Geology Reference
In-Depth Information
11.2
Restoration and Balance
This section covers general concepts and terminology used in all the balancing and
restoration techniques to follow.
11.2.1
Boundaries
Ideally, the boundaries of a section to be restored are chosen so that the section will
restore to a rectangle (Fig. 11.5a). The side boundaries are pin lines, and the upper
boundary is a reference bed that will be returned to its original depositional geometry
(Dahlstrom 1969; Elliott in Geiser 1988; Marshak and Woodward 1988). The original
position of a horizon, including both its shape and elevation, is known as the
regional
datum
, commonly shortened to just the
regional
(McClay 1992). The restored posi-
tions of all other horizons are determined with respect to the reference horizon. The
base of the section is normally either a stratigraphic marker or a detachment horizon
(Fig. 11.5), but may be simply the lowest visible unit. The bounding pin lines are lead-
ing and trailing pins, according to their position in the structure with respect to the
transport direction. A locally balanced structure is one in which bed-normal pins on
either side of the structure of interest define a region in which the area has remained
Fig. 11.5.
Pin lines bounding a region
of interest.
LPL:
leading pin
line;
TPL:
trailing pin line;
WPL:
working pin line.
a
Un-
deformed.
b
Locally balanced.
c
Regionally balanced with
transport of material out of
the structure.
d
Regionally
balanced with simple-shear
transport of material into the
structure
