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The AAPG/Datapages Combined Publications Database
Misleading statements are commonly seen regarding omission and repetition of beds by faulting both in wells and in outcrop, and the speaker has been unable to find in the literature any adequate discussion of the problem. The most glaring oversight in the past has been failure to recognize the importance of ground slope on repetition and omission. While the discussion applies principally to strike faults, it would also be appropriate for oblique faults.
The problem is simple in vertical holes, for reverse faults repeat and normal faults omit section, except, where beds dip steeper than the fault, the opposite takes place.
In outcrop the effects are more complex due to the presence of ground slope. Factors influencing the results are the direction and amount of dip of (1) the fault, (2) the beds, (3) the ground slope, and (4) the kind of the fault (normal or reverse). For any fault, either repetition or omission can occur at the surface depending on the ground slope. Thus, it can not be determined from repetition or omission alone whether a fault is normal or reverse in well or outcrop.
An illustration is shown classifying the twelve possibilities based on the location of the ground surface with respect to the angle formed by the intersection of the beds with the fault. The classification fails in the case of folded and inverted beds, variations in ground slope beyond the limits of the classification, and in places in the case of absolutely vertical or horizontal beds or faults.
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