(1) Consultants, Corpus Christi, TX
(2) Consultants, Houston, TX
Abstract: Fundamental concepts and key applications of sequence stratigraphy
Wide use of sequence stratigraphy has lead to specialization on specific applications, such as sequence stratigraphy of carbonates, estuarine sands, incised valleys, deep-water sands, or outcrop distribution of facies within parasequences. It may be time to review first some fundamental concepts that get a bit lost in the details, and then some major applications that have won their spurs as well as some still needing encouragement.
Basically, sequence stratigraphy is about the age-old problem of marrying time and rocks. A crucial concept is that a regionally extensive bedding surface (stratal surface) may represent a moment in geologic time or a significant hiatus along a discontinuity surface. Such a surface can be correlated in well logs, seismic profiles and outcrops.
Cyclic stratification of sedimentary rocks is a response to the interaction of subsidence, sea-level change and sediment supply to create variations in shelf accommodation space. Classic third-order cycles, thought to be generated primarily by sea-level changes, form sequences and systems tract. Higher-frequency cycles form parasequences, which are the basic building blocks of time-stratigraphy. They control the parallelism of seismic reflections and stratal surfaces.
The key industrial application of sequence stratigraphy is the recognition, environmental interpretation, and volume and risk analysis of hydrocarbon reservoirs, seals, and source rocks. Interpretation consists of integrated analysis of seismic facies, well-log signatures, cores, and biostratigraphic information. While seismic applications are widely used, time-stratigraphic interpretation of sequences in well logs remains under-utilized.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana