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• 1. [Article] Late Pleistocene and postglacial sedimentation and stratigraphy of deep-sea environments off Oregon

  Citation × Citation Citation Abstract Copy Title: Late Pleistocene and postglacial sedimentation and stratigraphy of deep-sea environments off Oregon Author: Duncan, John Russell Jr Title: Late Pleistocene and postglacial sedimentation and stratigraphy of deep-sea environments off Oregon Author: Duncan, John Russell Jr Close

• 2. [Article] Paleomagnetic inclination shallowing in deep-sea sediments

  In this thesis anomalous downcore shallowing of paleomagnetic inclinations is interpreted to be caused by sediment compaction. Thus, compaction-induced inclination shallowing may influence tectonic reconstructions ...

  Citation × Citation Citation Abstract Copy Title: Paleomagnetic inclination shallowing in deep-sea sediments Author: Arason, Pórdur In this thesis anomalous downcore shallowing of paleomagnetic inclinations is interpreted to be caused by sediment compaction. Thus, compaction-induced inclination shallowing may influence tectonic reconstructions that are based on inclinations from deep-sea sediment cores. Progressive downcore shallowing of the remanent inclination was observed in a 120-m section of Plio- Pleistocene sediments at Deep Sea Drilling Project (DSDP) site 578 in the northwest Pacific. Near the top of the section the average inclination corresponds to the expected geocentric axial dipole value of 53° but shallows downcore by about 6° to 8°. In sediments spanning the same time interval of neighboring site 576, no inclination shallowing was observed. This second site has considerably lower sedimentation rates, and the Plio- Pleistocene is represented by a 26-m sedimentary section. The inclination shallowing at site 578 was correlated to a downhole decrease in porosity, and these results are interpreted to suggest that both the downhole inclination shallowing and decrease of porosity in site 578 were caused by sediment compaction. Microscopic models demonstrate that sediment compaction may lead to inclination shallowing of the magnetic remanence. Furthermore, it is shown that inherent initial within-sample dispersion of the magnetic moments will transform any form of microscopic mechanism to an equation of a standardized form: tan (I-ΔI) = (1-a ΔV) tan I, where I is the inclination of the ambient field, ΔI is the inclination shallowing, a is a constant and ΔV the compaction. Paleomagnetic inclinations of Cretaceous DSDP sediments from the Pacific plate are known to be systematically shallower than predicted from paleolatitudes of hot spot reconstructions. Published paleomagnetic data were reexamined and the shallow Cretaceous inclinations explained as a result of sediment compaction. The Cretaceous data are used to estimate the parameter a. The resulting a values are comparable to those of previous studies of compaction-induced inclination shallowing, both from laboratory experiments and the considerably younger deep-sea sediments at site 578. Values of the parameter a suggest that it might be controlled by sediment lithology with greater shallowing for clayey than calcareous sediments. Title: Paleomagnetic inclination shallowing in deep-sea sediments Author: Arason, Pórdur In this thesis anomalous downcore shallowing of paleomagnetic inclinations is interpreted to be caused by sediment compaction. Thus, compaction-induced inclination shallowing may influence tectonic reconstructions that are based on inclinations from deep-sea sediment cores. Progressive downcore shallowing of the remanent inclination was observed in a 120-m section of Plio- Pleistocene sediments at Deep Sea Drilling Project (DSDP) site 578 in the northwest Pacific. Near the top of the section the average inclination corresponds to the expected geocentric axial dipole value of 53° but shallows downcore by about 6° to 8°. In sediments spanning the same time interval of neighboring site 576, no inclination shallowing was observed. This second site has considerably lower sedimentation rates, and the Plio- Pleistocene is represented by a 26-m sedimentary section. The inclination shallowing at site 578 was correlated to a downhole decrease in porosity, and these results are interpreted to suggest that both the downhole inclination shallowing and decrease of porosity in site 578 were caused by sediment compaction. Microscopic models demonstrate that sediment compaction may lead to inclination shallowing of the magnetic remanence. Furthermore, it is shown that inherent initial within-sample dispersion of the magnetic moments will transform any form of microscopic mechanism to an equation of a standardized form: tan (I-ΔI) = (1-a ΔV) tan I, where I is the inclination of the ambient field, ΔI is the inclination shallowing, a is a constant and ΔV the compaction. Paleomagnetic inclinations of Cretaceous DSDP sediments from the Pacific plate are known to be systematically shallower than predicted from paleolatitudes of hot spot reconstructions. Published paleomagnetic data were reexamined and the shallow Cretaceous inclinations explained as a result of sediment compaction. The Cretaceous data are used to estimate the parameter a. The resulting a values are comparable to those of previous studies of compaction-induced inclination shallowing, both from laboratory experiments and the considerably younger deep-sea sediments at site 578. Values of the parameter a suggest that it might be controlled by sediment lithology with greater shallowing for clayey than calcareous sediments. Close

