Attributes of Key Surfaces
The previous chapters have described in general terms how depositional sequences form and the general facies patterns that characterize them. The important observation was made that stratigraphic successions generally can be subdivided into repetitive or cyclic stratigraphic units at varying scale. The objective of this chapter is to illustrate the well-log and facies signatures of the key surfaces that bound and punctuate these stratigraphic units to form sequences and systems tracts.
As discussed previously, cyclic variations of accommodation in either marine or continental settings result in regressive-transgressive cycles that comprise generally predictable facies associations and stratal patterns. As discussed in Chapter 2, whenever these cycles are bounded by unconformities, at least locally, they are defined as sequences. The facies associations that characterize the different phases of cyclic sedimentation within a sequence can be grouped together as systems tracts. Systems tracts comprise linked depositional systems bounded by key stratigraphic surfaces (Posamentier et al., 1988). The most important of these surfaces are the sequence boundary, the transgressive surface, the downlap suiface, and the maximum flooding surface.
Sequences can be defined and subdivided using core, outcrop, well log, and seismic data by identifying these key surfaces (Posamentier et al., 1988; VanWagoner et d., 1990; Bhattacharya, 1993). Subsequently, analysis of the stratigraphic architecture between these surfaces leads to the identification of component systems tracts. As always, it is important to note that interpretations should not be based solely on a single dat set, but must be based on the integration of all available
Figures & Tables
Siliciclastic Sequence Stratigraphy-Concepts and Applications - Sequence stratigraphy has experienced a virtual explosion of applications in recent years. During that time, the concepts upon which sequence stratigraphy is based have been evolving to conform to new observations as well as new types of data. This volume summarizes the current status of this discipline as it applies to siliciclastic deposits. The emphasis in this volume is on sequence stratigraphy as an ?approach? to geological analysis, rather than as a model to which all data sets must conform. The expression of sequence architecture and the nature of bounding surfaces is illustrated through examples and applications drawn from a range of data types, including outcrop, core, wireline log, and 3-D seismic data. In addition, sequence expression also is illustrated using examples of modern landforms.