Cretaceous–Palaeogene Boundary Events in Texas: New Sections, Revised Micropalaeontological Interpretations, and Clarification of the Stratigraphy

Recent fieldwork (2009–2012) in the Brazos River area, Falls County, Texas, has resulted in the discovery of a number of new exposures that have allowed a reinterpretation of the Cretaceous–Palaeogene boundary events. Our data indicate that there was a single impact event with the seismic shock and resulting tsunami eroding the uppermost Maastrichtian surface, prior to the deposition of a number of storm-generated sandstones, the lower of which contains altered spherules, shell fragments, ichthyolith debris, and reworked microfossils. The overlying lower Palaeocene succession of mudstones and siltstones was deposited in a midshelf setting that is quite similar to that of the preceding uppermost Maastrichtian. The lower Palaeocene appears to record a Milankovitch cyclicity and, potentially, the Dan-C2 hyperthermal event.