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)