Lauren O'Connor, Emily Dearing Crampton-Flood, Rhodri Jerrett, Gregory Price, B. David A. Naafs, Richard D Pancost, Paul McCormack, Aris Lempotesis-Davies, Bart van Dongen, Sabine Lengger

The Cretaceous-Paleogene (K-Pg) boundary marks one of the five major mass extinctions of the Phanerozoic. How the climate system responded to a bolide impact and extensive volcanism at this time over different timescales is highly debated. Here we use the distribution of branched tetraether lipids (brGDGT) from fossil peats at two sites in Saskatchewan, Canada (paleolatitude ~55°N), to generate a high-resolution (millennial) record of mean annual air temperature (MAAT) spanning the last ~4 ka of the Cretaceous and first ~30 ka of the Paleogene. Our study shows that MAATs ranged from 16–29°C, with the highest value in the first millennia of the Paleogene/ The earliest Paleogene averaged ~25°C—maintaining or enhancing warmth from the latest Cretaceous—followed by a general cooling to ~20°C over the following ~30 ka. No abrupt post-boundary cooling (e.g., an “impact winter”) or abrupt warming are evident in our data, implying that if such phenomena occurred, their duration was relatively short-lived (i.e., sub-millennial). Further, no long-term impact- or volcanism-driven warming is evident. The range of temperature change observed is considerably greater than that derived from marine proxy records over the same time interval. Our findings therefore more properly place bounds on the magnitude and duration of temperature change on land during this critical interval—the main setting for the demise of non-avian dinosaurs and the rise of mammals.