AS Structural Geology Flashcards
Bed
a unit of sedimentation, which can vary considerably in thickness.
Bedding planes
mark a break between beds. They represents a break in sedimentation, a change in the composition or grain size, or a change in colour of the sediments.
Dip
the maximum inclination of a bed measured from the horizontal using a clinometer.
True dip
the actual angle of dip measured at right angles to the strike.
Apparent dip
a dip that is measured to be less than the maximum inclination.
Strike
the horizontal line on a bedding plane, measured as a bearing from north using a compass. It is at right angles to the dip.
Fault
a fracture in a rock along which there has been an observable amount of displacement.
Fault plane
a plane of fracture, along which the rocks have been displaced.
Upthrow
the side of the fault where the movement is upwards, in relation to the other side.
Downthrow
the side of the fault where the movement is downward, in relation to the other side.
Throw
the vertical displacement of rocks along the fault plane.
Footwall
the side of the fault that lies below the fault plane, if the fault is not vertical.
Hanging wall
the side of the fault that lies above the maximum inclination of the fault plane as measured from the horizontal.
Slickensides
the striations and polishing found on a fault plane indicating the direction of relative movement.
Fault breccia
composed of fragments produced by rocks fracturing during faulting. It is found along the fault planes.
Fault gouge
composed of very finely ground particles, produced by grinding of rock during faulting. These are often fused together due to frictional heat and found along fault planes.
Mylonite
a rock produced by dynamic recrystallisation of minerals on a fault plane.
Anticline
an upright fold with the oldest rocks in the core.