Phanerozoic Canada Geology Notes (Lecture 10)

The Phanerozoic: Canada’s Geologic Journey (Lecture 10)

  • Outline highlights
    • The Great Unconformity
    • Paleozoic Cover
    • The Appalachian Orogeny: closure of the Iapetus Ocean and formation of Pangea
    • Terrane accretion
    • Foreland and intracratonic basins
    • Life in the Paleozoic
    • Mesozoic breakup of Pangea and the Cordilleran Orogeny
    • Western Canada Sedimentary Basin

The Great Unconformity and Paleozoic Cover

  • The Great Unconformity
    • A major time gap between Precambrian basement rocks and overlying Paleozoic rocks
    • Approximate age gap:
    • 450 <br/>Ma450\,<br /> \mathrm{Ma} (Megaannum) for the classic unconformity seen in many places
    • Marmora as a key location showing reddish Precambrian rocks beneath layered Paleozoic rocks
  • Paleozoic cover rocks
    • Drape over the Canadian Shield craton: Paleozoic strata rest on Precambrian basement
    • These cover rocks are later deformed during orogenic events (e.g., Appalachian orogeny)
  • The four-layer model (today’s surface geology below the classroom, from bottom up)
    • Layer 1: Precambrian basement (> 1000 Ma1000\,\mathrm{Ma})
    • Layer 2: Phanerozoic/Paleozoic cover rocks (roughly 600−2 Ma600-2\,\mathrm{Ma})
    • Layer 3: Glacial sediments (< 2 Ma2\,\mathrm{Ma})
    • Layer 4: Built landscape and historic fill materials (human-modified/constructed materials)
  • Dimensions of the crustal blocks in southern Ontario (illustrating cover over shield)
    • Canadian Shield exposed at the surface in parts
    • Buried craton with sediments accumulating as a thick cover elsewhere
    • Map-like view shows the extent of younger cover rocks over an ancient craton

The Paleozoic Platform and Ontario's Geology

  • The Paleozoic Platform (Ontario)
    • Paleozoic cover rocks overlie the shield; in the south they dip to the southwest
    • Strike direction is NW–SE
    • Southern Ontario Paleozoic rocks form a platform over the shield, later deformed by orogenic events
  • Fossils of Ontario (Paleozoic life implications)
    • Marine life in Paleozoic tropical seaways:
    • Gastropods
    • Crinoids
    • Corals
    • Brachiopods
  • Ontario’s Great Unconformity context (regional)**
    • The contact between Precambrian basement and Paleozoic cover is a key stratigraphic boundary
  • Niagaran/Escarpment features (local stratigraphy)
    • Niagara Escarpment as a major surface feature
    • Dip slope across the escarpment
    • Dolostone cap rock atop the Simcoe Group limestones
    • Queenston Formation shales and Whirlpool Sandstone as part of the upper Paleozoic sequence
    • The Ontario platform records a shift from shield to cover dynamics over time

From Rodinia to Laurentia: Building North America

  • Ontario in the global tectonic assembly timeline
    • 1.5–1.0 Ga: Rodinia forms; Grenville Orogeny later deforms Rodinia, creating a major mountain belt (Grenville orogeny)
    • ~1.0 Ga1.0\,\mathrm{Ga}: Grenville Mountains form in the center of Rodinia (as shown on the Ontario map section)
    • 0.6–0.3 Ga: Formation of Pangea; subsequent accretion and assembly of major continental blocks
    • 0.25 Ga: Breakup of Pangea leads toward modern plate configurations
  • Laurentia: the formation of an independent North America
    • “Laurentia” represents the tectonically quiet era with lots of passive margins
    • This setting favored the accumulation of large sedimentary packages over a stable craton

