Mapwork terms Flashcards
Angular unconformity
An unconformity surface with the beds above non-parallel to the beds below.
Anticline
A fold with the oldest rocks in the core; usually arch shaped
Apparent dip
The angle of dip of a surface measured in the direction other than the line of greatest slope
Attitude
The ‘3D orientation’ of a line or plane
Axial plane of a fold
The plane containing successive hinge lines of the folded surfaces
Axial trace of a fold
The intersection of the fold axial plane with the ground surface
Axis of a fold
The direction in space parallel to the hinge lines, but without any particular position on the fold
Bedding
accumulation surfaces in sedimentary or volcanic rocks; often originally sub-horizontal
Geological boundary
line of intersection of a geological contact with the ground surface
Cleavage (rock)
Alignment of minerals in a metamorphic rock (due to heat and pressure) promotion a tendency to fracture
Geological contact
Planar surface between 2 geological units; may be stratigraphic or faulted
structural contour
lines joining points of equal height in a geological surface
topographic contour
lines joining points of equal height on the ground surface
core of a fold
the concave inner arc of the fold
cross-section
the trace of geology and topography on a planar cut through the earth, usually vertical
dextral fault
a fault where the far side is displaces to the right with respect to the near side
True dip
The angle between the line of greatest slope in a surface and the horizontal projection of the line
Direction of dip
the angle between north and the horizontal projection of the line of greatest slope in a surface
Dip-slip fault
A fault with displacement up and down the dip of the fault plane
Downthrow side of a fault
the side which is displaces downward relative to the other
drift map
geological map showing essentially Quaternary rocks
fault
fracture with appreciable shear displacement across it
fold
a curviplanar geometry of originally planar geological units
hinge line
a line joining points of maximum curvature on a fold
inlier
an outcrop of older rock completely surrounded by younger rocks
normal fault
A fault that dips towards its downthrow site
outcrop
the intersection of geological units or structures with the ground surface, even if covered by a thin veneer of superficial sediments
outlier
an outcrop of younger rocks completely surrounded by older rocks
parallel unconformity
an unconformity surface with beds above parallel to the beds below
plunge of a line
the angle between a line and its horizontal projection
reverse fault
a fault that tips towards its upthrow site
Sinistral fault
a fault where the far side is displaced to the left with respect to the near side
solid map
geological map showing essentially pre-Quaternary rocks
stratigraphic contact
a contact between geological units resulting from their original accumulation rather than later faulting
stratigraphic throw of a fault
the difference in vertical height across a fault of structure contours for the same contact
strike of a surface
the angle (usually measured clockwise) between north and the horizontal line in a surface
strike line
line on a map parallel to the strike of a surface at that point; equivalent to a structure contour if structure contours are straight
strike separation of a fault
the horizontal difference along the fault between the ends of two like contours on either side
strike-slip fault
a fault with displacement along the strike of the fault plane
geological structure
geometrical arrangement of rocks, e.g. folds, faults
subcrop map
a map of the rocks immediately below an unconformity surface
Syncline
a fold the youngest rocks in its core; usually trough shaped
stratigraphic thickness
distance between the bounding contacts of a geological unit, measured perpendicularly to the contacts
vertical thickness
vertical distance between the bounding contacts of a geological unit
topographic profile
the trace of the ground surface on a cross-section
topography
geographical features of ground surface
trend of a line
the angle (measured clockwise) between north and the horizontal projection of the line
unconformity
a geological surface representing a gap in time during deposition of a geological sequence
geological unit
3D rock body, distinct in rock type from adjacent units
upthrow side of a fault
the side which is displaced upward relative to the other
V-ing
the V-shaped pattern made by boundaries of dipping units as they cross ridges or valleys. The points of the V usually points up-dip on a ridge and down-dip in a valley
