Geology Chapter: Tectonic Structures and Faults

Faults are fractures in the Earth's crust where rocks on opposite sides have moved relative to each other.

The hanging wall is the block of rock above the fault plane.

The footwall is the block of rock below the fault plane.

Throw is the vertical displacement of a fault, measuring how much rocks have moved up or down.

Heave is the horizontal displacement of a fault, measuring how much rocks have moved sideways.

Hade is the angle between the fault plane and the vertical.

Dip is the angle between the fault plane and the horizontal.

A normal fault occurs when the hanging wall moves down relative to the footwall, usually due to extensional forces.

Asymmetrical ripple marks are formed by unidirectional currents like wind or water, featuring a gentle up-current slope and a steeper down-current slope.

Symmetrical ripple marks are formed by waves, with a symmetrical profile and sharp crests (peaks) and rounded troughs.

Cross-stratification (or cross-bedding) is layering within a stratum deposited at an angle to the main bedding plane.

Tabular cross-beds have planar bounding surfaces and are formed by migrating straight-crested ripples and sand waves.

Trough cross-beds have curved lower surfaces, forming a scoop-shaped depression. They are associated with migrating sand dunes.

A surface of erosion or non-deposition that separates younger strata from older rocks.

An unconformity where horizontally parallel strata of sedimentary rocks are deposited on tilted and eroded layers.

An unconformity surface separating essentially parallel strata, marked by a visible irregular or uneven erosional surface.

The lowest point of a syncline fold, where the rock layers curve downwards.

The sides of a fold, representing the inclined rock layers.

A surface separating igneous or metamorphic rocks from overlying sedimentary strata, indicating a long period of erosion.

A fold where the rock layers curve upwards, with the oldest rocks at the center.

A type of unconformity where strata above and below the contact are parallel, lacking visible erosional surface or evidence.

A fold where the rock layers curve downwards, with the youngest rocks at the center.

Primary Sedimentary structures are those which develop at the time of the deposition of the rocks.

The deposition of sediments or fragments in beds that differ in mineralogy, rock type, color or other characteristics.

A fold with a circular or elliptical shape, where the rock layers dip uniformly away from the center, oldest rocks at the center.

Wave-like structures produced in granular sediments by unidirectional currents of wind or water.

A fold with a circular or elliptical shape, rock layers dip uniformly towards the center, youngest rocks at the center.

Angular discordance between tilted (older) and horizontal (younger) sedimentary layers.

A fold where the axial plane is vertical, resulting in equal dip angles for both limbs.

A fold where the axial plane is tilted, resulting in different dip angles for the limbs.

A paraconformity is an unconformity where layers appear continuous but are separated by a period of non-deposition or erosion.

A fold with an inclined axial plane where both limbs have been tilted in the same direction, generally at different angles.

A fold that has an essentially horizontal axial plane, resulting in a flattened appearance.

A type of fold where the fold axis is horizontal.

A type of fold where the fold axis is inclined.

A type of fault where the hanging wall moves upward in relation to the footwall. This occurs in areas with compressive stress.

A special type of reverse fault characterized by a low fault angle (less than 45 degrees).

A fault caused by shearing along the adjacent fault blocks. Movement is parallel to the strike of the fault plane, and can be left or right-lateral depending on the direction.

A fault caused by both extensional and shear stresses. Movement is inclined to both the strike and dip of the fault surface.

Faults where movement occurs along the dip (direction of inclination) of the fault plane. These can be normal or reverse, depending on the movement direction.

Faults with movement parallel to the strike of the fault plane. They can be classified as right-lateral or left-lateral, based on the observed movement.

Faults that exhibit both dip-slip and strike-slip movements.

A block of rock pushed upward relative to adjacent blocks, formed by bounding faults dipping away from each other.

A block of rock lowered or down-dropped relative to adjacent blocks, formed by bounding faults dipping towards each other.

A series of parallel faults that are all inclined in the same direction. These faults create a staircase-like pattern.