• 3. [Article] Clay mineral origin and distribution on Astoria Fan

  Clay minerals from sediment samples obtained on Astoria Fan were analyzed by X-ray diffraction. Clay minerals are defined for the purpose of this study as crystalline phyllosilicates less than two microns ...

  Citation × Citation Citation Abstract Copy Title: Clay mineral origin and distribution on Astoria Fan Author: Russell, Kenneth Lloyd Clay minerals from sediment samples obtained on Astoria Fan were analyzed by X-ray diffraction. Clay minerals are defined for the purpose of this study as crystalline phyllosilicates less than two microns in equivalent settling diameter. The clay minerals are subdivided into the five common families: montmorillonite, chlorite, vermiculite, illite, and kaolinite. One X-ray scan of a magnesium ion saturated, ethylene glycol treated sample was sufficient for the identification of all the clay minerals. A typical Recent hemipelagic sediment contains about 40 percent montmorillonite, 30 percent illite, and 30 percent chlorite. Neither kaolinite nor vermiculite is detectable in these samples. These concentrations are similar to those reported for Columbia River sediments. The surface sediments have an identical clay mineral assemblage from the head of Astoria Canyon to the outer edge of the fan approximately 250 kilometers offshore. All of the Recent sediments in piston cores from Astoria Fan are the same as the surface sediments on the fan. This similarity indicates an unchanging source during Recent time and a lack of any visible marine diagenesis after burial. X-ray traces of Pleistocene clay minerals are distinctly different from those of the Recent. One can use this change in clay mineralogy as a time marker across the fan. Presumably the Pleistocene clays were formed under different weathering conditions caused by different climatic conditions. Title: Clay mineral origin and distribution on Astoria Fan Author: Russell, Kenneth Lloyd Clay minerals from sediment samples obtained on Astoria Fan were analyzed by X-ray diffraction. Clay minerals are defined for the purpose of this study as crystalline phyllosilicates less than two microns in equivalent settling diameter. The clay minerals are subdivided into the five common families: montmorillonite, chlorite, vermiculite, illite, and kaolinite. One X-ray scan of a magnesium ion saturated, ethylene glycol treated sample was sufficient for the identification of all the clay minerals. A typical Recent hemipelagic sediment contains about 40 percent montmorillonite, 30 percent illite, and 30 percent chlorite. Neither kaolinite nor vermiculite is detectable in these samples. These concentrations are similar to those reported for Columbia River sediments. The surface sediments have an identical clay mineral assemblage from the head of Astoria Canyon to the outer edge of the fan approximately 250 kilometers offshore. All of the Recent sediments in piston cores from Astoria Fan are the same as the surface sediments on the fan. This similarity indicates an unchanging source during Recent time and a lack of any visible marine diagenesis after burial. X-ray traces of Pleistocene clay minerals are distinctly different from those of the Recent. One can use this change in clay mineralogy as a time marker across the fan. Presumably the Pleistocene clays were formed under different weathering conditions caused by different climatic conditions. Close

• 4. [Article] Marine geology of the continental margin off southern Oregon

  The continental margin off southern Oregon, which includes the shelf and slope from Cape Blanco to the Oregon-California border, exhibits a distinctive marginal-plateau structural pattern which divides the ...

