Geology Reference
In-Depth Information
Fig. 11.42.
Restoration of a cross section
by vertical simple shear above
a fault. The net restoring dis-
placement is parallel to the
solid arrows.
D:
block dis-
placement;
HWC:
hangingwall
cutoff of reference bed
Fig. 11.43.
Cross section of the thrust-cored Wheeler Ridge anticline, California (Medwedeff 1992). Wells
show logs used for correlation of units
11.7.1.2
Pitfalls in Flattening
Restoration requires deciding whether a fold or fault is a pre-existing feature, to be
passively deformed by the restoration, or is to control the restoration (an active fea-
ture). Fault-fold relationships are severely distorted if the hangingwalls of the active
faults are not restored separately from the footwalls. As an example of the difference
between restorations based on the active versus passive role of faults, consider the
Wheeler Ridge anticline (Fig. 11.43). The cross section can be restored by treating the
faults either as passive markers or as active elements with displacements that must be
removed during restoration. Both alternatives are illustrated using the vertical simple
shear technique. In both restorations the section is flattened to a datum at the top of
the Tertiary San Joaquin Formation (Tsj). Assuming that the faults were passive mark-
ers, restoration (Fig. 11.44a) deforms the fault wedge but does not displace it horizon-
