--> Abstract: The Wider than Longer Sand Lobe of the Hyperpycnal Panther Tongue Delta, Cretaceous, Utah, Usa, by C. Olariu, R. J. Steel, and A. Petter; #90090 (2009).

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The Wider than Longer Sand Lobe of the Hyperpycnal Panther Tongue Delta, Cretaceous, Utah, Usa

Olariu, Cornel 1; Steel, Ronald J.1; Petter, Andrew 1
1 Geosciences, The University of Texas at Austin, Austin, TX.

The Cenomanian Panther Tongue in Central Utah exhibits a coarsening-upward trend, is about 30 m thick and has been interpreted as a fluvial-dominated delta. At the base of the succession the beds are mostly composed of silts alternating with cm-thick very fine sandstones. The basal thin beds are overlain by dm- to m-thick sandstones alternating with thin cm to dm siltstones. The top of the succession contains thick (> 1m) flat-laminated sandstone beds, and intervening erosional surfaces are common. The dominant process that formed the delta-front deposits was hyperpycnal flows. This interpretation is supported by the repeated, meter-thick plane-parallel laminated sandstone beds, and an alternation of sedimentary structures, from rippled to parallel laminated to rippled, or massive to parallel laminated to massive, in the same bed which suggests waxing to waning flow conditions.

The Panther Tongue outcrops have kilometers lateral continuity and individual beds can be mapped laterally. Individual sandstone beds were mapped over the extent of the outcrop (over 1 km) using photomosaics and LIDAR (Light Detection and Ranging) data. The planes formed by the delta front beds are dipping southward whereas the paleocurrents are south-south west. The difference is thought to be due to changes in the orientation of the flow during the bed aggradation. The thick sandstone beds dip basinward at about 2.5 degrees and thin rapidly at a rate of 0.5/100 from meters to decimeters over a distance of hundreds of meters. The cm thick beds were difficult to map but these were observed to have relatively constant thickness and gentle dips over distances of hundreds of meters in both dip and strike depositional direction.

An important finding is that delta-front beds thin at a lower rate along the strike dimension than along dip. Such geometry of the delta-front beds will result in a sand lobe that is more extensive along strike than along dip.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009