Chapter 3 - Geologic Map and Cross-Section Interpretation Flashcards
Allochthon
A fault block or rock mass moved from its place of origin
Autochthon
A rock mass underlying a thrust fault that has not moved from its location of origin
Blind Thrust
A thrust fault that dies out in the subsurface as it loses slip and stratigraphic separation
Detachment Fault
A low-angle normal fault associated with regional 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 listric fault
Fenster
A “window” into rocks underlying a thrust fault
Footwall Block
The block that underlies a non-vertical fault
Growth Fault
A fault that forms contemporaneously with deposition in 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
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 reversed
Ma
Abbreviation for Mega annum, one million years
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° and 90°
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 footwall. The dip of the fault is between 45° and 90°
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.
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°
Type Locality
The place where a geologic feature (such as a fossil species) was first recognized and described. It contains the type section
Type Section
The originally described strata that constitutes a stratigraphic unit to which other parts of the unit may be compared. It is preferable to describe the location where the unit attains its maximum thickness and where the top and bottom unit are exposed.
Unconformity
A gap in the geologic record; and interruption in the depositional sequence that implies uplift and erosion have removed part of the geologic record or non-deposition has occurred
