3 - Maps & Cross Section Interpretation

Blind Thrust

A thrust fault that does not reach the ground surface

Detachment Fault

A low angle normal fault associated with region extension

Dip slip Fault

A fault in which the movement is parallel to the dip of the fault plane, such as a normal, reverse, or a listric fault

Fenster

A "window" into rocks underlying a thrust fault

Footwall Block

The block that underlies a non-vertical fault

Ga

Giga-annum; one billion years

GIS

Geographic Information System

GPS

Global Positioning System

Growth Fault

A fault that forms contemporaneously with deposition in the sedimentary rock. The throw increases with depth and the sedimentary units on the downthrown side are thicker than the corresponding units on the upthrown side

Hanging wall Block

The block that overlies a non-vertical fault

Heave

The amount of horizontal displacement on a fault

Ka

Kilo-annum; one thousand years

Klippe

An outlier of a thrust sheet completely surrounded by the exposed footwall

Key Beds

A well defined, easily identified strata that is distinctive enough to be useful in correlation in mapping

Listric Fault

A fault with a curved fault plane. Near the surface the fault plane is steeply dipping, but it becomes progressively flatter with depth. Listric faults may be normal or reverse

Ma

Mega annum; one million years

Magnetic Declination

The angle between true North and magnetic North

Nappe

A sheetlike rock unit that has moved over other rocks (allochthonous) on a predominantly horizontal surface

Net Slip

The distance between two formerly adjacent points on either side of the fault, measured on the fault surface

Nonconformity

An unconformity formed by older igneous rocks in contact with younger sediments, indicating a missing time after the igneous intrusion

Normal Fault

A dip slip fault in which the hanging wall has moved down relative to the footwall. The dip of the fault is between 45 degrees and 90 degrees

Oblique slip Fault

A fault in which movement is not parallel to the strike or dip of the fault plane

Offset

The horizontal component of displacement measured perpendicular to the strike of the disrupted unit

Reverse Fault

A dip slip fault in which the hanging wall has moved up relative to the foot wall. Dip of the fault is between 45 and 90 degrees

Rule of V's

The outcrop pattern of a formation as it crosses a valley forms a V shape (as viewed on a map). The V points in the direction that the formation underlies the valley

State Plane Coordinate System

A two dimensional coordinate system developed by the National Geodetic Survey for use in states and counties

Strike Separation

The horizontal distance between a stratigraphic unit offset by a fault, measured along the strike of the fault. It is an apparent displacement

Strike slip Fault

A fault in which movement is parallel to the strike of the fault plane

Throw

The amount of vertical displacement on a fault, also, the vertical component of net slip

Thrust Fault

A reverse fault in which the fault plane dips less than 45 degrees

Unconformity

A gap in the geologic record; an interruption in the depositional sequence that implies uplift and erosion have removed part of the geologic record or non-deposition has occurred