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A stratigraphic study of the marine Cretaceous rocks near Mitchell, Oregon

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Title A stratigraphic study of the marine Cretaceous rocks near Mitchell, Oregon
Names McKnight, Brian Keith (creator)
Cummings, Jon C. (advisor)
Date Issued 1964-01-29 (iso8601)
Note Graduation date: 1964
Abstract Nearly 9,000 feet of Cretaceous mudstones, shales, sandstone,
and conglomerates are exposed along the northeast-trending Mitchell
anticline of central Oregon, These rocks are divided into two formations
on the basis of criteria developed in this investigation. The
lower formation, hereby designated the Meyers Formation, is 4,716
feet thick at its type section, and consists typically of mudstone
and siltstone with thin interbeds of sandstone. This formation rests
unconformably on Permian metasedimentary rocks and is conformably
overlain by strata hereby designated the Frizzell Formation. The
Frizzell Formation is 4,167 feet thick at the type section and consists
of three sandstone and conglomerate units separated by thin mudstone units. It is unconformably overlain by terrestrial volcanic
rocks of the Clarno Formation of Eocene age. Rapid facies changes
are common in both the Meyers and Frizzell Formations.
A late early Cretaceous age has been established for these
formations by ammonites and other molluscs that they contain. The
Meyers Formation is Early to Late Albian and the lower part of the
Frizzell is Late Albian in age; no fossils have been found in the
upper part of the Frizzell Formation.
The basal sandstone unit of the Meyers Formation was deposited
in a littoral or upper neritic marine environment. Abundant ammonites
and the paucity of macroscopic benthonic fossil types indicate that
the thick mudstone units of the Meyers Formation were deposited in a
bathyal environment. Thin sandstone beds, possibly deposited by turbidity
currents, are interbedded with the sandstones and mudstones.
The lower part of the overlying Frizzell Formation is shallow marine
in origin; however, the upper part of this formation displays channeling,
oxidized zones, large -scale cross -bedding, lateral pinchouts,
and associated features indicative of fluvial rather than marine sedimentation.
The composition of pebbles and sand grains in these strata indicate
that supracrustal rocks were the primary source for the sediments.
A progressive increase in granitic detritus higher in the
stratigraphic section implies the gradual uncovering of plutonic
rocks in the source area. A topographic high to the south and southeast
of the Mitchell area may have been the source of most materials
in the Cretaceous rocks. The implied current directions support this
conclusion, for sole markings suggest that the depositing currents
moved N. 10 -15°W.
Genre Thesis/Dissertation
Topic Geology, Stratigraphic -- Cretaceous
Identifier http://hdl.handle.net/1957/49186

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