Detailed palaeontologic and taphonomic techniques to reconstruct an earliest Paleocene fossil flora: An example from southwestern North Dakota, USA

In a biostratigraphical prospective, the specimens recovered represent a low-diversity Fort Union flora composed exclusively of dicots that do not exist in the Hell Creek Formation. Preliminary palynological analysis reveal a Cretaceous age for the entire stratigraphic section, implying that the studied leaf mat is part of the FU0 megafloral zone (as defined by the occurrence of a Fort Union flora with Cretaceous palynomorphs). However, this Cretaceous age attribution for the entire section is questioned due to the occurrence of Paranymphaea crassifolia (part of the Paleocene FUI megafloral zone) within another leaf mat located 266 cm above the base of the coal representing the formational contact, and the occurrence of Paleocene PU1 mammals, reported from sediment within the leaf block interval.