– Gondwana - Africa, Antarctica, Australia,
Florida, India, Madagascar, and parts of the
Middle East and southern Europe
– Laurentia - most of present North America,
Greenland, northwestern Ireland, and
Scotland
Six Major Paleozoic Continents (others)
– 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
– Kazakhstan - a triangular continent centered on
Kazakhstan, but considered by some to be an
extension of the Paleozoic Siberian continent
– 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 microplates
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 Evolution of
North America
• The geologic history of the North American
craton may be divide into two parts
– stable continental interior over which epeiric
seas transgressed and regressed
– mobile belts where mountain building occurred
Cordillera
orogenies
Cratonic Sequences of N. America
Appalachian orogenies
• White areas represent sequences of rocks That are separated by
large-scale unconformities shown in brown
Cratonic Sequence
• A cratonic sequence is
– a large-scale lithostratigraphic unit
– representing a major transgressiveregressive cycle
– bounded by cratonwide unconformities
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
– 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
• White areas = sequences of rocks
• Sauk
sequenc
e
The Sauk Sequence:
Middle Cambrian Period
• North America was located in a tropical climate at this
time
– there is no evidence of any terrestrial vegetation, NO
plants!
– Rapid weathering and erosion of the exposed
Precambrian basement rocks
– the transgressive phase of the Sauk
– began with epeiric seas encroaching over the craton
Transcontinental Arch
• By the Late Cambrian,
– the epeiric seas had covered most of North America,
– 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 equator
• Transcontinental
Arch
Sauk Carbonates
• Many of the Sauk carbonates (limestones) 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 finer away from land
– 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
marine environment 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 time,
• 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
craton
• on continental shelves and slopes
Transgression
• A transgression covered
– the Grand Canyon region.
– The Tapeats Sandstone represents the shoreline
deposits
are clean, well-sorted sands
– of the type one would find on a beach today
• As the transgression continued into the Middle
Cambrian,
– muds of the Bright Angle Shale
– were deposited over the Tapeats Sandstone
–
Continued Transgression
• The Sauk Sea had transgressed so far
onto the craton
– 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
Cambrian Transgression
• Cambrian strata exposed in the Grand
Canyon
• The three formations exposed
– along the Bright Angel Trail, Grand Canyon
Arizona
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
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
Cratonic Sequences of N.
America
• White areas = sequences of rocks
• brown
areas =
largescale
unconformities
• 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
Sandstone,
– an almost pure quartz sandstone used in
manufacturing glass
Ordovician Period
• Paleogeography of
North America
– showing
change in the
position of
the the
equator
• The continent
– was rotating
counterclockwise
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
deposition
– by
calcium carbonatesecreting organisms
such as
•
•
•
•
corals,
brachiopods,
stromatoporoids,
and bryozoans
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 as today
Modern Reef Requirements
present-day reefs are confined
– To 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
Michigan Basin Evaporites
• The Middle Silurian rocks of the present-day
Great Lakes region Tippecanoe sequence
are 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-IllinoisKentucky areas
Tippecanoe Regression and
Evaporites
• As the Tippecanoe Sea gradually
regressed
– from the craton during the Late Silurian,
– precipitation of evaporite minerals occurred
in the Michigan Basin
– approximately 1500 m of sediments were
deposited,
– nearly half of which are halite and anhydrite
(gypsum)
Origin of Thick Evaporites
(Gypsum, Halite)
• How did such thick sequences of evaporites accumulate?
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
sedimentatio
n by direct
precipitation
from
seawater
– Vertical
scale is
greatly
exaggerate
d
Basin Brines
• Because North America was still near the
equator during the Silurian Period,
– temperatures were probably high
Reefs in a Highly Saline
Environ-ment?
• Organisms
constructing
reefs could
not have
lived in such
a highly
saline
environment
No Model Is Perfect
• How then, can such contradictory features
be explained?
– Numerous models have been proposed,
ranging from
• cessation of reef growth followed by evaporite
deposition,
• to alternation of reef growth and evaporite
deposition
– no model yet proposed completely explains
various reef, carbonate, and evaporite facies
The Appalachian Mobile Belt
– where the first Phanerozoic orogeny
– began during the Middle Ordovician
– How would a mountain range influence
– the climate and sedimentary history of the
craton?
Mountain Building
• Global tectonic regime
– 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
– Sandstone – shale - carbonate
Iapetus Ocean
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-continent convergent
plate boundary
• the Appalachian mobile belt was born
Appalachian Mobile Belt
• Evolution of the Appalachian mobile belt
• 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
Eastern Sediment Source
• The subduction of the Iapetus plate
beneath Laurentia
– 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
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 sediments
• were deposited adjacent to an uplifted area
• and become thinner and finer grained away from the source
area,
• eventually grading into the carbonate cratonic facies
• 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
– coarsegrained
detrital
sediments
near the
highlands
– thins
laterally
into finergrained
sediments
on the
craton
• Taconic
Highland
s
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 Silurian
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
episode
– 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