Folds, Faults and Other Records of Deformation
Significance to CCS
Fundamental to trapping configuration Important for caprock integrity
Stress
Force per unit area Compression Tension (rare) Shearing
Or, principal compressivestress vertical
Brittle Versus Ductile Deformation
Brittle: material fractures (breaks)
Brittle Versus Ductile Deformation
Brittle: material fractures (breaks) Ductile: plastic deformation, no fractures
Folded gneiss and marble
Brittle Versus Ductile Deformation
Brittle: material fractures (breaks) Ductile: plastic deformation, no fractures Brittle favored by:
Brittle Versus Ductile Deformation
Brittle: material fractures (breaks) Ductile: plastic deformation, no fractures Brittle favored by:
low temperatures
Brittle Versus Ductile Deformation
Brittle: material fractures (breaks) Ductile: plastic deformation, no fractures Brittle favored by:
low temperatures low confining pressures
Undeformed Low confining pressure
High confiningpressure
Brittle Versus Ductile Deformation
Brittle: material fractures (breaks) Ductile: plastic deformation, no fractures Brittle favored by:
low temperatures low confining pressures high strain rates
Rock type
Brittle diabase, ductile marble
Mapping Geologic Structures
Strike Dip
Mapping Geologic Structures
Strike Dip Constructing cross sections
FoldsBending of rocks, often as a result of compression
Anticlines and Synclines
Raplee anticline and San Juan river, Utah
Limbs, axial planes, fold axes
Plunge
Plunging folds near Harrisburg, PA
Plunging folds near Harrisburg, PA
Plunging anticline, SW Montana
Symmetrical, Asymmetrical, Overturned
Limbs of equal length
Limbs of unequal length
Overturned (almost?) anticline
Structural domes and basins
Faults and Joints
Fractures in rock
Joints
No visible displacement Types
Unloading (exfoliation)
Unloading joint, Yosemite NP, CA
Joints
No visible displacement Types
Unloading (exfoliation) Cooling joints
Devil’s Postpile, CA
Devil’s Tower, WY
Joints
No visible displacement Types
Unloading (exfoliation) Cooling joints Regional (tectonic) joints
Joints in Navajo Sandstone, Arches NP, UT
Faults
Visible displacement Hanging wall and footwall
Faults
Visible displacementHanging wall and footwallDip-slip faults
Normal
Normal fault, UT
Faults
Visible displacementHanging wall and footwallDip-slip faults
Normal Reverse
Faults
Visible displacementHanging wall and footwallDip-slip faults
Normal Reverse Thrust
Thrust: reverse motion with fault plane dipping <45°
Chief Mountain Klippe, Montana
Faults
Visible displacementHanging wall and footwallDip-slip faults
Normal Reverse Thrust
Strike-slip faults Left lateral Right lateral
Faults Visible displacement Hanging wall and footwall Dip-slip faults
Normal Reverse Thrust
Strike-slip faults Left lateral Right lateral
Oblique-slip faults
Rocks/textures created by faulting
Fault breccia (visible angular fragments) Fault gouge (incohesive, fine powder) Mylonites (ductile flow/recrystallization) Pseudotachylites (frictional melting)
Fault gouge
Mylonite
Pseudotachylite
Features associated with fault planes
Slickensides (grooves or striations) "Drag" folds
Horsts, grabens, and rifts
Wildrose graben, Panamint Valley, southern California
Structural Traps for Hydrocarbons and CO2
Fault traps Fold traps
Lander Dome oil field, Wind River Basin, Wyoming
Structure Photos….
Joints in Navajo Sandstone, Arches NP, UT
1964 Alaska (M 9.2) Hanning Bay fault scarp on Montague Island. Vertical displacement 12 - 14 feet. (USGS photo)
