THE OLIGOCENE MARINE MOLLUSCAN FAUNA OF THE EUGENE FORMATION IN OREGON

124 pagesTuffaceous marine sandstone and siltstone of the Oligocene Eugene Formation occur in the southern portion of the Willamette Valley in Oregon from Cottage Grove northward along the margin of the Coburg Hills to Brownsville and Lebanon and into the Salem and Eola Hills west of Salem. The faunal assemblages and associated rocks indicate that the Eugene Formation was deposited in shallow water, 0-40 fathoms. The fauna contains a mixture of subtropical and temperate forms which coexisted in what is interpreted as a gradually cooling environment. Relatively undisturbed assemblages of infaunal pelecypods and scaphopods are common along with concentrated layers of reworked infaunal assemblages containing a variety of epifaunal species. The age of the fauna is believed to span portions of the lower and middle Oligocene. The fauna is partly intermediate between the faunas of the Keasey and Pittsburg Bluff Formations in northwestern Oregon and is considered the partial time equivalent of these formations and the missing interval between them. The author collected several thousand fossil specimens from localities throughout the formation and incorporated them into the collections at the University of Oregon. In addition, previous collections housed at the University of California, California Academy of Sciences, Stanford University, and the U.S. Geological Survey at Menlo Park, California, were examined. Sixty-seven species, representing 48 genera and 31 families, are discussed and figured; and their affinities and stratigraphic ranges are analyzed. Supplementary descriptions are given for previously described species. In addition, nine new taxa are proposed and described: Nemocardium formosum, Tellina aduncanasa, Semele willamettensis, Martesia turnerae, Pandora laevis, Dentalium laneensis, Neverita thomsonae, Bruclarkia vokesi, and Acila nehalemensis subsp. minima