Three widely distributed sandstone bodies—the Cedar Mesa, De Chelly, and Coconino-Glorieta sandstones—are conspicuous components of the Permian System of the Colorado Plateau. All are light colored, highly cross-stratified, quartzose sandstones, but they differ radically in geometric configuration, geographic distribution, source area, primary bedding features, and depositional environment.
The Cedar Mesa sandstone is present in the western part of the plateau as a thick sequence of light colored, nearshore-marine to littoral deposits that occur in a linear north-south trend. The unit grades eastward through abrupt facies changes into lagoonal red beds of the Cutler group that were derived from a different source.
The De Chelly sandstone is considerably more widespread, and is present over most of the province, except southwestern Colorado. The red sands were derived from Cutler sediments and distributed by northeasterly winds, forming an eolian desert in the greater Four Corners area, that graded southward into horizontally bedded marine deposits along the southern margin of the plateau. The sea encroached upon the vast dune area from the south and reworked the eolian deposits in its path, but did not reach the northern desert.
The Coconino-Glorieta sandstone was deposited as a fan-shaped wedge in northern Arizona, by eolian processes. The central Arizona source also supplied sands to a relatively stable marine area in central New Mexico, where they were deposited in shallow-marine to littoral environments. The marine deposits were widely and uniformly distributed—in marked contrast to their eolian counterparts in Arizona that were physically separated by the slightly positive Defiance uplift near the Arizona-New Mexico State line. The geometric configuration of the dual-environment formation is very distinctive.
Figures & Tables
Geometry of Sandstone Bodies
This volume contains the eight papers presented as a symposium of the Research Committee of The American Association of Petroleum Geologists at the 1960 annual meeting in Atlantic City, New Jersey. One paper presented in the General Session at that meeting, one reprinted paper, and three other solicited papers are also included.
The choice of “Geometry of Sandstone Bodies” as a timely and pertinent subject lor the 1960 symposium was made after an extensive canvass of Research Committee members and about fifty other geologists vitally interested in research in petroleum geology. From a group of about 15 proposed subjects, this one was selected as first choice by almost all those canvassed. Partly because of this high level of interest, the decision was made to attempt publication of the symposium as a special volume of The American Association of Petroleum Geologists. The word geometry in the title probably had several different meanings among the selectors, and for this reason an attempt was made to define the term adequately in order to establish uniformity of communication among symposium participants.
The dictionary definition of the word “geometry” is the science of magnitudes in space. In applying the term to the symposium theme, some modification and interpretation of its formal meaning were needed, and the following definition was therefore proposed for use in this volume—
Geometry of Sandstone Bodies—Spatial relationships of sandstone deposits within the sedimentary framework.
As used in this book, the subject is more than just a three-dimensional study in which thickness is added to areal distribution.