Abstract: Cretaceous Wave-Dominated Delta, Barrier Island, and Submarine Fan Depositional Systems of the Rocky Mountains: Clastic Models for Hydrocarbon Exploration

By

John K. Balsley

The distinctive characteristics of the three sand-dominated depositional systems are described with emphasis upon criteria useful in recognizing the systems in outcrop and subsurface settings. Interrelationships between the systems are examined with the aid of a complete sediment dispersal network extending from fluvial coastal plain through wave-dominated delta, strand plain, and barrier island systems to basin floor submarine fans. This network was deposited along the western margin of the Cretaceous Interior Seaway and was subsequently exposed in the Book Cliffs of Utah and Colorado.

Wave-dominated deltas are commonly cuspate to arcuate in plan, end sheet-like in cross section. Apparent widths range up to 40 miles 164 kilometers). Typical delta front facies tracts consist of laterally extensive shoreface-foreshore sequences locally replaced by distributary mouth bar deposits. The bar deposits reflect density flow processes and hyperpycnal inflow at the shoreline. Extensive coals and thin transgressive units cap the delta front sequences. The deltas occur in both vertically stacked and imbricate patterns.

The barrier island system is characterized by a sheet sandbody geometry, and by a dip-oriented facies tract consisting of a shoreface-foreshore barrier sequence replaced in a landward direction by tidal inlet and flood tidal delta deposits. Brackish-water lagoonal sediments overlie the entire tract. Characteristics of the system indicate deposition in a microtidal setting.

Submarine fans occur in distal settings beneath the prograding delta and barrier island systems. Fan deposits are lenticular in cross section and isolated in basinal shale. The deposits range from thickening-upward sandstone-shale sequences reflecting deposition in outer fan environments to thick, sand-dominated, channelized sequences reflecting deposition in more proximal fan environments.

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