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The Extent of Individual
Hyperpycnal-Flow Beds in the Cretaceous Panther Tongue Delta, Utah, USA*
By
Cornel Olariu1,
Ron J. Steel1,
and Andrew L. Petter1
Search and Discovery Article #50071 (2008)
Posted
*Adapted from extended abstract prepared for
AAPG Hedberg Conference, “Sediment
Transfer from Shelf to Deepwater – Revisiting the Delivery Mechanisms,”
March
3-7, 2008 – Ushuaia-Patagonia, Argentina
1Jackson
Introduction
The distance over which river-generated
hyperpycnal flows
travel on the shelf and the extent of the resultant deposits are not
well
documented. The geometry and thickness of the beds are a reflection of
the
hyperpycnal-flow plume behavior. River-generated hyperpycnal flows will
expand
off the river mouths because of the lack of confinement and bottom
friction. In
this paper we document the extent and thickness variation
of the
individual
hyperpycnal beds of the Cretaceous Panther Tongue Delta,
variation
.
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Panther Tongue
Sandstone, a regressive sandstone wedge of
late Campanian age, crops out in The Panther Tongue succession has a coarsening- and thickening-upward trend and is about 30 m thick. Based on the sedimentary facies, the deposits are interpreted as fluvial- dominated delta deposits. At the base of the succession the beds are composed of siltstones 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 has a series of thick (>1 meter) amalgamated sandstone beds. Erosional surfaces between sandstone beds, especially in the upper part of the succession, are common. Sedimentary structures that indicate hyperpycnal flows are: unusually thick intervals (>1 meter) of plane-parallel lamination in the sandstone beds and thick beds containing rippled to parallel-laminated to rippled, or massive to parallel laminated to massive, in the same bed (Figure 2). The Panther Tongue outcrops have kilometers of lateral continuity and individual beds can be mapped laterally. Individual sandstone beds were mapped using photomosaics and LIDAR (Light Detection and Ranging) data. The bedding diagram oriented down the depositional dip indicates that the beds are continuous over the extent of the outcrop (> 1 km) and dip southward; i.e., in the downcurrent direction. The thick sandstone beds dip basinward at about 2.5 degrees and thin 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 relative constant thickness and gentle dips over hundreds of meters in both dip and strike depositional directions (Figure 3). The geometry
and thickness of the Panther Tongue beds are
indicators of the hyperpycnal flow plume behavior. The hyperpycnal
flows that
are river generated will expand off the river mouths because of the
lack of
confinement and the bottom friction. A modern analog of Panther Tongue
Delta
might be the Yellow River Delta in
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