BULKING-UP THE SAMPLE SIZE OF THE FIRST UINTA C MICRO-MAMMAL FAUNA FROM THE UINTA BASIN

A one-ton test bulk sample collected in 2007 confirmed the presence of micro-mammal remains at locality WU-26 (Washington University- 26). The site is stratigraphically located in the upper portion of the middle Eocene Uinta C member of the Uinta Formation in Uintah County, Utah. This is the first micro-mammal site discovered in the Uinta C member. Bulk samples collected in subsequent field seasons have enlarged the sample size and diversity and indicated that most micro-mammal remains are located in the green clays and not the red clays in the small lake deposit. The presence of a small omomyid primate not reported previously from the Uinta Formation suggests that published reports of primate species diversity declines from Uinta B to Uinta C resulted from insufficient collection techniques and not supposed climate deterioration. During the 2010 field season, the authors collected 5.3 tons of bulk sample from the green clay facies at WU-26. This volume was reduced to one-half ton through screen-washing in the Green River. Further treatment with varsol and re-screening will allow microscopic search and recovery of new micro-mammal remains. We expect to double the WU-26 micro-mammal sample size with the 2010 bulk sample.