Sedimentology, Sedimentary Architecture and Stratigraphy of Isolated Inner Shelf Channels, Upper Cretaceous Aberdeen Member, Green River Embayment, Book Cliffs, eastern Utah, U.S.A.: Implications for Shoreface-to-Shelf Facies Models

Pattison, Simon A.J.¹, R. Bruce Ainsworth² (1) Brandon University, Brandon, MB (2) Australian School of Petroleum, University of Adelaide, Adelaide, Australia

New evidence from the upper Aberdeen Member (Campanian) in the Green River embayment region of the Book Cliffs, eastern Utah has highlighted the important role that turbidity currents can play in the offshore transport of fine-grained sediments. Isolated, turbidite-filled submarine channels are clustered in at least eleven different areas, and are tens of kilometers basinward of their time equivalent shoreface deposits. Paleocurrent data reveals an overwhelmingly dominant across-shelf, offshore-directed transport trend.

Most channel-fill deposits have an abundance of organic-rich siltstones and mudstones, finely comminuted plant material, a low diversity trace fossil assemblage, mild bioturbation and rare coal fragments. The paucity of wave ripples in the background facies suggests deposition below fair weather wave base. Very fine- to fine-grained Bouma-like Tbc or Tc sandstone beds with combined-flow and wave ripples provide evidence for deposition above storm wave base. Stacked Bouma-like Tbcbc or Tcbc beds indicate deposition from longer-lived and sustained turbidity currents and are interpreted as wave-influenced hyperpycnites. Individual channel-fill units are 0.5 to 7 m thick, 5 to 40 m wide and stack together to form multistorey channel-fill complexes, which are 2 to 15 m thick and are comprised of up to seven nested channel-fill units.

The upper Aberdeen Member channels were mostly cut and filled by wave-supported gravity flows and provide evidence for across-shelf transport of fine-grained sediments. Isolated shelf channels are recognized in older and younger strata implying that wave-supported gravity flows were a recurrent phenomena in the Campanian of Utah. Shoreface-to-shelf facies models should be revised to incorporate turbidite-rich shelf deposits in some inner shelf settings.