Geological Principles, Extinctions, and Rock Deformation

Posted on Feb 28, 2025 in Geology

Geological Principles

  • Original Horizontality
  • Superposition
  • Lateral Continuity
  • Cross-cutting Relationships
  • Baked Contacts
  • Inclusions
  • Fossil Succession

Types of Unconformity

  • Angular Unconformity
  • Nonconformity
  • Disconformity

The Great Oxygenation Event (GOE)

The Great Oxygenation Event (GOE) was the introduction of free oxygen into our atmosphere. It was caused by cyanobacteria doing photosynthesis.

Mass Extinction Events

  1. Ordovician-Silurian (443 Ma)

    • 3rd largest, two peaks
    • Trilobites, brachiopods, and graptolites. 85% sea life
    • Southern hemisphere ice sheet, climate change, fall in sea level, and associated changes to the chemistry of the oceans.

  2. Late Devonian (359 Ma)

    • 75% of all species extinct
    • Possibly several events over millions of years
    • Asteroid impacts, sea level changes, climate change, and soil changes due to new plant species
    • Ocean oxygen levels plummeted – only suitable for bacteria
    • Shallow sea life most impacted, including coral reefs

  3. Permian (248 Ma)

    • The Great Dying
    • 96% of species extinct
    • Merostomata (sea scorpions) & trilobites
    • Insect mass extinction
    • All life on earth today descended from the surviving 4%

  4. Triassic-Jurassic (200 Ma)

    • 50% extinction
    • 2 or 3 phases
    • Marine reptiles, some large amphibians, many reef-building creatures, large numbers of cephalopod mollusks
    • Plants not impacted as seriously
    • Climate change, flood basalts, asteroid impact

  5. Cretaceous-Tertiary (K/T) – 65 Ma

    • Dinosaurs, ammonites, many flowering plants, and last pterosaurs
    • Bolide impact near Yucatan Peninsula, Mexico
    • Flood basalt eruptions, climate change & associated sea level fall

Mountain Building

Causes of Mountain Building

  1. Subduction
  2. Continental Collisions
  3. Rifting

Why are Mountains High?

  1. Isostasy: balance between forces due to gravity
  2. Compression: shortening and thickening due to horizontal compression
  3. Added Igneous Rock: volcanic material added to the surface
  4. Rift Heating & Thinning

Rock Deformation

Types of Deformation

  1. Displacement: change in location
  2. Rotation: change in orientation
  3. Distortion: change in shape

Factors Affecting Deformation

  1. Temperature
  2. Pressure
  3. Deformation rate (…silly putty)
  4. Composition

Faults

  1. Normal Fault

    The hanging wall moves down relative to the footwall. Results from extension.

  2. Reverse Fault

    The hanging wall moves up relative to the footwall. Results from compression.

  3. Thrust Fault

    A special kind of reverse fault. The slope (dip) of fault surface is much less steep.

Seismic Waves

P-waves (primary or compressional waves). Waves travel by compressing and expanding material. Material moves back and forth parallel to wave direction.

  • P-waves are the fastest.
  • They travel through solids, liquids, and gases.

S-waves (secondary or shear waves).

  • Waves travel by moving material back and forth.
  • Material moves perpendicular to wave travel direction.
  • S-waves are slower than P-waves.
  • They travel only through solids, never liquids or gases.

W. Norton & Company
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PowerPoint slides prepared by Rick Oches, Professor of Geology & Environmental Sciences, Bentley University, Waltham, Massachusetts

Severity of Shaking and Damage Depends On:

  1. Magnitude (energy) of the earthquake
  2. Distance from the focus
  3. Material characteristics
    • Bedrock transmits seismic waves quickly = less damage.
    • Sediments reflect and refract waves = amplified damage.
  4. Earthquake wave frequency

Metamorphic Processes

  1. Recrystallization: minerals change size and shape.
    • Mineral identity doesn’t change.
  2. Phase Change: New minerals form with:
    • The same chemical formula.
    • Different crystal structure.
  3. Neocrystallization: new minerals form from old.
    • Initial minerals become unstable, change to new minerals.
  4. Deformation:
    • Mineral grains partially dissolve.
    • Dissolution requires small amounts of water.
    • Minerals dissolve where their surfaces press together.
  5. Plastic Deformation: mineral grains soften & deform.

The Four Agents of Metamorphism Are:

  1. Heat (250-850) (T)
  2. Pressure (P)
  3. Compression and shear
  4. Hot fluids

Foliated: slate, phyllite, schist, gneiss, metaconglomerate, migmatite.

Non-foliated: quartzite, hornfels, marble.