Sediments on the inner portion of the Oregon continental shelf
consist of clean, well-sorted, detrital sand. This sand has an average
median diameter of 2.53Φ (. 173 mm) and is both positively and
negatively skewed. Deposits with median diameters in the coarse
sand and gravel classes occur at depths of 20 to 40 fathoms and
probably represent ancient beach or fluviatile deposits formed during
lower stands of sea level.
The outer shelf and upper slope are covered by poorly sorted
sediments with median diameters in the fine sand to fine silt classes.
Mean diameters of the sediments are almost always smaller than
their median diameters and the sediments are positively skewed.
The heavy mineral assemblages are dominated by the amphibole
and pyroxene groups and the opaque-garnet association.
Pyroxenes are most abundant in the coarser-grained sediments of the inner shelf and decrease in abundance offshore. Amphiboles are
most abundant in the finer-grained sediments of the outer shelf and
upper slope. Highest concentrations of the opaque-garnet association
also are found in the inshore samples.
Sediments of the continental shelf are derived from two principal
sources, rivers and erosion of coastal terrace deposits.
Rivers are probably contributing only fine-grained material to the
shelf as much of the coarser fluviatile material is thought to be
trapped in the estuaries. The terrace deposits are actively being
eroded and are thought to contribute about 21,000,000 cubic feet
(.00013 cubic miles) of sediment to the continental shelf annually.
Evidence suggests that much of the inner-shelf sand is probably
a relict transgressive sheet sand that was deposited during the
last rise in sea level. Most of the deposition of the modern sand on
the shelf has been confined to the inner portion of the inner shelf.
Finer-grained sediments have been deposited on the outer shelf and
upper slope.
Characteristics of the sediments on the present continental
shelves may be useful in identifying continental shelf deposits in
the geologic column. / Graduation date: 1966
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28108 |
| Date | 01 December 1965 |
| Creators | Runge, Erwin John |
| Contributors | Byrne, John V. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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