Janok P. Bhattacharya¹, Adam B. Robinson², Cornel Olariu², Michael M. Adams¹, Charles D. Howell¹

(1) University of Texas at Dallas, Richardson, TX
(2) University of Texas at Dallas

ABSTRACT: Terminal Distributary Channels, Cretaceous Panther Tongue Sandstone, Utah

The Panther Tongue sandstone in Utah was deposited as a river-dominated delta into the Cretaceous western interior seaway of North America. Cliff exposures along Sowbelly Gulch, oriented at high angles to the progradation direction, show the cross sectional facies architecture of proximal delta front deposits. Photomosaics reveal an intimate interfingering of shallow channels and bars, interbedded with low-angle dipping sheet sandstones. Channel sandstones are floored by mud chip conglomerates and contain dune-scale cross bedding. Sheet sandstone beds are structureless to normally graded and capped by current ripple cross lamination. The proximal delta front environment thus represents a rapid shifting of areas dominated by confined flows, in the bars and channels, versus unconfined flows associated with the bar front. The graded beds are interpreted as density underflows indicating that inertial forces dominated the Panther Tongue delta. Abundant soft sediment deformation also indicates bar failure that possibly generated the delta front sediment gravity flows.

In deltas possessing multiple bifurcations of river channels, this example suggests that terminal distributaries are narrow and shallow, versus wide and deep, such as the channels that characterize the modern Mississippi delta. The Panther Tongue is analogous to modern shoal-water deltas such as the Atchafalaya or Wax Lake deltas in the Gulf of Mexico or the Lena Delta in the Russian Arctic, which contain numerous shallow terminal distributary channels. In deltas that show several orders of branching there is thus no such thing as one-scale of distributary channel and the smallest-scale terminal distributaries lie within the delta front.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado