Early Paleozoic Earth History

1
Chapter 10
Early Paleozoic Earth History
2
The First Geologic Map

• William Smith,
• a canal builder, published the first geologic map
• on August 1, 1815

3
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

4
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

5
Continental Architecture

• Cratons typically consist of two parts
• a shield
• and a platform

6
Platforms

• Extending outward from the shields are buried
  Precambrian rocks
• The sediments over the platforms were deposited
  in widespread shallow seas

7
Paleozoic North America

• Platform

8
Epeiric Seas

• The transgressing and regressing shallow seas
• called epeiric seas
• common feature of most Paleozoic cratons

9
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

10
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

11
Paleozoic North America

• Mobil belts

12
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

13
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

14
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

15
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

16
Paleogeography of the World

• For the Late Cambrian Period

17
Paleogeography of the World

• For the Late Ordovician Period

18
Paleogeography of the World

• For the Middle Silurian Period

19
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,
  

20
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 Laurentias 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

21
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

22
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

23
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

24
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

25
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
  

26
Cratonic Sequences of N. America

• White areas sequences of rocks

• Brown areas large-scale uncon-formities

• Sauk sequence

27
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

28
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

29
Cambrian Paleogeography of North America

• During this time North America straddled the
  equator
• Trans-continental Arch

30
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

31
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

32
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

33
Cambrian Transgression

• Cambrian strata exposed in the Grand Canyon

• The three formations exposed
• along the Bright Angel Trail, Grand Canyon Arizona

34
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

35
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,
• thus illustrating the time-transgres-sive nature
  of formations and facies

younger shale
older shale
36
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

37
Same Facies Relationship

• By the end of Sauk time, much of the craton
• was submerged beneath a warm, equatorial epeiric
  sea

38
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

39
Upper Cambrian Sandstone

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

40
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

41
Ordovician Period

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

42
Cratonic Sequences of N. America

• White areas sequences of rocks

• brown areas large-scale uncon-formities

• Regression

• Tippecanoe sequence

43
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

44
Transgression of the Tippecanoe Sea

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

45
St. Peter Sandstone

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

46
The Tippecanoe Sequence

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

47
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

48
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

49
Present-Day Reef Community

• with reef-building organisms

50
Reef Environments

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

51
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

52
Barrier Reef

• Barrier Reef

• Fore-reef slope

53
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

54
Ancient Reefs

• Reefs have been common features since the
  Cambrian
• The first skeletal builders of reef-like
  structures
• were archaeocyathids

55
Stromatoporoid-Coral Reefs

• Beginning in the Middle Ordovician,
• stromatoporoid-coral reefs became common
• similar reefs throughout the rest of the
  Phanerozoic Eon

56
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

57
Silurian Period

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

58
Northern Michigan Basin

• Northern Michigan Basin sediments during the
  Silurian Period

59
Stromatoporoid Reef Facies

• Stromato-poroid barrier-reef facies of the
  Michigan Basin

60
Evaporite

• Evaporite facies

61
Carbonate Facies

• Carbonate Facies

62
Silled Basin Model

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

63
Basin Brines

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

64
Order of Precipitation

• calcium carbonate first,
• followed by gypsum
• and lastly halite

65
Reefs in a Highly Saline Environ-ment?

• Organisms constructing reefs could not have lived
  in such a highly saline environ-ment

66
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

67
The Appalachian Mobile Belt

• the first Phanerozoic orogeny
• began during the Middle Ordovician

68
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

69
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

70
Appalachian Mobile Belt

• Evolution of the Appalachian mobile belt
• Late Proterozoic opening of Iapetus Ocean

• with passive continen-tal margins
• and large carbon-ate plat-forms

71
The Taconic Orogeny

• The resulting Taconic orogeny,
• named after present-day Taconic Mountains of
• eastern New York,
• central Massachusetts,
• and Vermont

72
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

73
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

74
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

75
Appalachian Mobile Belt

• Middle Ordovician transition to convergence
  resulted in orogenic activity

76
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

77
Queenston Delta Clastic Wedge

• The clastic wedge resulting from the erosion
• of the Taconic Highlands
• referred to as the Queenston Delta

78
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

79
A European Orogeny

• As the Iapetus Ocean narrowed and closed,
• another orogeny also occurred in Europe during
  the Silurian (Caledonian Orogeny)

80
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

81
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

82
Salt and Oil

• Thick deposits of Silurian evaporites,
• mostly rock salt (NaCl)
• and rock gypsum (CaSO4H2O) 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

83
Summary

• 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

84
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

85
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

86
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

87
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

88
Summary

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