Biostratigraphically significant palynofloras from the Paleocene–Eocene boundary of the USA

Abstract

Pollen and spores were recovered from the Paleocene Fort Union Formation and Paleocene–Eocene Willwood Formation of the Bighorn Basin (BHB), northwestern Wyoming, USA. In many local stratigraphic sections in the BHB, the base of the Eocene has been identified by the characteristic negative carbon isotope excursion (CIE) that marks the beginning of the Paleocene–Eocene Thermal Maximum (PETM). The palynotaxa from outcrop samples were examined using light microscopy (LM) and scanning electron microscopy (SEM). Seven new species are formally described (Tricolpites vegrandis, Rousea spatium, Striatricolporites astutus, Striatopollis calidarius, Friedrichipollis geminus, Retistephanocolporites modicrassus and Retistephanocolporites pergrandis). The temporal and geographic distributions of many of these palynotaxa suggest that hotter and more seasonally dry climates facilitated their northward range shifts during the PETM from the tropics or subtropics of the USA. For the temperate palynotaxa, the hotter and seasonally dry conditions resulted in local extirpation. A re-evaluation of the palynostratigraphic schemes established for the Paleocene–Eocene boundary confirms that the first appearance of Platycarya platycaryoides denotes the Paleocene–Eocene boundary in the Rocky Mountains region. A new Striatopollis calidarius Subzone, associated with early Wasatchian (Wa) Wa-0 and Wa-R faunas, is also recognized for CIE body localities in the BHB.

Keywords:

• Paleocene–Eocene
• PETM
• USA
• pollen
• spores
• taxonomy
• biostratigraphy

Acknowledgements

Scott Whittaker and Rina Morisawa of the Scientific Imaging Laboratory at the National Museum of Natural History, Smithsonian Institution, are thanked for their assistance in generating SEM images of the illustrated palynomorphs. Professor Steven R. Manchester of the Florida Museum of Natural History is thanked for providing slides of Landeenia pollen. Neil Campion and Petrostrat Ltd. are thanked for providing information on the occurrences of species along the Texas–Alabama Gulf Coast. Dr. Annette Götz is also thanked for providing a copy of the original Krutzsch (1959b) publication. Dr. Regan Dunn is thanked for her assistance with species identification.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Funding for this research was provided through a Smithsonian Institution Peter Buck Postdoctoral Fellowship Award to VAK. VAK is currently funded by the Elizabeth and Vernon Puzey Fellowship Award. PEJ and JG are currently funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under project numbers 443701866 and 444920835, respectively. DAW is funded by the US Geological Survey’s Land Change Science/Climate Research & Development Program. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.