Recent forward modeling of inertial, river-dominated deltas asserts that stratigraphic architecture is controlled primarily by gradient of the sediment-water interface and initial water depth where channel flow becomes unconfined (Edmonds et al., 2011). This model predicts that shallow water, low gradient deltas differ from deep water, high gradient deltas in two important ways: the depth of channel incision, and the ratio of topset-to-foreset stratal thickness. Topset strata are composed of channels and interdistributary muds while foreset strata are constituted by amalgamated mouth bars. Using this criterion, a delta can longitudinally transfer from topset-dominated to foreset-dominated stratigraphic architecture. This transition is predicted to occur in proximal areas for deltas with deep water and high gradient, and in distal positions for deltas with shallow water and low gradient. The model further predicts topset-dominated deltas to have a higher ratio of channel depth to total delta thickness than foreset-dominated deltas. While geometrically reasonable, this model has not yet been tested in natural systems.

This study will use outstanding Iles Formation outcrops in western Colorado to document the three-dimensional stratigraphic architecture and facies distributions of delta with deep water and high gradient. Channel depth; topset, foreset, and bottomset thickness; and facies will be documented. A companion study will examine a delta with shallow water and low gradient. The comparison of these two studies will test Edmonds' model, while documenting how initial water depth and gradient affect facies distribution. This study will enhance predictive ability of sub-seismic stratigraphy, increasing reservoir modeling accuracy and reducing uncertainty.