PALEOBOTANICAL OVERVIEW OF THE NESLEN FORMATION (LATE CRETACEOUS: CAMPANIAN) FROM THE BOOK CLIFFS OF EASTERN UTAH

The Neslen Formation in the Book Cliffs of eastern Utah preserves a Campanian age flora and fauna that lived along the eastern margin of Laramidia. Previous work on fossil assemblages from the Laramidian subcontinent have supported the presence of basin-scale endemism and/or provinciality in some vertebrate taxa. However, Laramidian floral biogeography is more poorly studied and does not appear to mirror the same provincial patterns.

In this contribution, we provide a paleobotanical overview of the Neslen Formation and identify plant fossils from localities previously collected by the Prehistoric Museum at Utah State University Eastern and the Denver Museum of Nature & Science. Approximately 500 fossil plant specimens have been analyzed and most have been morphotyped. Plant fossils were discovered in fine-grained sandstones, coalified shales, and mudstones using both traditional quarrying and surface collection techniques. Fossil leaves are classified using the morphotyping system. The paleobotanical diversity of this formation is growing, with two quarries containing over 30 morphotypes each.

So far, we have identified over 40 plant morphotypes from the formation. We identified multiple polypodipsoida, including Equisetum, an aquatic fern in the genus Hydropteris, and at least three other fern morphotypes. Gymnosperms include the genera Metasequoia, Araucaria, and Protodammara. Though many localities consist of over 60% gymnosperms, two recently discovered sites are dominated by angiosperm fossils. Angiosperms are a diverse component of the flora in the Neslen Formation, with both terrestrial and aquatic taxa present. These include the floating aquatic monocot Cobbania, the palm Sabalites, and the terrestrial dicot “Ficus” planicostata. Those taxa are commonly found in other Laramidian floras as well. Other identifiable genera include Paleoaster, Paleonelumbo, Brassenites, and Gunnera. Overall, preservation of plants within the Neslen Formation is patchy and rare. Inconsistencies in preservation raise questions about plant transport and preservation bias within the formation across different groups of plants.