Geology Reference
In-Depth Information
Fig. 4.10.
Thickness of a bed folded into
a circular arc. The dip of the
bed and the well are co-planar.
C
is the center of curvature
where the poles to bedding
intersect
Fig. 4.11.
Example of thickness determi-
nation of a circularly folded
bed.
a
Field data: bedding dips
are shown by
heavy lines
, dis-
tance between exposures of
upper and lower contacts is
300 ft on a line that plunges 10°.
b
Angles required for the thick-
ness calculation
where
ρ
2
and
r
2
=, respectively, the angle between the bed pole and the well and the
radius associated with the larger angle, and
γ
=
ρ
2
-
ρ
2
. Substitute Eqs. 4.13 and 4.14
into 4.12 and replace sin (180 -
ρ
2
) with sin
ρ
2
to obtain the thickness:
t
=(
L
/sin
) (sin
ρ
2
-sin
ρ
1
) .
(4.15)
γ
A typical data set is shown in Fig. 4.11a. The cross section is in the dip direction.
The angles between the line of measurement and the poles to bedding are determined
as well as the acute angle between the poles (Fig. 4.11b). From Eq. 4.15, the true thick-
ness of the bed is 234 ft.
