Page 112 - Petroleum Geology

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Fig. 4-11. Seismic record section showing stratigraphic detail. (Courtesy of Esso Australia
Ltd.)

The first step is to identify sequences of conformable reflections and the
sequence boundaries, which are ‘unc~nformities’~ (an unfortunate choice of
term, but perhaps its usage has become so imprecise that another matters
little), and their correlative disconformities and conformities. In Fig. 4-10
there is a clear unconformable boundary (a true unconformity, also) marked
A, which truncates the reflectors below. In Fig. 4-11, two clear offlapping
sequences can be seen, A-B and above and to the left of the letter D, where
reflectors terminate on the lower boundary. The boundary B is an uncon-
formable boundary in seismic stratigraphic terminology, but here it is more
in the nature of truncated foreset beds.
Sequences and groups of sequences can be correlated, and their geological