EXAMINING PALEOCLIMATE ACROSS THE CRETACEOUS-PALEOGENE (K/PG) BOUNDARY IN NORTHEASTERNMONTANA

The Cretaceous-Paleogene (K/Pg) boundary is marked by a major mass extinction resulting in global biotic turnover, notably the extinction of non-avian dinosaurs. Causal mechanism(s) of the mass extinction is believed to have been bolide impact, volcanism, climate change, or some combination thereof. The Hell Creek area in northeastern Montana contains some of the most well-studied vertebrate localities recording this mass extinction; however, very little is known about floral changes in this area. Plant fossils lend unique insight not only into the fate of vegetation at the K/Pg boundary, but also into the climate conditions in the lead up and immediate aftermath of the mass extinction. Here, we examine the hypothesis that regional climate change exacerbated the extinction magnitude at the K/Pg boundary and impacted the timing of recovery after the K/Pg mass extinction. We present preliminary results from a series of floras spanning approximately 2 m.y. around the K/Pg boundary to estimate paleoclimate conditions in this critical interval. We utilize the digital leaf physiognomy (DiLP) method in combination with univariate methods (i.e., leaf margin and area analyses) to estimate mean annual temperature and precipitation. We also compare this climate record to estimates of paleoclimate derived regionally (floral studies in North Dakota) and locally (clumped isotope paleothermometry) to evaluate and compare with our results. Our preliminary results indicate a temperate to tropical seasonal climate, with relatively warm conditions leading up to the K/Pg boundary. This is largely in agreement with previously reported local and regional patterns. However, we also examine climate in the early Paleocene, a previously unresolved time interval regionally. Our findings indicate that temperatures increased in the earliest Paleocene while communities were beginning to recover from the K/Pg mass extinction. These results give us insight into the role of climate change in the turnover and recovery of terrestrial plant communities at the K/Pg mass extinction. Information about paleoclimate conditions across the K/Pg boundary are crucial for resolving and interpreting patterns of terrestrial biotic community change during this interval.