RECONSTRUCTION OF THE LATE PALEOCENE CLIMATE USING FOSSILS FROM ALMONT, NORTH DAKOTA

The Sentinel Butte Formation near Almont, North Dakota is known for its exceptionally well-preserved Late Paleocene flora. The diverse flora, with over fifty genera, is encased in a brown to yellow-brown, siliceous shale. Angiosperms, such as Juglandaceae, Platanaceae, and Corylites, are common, as is Ginkgo. Gymnosperms are present, but less common. While much paleontological research has focused on the plant assemblages and their structure, little has been done to study the climate in which they grew. Previous comparisons of the Sentinel Butte fossil taxa to analogous modern plant and animal distributions suggest the Late Paleocene climate in the Almont, ND vicinity was warm temperate with a mesic moisture regime, not unlike modern-day southwestern China or the Carolinas in the southeastern USA. In order to more precisely ascribe climatic parameters, including mean annual temperature (MAT) and mean annual precipitation (MAP), to the terrestrial fossiliferous materials at the Almont site, we used leaf margin analysis following the method of Wilf (1997) as modified from Bailey and Sinnott (1916). Twelve genera of plant leaf fossils from the Sentinel Butte Formation, housed in the University of Wisconsin-Stevens Point collection, were used in the analysis. Our results indicate that the climate near Almont, ND in the late Paleocene was similar to that of the southeastern US or modern southwest China with a MAT of 19°C and a MAP of 110 cm. While our mean annual precipitation estimate might be low due to a bias of smaller leaves being more readily preserved compared to larger leaves, it is within the realm of moisture requirements for many of the modern members of the fossil genera present in the Almont sample.