Geology Reference
In-Depth Information
Fig. 11.32.
Flexural-slip restoration of an invalid cross section.
a
Deformed-state cross section. Pre-
served beds maintain constant bed thickness (after a problem in Woodward et al. 1985).
f:
hangingwall
fault ramp.
b
Flexural-slip restoration based on length measurements at the top and base of each unit
Fig. 11.33.
Restoration using local pin lines (after Woodward et al. 1989).
a
Deformed-state cross sec-
tion of eroded thrust sheets.
LP:
local pin line;
1-3:
thrust sheets;
a-c:
stratigraphic units.
b
Thrust
sheets individually restored from local pin lines.
c
Thrust sheets restored to minimum displacement
positions.
Dashed lines
are eroded beds
A simple measurement pitfall to avoid is including a fault length with the bed length.
In Fig. 11.32a, a portion of the base of the limestone is a fault ramp (f ) where the bed-
ding is truncated against the upper detachment. The fault ramp segment is not part of
the bed length of the base of the limestone. The fault ramp is separated from unfaulted
bedding by an axial surface which, in the case of constant bed thickness, bisects the
associated fold hinge (Sect. 6.4.1). Splitting the limestone bed by drawing many par-
allel beds within the unit would make the fault cutoffs, and hence the ramp, obvious.
Local pin lines (Fig. 11.33) should be used where erosion or lack of information
renders the connection between hangingwall and footwall uncertain. A local pin line
is placed in each block and the beds stretched out in both directions from the local pin.
The individual restored blocks can then reassembled by bringing the individual blocks
as close together as geologically appropriate.
