Changes in sea level during the past 20,000 years are recorded
in sediments taken from the continental shelf off the Rogue River,
Oregon. Sea level has risen approximately 125 m. during the
Holocene (Curray, 1965) and the general transgression has been
interrupted by several stillstands and minor regressions.
Box core samples taken in the area of investigation depict the
nature of sedimentation during the last rise of sea level as well as
present-day equilibrium sediment relationships. Three sediment
facies, a recent fine-grained mud, a basal transgressive sand, and
an intermediate sediment, believed to be a mixture of the other two,
are defined on the shelf on the basis of textural parameters. The
mud facies dominates surface sediment on the central shelf while
the sand facies is the most commonly exposed on both the inner and
outer shelf.
The percentage of sand generally increases with depth in the
box cores, often producing a change in sediment facies with depth and
demonstrating the transgressive nature of the sediments. Grain-size
analysis of the sand fraction of the offshore sediments reveals that
offshore sands are finer-grained and better sorted than those occurring
on the present beaches. The offshore sands most likely
represent relict nearshore deposits and not ancient beach sands
which would occur lower in the sediment sequence.
High concentrations of heavy minerals are found in the sand
fraction of the offshore sediments as well as in beach sands in the
area. Brief stillstands of sea level may be reflected in depths where
the offshore sands contain anomalously high percentages of heavy
minerals.
Opaque minerals, chiefly magnetite, occur in placer accumulations
on the present beaches and high percentages of these minerals
in the offshore sands may be indicative of submerged beach environments
associated with stillstands of sea level. The magnetite may be
concentrated in sufficient quantity in the placers to produce detectable
magnetic anomalies, several of which have been recorded in the area.
Other lines of evidence used to determine the depths of
probable stillstands of sea level are bathymetric relief, the distribution
of shallow water fauna in sediments from deep water, and the
distribution of rounded gravels on the shelf. A compilation of the
several lines of evidence suggests several stillstands of sea level
associated with the Holocene transgression occurring at depths of
18, 29, 47, 71, 84, 102, and 150 meters. / Graduation date: 1969
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28431 |
| Date | 25 September 1968 |
| Creators | Chambers, David Marshall |
| Contributors | Kulm, LaVerne D. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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