Seismicdata provide lateral continuity and 3D insights for sequence stratigraphicinterpretations. Seismic stratigraphic analysis techniques can provide somepredictability to the distribution of facies through the application ofsequence stratigraphic concepts (Vail, 1987). The fundamental unit of sequencestratigraphy is the sequence, which is a relatively conformable succession ofgenetically related strata enveloped by unconformities and their correlativeconformities (Mitchum et al., 1977). A sequence isdivided into systems tracts, which are defined by their position withinthe sequence and by the stacking pattern of parasequence sets.
Seismicsequence analysis defines seismic sequences and systems tracts by identifyingdiscontinuities recorded in reflectiontermination patterns. The analysis starts with establishing geometric relationshipsof seismic reflections on seismic profiles. Aggradation,progradation, and retrogradation are the three general stacking patterns usedto distinguish between different depositional systems (Figure 21). Sequence boundariesand other major surfaces are identified based on seismic reflectionterminations such as onlap, downlap, toplap, and truncation (Figure 22). Accordingto the reflection termination patterns, seismic reflections can be subdivided into systems tracts.
Well logs provide high resolution vertical stratigraphic data. Integrationof seismic and well log data provides more accurate stratigraphic models of thesedimentary fill (Van Wagoner, 1991). The well log sequence analysis performedin this study is based on GR logsresponse from available wells. GR logs measure the radioactivity of rocks and are commonly used as a good proxy for grainsize in siliciclatic systems (Van Wagoner, 1991). Abrupt changes in GRlogs responses are commonly related tosharp lithological breaks associated with unconformitiesand sequence boundaries (Krassay, 1998). Variationpatterns of GR logs indicate changes in the