NEARSHORE ALONG-STRIKE VARIABILITY: IS THE CONCEPT OF THE SYSTEMS TRACT UNHINGED? (Invited Presentation)

Sequence stratigraphic models assume that nearshore strata have relatively consistent and laterally persistent stacking at the systems tract scale and therefore may not fully describe the three-dimensional stratigraphic architecture in areas displaying marked nearshore along-strike variability. A stratigraphic model of nearshore deposits is presented that corrects for this assumption by explaining variations in along-strike stratal geometries in terms of a systematic change in the orientation of a shoreline trend or clinoform rollover, a scenario comparable to deflection around a hinge. The model defines hinge zones that are both fixed and moving with respect to time, and was created from outcrop, well-log, and seismic reflection data. Model end members predict contemporaneous progradational, aggradational, and retrogradational stacking bounded by surfaces displaying significant along-strike changes in architecture, implying that sequence stratigraphic surfaces can be diachronous. We advocate examining the impact of stratigraphic variations parallel to depositional strike by testing for the presence of uniform versus differential progradation, phenomena responsible for creating unhinged and hinged nearshore depositional systems, respectively. Understanding these differences will improve subsurface predictions and provide a more complete understanding of the stratigraphic evolution of sedimentary basins.