Establishing a Tephrochronologic Framework for the Middle Permian (Guadalupian) Type Area and Adjacent Portions of the Delaware Basin, West Texas and Southeastern New Mexico

B. L. Nicklen
Department of Geology, University of Cincinnati; Cincinnati, Ohio

A series of highly altered volcanic ash layers (bentonites) occur throughout the Delaware Basin of west Texas and southeastern New Mexico, including the Global Stratotype Sections of the Middle Permian (Guadalupian) in Guadalupe Mountains National Park. Although this area is well studied, time control among the various stratigraphic units remains poor, resulting in deficiencies in both stratigraphic correlation and global time scale generation. The objective of this study is to address these deficiencies by using the bentonites in establishing a stratigraphic and chronologic framework for this area (tephrochronology).

To accomplish this, primary volcanic mineral phases (phenocrysts) separated from these bentonites are being analyzed to provide chemical data that can be used in long distance stratigraphic correlation and the generation of high-precision radiometric dates. Initial samples have been collected from units within the Delaware Mountain Group in and adjacent to Guadalupe Mountains National Park, including a section that contains bentonite beds in both the Manzanita Member of the Cherry Canyon Formation and the Rader Member of the Bell Canyon Formation.

Results to date indicate that apatite trace element chemistry is useful in discriminating between samples from discrete bentonites, which is a prerequisite for correlation and allows chemical properties of samples from different localities to be compared. Zircon phenocrysts from select samples are currently undergoing U-Pb dating analysis. By combining results from bentonite correlations with high-precision U-Pb dating, a tephrochronologic framework will be established that will provide a basis for interpreting regional stratigraphic relationships and improving the global time scale.

AAPG Search and Discover Article #90087 © 2008 AAPG/SEG Student Expo, Houston, Texas