Transcript No Slide Title

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
• Five of the six geologic Paleozoic systems
– Cambrian, Ordovician, Silurian, Devonian, and
Carboniferous
• We use the same basic geologic principles to
interpret the geology of the Paleozoic Era
Cratons and Mobile Belts
• Pannotia supercontinent began broke apart
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 typically consist of two parts
– a shield
– and a platform
Platforms
• Extending outward from the shields are buried
Precambrian rocks
• The sediments over the platforms were
deposited in widespread shallow seas
Paleozoic North America
• Platform
Epeiric Seas
• The transgressing and regressing shallow seas
– called epeiric seas
– common feature of most Paleozoic cratons
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
Paleozoic North America
• Mobil belts
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, evaporates,
and coals
• as well as the distribution of plants and animals
Six Major Paleozoic Continents
– 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
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,
– six major continents
– dispersed at low tropical latitudes
• polar regions were mostly ice free
• By the Late Cambrian,
– epeiric seas had covered most areas of
• Laurentia, Baltica, Siberia, Kazakhstania, China,
Ordovician and Silurian Periods
• 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 Laurentia’s passive margin in the
Cambrian,
– an active convergent plate boundary formed 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 closed the northern Iapetus
Ocean
• Siberia and Kazakhstania moved from
– a southern equatorial position during the Cambrian
– 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 comings and goings of epeiric seas
– the second dealing with the mobile belts
In 1963, American geologist Laurence Sloss
proposed 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 largescale
Cordilleran
unconorogenies
formities
shown in
brown
Appalachian
orogenies
Cratonic Sequence
• A cratonic sequence is
– a large-scale lithostratigraphic unit
• greater than supergroup
– representing a major transgressive-regressive cycle
– bounded by craton-wide unconformities
• The six unconformities extend across
– the various sedimentary basins of the North
American craton
– and into the mobile belts along the cratonic margin
The Sauk Sequence
• Rocks of the Sauk Sequence
– during the Late Proterozoic-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 =
largescale
unconformities
• Sauk
sequence
The Sauk Sequence
• Because North America was located
– in a tropical climate at this time
– but there is no evidence of any terrestrial
vegetation,
– weathering and erosion of the exposed
– Precambrian basement rocks must have proceeded
rapidly
• During the Middle Cambrian,
– the transgressive phase of the Sauk
– began with epeiric seas encroaching over the craton
Transcontinental Arch
• By the Late Cambrian,
– the Sauk Sea 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
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
deposition
• The only difference
– between the shelf and craton deposits
– is that the shelf deposits are thicker
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
• 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
Cambrian Transgression
• Cambrian strata exposed in the Grand Canyon
• The three formations exposed
– along the Bright Angel Trail, Grand Canyon
Arizona
Transgression
• 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
Cambrian,
– muds of the Bright Angle Shale
– were deposited over the older Tapeats Sandstone
Time Transgressive Formations
• Faunal analysis of the Bright Angel Shale
indicates
– that it is Early Cambrian in age in California
– and Middle Cambrian in age in the Grand Canyon
region,
younger
• thus illustrating the time-transgresshale
sive nature of formations and facies
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
• By the end of Sauk time, much of the craton
– was submerged beneath a warm, equatorial epeiric
sea
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
– due to 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
• During the Early Ordovician, the Sauk Sea
regressed.
• The rocks exposed were predominately
– limestones and dolostones
– that experienced deep and extensive erosion
• The resulting craton-wide unconformity
– marks the boundary between the Sauk
– and Tippecanoe sequences
Ordovician Period
• Paleogeography of
North America
– showing
change in the
position of the
the equator
• The continent
– was rotating
counterclockwise
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
• The Tippecanoe basal rock is the St. Peter
Sandstone,
–
–
–
–
–
an almost pure quartz sandstone
occurs throughout much of the mid-continent
resulted from numerous cycles of weathering
and erosion of Proterozoic and Cambrian sandstones
deposited during the Sauk transgression
Transgression of the
Tippecanoe Sea
• Resulted in
the
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
• Reefs appear to have occupied
– the same ecological niche in the geological past
Modern Reef Requirements
• Present-day reefs
– grow between 30 degrees N and S of equator
• Reefs 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
Barrier Reefs
– typically long linear masses forming a barrier
between
– a shallow platform
– a deep marine basin
• Reefs create and maintain a steep seaward front
– that absorbs incoming wave energy
• As skeletal material breaks off
– from the reef front,
– it accumulates along a fore-reef slope
Barrier Reef
• Barrier Reef
• Fore-reef slope
The Lagoon
• 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 reef systems
– are the Florida Keys, Bahama Islands,
– and Great Barrier Reef of Australia
Ancient Reefs
• Reefs have been common features since the
Cambrian
• The first skeletal builders of reef-like structures
– were archaeocyathids
Stromatoporoid-Coral Reefs
• Beginning in the Middle Ordovician,
– stromatoporoid-coral reefs became common
– similar reefs throughout the rest of the Phanerozoic
Eon
Michigan Basin Evaporites
• Michigan Basin
– a broad, circular basin surrounded by large barrier
reefs
• Reef growth caused restricted circulation
– and precipitation of Silurian evaporates within
Upper Tippecanoe sequence of the basin
Silurian Period
• Paleogeography
of North
America during
the Silurian
Period
• Reefs developed
in the Michigan,
Ohio, and
Indiana-IllinoisKentucky areas
Northern Michigan Basin
• Northern
Michigan
Basin
sediments
during the
Silurian
Period
Stromatoporoid Reef Facies
• Stromatoporoid
barrierreef facies
of the
Michigan
Basin
Evaporite
• Evaporite facies
Carbonate Facies
• Carbonate
Facies
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
Order of Precipitation
– calcium carbonate first,
– followed by gypsum
– and lastly halite
Reefs in a Highly Saline Environment?