The Great Unconformity and Epicontinental Seas

  • Epicontinental seas and their global context
    • Strands of epicontinental seas form as shallow seas overlay continental crust during transgressions
    • Regions include the Baltic Sea area, Hudson Bay area, and the broader North Sea region as examples of epicontinental seaways
    • Epicontinental Seaways: water bodies that occupy shallow marine environments over continental crust
  • Subduction and ocean-floor aging (geodynamics context)
    • Ocean floor has a finite lifespan: older oceanic crust becomes cooler and more likely to subduct
    • By 480 Ma480\,\mathrm{Ma}, Iapetus Ocean starts to close, and subduction drives the collision of Baltica and North America (Laurentia)
  • Iapetus Ocean closure effects
    • Subduction of older oceanic crust drives tectonism; the collision leads to assembly of the Appalachian belt along Laurentia
    • Iapetus floods over continents to form an epicontinental seaway during certain intervals

Appalachian Orogeny, Foreland and Intracratonic Basins

  • Foreland basins during the Appalachian Orogeny
    • Formed adjacent to a growing mountain belt due to crustal flexure (downward bending of the crust)
    • Key features and examples in North America include:
    • Appalachian Foreland Basin
    • Williston Basin
    • Michigan Basin
    • Cincinnati Arch region
    • Illinois Basin
    • Nashville Dome and related basins
    • Ouachita belt interactions in the broader orogeny context
    • Conceptual cross-section: Forearc basin, backarc basin, magmatic activity, thrust belts, and related tectonics
  • Intracratonic basins
    • Formed where mantle downwelling occurs in the middle of the continent
    • Example: Michigan Basin
    • Mantle downwelling leads to subsidence and sedimentation within the continental interior
  • The Appalachian orogeny timing (approximate)
    • 400–300 Ma window for major collisional events and accretionary processes
    • The orogeny reflects far-traveled crustal blocks (terranes) being accreted to Laurentia
    • The orogeny culminates in the formation of Pangea and intense crustal deformation across the region

The Laurentia–Avalonia Puzzle: Terranes and Ophiolites

  • The concept of terranes and far-traveled crust
    • Maritime Canada and eastern USA share portmanteau of terranes that originated far from their current positions
    • The Appalachian belt includes displaced crustal blocks that have been accreted during the closure of Iapetus and subsequent collisions
  • Newfoundland’s ophiolites and island arcs
    • Three zones in Newfoundland: Humber Zone, Dunnage (island-arc volcanics and lapetus sediments), and Gander Zone
    • Bay of Islands Ophiolite Complex as a key remnant of the Iapetus Ocean
    • Ophiolite indicators: pillow basalts, sheeted dikes, gabbro intrusions; ultramafic rocks indicating oceanic mantle material
    • Avalonia, Gander, Humber, and Meguma microcontinents contribute to Maritime Canada’s complex crustal mosaic
  • The Iapetus–Gondwana–Laurentia connections
    • Docking of Avalonia and related terranes during the Cambrian–Ordovician
    • Closure of Iapetus and accretion of ocean-floor and arc materials to Laurentia
    • The Appalachian orogeny encapsulates these processes and foreshadows Pangea assembly

Newfoundland: Three Zones and the Iapetus Ophiolites

  • Three Newfoundland zones (as depicted):
    • 1) Continental margin of ancient North American Plate (now Humber Zone)
    • 2) Island-arc volcanic rocks and Iapetus Ocean sediments (Dunnage and Gander terranes)
    • 3) Left-behind arc and oceanic rocks including ophiolites
  • Ophiolite complexes and tectonic implications
    • Ophiolites represent remnants of the Iapetus Ocean crust preserved within Newfoundland
    • The ophiolite sequence includes pillow lavas, sheeted dikes, gabbro intrusions, and ultramafic rocks
    • Mantle material and crustal slices illustrate past ocean basins and subduction zones
  • The Humber Zone and associated structures
    • Post-accretion tectonics place Humber as a key zone in the Newfoundland mosaic
  • Implications for North American assembly
    • Newfoundland zones demonstrate the far-traveled crustal components that contributed to the Appalachian belt

