Bulletin-17—Pennsylvanian System in New Mexico

B y M. L. Thompson, 1942, 90 pp., 2 tables, 8 figs., 2 plates, 1 index.

Plans are outlined in this preliminary report for the stratigraphic classification of the Pennsylvanian system in NM, with special emphasis on the classification of the Pennsylvanian rocks of the central portion of the state. Most former students of the Pennsylvanian in NM have not considered these sedimentary rocks divisible into small stratigraphic units, and the entire system has been referred usually to one or two thick formations. Detailed lithologic and paleontologic studies, especially of the fusulinid faunas, indicate that the Pennsylvanian of NM can be subdivided into smaller recognizable stratigraphic units. It is the purpose of this report to set up a basis for a detailed classification of the Pennsylvanian of NM.

Data on which this study is based have been accumulated since the fall of 1939. Field studies have been made over most areas in which Pennsylvanian rocks occur at the surface in NM, except in the extreme southwestern part of the state. Also, detailed studies have been made of Pennsylvanian rocks and fusulinid faunas in east central AZ and extreme western TX for comparison with the NM section. Up to the present time, detailed descriptions and studies of faunal collections have been prepared of more than 50 stratigrpahic sections in NM, many of which include the entire Pennsylvanian system; the locations of some of these are shown on the accompanying outline map. General collections and generalized sections of the Pennsylvanian from various parts of NM have also been used in this study. However, only a few of these stratigraphic sections will be referred to specifically in this preliminary report.

The Pennsylvanian rocks of NM contain paleontologic zones and lithologic units which are recognizable over large portions of central NM from the Nacimiento Mountains, southward to the Hueco and Franklin Mountains of TX. In fact, thin lithologic units, bounded by definite and continuous paleontological zones, are recognizable over areas of thousands of mi² in the central portion of the state. Pennsylvanian rocks of many other regions in North America are of major importance as petroleum and natural gas reservoirs. The possible similar importance of the thick system of rocks of this age so widespread in NM should not be overlooked. Furthermore, the recent discovery of petroleum and gas in basal Pennsylvanian rocks in the Rattlesnake field, San Juan County, NM, adds obvious importance from a purely commercial point of view to the Pennsylvanian strata of the western and central portion of the state.

In recent years numerous geologists, more especially the geologists of oil companies, have made inquiries in regard to available published information about the Pennsylvanian sediments of NM. A large general report on the detailed stratigraphy and fusulinid faunas of the Pennsylvanian of NM is now in the process of completion. However, it is considered advisable to present at this time a preliminary classification and general discussion of the Pennsylvanian rocks of NM in order that this general information may be available immediately to those who are especially interested in the basic geology of this region. More nearly complete supporting data for the conclusions reached in this report, a more detailed classification of the rock units, and descriptions of the contained fusulinid faunas will be included in the larger report.