Paper No. 45-7
Presentation Time: 10:30 AM
MAGNETOSTRATIGRAPHY OF UPPER CRETACEOUS THROUGH LOWER PALEOCENE STRATA FROM THE DAWSON CREEK SECTION, BIG BEND NATIONAL PARK, WEST TEXAS, USA
Upper Cretaceous to lower Paleocene alluvial deposits of the Dawson Creek section in Big Bend National Park present an excellent opportunity to study the interplay between terrestrial ecosystems and cyclostratigraphy. Previous sedimentological and stratigraphic work at the Dawson Creek section has produced a paleoclimatic and sequence stratigraphic framework of the Upper Cretaceous Aguja and Javelina formations and the lower Paleocene Black Peaks Formation, and research on the dinosaur and mammalian faunas from the section have been used to reconstruct the biostratigraphy and to constrain the approximate position of the Cretaceous-Paleogene (K-Pg) boundary. Existing age models for the Dawson Creek section are based on a combination of biostratigraphy, estimates of sedimentation rates based on paleosol maturity, and correlations of local isotope stratigraphy to marine isotope curves. However, our reevaluation of the mammalian fauna from the Black Peaks Formation indicates that the taxa thought to be zone taxa for the earliest Paleocene Puercan North American land-mammal age (NALMA) were incorrectly identified and instead are indicative of the younger Torrejonian NALMA. This demonstrates that the biostratigraphic constraints for the Paleocene portion of the Dawson Creek section are incorrect and suggest that the age model for the entire section should be reexamined using independent methods. Here we construct a local polarity history of the sediments, which will allow the existing sequence stratigraphic analyses and the dinosaur and mammalian faunas at Dawson Creek to be placed into a revised chronostratigraphy. Preliminary results indicate that intervals of the Javelina and Black Peaks formations across the biostratigraphically-defined K-Pg boundary are of a reversed polarity, suggesting a possible correlation to C29r. The remaining local polarity stratigraphy for the Dawson Creek section will be correlated to the geomagnetic polarity time scale. The development of a local polarity stratigraphy will allow for future work correlating the Dawson Creek section and its faunas to equivalent strata within the San Juan Basin, as well as for direct comparisons of climates, depositional environments, cyclostratigraphy, and faunas of correlative strata across the Western Interior of North America.