The Cretaceous-Paleogene contact in the Tornillo Group of Big Bend National Park, West Texas, USA

Abstract The Cretaceous-Paleogene (K-Pg) contact interval is constrained by vertebrate fossil sites at seven in the Tornillo Group and lies within an 80–100-m stratigraphic section between top of Javelina Formation base “log jam sandstone” marker bed Black Peaks Formation. In western exposures this interval, highest occurrence situ dinosaur specimens lowest Paleocene mammal are separated unusual conglomerate bed. This thin coincides with Cretaceous Paleogene strata contains reworked fossils. It superficially similar to beds elsewhere attributed effects tsunamis generated Chicxulub impact; however, maximum depositional age ca. 63 Ma based on detrital zircons indicates that was deposited about three million years after K-Pg boundary event. mammalian fossils from immediately above represent a fauna can be no older than middle Torrejonian (To2 zone). therefore disconformal represents hiatus least years. A condensed occurs westernmost exposure contact, where 80 m absent below bed; these present farther east. likely records erosional event resulting uplift deformation nearby Terlingua monocline. Although poorly fossiliferous, several clearly indicate entire Late age. There compelling evidence for preservation horizon any Group, so represented Cretaceous/Paleocene here also includes some part latest time. Mammalian sandstone,” ~40 sites, early Tiffanian (Ti1 Latest (To3) have not been recognized, second disconformity