diverse Arikareean (Oligocene) faunas in the world. The John Day Formation is composed of fossil-
bearing volcaniclastic sediments and tuff layers, many of which have been radiometrically dated. The
well-defined stratigraphy exposed in the John Day facies, along with the geologically short spans of time
between tuff layers, allows us to assign ages to the fossils found both in-situ and on the surface.
Microfossils, the fossilized remains of tiny organisms, represent populations of abundant small species,
which are often underrepresented in museum collections due to collection and preservational biases. In
the case of the John Day Formation, existing museum collections, including tens of thousands of
specimens, show a strong bias towards larger taxa. Screen washing sediments in fossiliferous units
helps to reduce these collection biases, providing a more complete picture of past ecosystems. A series
of screen washing experiments, involving different lithological units, wash methods, and chemical
treatments were undertaken to test the efficacy of screen washing John Day Formation strata.
Qualitative and quantitative analyses of these experiments has allowed us to develop a reliable screen
washing procedure, which has yielded a diverse assemblage of underrepresented specimens from the
region, and has proven to be an effective microfossil recovery method that can be utilized by the park.
These finds will aid current and future studies in biostratigraphy, paleoecology, and evolution.
(This is a Geocorps submission)
Preferred Presentation Type: Either Oral or Poster