Geology Reference
In-Depth Information
Fig. 6.45.
Dip domains in conical fold.
a
Dip-domain map of middle horizon.
b
Structure contour map
of middle horizon showing lines of cross section (
heavy EW lines
)
Fig. 6.46.
Tangent diagram of conical
fold in Fig. 6.45 showing the
directions of the 3 section
lines that preserve bed thick-
ness in local areas. In the north
the fold crest is horizontal, and
in the south it plunges 11, 180
tion trends (110° and 250°). In the region of the 11° south plunge, a section normal to
plunge is normal to bedding (Fig. 6.46) but will give an exaggerated thickness where
beds are horizontal.
The simplest procedure is to map axial surfaces on straight, vertical cross sections
(Fig. 6.47), or from multiple map horizons. An axial surface is by definition the surface
through successive hinge lines. This relationship applies regardless of whether or not
the profile is perpendicular to the bedding or to the hinge lines. Axial surfaces on
successive cross sections are correlated and then mapped in 3-D (Fig. 6.48a). Axial
surfaces in conical folds will intersect in three dimensions, and the intersection lines
must be located (Fig. 6.48b). Once the axial surfaces and their intersections are con-
structed, the marker horizons can be mapped across the region (Fig. 6.49). Because a
dip domain is a region of uniform dip, once the domain boundaries have been located,
bedding attitudes may be projected anywhere within a single domain. Bedding sur-
faces can be projected throughout the entire domain from a single observation point.
