--> ABSTRACT: Fluvial/Marginal-Lacustrine Sands in the Green River Formation, NE Utah, by Victor A. Pusca and Ron J. Steel; #90906(2001)

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Victor A. Pusca1, Ron J. Steel1

(1) University of Wyoming, Laramie, WY

ABSTRACT: Fluvial/Marginal-Lacustrine Sands in the Green River Formation, NE Utah

Most of the sand fraction in the fluvial/marginal-lacustrine interval of the Green River Formation in Uinta Basin (NE Utah) is contained within small-scale, laterally disconnected sandbodies of fluvial, deltaic or mixed (fluvio/deltaic) origin. Sandbody dimensions and stacking patterns change along depositional strike.

Fluvial sandbodies are produced by meandering rivers and display marked point bar accretion surfaces. Even though the majority of sandbodies generated this way are amalgamated channel belts, they do not extend laterally for more than 2 miles, before pinching out into either overbank or open lacustrine fines. The less frequent single-storey sandbodies do not extend laterally for more than * mile.

Deltaic sandbodies commonly occur as mouth-bar complexes with divergent lobes and steeply dipping foresets (10-15°); they are less than half a mile in diameter but sometimes have large thickness/width ratios. They pinch out into lacustrine fines along either the top of the farthest prograding lobe or along a composite surface generated by backstepping lobes.

Sandbodies of mixed (fluvio-deltaic) origin consist of fluvial deposits that incise into the underlying deltaic interval. Depth of incision varies laterally; thus, some segments have the deltaic interval completely removed while adjacent segments entirely preserve it.

Within the study area, thickness, width, and width/thickness ratio of sandbodies change along the E-W trending depositional strike. 200m-thick sections measured in the western area have 5-10 sandbodies that can extend laterally for up to 2 miles, whereas in the equivalent eastern area there are only 2-3 bodies, much thicker and less laterally extensive.

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