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Three palynological assemblage zones, based on two major floral changes, are established within the upper Lance (Late Cretaceous) and Fort Union (Paleocene) Formations in and adjacent to the type Lance area in southeastern Wyoming. The lower palynological change essentially coincides with the Cretaceous-Paleocene (Maestrichtian-Danian) boundary, which is based on the vertebrate, fossil leaf, and foraminiferal evidence of previous workers. The upper palynological change occurs in the lower part of the Lebo Shale Member of the Fort Union Formation.

The oldest palynological assemblage (Assemblage A) is of Maestrichtian age and is characterized by diverse and abundant angiosperm pollen, particularly species of the genera Gunnera, Proteacidites, Aquilapollenites, and Cranwellia. The middle assemblage (Assemblage B) is, in part, of Danian age and is composed mostly of fern and moss spores and small tricolpate and tricolporate angiosperm pollen. The youngest assemblage (Assemblage C) is of Paleocene age and consists primarily of taxodiaceous-cupressaceous pollen with secondary but significant quantities of betulaceous and juglandaceous pollen.

These defined floral assemblages occur regionally and are considered to be synchronous. The Assemblage A-Assemblage B boundary coincides with the Hell Creek (Lance) -Fort Union contact in the Cave Hills area of South Dakota (Stanley, 1965; this study), in the type area of the Hell Creek Formation in Montana (Norton, 1963; Tschudy, 1968, oral commun.), and in the type area of the Cannonball Member of the Fort Union Formation in North Dakota. The Assemblage B-Assemblage C boundary occurs in the lower part of the Tongue River Member of the Fort Union Formation in the type Cannonball area and in the lower Fort Union Formation in central and western Wyoming.

Occurrences of Assemblage B in the lower Tongue River Member in the Cave Hills and type Cannonball areas of northwestern South Dakota and central North Dakota indicate that the lower Tongue River in these areas is older than the lower Tongue River in the Powder River Basin of Wyoming.

Two new genera, Maceopolipollenites and Insulapollenites, and sixteen new species have been described, and the generic description of Kurtzipites has been emended.

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