EARLY FLUVIAL (CATHEDRAL BLUFFS) DEPOSITION INTO A LACUSTRINE BASIN (GREEN RIVER) AND THE RESULTING PRESERVATION OF AN UNUSUAL TERRESTRIAL VERTEBRATE ASSEMBLAGE, HONEYCOMB BUTTES, WYOMING
Detailed biostratigraphic analyses of the South Pass section show that the basal Cathedral Bluffs deposits along the outcrop belt are uniformly early Bridgerian (Br1a, Lower Palaeosyops fontinalis Assemblage Zone) in age. In addition, the preserved vertebrate assemblages have a distinctive, Basin-Margin nature to them in that they are characterized by high taxonomic diversity, unique species, and the co-occurrence of presumed ancestor-descendant species couplets.
A modest vertebrate assemblage (125 specimens) has been recovered from the early Cathedral Bluffs deposits at the eastern end of Honeycomb Buttes. The assemblage differs in a number of ways from the typical Br1a Basin-Margin assemblages of South Pass, most notably the occurrence of Basin-Center species of turtles, crocodilians, and Brachianodon. These difference may be due to the earlier deposition of the Cathedral Bluffs in this area leading to the preservation of a basal Bridgerian (Br0, Eotitanops borealis Assemblage Zone) assemblage and/or the preservation of a Basin-Center Br1a assemblage before typical Basin-Margin conditions developed on the flank of the still-active Wind River Uplift. Since the two brontothere specimens collected thus far cannot be assigned with certainty to either Palaeosyops or Eotitanops, the precise age determination of this assemblage awaits collection of more diagnostic material.