Abstract

We analyzed samples for paleomagnetism, 40Ar/39Ar detrital sanidine ages, and mammalian fauna to produce a precise chronostratigraphic framework for the Upper Cretaceous to Lower Paleocene Dawson Creek section of Big Bend National Park, west Texas. Prior to this work, the absolute ages and durations of the Upper Cretaceous Aguja and Javelina Formations and Paleocene Black Peaks Formation were relatively poorly constrained. The documented polarity zones can be correlated to C32n-C31n, C29r, and C27r of the geomagnetic polarity time scale, with three hiatuses spanning more than 1.5 m.y. each. Rock magnetic analyses indicate that the dominant magnetic carrier in the Aguja and Black Peaks Formations is titanomagnetite, while the Javelina Formation has varying magnetic carriers, including hematite, magnetite, and maghemite. An overprint interval surrounding the Cretaceous-Paleogene boundary suggests the primary magnetic carrier, titanohematite, was likely reset by burial and/or overlying basaltic flows. These are the first independent age constraints for the Cretaceous–Paleocene strata at the Dawson Creek section that determine the age and duration of deposition of each formation in the section, as well as the age and duration of multiple unconformities through the succession. As a result, these age constraints can be used to reassess biostratigraphic and isotopic correlations between the Big Bend area and other Cretaceous–Paleogene basins across North America. Based on this new data set, we reassign the age of the mammalian fauna found in the Black Peaks Formation from the Puercan to the Torrejonian North American Land Mammal age. Our age constraints show that the dinosaur fauna in the Javelina Formation in the Dawson Creek area is latest Maastrichtian and restricted to chron C29r. Thus, the Javelina dinosaur fauna is correlative to the Hell Creek Formation dinosaur fauna from the Northern Great Plains, indicating differences between the faunas are not due to differences in age, and providing support for the hypothesis of provinciality and endemism in dinosaur communities in the late Maastrichtian. Further, the age constraints indicate that the previously documented mid-Maastrichtian and late Maastrichtian greenhouse events were rapid (<200 k.y.) and correlate closely with climate events documented in the marine record.

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