PALEOBOTANY OF THE SYKES MOUNTAIN FORMATION (EARLY CRETACEOUS), BIGHORN BASIN, SHELL, WYOMING

This study analyzed plant remains from the Sykes Mountain Formation (Cretaceous Albian) in order to better characterize its paleoenvironment. The Sykes Mountain Formation consists of transitional marine to marine mudstone and sandstone deposits. The primary study area is located at the eastern margin of the Bighorn Basin, several miles north of Shell, Wyoming, in a seven meter thick mudstone unit. The macrofossils found in the quarry range from ferns and fern-like foliage to conifer needles and woody material. Several specimens of petrified wood were also collected from this site as well as another location in the formation. Preliminary identifications of the plant macrofossils have yielded fossil ferns from several different families, possibly Matoniaceae and Gleicheniaceae, and three different possible angiosperm leaves. Because ferns as well as many deciduous trees prefer wetter environments, they help support the mudstone evidence for a swampy, transitional marine environment. The fragmented plant debris fossilized on top of one another shows that the material was transported for a distance as well. The paleobotanical study of the Sykes Mountain Formation will help create a more accurate picture of the paleoenvironment for the Early Cretaceous of this region. The possible angiosperm leaf fossils are significant because angiosperms first appeared in the Early Cretaceous. This study may yield new species for this time period and extend downward the range of already known species or genera. Thin sections of the petrified wood samples will be used to determine the wood type, deciduous or coniferous. Previous work done in the area has yielded coniferous specimens, however deciduous wood has yet to be recognized, which would be significant.