Deformation, Mountain Building, and the Continents - The Changing Earth: Exploring Geology and Evolution - page 250

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Figure 10.7 Anticlines and Synclines

a Folded rocks in the Calico
Mountains of southeastern
California. Compression was
responsible for these folds, which
are, from left to right, a syncline, an
anticline, and a syncline.

b Anticlines and synclines are
usually found in a series as in (a);
however, the Barstow syncline shown
here, also in southern California, is
unusual because it is a single fold
with no adjacent anticlines.

anticlines and toward the axis in plunging synclines. The
oldest exposed rocks are in the core of an eroded plunging
anticline, whereas the youngest exposed rock layers are found
in the core of an eroded plunging syncline (Figure 10.12b).
In Chapter 6, we noted that anticlines form one type of
structural trap in which petroleum and natural gas might
accumulate (see Figure 6.29b). As a matter of fact, most of
the world's petroleum production comes from anticlines,
although other geologic structures and stratigraphic traps
are important, too. Accordingly, geologists are particularly
interested in correctly identifying geologic structures in
areas of potential hydrocarbon production.

Domes and Basins Anticlines and synclines are elongate
structures, meaning that their length greatly exceeds their
width. In contrast, folds that are nearly equidimensional,
that is, circular, are domes and basins . In a dome , all of the
folded strata dip outward from a central point (as opposed
to outward from a line as in an anticline), and the oldest ex-
posed rocks are at the center of the fold (

Figure 10.13a, b),
so we characterize a dome as the circular equivalent of an
anticline. In contrast, a basin , the circular counterpart of
a syncline, has all strata dipping inward toward a central
point and the youngest exposed rocks are at the fold's center
(Figure 10.13c).

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