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<gallery mode=packed heights=200px widths=200px>
<gallery mode=packed heights=200px widths=200px>
File:ST53_Part01_Pg03A.jpg
File:ST53_Part01_Pg03A.jpg|{{figure number|1}}
File:ST53_Part01_Pg03B.jpg
File:ST53_Part01_Pg03B.jpg|{{figure number|2}}
File:ST53_Part01_Pg04.jpg|Folds in seismic sections.
File:ST53_Part01_Pg04.jpg|{{figure number|3}}Folds in seismic sections.
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Folds are classified based on whether or not the thickness of stratigraphic layers changes in dip domains or across axial surfaces.
Folds are classified based on whether or not the thickness of stratigraphic layers changes in dip domains or across axial surfaces.
Parallel folds preserve layer thickness, and are common in strata that deformed predominantly by flexural slip (see inset at right). Axial surfaces bisect inter-limb angles in parallel folds.
Parallel folds preserve layer thickness, and are common in [[strata]] that deformed predominantly by [[flexural slip]] (see inset at right on [[:file:ST53_Part01_Pg05A.jpg|Figure 4]]). Axial surfaces bisect inter-limb angles in parallel folds.
<gallery mode=packed heights=200px widths=200px>
<gallery mode=packed heights=200px widths=200px>
File:ST53_Part01_Pg05A.jpg
File:ST53_Part01_Pg05A.jpg|{{figure number|4}}
File:ST53_Part01_Pg05B.jpg
File:ST53_Part01_Pg05B.jpg|{{figure number|5}}
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Parallel folds commonly form by a deformation mechanism called flexural slip, where folding is accommodated by motions on minor faults that occur along some mechanical layering — usually bedding. Flexural-slip surfaces, which can be observed in core or outcrop, may vary in spacing from a few millimeters to several tens of meters in spacing.
Parallel folds commonly form by a deformation mechanism called flexural slip, where folding is accommodated by motions on minor [[fault]]s that occur along some mechanical layering—usually bedding. Flexural-slip surfaces, which can be observed in [[core]] or [[outcrop]], may vary in spacing from a few millimeters to several tens of meters in spacing.
==Shortcomings in seismic images of folds==
==Shortcomings in seismic images of folds==
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<gallery mode=packed heights=200px widths=200px>
File:ST53_Part01_Pg06A.jpg
File:ST53_Part01_Pg06A.jpg|{{figure number|6}}
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<gallery mode=packed heights=200px widths=200px>
File:ST53_Part01_Pg06B.jpg
File:ST53_Part01_Pg06B.jpg|{{figure number|7}}
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==Interpreting folds in poorly imaged zones==
Poorly imaged zones on folds are commonly caused by, and interpreted as, faults or steep limbs. Both solutions are often permissible and should be evaluated. In [[:file:ST53_Part01_Pg07.jpg|Figure 8]], a method of interpreting parallel folds in poorly imaged zones is described.
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File:ST53_Part01_Pg07.jpg|{{figure number|8}}
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