• Organisms
constructing
reefs could
not have
lived in
such a
highly
saline
environment
The End of the
Tippecanoe Sequence
• During this regression,
– marine deposition was initially restricted to
– a few interconnected cratonic basins
By the Early Devonian,
– the regressing Tippecanoe Sea retreated to
the craton margin
– exposed an extensive lowland topography
The Appalachian Mobile Belt
• the first Phanerozoic orogeny
– began during the Middle Ordovician
Mountain Building
• part of the 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
Iapetus Ocean
• During this time,
– the Iapetus Ocean was widening
along a divergent plate boundary
• the Appalachian mobile belt was born with the
onset of subduction of the Iapetus plate beneath
Laurentia
Appalachian Mobile Belt
• Evolution of the Appalachian mobile belt
• Late Proterozoic 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
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
• Formed during the Sauk Sea transgression
Deep-Water Deposits
• Replaced by deep-water deposits (second
depositional environment) during middle Ordovician
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
Sediment Source
• Sediment shed from
– the Taconic Highlands
– and associated volcanoes
The subduction of the Iapetus plate beneath Laurentia
– resulted in volcanism and downwarping of the
carbonate platform
Appalachian Mobile Belt
• Middle Ordovician transition to convergence
resulted in orogenic activity
Orogeny Timing
• Other evidence in the area from present-day
Georgia to Newfoundland includes
– volcanic activity in the form of deep-sea lava flows,
– volcanic ash layers,
– and intrusive bodies
• These igneous rocks show a clustering
– of radiometric ages between 440 to 480 million
years ago
• In addition, regional metamorphism
– coincides with the radiometric dates
Queenston Delta Clastic Wedge
• The clastic wedge resulting from the erosion
– of the Taconic Highlands
– referred to as the Queenston Delta
Queenston Delta Clastic Wedge
• Queenston Delta clastic wedge
– consists of
thick,
coarsegrained
detrital
sediments
nearest the
highlands
– and thins
laterally into
finer-grained
sediments
on the
craton
• Taconic
Highlands
A European Orogeny
• As the Iapetus Ocean narrowed and closed,
– another orogeny also occurred in Europe during the
Silurian (Caledonian Orogeny)
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
• An Important sources of industrial or silica sand
is
– the Middle Ordovician St. Peter Sandstone
Salt and Oil
• Thick deposits of Silurian evaporites,
– mostly rock salt (NaCl)
– and rock gypsum (CaSO4•H2O) altered to rock
anhydrite (CaSO4)
– and are important sources of various salts
• In addition, barrier and pinnacle reefs
– are reservoirs for oil and gas in Michigan and Ohio
Summary
• Six major continents existed
– at the beginning of the Paleozoic Era
– four of them were located near the paleoequator
• During the Early Paleozoic — CambrianSilurian
– Laurentia was moving northward
– and Gondwana moved to a south polar location,
– as indicated by tillite deposits
Summary
• 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
regressions
Summary
• 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 islands
• The Tippecanoe sequence began with
– deposition of an extensive sandstone over
– the exposed and eroded Sauk landscape
Summary
• During Tippecanoe time,
– extensive carbonate deposition took place
• In addition, large barrier reefs
– enclosed basins,
– and resulted in evaporite deposition within
these basins
• The eastern edge of North America
– was a stable carbonate platform during Sauk
time
Summary
• During Tippecanoe time
– an oceanic-continental convergent plate
boundary formed,
– resulting in the Taconic orogeny,
• the first of several 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
Summary
• Early Paleozoic-age rocks contain a variety
of mineral resources including
–
–
–
–
–
–
building stone,
limestone for cement,
silica sand,
hydrocarbons,
evaporites
and iron ores