Abstract

This volume is a collection of papers dealing with regional and subregional interpretations of selected intervals of Paleozoic rocks in the Rocky Mountain region and Nevada. Contributing authors were given wide latitude in choosing a topic and approach for their papers. Some present interpretations based on the latest concepts of sequence stratigraphy. Others provide more traditional interpretations based on study of depositional textures and fossils. All authors, however, provide their insights, commonly based on years of research and data collection, into some of the interesting and, in many cases, economically significant intervals in the Paleozoic section of the Rocky Mountain region.

An important point to emerge from this collection of papers is that no single approach or technique is most useful in the interpretation of sedimentary rock packages. Some stratigraphic intervals such as the Devonian carbonate platform in Nevada and the Upper Pennsylvanian Honaker Trail Formation along the Colorado River in Utah were deposited in settings (and are so well exposed in outcrops) that make them ideal candidates for interpretation using modern concepts of sequence stratigraphy. Other intervals such as the Upper Ordovician Red River Formation in the Williston Basin, and possibly the Upper Paleozoic evaporite deposits of the northern Denver Basin (which are poorly exposed in outcrop and generally studied with data from oil and gas wells), were deposited in barred or silled basins sufficiently isolated from global seas that they developed depositional sequences relatively independently of eustatic fluctuations. Still other rocks, such as the complexly faulted Ordovician section in western Utah and Nevada, demand detailed paleontologic study to document stratigraphic correlations before regional depositional facies relationships can be defined.

The rock packages discussed here represent deposition under a range of tectonic, climatic, and paleogeographic settings. Some, such as the Cambro-Ordovician section in the Williston Basin, the Devonian and Mississippian carbonates of Nevada, and the Mississippian Madison Limestone of Wyoming, represent deposition during “greenhouse” times when sea level was relatively stable and the climate in the Rocky Mountain region was generally warm. Others, such as the Pennsylvanian deposits of the Paradox and Denver basins were deposited during “icehouse” times when major fluctuations in sea level resulted from the waxing and waning of polar ice caps. Contrasting the styles of deposition during these various times provides just one example of the useful information that can be gained from comparing the papers presented in this volume.