Print this pageStratigraphic Coupling of Shelf to Slope Environments and Its Role in Stratigraphic Prediction and Modeling
CROSS, TIMOTHY A., and MARGARET A. LESSENGER
Constructing quantitative stratigraphic models and predicting deep-water facies distributions, sediment volumes, and stacking patterns of genetic units requires a knowledge of stratigraphic coupling across shelf and slope facies tracts. Stratigraphic models simulate the interdependent processes which store sediment on the shelf, transport it across the shelf, and redistribute it into shelf and slope basins. Most of the data from which predictions will be made reside in strata from shelf environments. If the nature of stratigraphic coupling between the shelf and slope is understood, then data from shelf strata are useful for predicting deep-water stratigraphy.
Sediment is transported across the shelf, stored near the shelf margin, and redistributed to the slope and outer shelf basins by two principal mechanisms. One is by progradation of deltas across the shelf to the shelf edge. The other is by repeated shaving off the shelf surface and downslope sediment transport by the wave-base razor. Wave base is the effective limit to which sediment may aggrade on shelves. Sediment within wave base is remobilized during storms and swept across the platform to sites below wave base. The wave-base razor is active during both regression and transgression on shelves within storm wave base.
Low sea level enhances the efficiency of the wave-base razor, and sediment accumulates along the shelf margin and slope. As sea level rises, more accommodation at the shelf margin enhances the aggradation of sediment, causing increased sediment thickness and mechanical instability. As sea level continues to rise, the added weight initiates mass failures, and the shelf margin develops a scalloped scarp topography. The products of the remobilized sediment mass are sediment gravity flows of varying rheology and therefore varying texture and composition.