Fig. 1

Map of continental Cretaceous-Paleogene boundary (KPB) locations in the Western Interior of North America with new KPB sections highlighted in red boxes (left panel) and typical KPB-coincident facies changes (right panel) (map from Ron Blakey [Deep Time Maps]; note that this artistic reconstruction is meant to illustrate major landscape features in the Western Interior near the KPB, not to imply support for landscape interpretations; see Supplementary Table 1 for a full list of KPB localities). The pie chart indicates the relationship between impact-identified KPBs and local facies changes. Despite being geographically and paleoenvironmentally disparate, most KPBs are previously recognized to coincide with a facies shift, either at a formational contact (red stars) or within a formation (yellow circles). In the right panel, note that the uppermost Cretaceous strata are dominated by overbank mudstone beds and thin fluvial-channel or crevasse-splay sandstone beds. In contrast, lowermost Paleogene strata are dominated by thick, cliff-forming sandstone beds representing multistoried fluvial-channel deposits (Raton and Bighorn basin panels) or thin, gently dipping, alternating mudstone-sandstone beds representing point-bar deposits (Williston Basin panels). Putative ‘exceptions’ to the KPB-coincident facies change (white-to-blue symbols), which we challenge below (see ‘Abiotic drivers are insufficient to explain KPB facies shifts’ section and Supplementary Discussion), are localities where reported KPBs lie within centimeters below an intraformational coal (a, white pentagon), atop a formation-defining coal (b, light-blue triangle), below a formation-defining coal (c, inverted royal-blue triangle), or within an intraformational coal (d, dark blue square). Note that in some places multiple KPBs have been reported from the same set of outcrops (see Supplementary Table 1). See main text and Supplementary Discussion for details. Photograph credit: PK (Raton Basin), LNW (Bighorn Basin, Hell Creek), TST (Mill Iron).