Graduation date: 1971

This study examined the foraminifera and the ecologic conditions of the benthic environment of the Oregon shelf and the uppermost slope (75-550 m depth) between 143°45' N and 144°40' N. Seasonal collections monitored the near-bottom marine environment and the sedimentary substrate at 16 stations. The foraminiferal benthic fauna was examined from eight seasonal stations and two additional stations. Use of a multiple corer provided randomly selected subsarnples of the sediment for ecologic and faunal analyses. Use of water bottles that triggered upon bottom impact provided measurements of the water as close to the bottom as 0. 6 m. Computerized data processing and statistical analyses aided the ecologic and faunal evaluations. The environmental study showed the existence of considerable variation in the hydrography of near-bottom waters, especially between summer and winter (upwelling and non-upwelling) collections at the same station. Upwelling conditions directly affect the benthic Redacted for Privacy environment. In addition, the water at any one place, at least dciring upwelling, was so well mixed that vertical stratification did not exist between 0.6 and 5.0 m off the bottom. Statistically significant sea-. sorial variations in surface sediments at the same station were not observed. The living benthic foraminiferal fauna exhibited considerable within-station variation both in species composition and in specimen size of selected species. The percent abundance of individual dominant species varied in adjacent cores (subsamples) by amounts up to 46%. Living specimens of a single species were found that were three times as large as the smallest living specimen from the same sample, yet there was no evidence of a multimodal size distribution resulting from age classes. The author suggests that the dominant species are aggregated and that the aggregations are colonies of asexually produced siblings. Lack of fit of species-frequency curves to the lognormal distribution indicated that relatively few species are fit to reproduce in a particular environment; most juvenile specimens that enter a particular environment belong to species that will not thrive there and either die or simply maintain growth with little chance of reproductive success. The existence of colonial aggregations of individuals is considered to provide the best explanation of the observed variations between adjacent samples. However, the observed variations could be due to sampling error or to substrate microheterogeneity. A possible natural community of 15 dominant species has been determined for those species that form a consistent part of each other's biologic environment. The community crossed the depth and substrate boundaries upon which the stations were selected and appeared to be a general community for the Oregon outer shelf. The limits of the community appear to be determined mostly by water depth, with approximate boundaries at 75-100 m and somewhere between 200-500 m. Regression analyses to determine the ecologic control on the foraminiferal fauna did not indicate a close correspondence between faunal parameters and environmental variables. Regression analyses to determine the ecologic control on mdividual species indicated that most species depended upon a set of two to four environmental variables rather than upon one single limiting factor. The set for each species was different. Temperature. phosphate concentration and oxygen concentrations were common hydrographic members of sets; percent silt, percent sand, percent clay, organic carbon content and organic nitrogen were common sedimentary members of sets. / Graduation date: 1972

Recently obtained airgun-sonobuoy wide-angle refraction and reflection profiles provide data to study crustal velocities and structures along the continental margin of northern California and Southern Oregon. In the thick sedimentary wedge at the base of the continental slope, as many as five distinct layers can be seismically observed, which range in velocity from 2.13 to 3.32 km/sec. The basement layers beneath the wedge are disrupted. The profile which crosses the southeasternmost portion of the Gorda Basin near Cape Mendocino shows evidence of compression at the base of the slope. Velocities of 3.14 to 5.15 km/sec were obtained for this line. Off the central Oregon margin on the abyssal plain near the base of the slope, oceanic layers and 3 overlie a shallow mantle of velocity 7.65 km/sec. Basement velocities average 4.75 km/sec and sediment velocities varied from 1.60 to 2.78 km/sec. The lower slope of the northern California-southern Oregon margin is characterized by rough, folded structures which trend north-south. Little recent sediment cover is seen. A velocity of 2.25 km/sec was obtained for a 520 m-thick surface layer underlain by material with a refraction velocity of 2.68 km/sec. The abyssal plain sediments near Cape Mendocino appear to be in the process of being uplifted and folded into the lower slope, while near Cape Blanco the lower slope displays sediments which abut against the base of the slope below a prominent lower shelf bench. The upper slope shows large anticlinal folds which form the basement of the upper slope basins, particularly beneath the Klamath Plateau off Northern California. Velocities obtained from the sediments of the Klamath Plateau vary from 1.73 to 2.63 km/sec. The inner shelf region is formed by a synclinal basin controlled by an outer continental high which parallels the shelf break. Velocities were studied mainly from refraction arrivals with an assumed surface sediment velocity of 1.66 km/sec. The underlying sediment velocities range from 2.07 to 2.75 km/sec. Evidence of uplift, basement deformation, sediment deformation within structurally controlled basins, compression features, and the north-south trending folds all support an imbricate thrust model for this continental margin. / Graduation date: 1979

