REVISED MAGNETIC POLARITY STRATIGRAPHY FOR THE LOWER CHINLE FORMATION (UPPER TRIASSIC) AT PETRIFIED FOREST NATIONAL PARK

Recent revisions to the lithostratigraphy of the Upper Triassic Chinle Formation within Petrified Forest National Park (PEFO), northern Arizona, have demonstrated that a considerable gap exists in a previously published magnetiostratigraphic model. This study focused on outcrops in the southern park where there is strong biostratigraphic and geochronologic control among localities. Here we present new magnetic polarity chronology data for the lower Chinle Formation in PEFO that incorporates corrected lithostratigraphic correlations. The data set presented here includes new polarity information for the upper Mesa Redondo, lower Blue Mesa Member and upper Sonsela Member that were not sampled in previous work. The uppermost Mesa Redondo Member through the lower Petrified Forest Member strata typically carry a relatively well-defined and well-grouped magnetization. For example, the bedding corrected grand mean for the lower part of the Petrified Forest Member is D = 004.2°, I = 3.9°, α₉₅ = 3.8°, k = 146.57, N/No = 11/16. Polarity correlations at the local level are very good. When combined with absolute age determinations, correlation to the global geomagnetic polarity time scale is well-constrained. We suggest that the Blue Mesa Member is reasonably well correlated with GPTS chron UT16, the lower Sonsela Member with UT17 and the upper Sonsela Member with UT19 and lower UT20. However, correlation at a regional level continues to be problematic in the absence of absolute age data for other sections.