Pollen analysis of an early Pliocene lignite layer, Always Welcome Inn, Baker City, Oregon

Candice Burnette

Science Department, Badgley Hall, Eastern Oregon University, One University Boulevard, La Grande, OR 97850

ABSTRACT

              Gramineae (wild grass), Chenopodiaceae (Goosefoot family), Populus (cottonwood and quaking aspen), Ephedra (Mormon tea) and Pedicularis (lousewort) pollen found in a lignite layer at the Always Welcome Inn suggest an abundance of grassland vegetation, plus some shrub-bush steppe and sagebrush-steppe vegetation in the Baker City area during the early Pliocene.  The Always Welcome Inn pollen indicates that climate was dryer in the area during the early Pliocene that it was during the middle to late Miocene but not as dry as the sub-desert climate present in the area today.

INTRODUCTION

              The ~10 m thick sequence of early Pliocene (~4.8-4.3 Ma) diatomites, silts, volcanic ash, and fine-grained sands behind the Always Welcome Inn in Baker City, Oregon, has produced a wide variety of plant and animal fossils (Fig. 1, 2).  Fossils in the lower lacustrine part of the sequence includes fossils include diatoms, sponges, ostracods, bivalves, gastropods, charophytes, turtles, fish (sunfish and minnows), and the jaw of a beaver (Castor).  The upper fluvial part of the sequence has yielded fossil frogs and salamanders, snakes, fish (sunfish and suckers), birds, and small mammals (shrews, voles, pocket gophers, rabbits, beaver (Dipoides), and a grison).  Leaf fragments and small pieces of wood are common in the lower lacustrine part of the sequence, especially in two organic-rich lignite layers near the base of the sequence, but are too fragmented to identify what types of plants are present.

              The objective of this paper is to report the results of a pollen analysis of two samples from the lignite layer 0.7 m above the base of the Always Welcome Inn sequence.

Figure 1. Location of the Always Welcome Inn fossil site in Eastern Oregon.

Figure 2. Stratigraphy of the Always Welcome Inn sequence (modified from Van Tassell and others, 2007).

METHODS

              Two ~½ cm3 samples in volume were scraped off a sample of the lignite layer using a spatula.  These samples were placed in glass centrifuge tubes and were treated with a few ml of 10%HCl to remove carbonates from the samples.  When the reaction stopped, the tubes were centrifuged at 3,000 rpm for three minutes and the excess liquid was decanted.  Next a few ml of 10% KOH was added to the samples.  This solution was mixed on a vortex mixer, topped off with 10% KOH, and placed in a boiling water bath in a fume hood for 10 minutes (Fig. 3).  The residue was then washed through a 63 micron sieve using distilled water and the contents of the sieve were then washed with distilled water back into the centrifuge tubes and centrifuged again at 3,000 rpm for three minutes.  This procedure was repeated twice.  Next, the sample was treated to remove organic material by 1) adding 2 ml of glacial acetic acid, mixing on the vortex mixer, centrifuging at 3,000 rpm for three minutes, and decanting the liquid; 2) adding a 9:1 mixture of acetic anhydride and concentrated sulfuric acid a few ml at a time to the sample mix until each tube was about one-half full; 3) placing the tubes in a boiling water bath for no longer than 1-3 minutes;  4) Removing the tubes from the boiling water bath and immediately adding 2 ml of glacial acetic acid to neutralize the reaction; and 5) Centrifuging the mixture at 3,000 rpm for 3 minutes and decanting the liquid.  1 ml of 10% KOH and distilled water was then added to each tube and the liquid was decanted.  A portion of the remaining sample was then spread on a microscope slide, dried on a hot plate at low heat, and then a cover slip was applied using epoxy.

Figure 3. Dr. Abel Mendoza demonstrates how to use the vortex mixer (left); Pollen samples in the hot water bath (right).

Results

              A total of 196 pollen grains were identified on the two slides from the Always Welcome Inn lignite layer.  Five types of pollen were found in the samples.  Grasses make up the majority of the pollen; trees account for only 7 percent of the pollen (Table 1).

TABLE 1. POLLEN AND RHIZOPODS IN THE ALWAYS WELCOME INN LIGNITE LAYER

              Gramineae (wild grass) pollen is the most abundant pollen found in the Always Welcome Inn lignite layer.  There appear to be several types of grass pollen (Fig. 4).  Pollen of the Chenopodiaceae (Goosefoot family) is also present (Fig. 5).  This family includes saltbush and goosefoot, but members of this family are very difficult to separate without electron microscopy (Kapp, 1969).  Pollen that may have come from Populus (cottonwood and quaking aspen) and Ephedra (Mormon tea) were also found (Fig. 6).  Pollen from the lousewort Pedicularis was also identified (Fig. 7).

Figure 4. Gramineae (Grass family—Wild Grasses) pollen from the lignite layer.  Scale divisions are equal to 2 microns in all pollen photos in this paper.

Figure 5. Chenopodiaceae (Goosefoot family) pollen.

