ANCIENT ASH BEDS IN THE TYPE AREA OF THE MIDDLE PERMIAN, GUADALUPE MOUNTAINS NATIONAL PARK, WEST TEXAS, USA

The Middle Permian (Guadalupian) strata of Guadalupe Mountains National Park (GMNP) contain one of the most frequently studied carbonate margins in the stratigraphic record. However, relatively little research has been conducted on the series of K-bentonite beds (altered volcanic ash) that have long been recognized throughout the section. The designation of the Global Stratotype Sections and Points (GSSP) for the three stages of the Guadalupian Series at GMNP has increased interest in using these important deposits to address a wide range of geologic questions. Here we report on several K-bentonites that occur in outcrops and roadcuts in the Guadalupian type area. We identify K-bentonite beds and potential K-bentonite beds in each stage of the Guadalupian, with the majority (at least 4 in outcrop) being present in the Middle Guadalupian (Wordian) Manzanita Member of the Cherry Canyon Formation (CCF). Two of these are present within GMNP at Nipple Hill, which serves as both the type locality for the Manzanita Member and the location for the Late Guadalupian (Capitanian) boundary GSSP in the overlying Pinery Limestone Member of the Bell Canyon Formation (BFC). At lease one additional bed is present in the Wordian section, occurring in the South Wells Member of the CCF. A new potential K-bentonite is recognized in the Early Guadalupian (Roadian) Brushy Canyon Formation southwest of Salt Flat Bench. In the Capitanian, at least one K-bentonite occurs in Rader Member of the BCF at a locality in the less frequently studied southwestern portion of GMNP. A second potential bed is present at a locality in Bear Canyon, although it occurs in sandstone of the BCF, approximately 2 meters below the base of the Rader Member. Analysis conducted thus far on several of the Manzanita Member K-bentonites, show apatite, biotite, and zircon to be the dominant phenocryst phases, while the clay mineral assemblage is comprised of mixed-layered illite/smectite and/or chlorite/smectite, with discrete phases of chlorite, kaolinite, and illite present in some samples. Whole-rock and phenocryst geochemical data indicate the K-bentonites were derived from a calc-alkaline series magma at a destructive plate margin. These data are consistent with the suggestion by King (1948) that the Las Delicias volcanic arc in northern Mexico is the source of the parent ash.