Distribution of Hyperpycnal Deposits in the Delta Front of Cretaceous Panther Tongue Delta, Utah, USA

Olariu, Cornel¹, Ron J. Steel¹ (1) University of Texas at Austin, Austin, TX

River-derived turbidity flows have been recognized as a process that transfers significant volume of sand from rivers to basin. We document a series of beds from Cretaceous Panther Tongue sandstone in Utah that are typical for hyperpycnal deposits. These deposits form the bulk of the southward dipping delta-front clinoforms that have inclinations of up to eight degrees. The hyperpycnal sand deposits of the delta front are linked with subaqueous channels toward the NW and have the tendency to pinch out toward the E-SE.

We distinguished four main sub-environments: subaqueous channel, mouth bar, proximal delta front, distal delta front. The data collected show that channel and mouth bar, with erosional surfaces and scours, commonly represent bypass areas for the hyperpycnal flows. Proximal and distal delta-front environments, with alternation of mud and sand beds, represent depositional areas for such flows. Some of the proximal delta-front beds are coarser than those from the overlying mouth-bar deposits suggesting that higher energy flows bypassed mouth-bar areas and deposited coarser sediments distally.

The delta-front clinoforms dip south and are relatively steep for such fine sand, suggesting high discharge and depositional rates. Our results suggest that despite high discharge and common hyperpycnal flow in the Panther Tongue system the underflows did not travel too far into the basin. To have a longer bypass area into deeper water a longer or steeper delta-front gradient to sustain the hyperpycnal flow is required.