Geology Reference
In-Depth Information
Fig. 11.35.
Northwest Velma and Cruce oil fields.
a
Cross section based on wells and a seismic line
(redrawn from Perry 1989).
P:
Permian red sand and shale;
Pc:
Cisco Group;
Ph:
Hoxbar sand, shale
and limestone;
Pd:
Deese sand, shale and limestone;
Pa:
Atoka Formation;
PMs:
Springer sand and shale;
Mc:
Caney shale;
MOws:
Woodford shale, Hunton limestone and Sylvan shale;
Ov:
Viola limestone;
Os:
Simpson Gp. including Bromide and Oil Creek sands;
OCat:
Arbuckle Gp. limestone and Timbered
Hills Gp. limestone and sandstone;
Cc:
Carlton Rhyolite.
b
Flexural-slip restoration
A cross section of a convergent-wrench structure from central Oklahoma provides
an example of flexural-slip restoration where variable stratigraphic thicknesses are to
be preserved (Fig. 11.35a). The section is located across the down plunge extension of
the Wichita uplift, a basement cored anticline demonstrated by McConnell (1989) to be
a convergent wrench-fault structure. The presence of folding as well as faulting sug-
gests that the flexural-slip restoration technique is appropriate, as modified for vari-
able original bed thickness. The pin line is placed in the horizontal beds on the right
side of the cross section and the top of the Pd is restored to horizontal. The restoration
proceeds to the left and downward from the pin line in the uppermost bed. The Velma
fault is a major discontinuity in bed thickness and so the restoration from the pin line
is stopped at the fault. A local pin line is placed perpendicular to bedding in the
hangingwall of the Velma fault and the restoration continued to the left. The restora-
tion (Fig. 11.35b) is good, indicating that the cross section is valid and, in addition,
provides information about the geological evolution. The restoration is geometric, not
palinspastic. The Velma fault marks a significant stratigraphic discontinuity on the
restored section, as would be expected if it has an unrestored strike-slip component.
Some amount of unrestored vertical-axis rotation of the cross section is also possible
(c.f., Sect. 11.2.2). Restoration to the top Pd removes the displacement on the Velma
fault but preserves the Velma anticline and the West Velma fault, showing that they
formed earlier.
