The southern half of the upper Nehalem River basin contains
the most complete section of lower to middle Tertiary marine sedimentary
and volcanic rocks in northern Oregon. Determination of
stratigraphic relationships of six formations, and their depositional
environments and provenance is the chief objective of this paper.
More than 75...
A sequence of volcanic, volcaniclastic, and epiclastic deposits from Oligocene to Recent age are exposed in the region from Lake
Simtustus to Madras in central Oregon. The epiclastic sediments of the Oligocene John Day Formation are unconformably overlain by two flows of the middle Miocene Columbia River Basalt Group. The...
The middle to late Eocene tholeiitic Tillamook Volcanics compose the oldest rock unit in the Hamlet-North Fork of the Nehalem River area. Geochemical plots and field relationships indicate that these rocks were produced in an extensional tectonic setting in the developing forearc and formed an extensive tholeiltic oceanic island. The...
Six Tertiary rock units are exposed in the Buster Creek-Nehalem Valley area. They are, from oldest to youngest: upper Eocene
Tillamook Volcanics; upper Eocene Cowlitz Formation; upper Eocene Keasey Formation; upper Eocene Vesper Church formation (informal); upper Eocene to Oligocene Pittsburg Bluff Formation; and middle Miocene Depoe Bay Basalt. The...
An ancient delta complex is partly recorded by the upper seven
formations of the Cretaceous Nanaimo Group exposed on Mayne and
Samuel Islands of southwestern British Columbia. Features especially
suggestive of deltaic sedimentation here are: upward-coarsening
marine to fluvial sequences, cyclic repetition of facies, subaqueous
slumping, fluvial-marine interfingering, facies changes,...