Ch.%202,%20Part-IIb%20Geologic%20Structures

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Ch. 2, Part-IIbGeologic Structures
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Geologic Structures

• Generally planar features within, cross-cutting,
  or disrupting the rock materials/strata (layers)
• Important in environmental geology as
• Discontinuities
• Topography/landforms
• Indicators of tectonics
• Implications for natural hazards
• Structural integrity
• Planes/zones of weakness
• Preferrentialpathways for fluid/contaminants

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Types of Geologic Structures

• Stratification (Layers Layering)
• Folding/Tilting
• Faulting
• Other Structures
• fractures
• joints
• crosscutting from forceful injections
  (dikes/sills)

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Layering/Strata
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• Tilted Layers
• Indicative of forces causing horizontal layers to
  be disrupted (tilted)

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Significance of Layering/Tilting

• Basic geologic structure
• Planar reference boundaries that define strata
  (boundaries between/within rock materials)
• Implications for landforms/topography?
• Potential pathways

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FOLDS
Topography similar to Appalachians
Indicative of directed (compressional) forces
(past or present)
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Dip Slip Faulting
Expressions of directed forces as
broken/displaced strata
Strike Slip Faulting
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Significance of Fault Folds

• Areas of broken and/or disrupted crust
• Usually associated with topographic features
• Usually results in exposure of different types of
  rock materials at surface
• Indicative of past and/or present forces
• Potential for environmental hazard?
• Often associated with natural resources
  (minerals, petroleum, etc.)
• Effects on fluid pathways (as preferential
  pathways or barriers)

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Other Structures

• Fractures
• Joints
• Crosscutting material from forceful injections
• Dikes (cross-cuts layering)
• Sills (parallel to layering)

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Cross-Cutting RelationshipsDikes Sills
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Jointing
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Some Environmental Implications of Geologic
Structures

• Layering or Foliation

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Summary / Review

• Building blocks of rock materials atoms,
  molecules, minerals, rocks/rock materials
• Most abundant minerals are silicates
• Basic building block is the silica tetrahedra
• Rock properties determined by properties of
  component materials (minerals)
• Three main classes of rocks
• Igneous Formed from molten material
• Sedimentary Clastic, chemical, organic,
  combinations
• Metamorphic foliated, non-foliated

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Summary / Review

• Rock type provides various types of information
• Environment/setting in which they were formed
• Tectonic implications
• Implications for natural hazards
• Physical, chemical properties
• Etc.
• Geologic Structures
• Layering, tilting
• Folding
• Faulting
• Other types (fractures, jointing, cross-cutting
  features)
• Implications/significance of geologic structures

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Chapter (Section) Objectives

• Review of some of the important mineral and rock
  types and their environmental significance
• Relationships between atoms, minerals, rocks,
  rock materials
• Basic silicate building block(s)
• Properties of rocks minerals
• Basic rock types, basis for classification, types
  of information they tell us
• Appreciation/significance of geologic structures
• Layering
• Folds
• Faults
• Other structures (joints, dikes/sills, etc.)

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