Stratigraphic Architecture, Sedimentology and Ichnology of Late Cretaceous Storm-Flood, River-Dominated Deltas Versus Storm-Dominated Deltas

Abstract

The Book Cliffs are easily accessible and are frequently visited as outcrop analogues for oil-field scale reservoirs. In order to assess whether the Blackhawk Formation in Utah should be utilized as outcrop analogs for subsurface viscous- to heavy-oil reservoirs in Arctic Alaska, coeval outcrop successions (∼ 4,135 km apart) containing three progradational deltaic successions are evaluated using standard sedimentologic techniques. Deltaic deposits of the Upper Cretaceous (Santonian–Campanian) lower Schrader Bluff Formation, deposited at ∼ 83 to 84° N in the paleo–Arctic Ocean, are compared with the lower and mid-Campanian Kenilworth and Grassy members of the Blackhawk Formation, deposited at ∼ 42° N in the Western Interior Seaway. Stratigraphic architectures, sedimentology, and trace fossil assemblages indicate significant and quantifiable differences between these depositional systems. Stratigraphic architecture of the lower Schrader Bluff Formation contains amalgamated distributary-mouth bar and subaqueous terminal distributary channel complexes with minor swaley and hummocky cross-stratified wave-reworking. These successions are compared with the Blackhawk Formation that exhibits dominantly swaley and hummocky cross-stratified intervals with minor channel complexes. Results indicate that the lower Schrader Bluff Formation at Shivugak Bluffs is a storm-flood, river-dominated delta with minor wave-influence, while both members of the Blackhawk Formation contain storm-dominated deltas/shoreface successions. This investigation provides high-resolution detail of sandbodies that range from 33–54 m thick by ∼ 200 m wide and examines how two different depositional systems could easily be mistaken as the same type of system if interpretations were based solely on cored intervals.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016