  Citation × Citation Citation Abstract Copy Title: Marine geology of the continental margin off southern Oregon Author: Spigai, Joseph John The continental margin off southern Oregon, which includes the shelf and slope from Cape Blanco to the Oregon-California border, exhibits a distinctive marginal-plateau structural pattern which divides the margin into the continental shelf, the upper continental slope and its associated benches, and the lower continental slope. Lutum transport and deposition have dominated the sedimentary processes on the margin since the start of Holocene time. The structure of the southern Oregon margin is characterized by north-south trending compressional folds, and near-vertical faults which have been down-dropped to the west. Large-scale folds on the upper slope have ponded sediments behind them resulting in the formation of the Klamath Plateau, Cape Blanco Bench, and other bench-like features. Development of the structural pattern is most likely a result of the compressive underthrusting of the oceanic lithospheric plate beneath the southernmost Oregon-northern California margin and the crustal extension which exists throughout the nearby continent and ocean basin. Useful stratigraphic horizons within the late Pleistocene and Holocene margin deposits include Mazama Ash (6600 years B.P.) and several recognizable shifts in the abundance of Radiolaria and planktonic Foraminifera, particularly one dating from 5000-4000 years B.P. Holocene sedimentation rates vary from an average of 10 cm/ 1000 years on the upper slope to an average of 50 cm/1000 years on the lower slope, indicating that the lower slope is out-building and up-building more rapidly than the upper slope. The paleo-depth range of Pliocene fauna in sedimentary rocks from the margin suggests that subsequent to their deposition both uplift and subsidence occurred on the southern Oregon margin. Sediments from the southern Oregon margin consist primarily of olive gray lutite, gray lutite, and sand-silt layers. Olive gray lutite is Holocene in age and is ubiquitous on the margin, with the thickest accumulation (10 m average) found on the lower slope, while the distribution of Holocene lutite on the upper slope is thin and patchy (3-4 m or less). The gray lutite appears to be a late Pleistocene deposit, and the sand-silt layers reflect both ages. The surface sediment distribution pattern on the shelf consists of modern inner shelf sand, modern central shelf mud, and mixed deposits of both types. Relict deposits are present at the shelf edge. The lower slope consists entirely of modern mud, but the surface sediment on the upper slope and benches consists of both modern and relict deposits, and mixtures of the two. The mineralogy of the unconsolidated and consolidated sediments from the margin indicates that the Klamath Mountains have been the dominant source for these deposits since early Tertiary time. This is reflected in the abundance of blue-green hornblende and other heavy minerals indicative of the Mesozoic rocks of the Klamath Mountains; the same source is suggested for the abundant chlorite found in the clay fraction of margin sediments and rocks. There are indications in the mineralogy of lower slope sediments which suggest that the Tertiary strata of the southern Oregon Coast Ranges may be a secondary source for the deposits in this environment. When compared to the upper slope sediments, those from the lower slope have a higher feldspar content, a higher pyroxene-to-amphibole ratio, and an apparently higher illite content. As a result of the Holocene rise in sea level, the deposition of coarse clastics on the southern Oregon margin has been restricted to the inner shelf. Consequently, only the fine-grained lutum discharged from rivers is deposited on the outer margin environments. Submarine topography, oceanographic conditions, and gravity are important factors which effect transport and deposition of lutum on the margin. A model of modern lutum transport by bottom turbid layers and fine-particle suspensate is proposed for the southern Oregon margin. Long-period swell is believed to be responsible for much of the formation of bottom turbid layers on the shelf. Once formed, these turbid layers move north and west over the shelf under the influence of shelf currents, alternating tidal action, and gravity; upon reaching the slope they are funneled into submarine valleys and deposited on the lower slope and adjacent deep sea. Lutum deposited on the upper slope is eventually re-suspended and transported by southerly bottom currents into down-slope valleys; very little lutum remains behind on the upper slope. Deposition of the fine-particle suspensate as well as slumping and other gravitational processes contribute to the lower slope sediments. The end result of modern lutum transport is the continual up-building and out-building