The Western Canada: Accreted Terranes, Cordilleran Orogeny, and the Rocky Mountains

  • Accreted terranes and fusulinids
    • Fusulinids from China are found in western Canada, indicating transfer and accretion of far-traveled crustal blocks
    • The accreted terranes collectively form the Cordilleran Orogeny signal in western Canada
  • The Front Ranges and major thrusts
    • The Front Ranges of the Alberta-British Columbia region show a sequence of thrust sheets (e.g., Bourgeau Thrust Sheet)
    • The McConnell Thrust Sheet, Sulphur Mountain Th.S., Mount Rundle Th.S. highlight the stacking of Paleozoic and later rocks
  • The nature of the Western Canada Sedimentary Basin (WCSB)
    • Foreland basin fill associated with the Cordilleran orogeny
    • The WCSB contains a broad sequence of sedimentary rocks, overlain by later Mesozoic and Paleozoic cover rocks
    • The basement includes Precambrian rocks; accreted allochthonous and suspect terranes form part of the crustal mosaic
    • Platform cover above the Precambrian basement forms the “west coast” geological veneer
  • Soft vs hard lithologies in the ranges
    • Soft Mesazoic strata over hard Paleozoic carbonates and shales at times
  • The Cascades context
    • The Cascadia Subduction Zone and the associated megathrust earthquakes are a part of this western margin tectonics (Queen Charlotte Fault, Juan de Fuca Plate, Explorer Ridge, Cascadia zone)

The Western Canada Sedimentary Basin (WCSB) and Foreland vs Accreted Terranes

  • Foreland basin infill and tectonics in Western Canada
    • Foreland basins form as the crust flexes under the weight of the Cordillera range
    • Foreland basin fill comprises much of the WCSB rocks, overlain by platform cover at times
  • Accreted and suspect terranes in Western Canada
    • Accreted allochthonous blocks (crustal slices) and suspect terranes make up a significant portion of the western crust
    • The WCSB records the sedimentary history of the region following collision and accretion events
  • The structural map and lithology of the region
    • Foreland basins and thrust belts are evident in the Rocky Mountain and Western Canada region
    • The map shows the relationship among Precambrian basement, platform cover, high-grade metamorphic rocks, and the WCSB

Notable Localities, Fossils, and Key Evidence

  • Campbellton, New Brunswick (Plant life)
    • Early Paleozoic plant assemblages documented here
  • Joggins Fossil Forest, Nova Scotia
    • A world-famous fossil forest preserving plant life from the Carboniferous period
    • Evidence of coal formation and lush tropical flora in the Paleozoic
  • Miguasha, Quebec
    • Fossilized placoderms (e.g., Eusthenopteron) and other Devonian fauna
    • Notable for spectacular soft-tissue preservation in some specimens
  • Hylonomus (Lyelli)
    • One of the oldest known reptiles, illustrating the transition to terrestrial vertebrates
  • Other fossils and life in Paleozoic seas
    • The sea life includes brachiopods, corals, crinoids, gastropods, and other marine organisms

The Pangea Breakup and Cordilleran Orogenies (Late Paleozoic to Mesozoic)

  • Pangea formation and breakup
    • Late Paleozoic assembly of Pangea involved collisions of Laurentia with Gondwana and other terranes
    • Breakup of Pangea in the Late Jurassic–Cretaceous triggered the opening of the Atlantic Ocean and the development of modern margins
  • The Cordilleran Orogeny (Western North America)
    • Active margins along the western edge of Laurentia during Mesozoic time
    • The Cordilleran orogeny is associated with accreted terranes, thrust faulting, and the growth of the western margin
  • The “Collide and Slide” model
    • Tectonic process where far-traveled crustal blocks collide with and slide past the continental margin during basin development
    • Includes complex interactions of subduction, accretion, and basin formation

