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AAPG Bulletin


Sandstone-Body and Shale-Body Dimensions in a Braided Fluvial System: Salt Wash Sandstone Member (Morrison Formation), Garfield County, Utah1

John W. Robinson and Peter J. McCabe3


Excellent three-dimensional exposures of the Upper Jurassic Salt Wash Sandstone Member of the Morrison Formation in the Henry Mountains area of southern Utah allow measurement of the thickness and width of fluvial sandstone and shale bodies from extensive photomosaics. The Salt Wash Sandstone Member is composed of fluvial channel fill, abandoned channel fill, and overbank/flood-plain strata that were deposited on a broad alluvial plain of low-sinuosity, sandy, braided streams flowing northeast.

A hierarchy of sandstone and shale bodies in the Salt Wash Sandstone Member includes, in ascending order, trough cross-bedding, fining-upward units/mudstone intraclast conglomerates, single-story sandstone bodies/basal conglomerate, abandoned channel fill, multistory sandstone bodies, and overbank/flood-plain heterolithic strata. Trough cross-beds have an average width:thickness ratio (W:T) of 8.5:1 in the lower interval of the Salt Wash Sandstone Member and 10.4:1 in the upper interval. Fining-upward units are 0.5-3.0 m thick

┬ęCopyright 1997. The American Association of Petroleum Geologists. All rights reserved.

1Manuscript received March 25, 1996; revised manuscript received October 21, 1996; final acceptance February 24, 1997.

2Snyder Oil Corporation, 1625 Broadway, Suite 2200, Denver, Colorado 80202.

3U.S. Geological Survey, MS 939, P.O. Box 25046, Federal Center, Denver, Colorado 80225-0046.

This research was undertaken as part of a Ph.D. dissertation while J. W. Robinson was at Colorado School of Mines and was a volunteer for the Branch of Petroleum Geology at the U.S. Geological Survey. E. R. (Gus) Gustason at BP Exploration (Alaska), Inc., first suggested the project and was an active participant during many phases of the study. Simon Smith at KSEPL (Shell) helped construct the reservoir and flow simulation models and was a gracious host while J. W. Robinson was a visiting scientist at The Hague, Netherlands. We would like to thank the following companies and organizations for their financial and technical support of the project: BP Exploration (Alaska), Inc., BP International, Ltd., Koninklijke/Shell Exploratie en Productie Laboratorium (KSEPL), U.S. Geological Survey, Snyder Oil Corporation, Marathon Oil Company, ARCO Exploration and Production Technology, Nuclear Assurance Corporation, and the Department of Petroleum Engineering and the Department of Geology and Geological Engineering at Colorado School of Mines. Keith Shanley, Andrew Miall, and Michael Robinson provided helpful reviews of an earlier version of the manuscript.

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