Heavy mineral compositions of sands from Oregon beaches,
rivers and sea cliffs have been determined in order to examine the
causes of marked along-coast variations in the beach-sand
mineralogy. The study area extends southward from the Columbia
River to the Coquille River in southern Oregon. The heavy-mineral
compositions were determined by standard microscopic
identification with additional verification by X-ray diffraction
analyses. Initially the beach-sand samples were collected as single
grab samples from the mid-beachface, but significant selective
sorting of the important heavy minerals prevented reasonable
interpretations of the results. Factor analysis of multiple samples
from the same beach yielded distinct factors which correspond with
known mineral sorting patterns. The effects of local sorting were
reduced by the subsequent use of large composite samples,
permitting interpretations of along-coast variations in sand
compositions. Four principal beach-sand sources are identified by
factor analysis: the Columbia River on the north, a Coastal Range
volcanic source, sands from the Umpqua River on the south-Oregon
coast, and a metamorphic source from the Klamath Mountains of
southern Oregon and northern California. The end members identified
by factor analysis of the beach sands correspond closely to
river-source compositions, the proportions in a specific beach-sand
sample depending on its north to south location with respect to those
sources. During lowered sea levels of the Late Pleistocene, the
Columbia River supplied sand which was dispersed both to the north
and south, its content decreasing southward as it mixed with sands
from other sources. The distributions of minerals originating in the
Klamath Mountains indicate that the net littoral drift was to the
north during lowered sea levels. With a rise in sea level the
longshore movement of sand was interrupted by headlands such that
the Columbia River presently supplies beach sand southward only to
the first headland, Tillamook Head. At that headland there is a
marked change in mineralogy and in grain rounding with angular,
recently-supplied sands to the north and rounded sands to the south.
The results of this study indicate that the present-day central
Oregon coast Consists of a series of beaches separated by headlands,
the beach-sand compositions in part being relict, reflecting the
along-coast mixing at lower sea levels and subsequent isolation by
onshore migration of the beaches under the Holocene sea-level transgression. This pattern of relict compositions has been modified
during the past several thousand years by some addition of sand to
the beaches by sea-cliff erosion and contributions from the rivers
draining the nearby Coastal Range. / Graduation date: 1987
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/27779 |
| Date | 06 January 1987 |
| Creators | Clemens, Karen E. |
| Contributors | Komar, Paul D. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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