Abstract: Differential Compaction, Sedimentation and Sequence Stratigraphy on the Margins of Carbonate Platforms and Buildups

Dave Hunt, Tim Allsop

The influence of compaction-induced topography on patterns of sedimentation reflects the relative rates of deposition and compaction. When depositional rates are equal to or exceed those of compaction, any induced topography is subdued. The generation of relief by differential compaction is most important when rates of compaction exceed those of deposition. Recognizing these times is important when interpreting the sequence stratigraphy of carbonate platforms and buildups.

If sediments dewater at an equal or greater rate than that of deposition, a hydrostatic gradient is maintained, overburden is entirely supported by grain contacts, and compaction is said to be in an equilibrium state. In contrast, when rates of deposition exceed those of dewatering, pore-waters become overpressured, and strata are relatively undercompacted. However, if deposition were to cease, pore-fluid pressures are reduced by dewatering, and the weight of overlying sediments is gradually transferred back to grain contacts until a hydrostatic gradient is attained.

Changes of sea level can also affect pore-water pressures. Falling sea level can increase pore-fluid pressure gradients and, in turn, rates of dewatering and compaction. Rises of sea level have a similar effect. Furthermore, changes of sea level and/or environment can profoundly affect sedimentation rates. With this in mind, it is suggested that rapid progradation during the highstand systems tract can lead to the development of overpressure and non-equilibrium compaction. During the following lowstand and/or transgressive systems tract, there is positive feedback as the effects of reduced sedimentation and an increased rate of compaction combine, developing compactionally enhanced unconformities.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994