of the lower slope. Title: Marine geology of the continental margin off southern Oregon Author: Spigai, Joseph John The continental margin off southern Oregon, which includes the shelf and slope from Cape Blanco to the Oregon-California border, exhibits a distinctive marginal-plateau structural pattern which divides the margin into the continental shelf, the upper continental slope and its associated benches, and the lower continental slope. Lutum transport and deposition have dominated the sedimentary processes on the margin since the start of Holocene time. The structure of the southern Oregon margin is characterized by north-south trending compressional folds, and near-vertical faults which have been down-dropped to the west. Large-scale folds on the upper slope have ponded sediments behind them resulting in the formation of the Klamath Plateau, Cape Blanco Bench, and other bench-like features. Development of the structural pattern is most likely a result of the compressive underthrusting of the oceanic lithospheric plate beneath the southernmost Oregon-northern California margin and the crustal extension which exists throughout the nearby continent and ocean basin. Useful stratigraphic horizons within the late Pleistocene and Holocene margin deposits include Mazama Ash (6600 years B.P.) and several recognizable shifts in the abundance of Radiolaria and planktonic Foraminifera, particularly one dating from 5000-4000 years B.P. Holocene sedimentation rates vary from an average of 10 cm/ 1000 years on the upper slope to an average of 50 cm/1000 years on the lower slope, indicating that the lower slope is out-building and up-building more rapidly than the upper slope. The paleo-depth range of Pliocene fauna in sedimentary rocks from the margin suggests that subsequent to their deposition both uplift and subsidence occurred on the southern Oregon margin. Sediments from the southern Oregon margin consist primarily of olive gray lutite, gray lutite, and sand-silt layers. Olive gray lutite is Holocene in age and is ubiquitous on the margin, with the thickest accumulation (10 m average) found on the lower slope, while the distribution of Holocene lutite on the upper slope is thin and patchy (3-4 m or less). The gray lutite appears to be a late Pleistocene deposit, and the sand-silt layers reflect both ages. The surface sediment distribution pattern on the shelf consists of modern inner shelf sand, modern central shelf mud, and mixed deposits of both types. Relict deposits are present at the shelf edge. The lower slope consists entirely of modern mud, but the surface sediment on the upper slope and benches consists of both modern and relict deposits, and mixtures of the two. The mineralogy of the unconsolidated and consolidated sediments from the margin indicates that the Klamath Mountains have been the dominant source for these deposits since early Tertiary time. This is reflected in the abundance of blue-green hornblende and other heavy minerals indicative of the Mesozoic rocks of the Klamath Mountains; the same source is suggested for the abundant chlorite found in the clay fraction of margin sediments and rocks. There are indications in the mineralogy of lower slope sediments which suggest that the Tertiary strata of the southern Oregon Coast Ranges may be a secondary source for the deposits in this environment. When compared to the upper slope sediments, those from the lower slope have a higher feldspar content, a higher pyroxene-to-amphibole ratio, and an apparently higher illite content. As a result of the Holocene rise in sea level, the deposition of coarse clastics on the southern Oregon margin has been restricted to the inner shelf. Consequently, only the fine-grained lutum discharged from rivers is deposited on the outer margin environments. Submarine topography, oceanographic conditions, and gravity are important factors which effect transport and deposition of lutum on the margin. A model of modern lutum transport by bottom turbid layers and fine-particle suspensate is proposed for the southern Oregon margin. Long-period swell is believed to be responsible for much of the formation of bottom turbid layers on the shelf. Once formed, these turbid layers move north and west over the shelf under the influence of shelf currents, alternating tidal action, and gravity; upon reaching the slope they are funneled into submarine valleys and deposited on the lower slope and adjacent deep sea. Lutum deposited on the upper slope is eventually re-suspended and transported by southerly bottom currents into down-slope valleys; very little lutum remains behind on the upper slope. Deposition of the fine-particle suspensate as well as slumping and other gravitational processes contribute to the lower slope sediments. The end result of modern lutum transport is the continual up-building and out-building of the lower slope. Close