Holocene hemipelagic deposition of terrigenous silts and clays
dominates sedimentation on most of the Oregon and Washington continental
slope. The sources of these sediments, the mechanisms causing sediment
dispersal, and the relative contributions of the various continental
sources to the marine deposits have been investigated using quantitative
mineral and geochemical data for the 2-20 μm and the <2 μm size fractions.
In the 2-20 μm size fraction, material derived from the Klamath
Mountains and the California and Washington Coast Ranges contains
chlorite and illite, but only Klamath material contains hornblende.
Columbia River material lacks chlorite, and the Oregon Coast Range
source is dominated by smectite. In the <2 μm fraction, source area
compositions are less distinctive due to the ubiquity of smectite, but
the northern and southern sources again contain both chlorite and
illite. Regional and local mineralogic and textural variations in the
fluvial sediments reflect geologic and geographic changes between
drainage basins. Amorphous material is a minor component in the 2-20 μm
fraction of the fluvial sediments, but may form 25-50% of the <2 μm
fraction in some source areas.
Sediments derived from all source areas are transported north
and northwestward across the margin, either by a poleward-flowing
undercurrent along the slope, by wind-driven surface currents on the
shelf and associated turbid layers on the slope, or by a combination
of the two processes. Columbia River <2 μm material may also be carried
southward along the shelf and upper slope by summer surface currents.
The poleward undercurrent (an eastern boundary undercurrent) appears to
have limited sedimentological significance when compared to the role
of the western boundary undercurrent in sediment transport and deposition
on the continental slope and rise of the eastern United States.
Linear programming has been applied successfully to estimate source
area contributions to the 2-20 μm marine sediments. The influence of
each source is largest in proximal environments, and the contribution
estimates indicate that material derived from each source area is
transported northward along the margin. Similar estimates for the
<2 μm material are considered unreliable because of internal inconsistencies
and the uniform nature of the <2 μm compositions used in the
modelling. The contributions have been used to calculate a sediment
budget for the 2-20 μm fraction. This budget indicates that the mass
accumulating on the entire slope within the study area contains 47%
Columbia River, 32% Klamath Mountain, and 21% California Coast Range
material in the 2-20 μm fraction, and demonstrates the importance of
multiple sediment sources and sediment mixing in the formation of
hemipelagic sediments on the continental margin. / Graduation date: 1982
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28406 |
| Date | 13 April 1982 |
| Creators | Krissek, Lawrence A. |
| Contributors | Scheidegger, Kenneth F. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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