The distribution of surface sediments on the northern Oregon continental shell is characterized by a nearshore sandy facies and an outer shelf muddy facies, separated by a mid-shelf zone of mixed sand and mud. Currents which have been measured at 130 centimeters above the bottom indicate that the distribution of the surface sediment is a reflection of the hydraulic regime. The strongest bottom currents which were measured were in the nearshore region at a depth of 36 meters. Here currents of over 40 cm/sec generated by surface waves are capable of placing the nearshore sands in suspension, where they are transported shoreward by the wave surge. At mid-shelf, in 90 meters of water, the bottom current veolcity ranges from zero to over 25 cm/sec, although the mean is normally about 10 cm/sec. The strongest currents at this depth are capable of eroding some of the fine sediments, but probably do not rework the older sediments which have been compacted. Currents which are similar in character to those at mid-shelf were observed at the shelf edge in a depth of 165 meters. A significant departure, however, is the difference in frequency where the most energy is found. At the shelf edge the dominant frequency was about four cpd whereas the dominant frequency at mid-shelf was two cpd or lower. The dominant frequencies indicate that tides are important in the generation of continental shelf bottom currents. The twelve - hour period is that of the semi-diurnal tide; the six-hour period is the second harmonic of the semi-diurnal component. No indication of surface wave influence was found at mid-shelf or shelf-edge depths. Profiles of turbidity made at four east-west transects of the continental shelf indicate suspended sediment transport occurs principally at three levels in the water column. An upper layer is at the level of the seasonal thermocline, a mid-water layer is located at the level of the permanent pycnocline, and the third layer is at the bottom. The surface layer is important in transporting suspended sediment of the Columbia River plume, although there is also a contribution to the surface layer from the surf zone by the process of diffusion of fine particles. The mid-water layer thickens vertically and becomes less intense seaward, indicating a nearshore source for the suspended material. This source is diffusion of fine particles from the surf zone at mid-water depths. The mid-water layer is located at the level of the permanent pycnocline. The layer is sub-parallel to the bottom over the shelf but becomes diffuse at the shelf edge. Sediment transport in the mid-water layer provides a mechanism by which sediment bypasses the outer shelf and upper slope area. The bottom layer receives its suspended material from erosion of the bottom, from the water column above, and from fine material moving seaward from the surf zone. The amount of eroded material contributed to the bottom layer depends on the bottom current strength and on the bottom roughness characteristics. Over a rough bottom the erosive power of a given bottom current is increased drastically. For this reason, the presence or absence of rippling is important to sediment transport on the shelf. The fine material of the bottom layer may concentrate by settling during quiescent periods, allowing low-density flows to initiate. Several time-series observations of turbidity indicate that the bottom layer thickens and thins in response to increases and decreases in current velocity. The mid-water layer migrated somewhat in a vertical direction, but its thickness and intensity remained nearly the same. The thickness and intensity of the upper layer responded to changes in the structure of the thermocline, becoming thick and dispersed when the upper part of the water column is mixed. A model of sediment transport proposes that mid-water and bottom currents transport suspended sediments diagonally across the shelf toward the south-southwest. The sediments of the Columbia River plume are also transported in a southerly direction in the surface waters. Relatively little deposition takes place on the shelf and upper slope, with the bulk of the sediments bypassing the shelf and depositing on the lower slope and continental rise. / Graduation date: 1972

Opaque oxide minerals (ilmenite, chromite, and magnetite) in sands from the Oregon continental shelf have been studied to establish the provenance, dispersal, and grade of potential shelf placer deposits. The study area extends southward from offshore of the Columbia River in northern Oregon to the Klamath River in northern California.

Sea level and current observations made over the Oregon continental shelf exhibit wavelike characteristics in a frequency band from approximately 0.15 to 0.45 cpd. In a narrow band around 0.22 cpd the current-sea level relationship is consistent with the predicted values for the first mode of Robinson's continental shelf waves. In addition, an interesting relationship exists between the form of the sea level-current coherency spectra and the arrangement of the maximum frequencies for the first three shelf wave modes. The currents were measured in 100 m of water about seven nautical miles off Depoe Bay, Oregon. Current meters were placed at 25, 50 and 75 m depth. The duration of the experiment was from 18 April 1968 until 11 September 1968. Due to some instrument failures a complete current data set for this period was not obtained. Simultaneous and continuous measurements of surface elevation and atmospheric pressure were also obtained at Newport, Oregon, a nearby coastal station. Shelf wave dispersion curves and eigenfunctions for the Oregon coastal profile are computed using a new numerical technique. These are compared with a low frequency (about 0.03 cpd to 0.75 cpd) spectral analysis of the current, sea level and atmospheric pressure records. The relative vertical uniformity of the currents, as a function of frequency, is examined. The longshore component of the current appears to be substantially more barotropic than the onshore-offshore component. / Graduation date: 1972