Geology Reference
In-Depth Information
4.2.2
Dip-Domain Fold
The dip-domain method can be used to find or place bounds on the thickness of a unit
that changes dip from its upper to lower contact (Fig. 4.12). For constant bedding thick-
ness, the axial surface bisects the angle of the bend. The total thickness of the bed
along the measurement direction,
t
, is the sum of the thickness in each domain, found
from Eq. 4.1 as
t
=
L
1
cos
ρ
1
+(
L
-
L
1
) cos
ρ
2
,
(4.16)
where
ρ
2
=the
angle between the well and the pole to bedding of the lower bedding plane, and
L
1
=the
apparent thickness of the upper domain. If the position of the dip change can be lo-
cated, for example with a dipmeter, then it is possible to specify
L
1
and find the true
thickness. If the location of the axial surface is unknown, the range of possible thick-
nesses is between the values given by setting
L
1
= 0 and
L
1
=
L
in Eq. 4.16. The circu-
lar-arc thickness (Eq. 4.15) is usually half-way between the extremes that are possible
for dip-domain folding.
ρ
1
= the angle between the well and the pole to the upper bedding plane,
4.3
Thickness Maps
Thickness maps are valuable for both structural and stratigraphic interpretation pur-
poses. Because multiple measures of thicknesses can be mapped, care is required in
the interpretation. The calculated thickness is related to the dip and so uncertainties
Fig. 4.12.
Thickness of a dip-domain
bed that changes dip in the
measured interval, in a cross
section normal to the fold axis
