COMPARISON OF PLANT MACRO- AND MICROFOSSIL ASSEMBLAGES FROM THE MIDDLE EOCENE BITTER CREEK DELTA, WYOMING

The co-occurrence of plant macro- and microfossils in the Eocene Bitter Creek Delta provides the opportunity to describe and compare macro- and microflora assemblages recovered from the same rock unit to more accurately reconstruct the paleovegetation. Located approximately 40 miles east of Rock Springs, Wyoming, the Bitter Creek Delta is a Gilbert-type delta deposited in Lake Gosiute. The delta facies interfinger with the upper unit of the Laney Member of the Green River Formation. The delta complex progrades to the southwest and consists of well-defined bottomsets, topsets, and foresets of mudstone and very fine sandstone. The mudstone foreset beds contain abundant plant macrofossils, mostly consisting of dense plant debris. Rock samples from the same units have yielded abundant plant microfossils. This study hopes to avoid potential biases introduced by using only the macro- or microfossil record for paleovegetational reconstruction. Preliminary palynological data include the following taxa: Local Palynoflora – Pediastrum, Micrhystridium, and Pandaniidites; Extralocal Palynoflora – Laevigatosporites, Deltoidospora, Lygodiumsporites, Taxodiaceaepollenites, Alnipollenites, Momipites, Caryapollenites, and Ulmipollenites; Regional Palynoflora – Ephedripites, Pinuspollenites, Tsugapollenites, Podocarpus, and Quercuspollenites. In contrast, preliminary data for the macroflora includes: Local Flora – Typha and Equisetum; Extralocal Flora - Lygodium, Allophylus, Populus, Salix, Alnus, Platanus, Celtis, Anemia, Carpinus, and Cercidiphyllum. No elements of the regional flora have been discovered. Preliminary comparison between the macrofloral and microfloral records illustrates the importance of using both types of floral data when attempting paleovegetational reconstruction.