AAPG Bulletin, V. 84, No. 2 (February 2000), P. 183-209.
Revised Stratigraphy, Depositional Systems, and Hydrocarbon
Exploration Potential for the Lower Cretaceous Muddy Sandstone, Northern Denver Basin1
John P. Graham2
©Copyright 2000. The American Association of Petroleum Geologists. All rights
reserved.
1Manuscript received April 20, 1998; revised manuscript received May 3, 1999;
final acceptance August 22, 1999.
2Department of Geology, Colby College, 5800 Mayflower Hill, Waterville, Maine
04901-8858. Present address: Division of Biological and Physical Sciences, Lander
University, 320 Stanley Avenue, Greenwood, South Carolina 29649; e-mail: jgraham@lander.edu
This paper stems from doctoral research at Colorado State University conducted under the
tutelage of Frank G. Ethridge, who was an invaluable guide and mentor throughout this
study. Discussions with Debra Higley and James Schmoker of the U.S. Geological Survey,
Sharon Stonecipher of Marathon Oil Company, and Robert Weimer were very helpful. Don Tait
and his wife, Mary Lou Tait, provided funding for much of the study, as well as lively
discussions concerning the interaction of oil migration and groundwater flow throughout
the Denver basin. Constructive reviews by Jim Rogers, Michael Blum, and Steve Sonnenberg
improved the manuscript and were greatly appreciated. Amoco Production Company and
Marathon Oil Company provided core material as did the U.S. Geological Survey. Colby
College, Waterville, Maine, provided the space and financial support to complete this
paper.
ABSTRACT
The reservoir sandstones of the Lower Cretaceous Muddy Sandstone, the major
hydrocarbon-producing reservoir in the northern Denver basin, are restructured into six
informal members (MS-1 to MS-6) based on sedimentary structures, ichnofacies, geophysical
logs, bounding discontinuities, and sediment distribution patterns. Bounding
discontinuities defining allostratigraphic units are used to assign these six informal
members to three major depositional systems that may be used to redefine hydrocarbon
reservoirs, leading to new exploration targets in this "mature" basin.
