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

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 (<i>Tricolpites vegrandis</i>, <i>Rousea spatium</i>, <i>Striatricolporites astutus</i>, <i>Striatopollis calidarius</i>, <i>Friedrichipollis geminus</i>, <i>Retistephanocolporites modicrassus</i> and <i>Retistephanocolporites pergrandis</i>). 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 <i>Platycarya platycaryoides</i> denotes the Paleocene–Eocene boundary in the Rocky Mountains region. A new <i>Striatopollis calidarius</i> Subzone, associated with early Wasatchian (Wa) Wa-0 and Wa-R faunas, is also recognized for CIE body localities in the BHB.

研究从美国怀俄明州西北部大角盆地（BHB）的古新世福特联合组以及古新世-始新世维尔伍德组中回收了花粉与孢子。在大角盆地的多处地层剖面中，可借助标志古新世-始新世极热事件（PETM）起始的典型碳同位素负偏移（CIE）来识别始新统底界。通过光学显微镜（LM）与扫描电子显微镜（SEM）对露头样品中的孢粉类群进行了检视。本文正式描述了7个新种：*Tricolpites vegrandis*、*Rousea spatium*、*Striatricolporites astutus*、*Striatopollis calidarius*、*Friedrichipollis geminus*、*Retistephanocolporites modicrassus*以及*Retistephanocolporites pergrandis*。多数孢粉类群的时间与地理分布表明，在PETM期间，更温暖且季节性更干旱的气候促使它们从美国的热带或亚热带区域向北扩张分布范围。而对于温带孢粉类群而言，温暖且季节性干旱的环境导致了它们的局部灭绝。对古新世-始新世界线孢粉地层学方案的重新评估证实，*Platycarya platycaryoides*的首次出现可作为落基山脉地区古新世-始新世界线的标志。此外，本次研究还在大角盆地的CIE赋存层位中识别出一个与早期瓦萨奇阶（Wa）Wa-0及Wa-R动物群相关的*Striatopollis calidarius*亚带。