First Advisor

Richard E. Thomas

Date of Publication


Document Type


Degree Name

Master of Science (M.S.) in Geology






Fossil Foraminifera -- Oregon -- Polk County, Fossil Foraminifera, Oregon -- Polk County



Physical Description

1 online resource (146 p.)


One hundred and seventy-four species and varieties of fossil Foraminifera are recorded from thirty-eight localities in the Siletz River Volcanics, Yamhill and Nestucca Formations exposed along Mill and Gooseneck Creeks, in the Northern Coast Range of Oregon. Marginulina holmesi is described as new. The Foraminifera indicate that this sequence was deposited during late Ulatisian and Narizian time, in marine waters at bathyal or lower neritic depths, with cool surface temperatures. The Yamhill Formation can be correlated with Moody Shale member of the Toledo Formation and the Coaledo Formation of Oregon; the McIntosh and Aldwell Formations of Washington; and the upper part of the Canoas siltstone member of the Kreyenhagen Formation and the Alhambra Formation of California.

It is proposed to modify, in part, the type section of the Yamhill Formation. Approximately 2.2 miles of the section, south of the Yamhill River Fault, are excluded from the original type area. Biostratigraphic studies of foraminiferal faunae from adjacent sides of the Yamhill River Fault suggest only minor vertical displacement.


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