SEMI-QUANTITATIVE ANALYSIS OF THE DISTRIBUTION OF FOSSILS IN THE UPPER THIRD OF THE ALWAYS WELCOME INN SEQUENCE, BAKER CITY, OREGON
Jayson Kisselburg
Science Department, Badgley Hall, Eastern Oregon University, One University Boulevard, La Grande, OR 97850-2899, USA; kisselj@eou.edu
ABSTRACT
Semi-quantitative sampling of the floodplain and stream deposits in the upper third of the Always Welcome Inn fossil sequence in May and June 2006 yielded over 200 fossils. 40% of the fossils are the spines, vertebrae, scales, and bones of the skull of a new species of the sunfish, Archoplites. Another 40% of the collection consists of frog and salamander bones, including several different kinds of vertebrae and possible fibula, femur, pelvic, pectoral girdle, and skull bones. 8% of the fossils are root casts. A trough cross-bedded silty sand layer at 6.75-7 m above the base of the sequence yielded the majority of the frog and salamander fossils, plus two molars of a microtine rodent that resemble the teeth of the vole Transitional Mimomys sawrockensis-taylori reported from the Ellner locality of the 3.9 m.y. old Blufftop fauna of the Ringold Formation in Washington. If this is the rodent species present, it confirms the Pliocene (Blancan) age of the Always Welcome Inn fossil sequence.
Keywords: Fossils, Fish, Frogs, Salamanders, Voles, Pliocene, Blancan.
INTRODUCTION
There have been many exciting new fossils discovered in the outcrop of Pliocene sediments behind the Always Welcome Inn in Baker City, Oregon, since fossils were first discovered there in May 2002. The lower 7 m of the sequence contain three units of diatom-rich shallow lake and lake margin sediments alternating with massive laminated silts. These sediments have yielded abundant fish (a new species of Archoplites which most closely resembles the Archoplites species in the Ringold Formation of Washington), gastropods and bivalves (Gyraulus, Pisidium, Sphaerium, lymnaeids, and others), turtle shell fragments, a bird bone, plant fragments (reeds and rushes), planktic freshwater diatoms, and sponge spicules. The upper 3 m of the section includes stream channel and floodplain deposits, including laminated and trough cross-bedded sandy silts and sands that have produced the tooth of a large minnow (Acrocheilus), frog and salamander bones, the tooth of a beaver (Dipoides vallicula), the incisor of a muskrat (Pliopotamys?), the incisors and a molar of an arvicoline rodent, the incisor of a small carnivore, and root casts (Steele, 2004; Davis and others, 2005; Eastern Oregon University Historical Geology class, unpublished data, 2006). The beaver tooth suggests a late Miocene to earliest Pliocene age for the sequence, slightly older than the early Pliocene age suggested by Brooks and others for the sequence that includes the Always Welcome Inn section (1976). The discovery of two incisors and a broken molar of a small arvicoline rodent in the sequence in 2005 opened up the possibility of determining the age of the sequence more accurately, but it was not possible to identify the species of rodent without additional material.
The author and Jay Van Tassell, geology professor at Eastern Oregon University, went to collect fossils from the Always Welcome Inn site on May 25th and June 1, 2006 with two primary objectives: 1) to find additional rodent teeth that might facilitate identifying which species of rodent is present and help determine the age of the sequence, and 2) to locate the layer(s) that contained the greatest abundant of fish, frogs and salamanders, and mammal bones and teeth.
METHODS
Samples were collected at the Always Welcome Inn site at 0.25 m intervals starting at 6 m and ending at 9 m above the base of the section. Each sample consisted of ~0.01 m3 (0.5 ft3) of sediment. The sediment was sieved through 1.5 mm mesh screens and the fossils were picked out and put into labeled containers. After the initial sampling yielded a rodent tooth in the 6.75-7 m interval, additional fossils were sieved from this layer. The fossils were taken back to the laboratory, washed, examined and sorted using a Leica Zoom 2000 binocular microscope, and the numbers of fish bones, frog and salamander bones, plants and root casts, and rodent teeth in each interval were recorded.
RESULTS
The 6-9 m interval of the Always Welcome Inn section yielded a total of 167 fossils (Tables 1 and 2). The fish fossils that were found include spines, vertebrae, a maxilla, a lachrymal, and scales of the sunfish, Archoplites (a new species; Jerry Smith, written communication, April 2006). Based on comparison with the diagrams in Duellman and Trueb (1986), the frog and salamander bones appear to include several different types of vertebrae and possible fibula, femur, pelvic and pectoral girdle, and skull bones. The plants consist of fragments of reeds and rushes, some of which show signs of flattening and segmentation. The layer between 6.75-7 m yielded two rodent teeth. One of these is a three-rooted upper right third molar of an adult. The second is a two-rooted lower left second molar of a young adult (Fig. 1). Based on comparison with the rodent teeth illustrated by Hibbard (1941) and Zakrzewski (1967), Jay Van Tassell has tentatively identified these teeth as the molars of the vole, Transitional Mimomys sawrockensis-taylori illustrated by Repenning (2002; Ophiomys cf. mcknightii of Gustafson, 1978).
The quantitative sampling of the sequence showed that fish fossils and frog and salamander bones occur in approximately equal quantities and are the dominant fossils in this part of the Always Welcome Inn section (Table 1). The fossils are not uniformly distributed in the sequence. Where salamander fossils were abundant (8.0-8.5 m), fish fossils were less common and in intervals with abundant fish fossils (6.0-6.25 m, 6.75-7 m, 7.25-7.5 m, 7.75-8 m), frog and salamander bones were not abundant. Root casts are only abundant in the lower part of the sequence (6-6.25 m) and rodent teeth were only found in a layer between 6.75-7 m, the same interval that produced the rodent teeth that had been found previously. This layer consists of trough cross-bedded silty sands.
Bulk sampling of the interval where the rodent molar was found during the quantitative sampling (6.75-7 m) yielded a total of 146 fossils, which included 65 frog and salamander bones and 55 fish bones, plus plant fragments and an additional rodent tooth (Table 2). Fish fossils and salamander and frog bones make up 40% of the fossils collected from this interval. Approximately 10% of the fossils are plants and rodent teeth make up 1% of the fossils that were found (Fig. 2). The sampling showed that the fossils were not evenly distributed, but instead were concentrated in pockets scattered across the width of the layer.
Sunfish (Archoplites) Salamander and Frog
Plants
Teeth of a primitive vole
Figure 1. Fossils from the Always Welcome Inn site. Scale in mm.
Table 1
Fossils Found in ~0.01 Cubic Meter Samples Collected in 0.25 m Intervals in the Upper Third of the Always Welcome Inn Fossil Sequence
Sample |
Fish |
Frog/ Salamander |
Rodent |
Plants |
Other |
|
AW 8.75 – 9.0 |
6 |
2 |
0 |
0 |
0 |
|
AW 8.5 – 8.75 |
6 |
0 |
0 |
0 |
0 |
|
AW 8.25 – 8.5 |
0 |
23 |
0 |
0 |
0 |
|
AW 8.0 – 8.25 |
0 |
25 |
0 |
4 |
0 |
|
AW 7.75 – 8.0 |
8 |
0 |
0 |
2 |
5 |
|
AW 7.5 – 7.75 |
0 |
0 |
0 |
0 |
0 |
|
AW 7.25 – 7.5 |
21 |
0 |
0 |
0 |
7 |
|
AW 7.0 – 7.25 |
0 |
4 |
0 |
0 |
0 |
|
AW 6.75 – 7.0 |
12 |
2 |
1 RM-3 |
2 |
4 |
|
*AW 6.50-6.75 |
1 |
13 |
0 |
2 |
1 |
|
*AW 6.25-6.50 |
2 |
0 |
0 |
0 |
0 |
|
*AW 6.00-6.25 |
11 |
0 |
0 |
22 |
8 |
|
Total |
67 |
77 |
2 |
32 |
25 |
Total203 |
Total Percent |
33% |
38% |
1% |
16% |
12% |
100% |
Sample Collection - May 25, 2006 / *June 1, 2006
TABLE 2
Fossil abundance in the 6.75-7 m interval of the Always Welcome Inn Fossil Site
|
||||||
Fossil |
Quantitative Survey |
Bulk Sampling |
Total Abundance |
Percentage |
||
Fish |
12 |
55 |
67 |
40.1% |
||
Frog/Salamander |
2 |
65 |
67 |
40.1% |
||
Rodent |
1 |
RM3 |
1 |
LM2 |
2 |
1.2% |
Plant |
2 |
12 |
14 |
8.4% |
||
Other |
4 |
13 |
17 |
10.2% |
||
TOTAL |
21 |
146 |
167 |
100% |
||
~Sample Taken from Trough Cross-Bedded Silt/ Silty Sandstone layer
Figure 2. Relative abundance of the different fossil types in the 6.75-7 m interval of the Always Welcome Inn fossil sequence.
Discussion
The results of this study help confirm Davis and others' (2005) suggestion that the upper third of the Always Welcome Inn sequence includes stream channel and floodplain deposits. It seems likely that the climate was wetter than at present and that the landscape included numerous small lakes and ponds that fluctuated in depth due to climate changes. The interfingering of layers of sediments rich in fish fossils with other layers rich in frogs and salamander bones may be the result of stream channels migrating across the floodplain or they may be due to changes in the environments of deposition as climate fluctuated.
The abundance in some layers of the sunfish Archoplites, a rockfish that resides close to lake and river shorelines, and salamanders, along with the beaver and muskrat that have been found during previous studies, that live on the reeds and plants that bordered the shore and in floodplain marshes could be the result of due storm surges or floodwaters washing bones and plant fragments onto the floodplain. Another possibility is that these may be death assemblages, where all the fish, amphibians and mammals died in the same location, but the presence of trough cross-bedding argues for transportation away from the areas where death occurred.
The Always Welcome Inn molars somewhat resemble the primitive vole, Ogmodontomys poaphagus, has been found in Kansas, Nebraska and Indiana (Hibbard, 1941, 1950, 1956; Zakrzewski, 1967; Martin, 1975, 2003), Arizona (Czaplewski, 1990), Texas (Dalquest, 1978), but are more similar to the 3.9 m.y. old Transitional Mimomys sawrockensis-taylori from the Blufftop Formation in Washington. This helps confirm that the Always Welcome Inn sequence was deposited during the Blancan Mammal Age approximately 4.9 to 1.8 million years ago.
Conclusions
This study has confirmed that sunfish, frog, salamander, and plant fossils are common in the upper third of the Always Welcome Inn fossil sequence. They are especially abundant in cross-bedded silty sand and laminated sandy silt layers, where they are concentrated in pockets. This suggests that they were washed into the area by floods. Rodent fossils are rare, but two new teeth were found that may be from the vole Transitional Mimomys sawrockensis-taylori. If true, this would indicate that the sequence is Pliocene (Blancan) in age.
Further investigations of the fossil-rich layers in the upper part of the Always Welcome Inn sequence may uncover more mammal fossils and help better pin down the age of the outcrop and the nature of the environments and climate in the area at the time of deposition. Quantitative studies of fossil abundances in the lower two-thirds lacustrine portion of the Always Welcome Inn sequence would be of great value. The more fossils we find, the more we will know about the Always Welcome Inn outcrop and its geologic history.
ACKNOWLEDGMENTS
I would like to thank the Langrell family, the owners of the Always Welcome Inn, for allowing this study to occur and Dr. Jay Van Tassell, Professor of Geology at Eastern Oregon University, for helping me collect samples, analyze them in the laboratory, and editing this manuscript. I would also like to thank Dr. Van Tassell and Dr. Bob Hornvedt, Professor of Geology and Dean of Students at Colorado Northwestern Community College for making geology more fantastic over the years than I could ever have imagined. Thank you to all who have encouraged me over the years to open my eyes to the wonderful world of physical science.
REFERENCES CITED
Brooks, H.C., McIntyre, J.R., and Walker, G.W., 1976, Geology of the Oregon part of the Baker 1º x 2º quadrangle: Oregon Department of Geology and Mineral Industries GMS-7, 1:250,000.
Czaplewski, 1990, The Verde local fauna: Small vertebrate fossils from the Verde Formation, Arizona: San Bernardino County Museum Quarterly, v. 37, no. 3, p. 1-39.
Dalquest, W.W., 1978, Early Blancan mammals of the Beck Ranch local fauna of Texas: Journal of Mammalogy, v. 59, no. 2, p. 269-298.
Davis, C., Bluhm, L., Killgore, K., Kisselburg, J., Ledgerwood, R., Starner, K., Zolotoff, N., Van Tassell, J., Ferns, M.L., and Smith, G.L., 2005, Fossils, stratigraphy, and structure of the Always Welcome Inn outcrop, Baker City, Oregon: Geological Society of America Abstracts with Programs, v. 37, no. 6, p. 8.
Duellman, W. and Trueb, L., 1986, Biology of the Amphibians: Boston, McGraw-Hill, p. 335-365.
Hibbard, C.W., 1941, New mammals from the Rexroad fauna, upper Pliocene of Kansas: American Midland Naturalist, v.
26, no. 2, p. 337-368.
Hibbard, C.W., 1950, Mammals of the Rexroad Formation from Fox Canyon, Meade County, Kansas: University of Michigan Contributions of the Museum of Paleontology, v. 8, no. 6, p. 113-192.
Hibbard, C.W., 1956, Vertebrate fossils from the Meade Formation of southwestern Kansas: Papers of the Michigan Academy of Science, Arts, and Letters, v. 41, p. 145-203.
Martin, L.D., 1975, Microtine rodents from the Ogallala Pliocene of Nebraska and the early evolution of the Microtinae in
North America, in Hibbard, C.W., Smith, G.R., and Friedland, N.E., eds., University of Michigan Papers in Paleontology
no. 12, Studies on Cenozoic Paleontology and Stratigraphy in Honor of Claude Hibbard, p. 101-110.
Gustafson, E.P., 1978, The vertebrate faunas of the Pliocene Ringold Formation, south-central Washington: University of Oregon Museum of Natural History Bulletin 23, p. 1-62.
Martin, R.A., 2003, Biochronology of latest Miocene through Pleistocene arvicolid rodents from the central Great Plains of North America: Coloquios de Paleontologia, v. 1, p. 373-383.
Martin, R.A., Honey, J.G., Palaez-Campomanes, Goodwin, H.T., Baskin, J.A., and Zakrzewski, R.J., 2003, Blancan
lagomorphs and rodents of the Deer Park assemblages, Meade County, Kansas: Journal of Paleontology, v. 76, no. 6, p.
1072-1090.
Repenning, C.A., 2003, Chapter 17 Mimomys in North America: Bulletin American Museum of Natural History, no. 279, p.
469-512.
Steele, J., 2004, Fish and other fossils of the Always Welcome Inn outcrop, Baker City, Oregon: Unpublished senior thesis, Eastern Oregon University, 5 p.
Zakrzewski, R.J., 1967, The primitive vole, Ogmodontomys, from the Late Cenozoic of Kansas and Nebraska: Papers of the Michigan Academy of Science, Arts, and Letters, v. 52, p. 133-150.
Back to Eastern Oregon Geology home page