Facies and Log Expression of Systems Tracts
The preceding chapter discussed the identification and interpretation of key stratigraphic surfaces. This aspect of a sequence stratigraphic analysis is an essential part of the general approach, but the analysis and interpretation of sediment stacking patterns between these surfaces is equally important. As discussed in Chapter 2, a sequence deposited during a cycle of change in relative sea level (or in fluvial accommodation) can be subdivided into systems tracts, characterized by specific stacking patterns and bounded by key stratigraphic surfaces. For reasons discussed in Chapter 2, we suggest abandonment of type 1 and type 2 sequence nomenclature, replacing it with a single sequence type. A complete sequence comprises three systems tracts: lowstand, transgressive, and highstand. Each systems tract represents a specific sedimentary response to the interaction between sediment flux, physiography, environmental energy, and changes in accommodation.
In practical terms, a systems tract consists of a sedimentary succession with a specific type of stacking pattern (i.e., regressive,stationary, or transgressive—in the case of coastal and shelfal deposits; Fig. 2.5). Systems tracts generally are deposited during a specific phase of relative sea level, though the precise timing of deposition of systems tracts is a function of the local balance between sediment flux and rate of change of accommodation. Within a sequence, the transgressive surfaces and maximum flooding surfaces described in Chapter 3 mark the physical boundaries between systems tracts, across which changes of stacking patterns can bk observed. A regressive or progradational stacking pattern consists of a succession of discrete stratigraphic
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.