Download Rock and Rock Materials

Ch. 2, Part-IIb
Geologic Structures
Geologic Structures
• Generally planar features within, cross-cutting, or
disrupting the rock materials/strata (layers)
• Important in environmental geology as:
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Discontinuities
Topography/landforms
Indicators of tectonics
Implications for natural hazards
Structural integrity
Planes/zones of weakness
Preferrential“pathways” for fluid/contaminants
Types of Geologic Structures
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Stratification (Layers & Layering)
Folding/Tilting
Faulting
Other Structures
– fractures
– joints
– crosscutting from forceful injections
(dikes/sills)
Layering/Strata
Tilted Layers
Indicative of forces causing horizontal layers to be
disrupted (tilted)
Significance of Layering/Tilting
• Basic geologic structure
• Planar reference boundaries that define strata
(boundaries between/within rock materials)
• Implications for landforms/topography?
• Potential pathways
Folds
FOLDS
Topography similar
to Appalachians
Indicative of directed (compressional) forces
(past or present)
Expressions of
directed forces as
broken/displaced
strata
Strike Slip Faulting
Dip Slip Faulting
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)
Other Structures
• Fractures
• Joints
• Crosscutting material from forceful
injections
– Dikes (cross-cuts layering)
– Sills (parallel to layering)
Cross-Cutting Relationships:
Dikes & Sills
Jointing
Some Environmental Implications
of Geologic Structures
Layering or Foliation
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
Summary / Review
• Rock type provides various types of information
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Environment/setting in which they were formed
Tectonic implications
Implications for natural hazards
Physical, chemical properties
Etc.
• Geologic Structures:
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Layering, tilting
Folding
Faulting
Other types (fractures, jointing, cross-cutting features)
• Implications/significance of geologic structures
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.)