Changes

The purpose of the cross section is to determine which horizon can serve as the datum. Because it is shown as horizontal, the thickness variations of the units directly above and below the datum are most simply interpretable on the cross section. The cross section in [[:file:geological-cross-sections_fig1.png|Figure 1b]] uses the horizon labeled F as a datum because this has been interpreted as the top of a chronostratigraphic sequence.<ref name=pt06r122 />

The purpose of the cross section is to determine which horizon can serve as the datum. Because it is shown as horizontal, the thickness variations of the units directly above and below the datum are most simply interpretable on the cross section. The cross section in [[:file:geological-cross-sections_fig1.png|Figure 1b]] uses the horizon labeled F as a datum because this has been interpreted as the top of a chronostratigraphic sequence.<ref name=pt06r122 />

An unconformity is commonly used as a datum. In many circumstances, unconformities represent relatively uniform and geologically important time horizons and are therefore useful features on which to hang cross sections. However, caution must be used since the sedimentary layers may reflect paleotopographic relief.

An [[unconformity]] is commonly used as a datum. In many circumstances, unconformities represent relatively uniform and geologically important time horizons and are therefore useful features on which to hang cross sections. However, caution must be used since the sedimentary layers may reflect paleotopographic relief.

===Orientation and layout of the cross section===

===Orientation and layout of the cross section===