In sand-shale sequences, subsidence due to compaction may be as important as eustatic and tectonic effects in controlling relative sea-level variations that determine sediment accommodation space and extent of marine transgressions. Furthermore, stratigraphic configuration in coastal settings is more sensitive to relative sea-level changes than either continental or deeper marine environments. Thus, the contribution to local sea-level variations due to compaction and its effect on coastal stratigraphy merit special attention. Compaction in turn is determined by the control of stratigraphic architecture on dewatering, by depositional timing, and by the physical properties of the compacting sediments. In modeling contemporary hydrogeology in these settings, compaction plays a double role: (1) it affects aquifer geometry by way of changes in sediment accommodation space and depositional environment, and (2) it determines petrophysical properties that control water extraction and the ensuing subsidence. We have explored this interaction by using a numerical sedimentary process model coupled with a single-phase flow simulator to study the interaction of sedimentation, dewatering, and compaction in coastal environments. The results explain several features of the sedimentary record and present-day morphology observed in data from the Gulf of Mexico. Although compaction may be hard to separate from other causes of relative sea-level change in ancient environments, careful interpretation of sedimentation timing and quantitative modeling can identify the effect of each. The identification of sedimentation-compaction regimes in coastal settings provides a useful conceptual tool for the geologic interpretation of ancient coastal deposits identified in seismic and well-log data. Hydrogeologic modeling performed on deposits that are simulated by sedimentary process models benefits from a richness of detail that can enhance hydrogeologic predictions. Additionally, the values of petrophysical properties required for hydrogeologic modeling (such as porosity, permeability, and compaction coefficient) can be better constrained by this dual modeling approach, because they result from the prior geologic sedimentation and compaction model, which limits their range of possible values.
