MILKING HIGH RESOLUTION SEQUENCES TO INFER PALEOHYDRAULICS IN DEEP TIME SYSTEMS

Sequence stratigraphy shows that depositional system are linked through time and space, and show distinctively predictable 3D stratigraphic organization, which can be related to cycles of relative changes in accommodation and sediment supply. Only more recently have attempts been made to quantify the size and scaling relationships of the ultimate source areas on the basis of analysis of ancient depositional systems, and the use of these scaling relationships to predict the size of linked depositional systems along the Source to Sink (S2S) tract. Sequence stratigraphy also provides the context to find all-important trunk river systems, as well estimates of depositional slopes, critical in paleohydraulic evaluation.

Examination of ancient river systems in the rock record, and especially the largest trunk rivers, which are typically within incised valleys, can be used to estimate paleodischarge, which in turn can be linked to the drainage basin to make estimates about the size and sale of the source area. The best estimates can be made in basins with well-constrained data that allow details of cross-sectional or plan-view channel-architecture to be determined, such as extensive outcrops, or abundant subsurface data, and especially where higher resolution 3D seismic data are available. Paleodischarge estimates of lowstand Quaternary-age continental-scale ancient rivers from passive continental margins, using seismic data, are orders-of-magnitude higher (10,000's of cumecs) than smaller-scale Cretaceous lowstand systems that drained into the Western-Interior Seaway of North America (1000's of cumecs). Paleodischarge of rivers can also be estimated independently by integrating estimates of drainage basin area and paleoclimate. These can be compared with paleodischarge estimates based on the river deposits themselves.

A more quantitative approach to estimating the scale of sedimentary systems, and especially in the context of source areas, also puts constraints on the size and scale of potential hydrocarbon reservoirs and thus has economic value.