The Lower Chinle Formation (Late Triassic) at Petrified Forest National Park, Southwestern USA: A Case Study in Magnetostratigraphic Correlations

Abstract

Magnetic polarity stratigraphy is a method that can be invaluable for correlation of terrestrial strata when combined with other stratigraphic and/or geochronologic data sets. Recent revisions to the lithostratigraphy of the Chinle Formation within Petrified Forest National Park (PEFO), northern Arizona, have demonstrated that a stratigraphic gap comprising minimally nearly one-third of the section exists in the previously published magnetic polarity stratigraphy. Here we present a new magnetic polarity chronology for the lower Chinle Formation (Late Triassic) in PEFO that incorporates corrected lithostratigraphic correlations as well as recently published U-Pb dates. The uppermost Mesa Redondo Member, Blue Mesa Member, Sonsela Member, and Petrified Forest Member typically carry relatively well-defined and well-grouped magnetizations. Polarity correlations at the local level are reasonable and record both normal and reverse polarity chrons. Comparison to similar age sections in Chama Basin of New Mexico suggests the presence of significant depositional hiatuses or erosional events at the top and base of the Poleo Sandstone. A lack of geochronological or biostratigraphic information for the New Mexico sections hampers further correlation between eastern Arizona and New Mexico. When compared to the Newark Supergroup magnetic polarity chronology, reasonable correlation of the PEFO magnetostratigraphy is further constrained by a series of detrital zircon U-Pb dates aiding correlation. These correlations suggest that the lower Chinle Formation section sampled at PEFO encompasses most of the middle and early Norian Age. In addition, the magnetic polarity stratigraphy presented here contributes to assessing the timing of the Adamanian-Revueltian faunal turnover, the largest magnitude biotic change known within the Chinle Formation.