# Stratigraphic interpretation

Series Geophysical References Series Problems in Exploration Seismology and their Solutions Lloyd P. Geldart and Robert E. Sheriff 10 367 - 414 http://dx.doi.org/10.1190/1.9781560801733 ISBN 9781560801153 SEG Online Store

## Problem

Interpret the seismic section shown in Figure 10.15a.

### Solution

The most striking feature of this section is probably the progradational pattern ${\displaystyle AA'}$ indicating a source to the right of the section. These prodelta reflections (seaward of a river delta) show both toplap and downlap terminations. Note that these prograding reflections are more continuous at the right and left sides of the section than in the region under the surface channel. There may also be a slight sag in reflections under the channel, and they suffer similar quality deterioration. An interpreter would not interpret these quality changes as having stratigraphic significance.

The thin wedge above ${\displaystyle B}$ that pinches out about midway on the section shows downlap from the left, suggesting a shift in the source of the sediments from the time when the deeper prodelta sediments were being deposited. Downlap is seen onto ${\displaystyle DD'}$ and reflections below ${\displaystyle DD'}$ truncate against this reflection; it is probably an unconformity and possibly a sequence boundary.

Figure 10.15a.  Seismic section (courtesy Chevron Oil Company).

Note the change in overall character at reflection ${\displaystyle CC'}$; it is known from well control that ${\displaystyle CC'}$ separates marine sediments below from nonmarine sediments above. However, the decrease in multiplicity on this CMP section as one goes shallower (because of the mute applied in processing) might also produce a character change.

Dip is gently to the left on this section so the right dip at and below ${\displaystyle DD'}$ constitutes a dip reversal that may have structural significance.