Geology Reference
In-Depth Information
7.6
Growth Faults
A growth fault moves during deposition and controls the thickness of the deposits on
both sides if the fault. The classic Gulf of Mexico thin-skinned extensional growth
fault, from the region where the concept was developed (Fig. 7.26), is depositional on
both sides and the sediments thicken across the fault. A growth fault in a rifted envi-
ronment may show footwall uplift and erosion concurrent with deposition on the
hangingwall. Growth faults can be normal (Fig. 7.26) or reverse (Fig. 7.27); in fact, any
type of fault can record growth, including strike-slip faults.
7.6.1
Effect on Heave and Throw
Because the stratigraphic thicknesses are different on opposite sides of a growth fault,
the heave and throw determined from the fault cut depend on whether the marker
being mapped is in the hangingwall or footwall of the fault. The appropriate thickness
is that belonging to the section across the fault from the fault cut in the marker hori-
zon. For a marker on the hangingwall of a normal fault (Fig. 7.26a), the appropriate
fault-cut thickness is that of the footwall stratigraphic section. To map a footwall marker
in the same well (Fig. 7.26b), the appropriate thickness is that of the hangingwall strati-
Fig. 7.26.
Identical cross sections across
a growth normal fault show-
ing effect of growth on throw
and heave. The section is ver-
tical and in the direction of
fault dip. The fault cut is at
the same point in both sec-
tions.
a
The fault cutoff of a
hangingwall marker (
dashed
)
is extrapolated to the footwall
cutoff of the same marker
using dip and thickness values
from the footwall.
b
The fault
cutoff of a footwall marker
(
dashed
) is extrapolated to the
hangingwall cutoff of the same
marker using dip and thickness
values from the hangingwall
