USGS 5425 - College Hill (Eocene of the United States)

Also known as USGS 5425a-d, 17015, 17041, 17942; UO 12, 29, 127, 164, 128, 129; UC 4080-4084; #4 (Hickman)

Where: Lane County, Oregon (44.0° N, 123.1° W: paleocoordinates 44.4° N, 110.8° W)

• coordinate based on nearby landmark

• outcrop-level geographic resolution

When: Eugene Formation, Priabonian (38.0 - 33.9 Ma)

• Eugene Formation can be subdivided faunally: a lower unit correlating to the Keasey Fm, a middle unit correlating to the Gries Ranch Beds of WA, and a upper unit correlated with the Pittsburg Bluff Fm. Thickness of formation may be up to 15,000 feet, but probably around 5,000 feet. Most of the outcrops are scattered so it is difficult to estimate their relative stratigraphic placement

• bed-level stratigraphic resolution

Environment/lithology: transition zone or lower shoreface; lithified, tuffaceous, brown, gray, blue sandstone and tuffaceous, brown, gray, blue siltstone

• Retallack et al. (2000): Near-shore, shallow-marine environments are indicated by sedimentary structures such as hummocky cross-bedding, shallow water trace fossils such as Planolites and Thalassinoides and common glauconite and phosphate nodules (Mears, 1989).

•Hickman (1969): Several lines of evidence suggest that most of the Eugene Formation was deposited in shallow water, at depths no greater than 30 fathoms. The coarse, tuffaceous, and arkosic character of many beds and the interfingering of the Eugene Formation with non-marine tuffaceous rocks to the east and south indicates the proximity of the Oligocene shoreline. Although mollusks are generally not good indicators of depth, genera such as Panopea, Modiolus, Solen, and Spisula are presently restricted to depths of less than 40 fathoms. The high diversity of the benthonic fauna is an indication that the environment was not one of a bay or otherwise highly restricted environment. The absence of planktonic forms is typical of turbid, near-short environments. In the same units with these relatively undisturbed infauna! assemblages there are occasional thin layers of concentrated shell material which show definite signs of reworking and current sorting. The layers range from 1 to 10 cm in thickness and cannot be traced over great distances. The shells in these layers are small and include an admixture of infaunal and epifaunal species. The shells show little sign of wear or breakage, but many of the pelecypod valves are disarticulated, indicating some degree of transport. The scaphopods in these layers show parallel alignment by the current. There is also evidence that currents were intermittent and fluctuating in strength: the assemblages contain varying percentages of large shells mixed in with the smaller ones, and in some places there are higher proportions of broken and abraded shell debris mixed in.

• Tuffaceous and highly feldspathic sandstone or siltstone which is bluish-gray to olive when fresh and weathers to a buff or orange-brown color. Gray sandstone and siltstone beds may range from several to 50 feet in thickness and are interbedded with minor amounts of sandy sahel and clay shale, occasional beds of conglomerate, and thin lenses of gray or buff-colored volcanic ash

Size class: macrofossils

Preservation: mold/impression, trace

Reposited in the CAS

Collection methods: quarrying,

• Collections held at University of Oregon, University of California, Californian Academy of Sciences (CAS), United States Geological Survey (USGS), and Stanford University (NP).

Primary reference: C. J. S. Hickman. 1969. The Oligocene marine molluscan fauna of the Eugene Formation in Oregon. University of Oregon Museum of Natural History Bulletin 16:1-112 [A. Miller/A. Hendy/P. Wagner]more details

Purpose of describing collection: taxonomic analysis

PaleoDB collection 38936: authorized by Austin Hendy, entered by Austin Hendy on 17.05.2004, edited by Mark Uhen

Creative Commons license: CC BY (attribution)

Taxonomic list

• Exhaustive for mollusca
Bivalvia
 Cardiida - Mactridae
"Spisula eugenensis" = Mactromeris eugenensis
"Spisula eugenensis" = Mactromeris eugenensis Clark 1925 clam
Scaphopoda
 Dentaliida - Dentaliidae
Gastropoda
 Sorbeoconcha - Naticidae
Polinices washingtonensis Weaver 1916 moon snail
"Neverita thomsonae" = Glossaulax reclusiana Deshayes 1839 moon snail
 Neogastropoda - Perissityidae
Nekewis cf. nehalemensis Anderson and Martin 1914 snail
 Sorbeoconcha - Ficidae
Ficus modesta Conrad 1848 fig shell
 Neotaenioglossa - Calyptraeidae
Crepidula ungana Dall 1908 slipper shell
Cephalopoda
 Nautilida - Aturiidae
Aturia angustata Conrad 1849