Delta Asymmetry and Sequence Stratigraphy of the Cretaceous Ferron Notom Delta, Utah

The asymmetric wave-influenced delta facies model, developed on the basis of interpretations of modern systems, predicts sand dominated updrift shorefaces and muddier river-dominated facies downdrift. This model has not been well tested with ancient examples. 3D outcrops of the Cretaceous Ferron “Notom Delta” wedge in Central Utah, integrated with bentonite datums allow us to test the asymmetric wave-influenced delta model and evaluate the development of the Ferron clastic wedge in terms of shoreline trajectory. 41 detailed stratigraphic sections, photomosaics and walking out of key beds and surfaces shows the 120m thick Ferron Notom Delta to consist of 10 deltaic to shoreface marine parasequence sets, which pass into sandy to conglomeratic fluvial channel belts and coaly floodplain mudstones. Multistory fluvial channels overlie a regional truncation surface eroded into underlying marine facies, indicating two incised valley systems. Negative shoreline pathways in several parasequences indicate a relative sea level fall. In the south, the lower parasequences show storm-flood-dominated muddy delta front facies, indicated by rare bioturbation, abundant deformed HCS sandstones, and climbing ripples. These parasequences are interpreted to be on the downdrift margin of an asymmetric wave-influenced delta. To the north, the upper parasequences show more homogenous, sandy, wave-dominated shorefaces with high bioturbation levels. These sandy shorefaces are interpreted to lie on the updrift side of the delta. Parasequences in the middle of the Notom show parasequences that contain both downdrift delta front facies and updrift shorefaces, showing clear evidence of asymmetry within one delta lobe. The overall evolution from fluvial to wave-influenced deltas through time may reflect greater deflection to the south as the system evolved.