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

Yijie Zhu, Janok P. Bhattacharya, Daniel Garza, and Petter Dischington
Geosciences Department, University of Houston, Houston, TX

The asymmetric wave-influenced delta facies model, developed on the basis of plan form interpretations of modern wave-influenced deltas, predicts homogenous, sandy shorefaces updrift and muddier, river dominated deltaic facies downdrift. This model has not been well tested with ancient examples. Superbly exposed 3D outcrops of the Cretaceous Ferron “Notom Delta” wedge in Central Utah, integrated with chronostratigraphically significant bentonite beds allow us to test the asymmetric wave-influenced delta model and evaluate the development of the Ferron clastic wedge in terms of shoreline trajectory models.

50 detailed stratigraphic sections, photomosaics and correlation of key beds and surfaces shows the 120m thick Ferron Notom Delta to consist of up to 8 deltaic to shoreface parasequences, which pass upward into sandy to conglomeratic fluvial channel belts and coaly floodplains. Multistory fluvial channels overlie a regional truncation surface eroded into underlying shoreface and deltaic sediments, indicating an incised valley system. The Ferron thus contains at least one major sequence boundary. The existence of a negative shoreline pathway within the lower parasequences, where shoreline migrates basinward and downward, indicates a relative sea level fall and thus another sequence boundary.

In southern exposures, lower parasequences show storm-wave-influenced, flood-dominated muddy delta front facies, indicated by rare bioturbation, abundant deformed HCS sandstones, and climbing ripples. These parasequences are interpreted as the downdrift margin of an asymmetric wave-influenced delta. To the north, the parasequences show homogenous, sandy, wave-dominated shorefaces with high bioturbation levels. These sandy shorefaces are interpreted to lie on the updrift side of the delta.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas