59th Annual Report on Research 2014

Field work at the WU-26 fossil locality in the Uinta Basin in northeastern Utah was conducted in July & August of the 2013 field season. Four undergraduate and one graduate student assisted P. I. Westgate in the field. A total of two tons of bulk sample was removed from the 15 cm-thick target horizon in the WU-26 quarry. WU-26 lies in the upper part of the Uinta C Member of the Uinta Formation approximately 40 m. below the basal sand channels of the Brennan Basin Member of the Duchesne River Formation. The bulk sample was screen-washed in the Green River using 500 micron mesh bags and reduced to a concentrate of about 250 kg.

The concentrated sample was taken to the Paleontology Lab at Lamar University for further processing during the fall of 2013 and spring of 2014. Samples were processed by four part-time Geology major assistants. This involved microwave oven drying of the sample, overnight soaking in naptha, draining off the naptha, then overnight soaking in water. This process reduced sand-sized lithic claystone fragments to clay-sized particles. Samples were then screen-washed using screens with a 500 micron mesh. Clay, silt and fine sand passed through the screens and the field concentrate was reduced in volume by about 95%. After drying, the reduced samples were sorted by size using stacked Standard screens with mesh sizes of 707 microns, 850 microns, 1.0 mm, 1.4 mm, 2.0 mm, 2.8 mm & 4.0 mm. Fractions 2 mm and larger were sorted for fossils using the naked eye, while fractions smaller than 2 mm were processed using binocular microscopes.

Fig. 1. Student crew collecting WU-26 bulk samples.

In October, 2013, undergraduate student Christine Gartner and P. I. Westgate presented a progress report on our work at WU-26 at the Geological Society of America conference in Denver (Westgate, Townsend, Cope & Gartner, 2013). In November, 2013, two students who were part of the 2013 field crew, Christine Gartner and Erica Lassen, presented the results of our 2012 field season at the Sigma Xi Student Research Conference, Undergraduate Division, in Raleigh, NC (Gartner, Lassen & Westgate, 2013). They were awarded 1^st place prizes in the GeoScience Section. In February, 2014, P. I. Westgate presented research on the diversity of omomyid primates from the WU-26 locality at the 10^th North American Paleontology Convention in Gainesville, FL (Westgate, Cope & Townsend, 2014).

Fig. 2. Loading samples for screen-washing.

Fig. 3. Student crew reducing bulk samples in the Green River.

Prior to collecting new samples, the 2014 field crew comprised of four undergraduate students was shown the regional middle Eocene stratigraphic setting in the Uinta Basin via driving a north-south transit (opposite dip) through the basin and stopping at key outcrops to see the lithologic differences between the lacustrine Green River Formation; and fluvial deposits of the Uinta Formation Members A, B & C; and the fluvial Duchesne River Formation. As part of the regional geologic setting survey, we also examined Mesozoic sedimentary rocks in nearby Dinosaur National Monument.

The crew then excavated a 1400 kg bulk sample from WU-26. It was screen-washed in the Green River and reduced to 90 kg. The field crew also participated in a survey for additional potential micro-mammal sites in Uinta B. We collected a 900 kg bulk sample from the new H2 locality which lies near the top of the Uinta B Member. The presence of numerous large Amia vertebrate and Lepisosteus scales is evidence of standing water, so the site had similar conditions to those which existed at WU-26 and suggests potential for bearing micro-mammal remains. We also collected a test bulk sample of 100 kg from a stratum exposed at WU-2. These bulk samples from the new localities will be processed after the WU-26 sample.

Fig. 4. Stratigraphic location of the WU-26 locality near the top of Uinta C.

Results       

The processed sample collected during the 2013 field season at micro-mammal locality WU-26 increased the sample size collected from the site by about 40% and now totals more than 500 mammal specimens. Approximately 60% are rodents, 10% primates, 10% insectivores, 10% other placental mammals, and 10% are marsupials. Primate diversity is as high or higher than that known for all of the localities known from Uinta B. WU-26 is the first known Uinta C micro-mammal site and provides a unique glimpse into the mammal community which inhabited the Uinta Basin near the end of deposition of the Uinta Formation. Individual speciesÕ sample sizes are approaching the level where biostatistical analyses may be run with confidence in their results.

Students have benefitted from this research in multiple ways. They have learned many new paleontologic and stratigraphic field and lab techniques which are not taught in typical university courses. They have also learned to think as researchers and not just classroom students. And some have added publications to their resumes, which will be a plus in applying to graduate school. Project progress has brought the P. I. closer to the point where detailed manuscripts on the WU-26 fauna will be produced.