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Michael
D. Nowak, Fossil Pollen Diversity and Paleoecology of Two Late Paleocene Shales
from North Dakota: Does the Fossil Pollen Record Offer a Window into
How Global Climate Change is Working? This research investigates the dispersed pollen (palynoflora) that was isolated from two Late Paleocene fossil plant localities (Almont and Kate’s Butte) using standard palynological procedures (Traverse 1988). The two localities share a unique silicified lithology, and a similar stratigraphic position in the Fort Union Formation of western North Dakota. Images of pollen grains were captured with light microscopy and scanning electron microscopy for identification. The two localities have a palynofloral composition indicative of a warm temperate to subtropical climate, including representatives of the Juglandaceae, Betulaceae, Buxaceae, Taxodiaceae, Hippocastanaceae, Gentianaceae, and several other families. This is consistent with the present theory of rapid warming in the northern latitudes of North America culminating in the Paleocene/Eocene Thermal Maximum (Harrington 2001). The two localities in question are almost identical in megafossil composition (Crane et al 1991), yet they are over one hundred miles apart. The goal of this research is to quantitatively compare the two localities on the basis of palynofloral diversity, in order to clarify their relative stratigraphic position and degree of ecological similarity. Preliminary work has included a complete photographic and systematic compilation of taxon diversity at each site. Also a Morisita’s Index based upon preliminary relative abundance data collected from successive five hundred pollen grain counts from each site was accomplished. The Morisita’s Index of 48.55%, indicates that taxon diversity between the sites is very similar. By analyzing the relative abundance of several biostratigraphically important taxa (Pocknall 1987, Pocknall & Nichols 1996), it was found that the Kate’s Butte locality is somewhat younger than the Almont locality, and may lie very near the Paleocene/Eocene boundary. This is significant because the stratigraphic relationship of the two sites could yield quantitative data showing the temporal response of vegetation to rapid warming near the Paleocene/Eocene Thermal Maximum. This study of a rapid warming event in the past and its effect on plant communities may give insight into the effects of global warming today. Future work will concentrate on an intensive quantitative survey of the Almont palynoflora in an attempt to identify small ecological changes that may be recorded in the several feet of silicified sediment preserved there. Works Cited Crane, P.R., S.R.
Manchester, and D.L. Dilcher 1991. A preliminary survey of the fossil leaves and
well-preserved reproductive structures from the Sentinel Butte Formation
(Paleocene) near Almont, North Dakota. Fieldiana, Geology, no. 20, pub.
1418, FMNH, Chigago. Harrington, G. J., 2001, Pollen assemblages and Paleocene-Eocene Stratigraphy in the Bighorn and Clarks Fork Basins. In: Paleocene-Eocene Stratigraphy and Biotic Change in the Bighorn and Clarks Fork Basins, Wyoming (P.D. Gingerich, ed.) University of Michigan Papers on Paleontology, 33: 89-96 (2001) Pocknall, D.T., 1984, Palynomorph Biozones for the Fort Union and Wasatch Formations (upper Paleocene-lower Eocene), Powder River Basin, Wyoming and Montana, USA. Palynology, v.11, p.23-35. Pocknall, D.T., and Nichols, D.J., 1996, Palynology of coal
zones of Tongue River Member (upper Paleocene) of the Fort Union Formation,
Powder River Basin, Montana and Wyoming. AASP Contributions number 32 Traverse, A. 1988. Paleopalynology. Unwin Hyman, Boston. 600pp. |