AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Modeling Sediment Dynamics from Source to Sink
(1) Clastics Research Team, Shell International Exploration and Production, Houston, TX.
Sedimentary geology has made great progress in understanding sedimentary basins (e.g. sequence stratigraphy, basin evolution) and stratigraphic architecture of particular depositional environments. The source-to-sink (S2S) approach provides a broader perspective, synthesizing process and stratigraphic understanding across environments (mountain to deepwater) and time (events to Myr), in order to understand the “process filter” which translates tectonic, climate, and sea-level forcing into preserved stratigraphy on basin-to-continent scales. When combined with reconstructions of forcing (e.g. plate tectonics, climate, paleotopography), process-based models of S2S sediment dispersal have great potential to improve predictions of reservoir presence and quality in frontier exploration. Furthermore, by incorporating the full “process filter”, S2S sediment dynamics models can improve the accuracy of paleo-reconstructions extrapolated from the preserved sedimentary record. Here we demonstrate the value of this approach with a S2S model for terrestrial (bedrock, alluvial) environments sculpted by rivers and marine (shelf, deepwater) environments sculpted by waves and currents. Our event-based morphodynamic approach upscales hydrodynamics and sediment transport into flux laws governing surface evolution on geologic timescales. On S2S scale dip-section topography evolves via a nonlinear advection-diffusion equation whose coefficients vary weakly within an environment but strongly between environments. Quasi-equilibrium morphology reflects both process and forcing, and can be used to calibrate transport coefficients by inverting observed large-scale morphology. This is demonstrated using the present-day Amazon S2S system. Morphodynamic style strongly affects propagation of erosion-deposition signals through S2S systems. Diffusive environments (alluvial rivers, deepwater canyons and fans, most shelves) propagate signals both upstream and downstream, and act as low-pass filters. Signal propagation in advective environments (bedrock rivers, some shelves) is frequency independent but unidirectional (e.g. upstream migrating knickpoints). Boundaries between environments migrate on geologic timescales, and boundary dynamics commonly dominate S2S surface evolution and signal propagation. Moving boundary paleo-kinematics preserved in the sedimentary record (e.g. shoreline trajectories) offer important clues to the evolution and subsurface architecture of ancient S2S systems.