Figure 6. Salicaceae (Populus—Cottonwood or aspen) pollen (left) and Ephedraceae (Ephedra—Mormon tea) pollen (right)

Figure 7. Possible Pedicularis (Lousewort) pollen grain.

ENVIRONMENTAL INTERPRETATION

              Van Tassell and others (2007) suggested that the Always Welcome Inn sediments were deposited in an environment where a stream flowed into a lake.  Fish, salamanders and frogs, birds, and small mammals thrived along the lake and stream margins.  The pollen found in this study suggests an abundance of grassland vegetation, some shrub bush (Ephedra) steppe vegetation, and Populus (cottonwood and/or quaking aspen) trees growing in riparian areas where beaver (Castor and Dipoides) lived.  Some species of the lousewort Pedicularis are found in modern sagebrush-steppe plant communities (Hitchcock and Cronquist, 1973).

COMPARISON WITH OTHER SEQUENCES

              Plant fossils are well-documented in the middle and late Miocene sequences along the south flank of the Wallowa Mountains northeast of Baker City (Gilluly, 1937; Chaney, 1959; Hoxie, 1965).  The middle Miocene (14-16 Ma) Sparta flora includes a large number of deciduous trees and conifer, including Ginko.  The late Miocene (~9 Ma) Keating flora has fewer tree species compared to the Sparta flora, but many more than those recorded in the early Pliocene pollen sequence at the Always Welcome Inn (Table 2).  The pollen found in the Always Welcome Inn sequence indicates vegetation that was more similar to the modern sub-desert vegetation in the Baker City area, which contains a large percentage of grasses and some shrub-bush steppe vegetation (USDA, 1987), than to the vegetation that was present along the flanks of the Wallowa Mountains during the Miocene.  This reflects the overall drying of Eastern Oregon since the Miocene due to the uplift of the Cascade Mountains and global climate change.

              The pollen in the lacustrine and lower floodplain facies of the lower part of the early to late Pliocene Glenns Ferry Formation of the Lake Idaho sequence of the Snake River Plain of Idaho (Leopold and Wright, 1985) contains many of the species found in the Always Welcome Inn sediments.  Overall, vegetation indicated by the Always Welcome Inn pollen is more like that of the Glenns Ferry Formation than it is to the Miocene Sparta and Keating floras from the flanks of the nearby Wallowa Mountains.

TABLE 2.  COMPARISON OF THE PLANTS AND POLLEN FOUND AT THE ALWAYS WELCOME INN AND NEARBY AREAS

CONCLUSIONS

              Gramineae (wild grass) pollen is the most abundant pollen found in the Always Welcome Inn lignite layer.  Chenopodiaceae (Goosefoot family), Populus (cottonwood and quaking aspen), Ephedra (Mormon tea) and Pedicularis (lousewort) pollen were also identified.  The pollen found in this study suggests an abundance of grassland vegetation, plus some shrub-bush steppe and sagebrush-steppe vegetation in the Always Welcome Inn area.  The Always Welcome Inn pollen suite indicates vegetation more similar to that present in the western Snake River Plain during the deposition of the Glenns Ferry Formation than during the middle and late Miocene in the Keating area.

              Analysis of the pollen from samples from the Always Welcome Inn lacustrine and fluvial sequences in addition to those of samples from the lignite layer described in this study may help paint a clearer picture of the vegetation present in the Powder Valley and surrounding mountains during the early Pliocene.

ACKNOWLEDGMENTS

              My foremost thanks go to Dr Jay Van Tassell.  This paper would have not been possible without his inspiration and encouragement.  Special thanks go to Dr. Abel Mendoza for all his help in the lab.

REFERENCES CITED

Chaney, R.W., 1959, Miocene flora of the Columbia Plateau, part 1. Composition and interpretation:  Carnegie Institute of Washington Publication 617, p. 1-134.

Gilluly, J., 1937, Geology and mineral resources of the Baker quadrangle, Oregon:  U.S. Geological Survey Bulletin 879, 119 p.

Hitchcock, C.L. and Cronquist, A., 1973, Flora of the Pacific Northwest: An illustrated manual: Seattle, University of Washington Press, 730 p.

Hoxie, L.R., 1965, The Sparta flora from Baker County, Oregon: Northwest Science, v. 39, no. 1, p. 26-35.

Kapp, R.O., 1969, How to know pollen and spores: Dubuque, Iowa, William C. Brown,            249 p.

U.S. Department of Agriculture, 1987, Soil survey of Baker County area, Oregon, 341 p.

Van Tassell, J.; Bergey, E.; Davis, C.; Davis, M.; Grimshaw, B.; Kisselburg, J.; Ledgerwood, R.; Miller, S.; Morris, C.; Wehymiller, C.; Ferns, M.L.; Smith, G.R.; McDonald, H.G.; Mead, J.L.; and Martin, R.A., 2007, Early Pliocene               (Blancan) Always Welcome Inn local fauna, Baker City, Oregon: Oregon Geology, v. 68, no. 1, p. 3-23.