LATE PALEOCENE PLANTS FROM NORTH DAKOTA: NEW LOCALITIES AND INSIGHTS FROM THE ALMONT FLORA

The Almont Flora of central North Dakota and equivalent Beicegal Creek floras in western North Dakota are among the best preserved and most diverse (50 genera in 20 families) assemblages of Late Paleocene fossil plants in the world. Fossils are preserved in siliceous shales that reveal both internal structure of fruits and seeds and outer surface features of plant organs. Fossil plants from the original Almont site, known for the past two decades, were recovered from subsurface deposits, making determination of stratigraphic relationships difficult. Investigations of additional sites from the Beicegal Creek area, including one outcrop with the siliceous shale in place, now enable correlation with other units and suggest a Tiffanian (Ti3-Ti5) age based on correlations with published freshwater molluscan and fossil mammals-bearing sites. Based on anatomy, these floras are significant for documenting the oldest reliable occurrences of Cornus (dogwood) and probably Acer (maple) in the fossil record. Mid-high latitude Northern Hemisphere Paleocene floras have typically been characterized as temperate, deciduous and relatively uniform in composition, dominated by such floristic elements as Ginkgo, taxodiaceous conifers, Betulaceae, Platanaceae, Trochodendraceae and Junglandaceae. The Almont and Beicegal Creek floras contain these elements but also document the early occurrences of families that are poorly known in the Paleocene but important in later Tertiary times (Actinidiaceae, Myrtaceae). Among these are the mostly herbaceous family Ranunculaceae which is rarely present in the fossil record prior to the late Neogene. Tropical taxa (Icacinaceae, Menispermaceae, Meliosmaceae) are also represented in these floras. The Almont and Beicegal Creek floras provide a snapshot of a pivotal moment of geologic time as the plants occurring well after the K/T boundary events and preceeding the dramatic changes of the Paleocene-Eocene thermal maximum.