1. Ch. 2, Part-IIb Geologic Structures

2. 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 –Preferrential“pathways” for fluid/contaminants

3. Types of Geologic Structures Stratification (Layers & Layering) Folding/Tilting Faulting Other Structures –fractures –joints –crosscutting from forceful injections (dikes/sills)

4. Layering/Strata

5. Tilted Layers Indicative of forces causing horizontal layers to be disrupted (tilted)

6. Significance of Layering/Tilting Basic geologic structure Planar reference boundaries that define strata (boundaries between/within rock materials) Implications for landforms/topography? Potential pathways

8. FOLDS Indicative of directed (compressional) forces (past or present) Topography similar to Appalachians

11. Expressions of directed forces as broken/displaced strata Strike Slip Faulting Dip Slip Faulting

13. 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)

14. Other Structures Fractures Joints Crosscutting material from forceful injections –Dikes (cross-cuts layering) –Sills (parallel to layering)

15. Cross-Cutting Relationships: Dikes & Sills

18. Jointing

19. Some Environmental Implications of Geologic Structures Layering or Foliation

23. 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

24. 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

25. 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.)