The Cascadia Subduction Zone and Modern Margin Dynamics

  • The Cascadia margin features
    • Cascadia Subduction Zone (megathrust system)
    • Queen Charlotte Fault as a major transform fault boundary
    • Juan de Fuca Plate subducting beneath the North American Plate
    • Associated Cascade volcanic arc (Vancouver Island, Vancouver, Seattle region)
  • Implications for earthquakes and hazards
    • Megathrust earthquakes represent substantial seismic hazard along the Cascadia margin
    • Ongoing tectonic interaction shapes modern western North American geology

The Final Stage: Paleogeography, Ophiolites, and The Westward Shift

  • Newfoundland ophiolites and the Iapetus remnants
    • Bay of Islands Ophiolite Complex: pillow lavas, sheeted dikes, gabbro intrusions, ultramafic rocks
    • Three Newfoundland zones illustrate the Iapetus Ocean’s remnants and arc accretion processes
  • Fusulinids in Western Canada
    • Evidence for far-traveled faunas indicating corridor-like crustal transfer and accretion events
  • The modern Western Canada Sedimentary Basin context
    • The region records a long history of foreland basin development, accretion, and tectonic evolution from Paleozoic to Mesozoic and beyond

Summary of Key Concepts and Connections

  • The Great Unconformity marks a major hiatus that separates Precambrian basement from younger Paleozoic rocks; its recognition is central to understanding North American stratigraphy and paleogeography
  • The four-layer model helps visualize present-day geology: Precambrian basement, Paleozoic cover, glacial sediments, and built landscape materials
  • The Grenville Orogeny (≈ 1.0−1.3 Ga1.0-1.3\,\mathrm{Ga}) and the Penokean Orogeny contributed to the long growth of the North American continent and its assembly
  • The Iapetus Ocean's closure (~480 Ma480\,\mathrm{Ma}) set the stage for the Appalachian orogeny and the assembly of Pangea; epicontinental seaways were common during these transformations
  • Foreland and intracratonic basins record distinct tectonic responses to mountain belt loading and mantle dynamics; Michigan, Williston, Cincinnati, and Illinois basins illustrate intracratonic and foreland processes
  • Terrane accretion and ophiolite remnants (e.g., in Newfoundland) reveal the paleogeography of far-traveled crust and the dynamic processes of continental assembly
  • The Cordilleran Orogeny and the Western Canada Sedimentary Basin reflect the complex interaction of accreted blocks, thrusting, and long-term basin development along a western passive-to-active margin transition
  • The modern margin (Cascadia) demonstrates ongoing subduction, megathrust earthquakes, and morphologic evolution of a tectonically active boundary
  • Key fossil localities (Joggins, Miguasha, Campbellton) provide essential windows into Paleozoic life and climate, including terrestrial and marine ecosystems
  • The Newfoundland zones, Bay of Islands ophiolite, and three-zone structure illustrate the Iapetus Ocean’s role in shaping Atlantic-type margins and crustal assembly

Equations and Timelines (selected references in LaTeX)

  • Great Unconformity age gap: ≈450 Ma\approx 450\,\mathrm{Ma}
  • Paleozoic cover age range: 600 Ma to 2 Ma600\,\mathrm{Ma} \text{ to } 2\,\mathrm{Ma}
  • Rodinia formation window: around 1.3−1.5 Ga1.3-1.5\,\mathrm{Ga}
  • Grenville Orogeny timing: within 1.0−1.3 Ga1.0-1.3\,\mathrm{Ga}
  • Iapetus Ocean closure: ≈480 Ma\approx 480\,\mathrm{Ma}
  • Pangea breakup timing (final stages): < 200\,\mathrm{Ma}
  • Foreland basins vs intracontinental basins (conceptual):
    • Foreland: crust flexure adjacent to a mountain belt
    • Intracratonic: mantle downwelling in the interior of a craton

Next Up

  • Next Week: Layer 3 (Glacial sediments and built landscape materials) and deeper discussion of Layer 2 (Phanerozoic/Paleozoic cover rocks)