Marine geology of the continental margin off southern Oregon

Spigai, Joseph John

doi:10.5962/bhl.title.59722

Cited by 9 publications

(10 citation statements)

References 17 publications

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“…Furthermore, a number of small anticlinal structures apparently are developing on the abyssal plain immediately adjacent to the continental slope ( Figure 9, c-b). Similar structures were noted at the base of the slope on the southern Oregon margin (Spigai, 1971, Figure 18). In most reflection profiles across the steeply dipping lower continental slope-abyssal plain interface, there is a complex seismic signal and the nature of the contact is therefore uncertain.…”

Section: Continental Slopesupporting

confidence: 50%

Site Survey of the Northern Oregon Continental Margin and Astoria Fan

Kulm¹,

Prince²,

Snavely³

1973

Initial Reports of the Deep Sea Drilling Project

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Section: Continental Slopesupporting

confidence: 50%

Site Survey of the Northern Oregon Continental Margin and Astoria Fan

Kulm¹,

Prince²,

Snavely³

1973

Initial Reports of the Deep Sea Drilling Project

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“…Mendocino, is sensitive to southward translation of the polar front zone (the boundary between the subarctic and subtropical gyres) because it is near the southern boundary of the transition zone between these gyre systems. Today, year-round flow is southward (Figure 1) Spigai, 1971], and type 3 is AMS •nc on planktic or benthie foraminifera.…”

Section: Our Transect Located Between Cape Blanco and Capementioning

confidence: 99%

“…solid squares mark the last glacial maximum (LGM) samples identified by carbonate stratigraphy and AMS?C dating. Some carbonate data for 6706-2 are fromSpigai [1971]. Carbonate data for W8709A-13PC, 13TC, W8709A-8PC, TC, and W8709A-1BC from Lyle et al[1992].…”

mentioning

confidence: 99%

The California Current of the Last Glacial Maximum: Reconstruction at 42°N based on multiple proxies

et al. 1997

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Multiple paleoceanographic proxies in a zonal transect across the California Current near 42øN record modern and last glacial maximum (LGM) thermal and nutrient gradients. The offshore thermal gradient, derived from foraminiferal slx•ies assemblages and oxygen isotope data, was similar at the LGM to that at present (warmer offshore), but average temperatures were 3.3 ø +1.5øC colder. Observed gradients require that the sites remained under the southward flow of the California Current, and thus that the polar front remained north of 42øN during the LGM. Carbon isotopic and foraminiferal flux data suggests enhanced nutrients and productivity of foraminfera in the northern California Current up to 650 km offshore. In contrast, marine organic carbon and coastal diatom burial rates decreased during the LGM. These seemingly contradictory results are reconciled by model simulations of the LGM wind-field, which suggest that wind stress curl at 42øN (and thus open-ocean upwelling) increased, while offshore Ekman transport (and thus coastal upwelling) decmasexl during the last ice age. The ecosystem of the northern California Current during the LGMapproximated that of the modern Gulf of Alaska. Cooling and production in this region was thus driven by stronger open-ocean upwelling and/or southward flow of high-latitude water masses, rather than by coastal upwelling.

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“…In the NE Pacific, the last glacial/interglacial is marked by a shift from low to high radiolaria/foraminifera ratios in the >63 gm fraction and a change from grey to olive grey color [Duncan et al, 1970; Barnard and McManus, 1973].The Mazama ash layer (6.7 kyr) often gives a useful stratigraphic horizon. Using these markers and radiocarbon ages on piston cores, Duncan[1968] andSpigai [1971] found that sedimentation rates along the margin generally varied from -•0-120 cm/kyr. In our gravity cores, coarse fraction analyses give very Ngh rad/foram ratios and none of the cores contain the Mazama ash horizon; Bar diagrams of the coefficients of variability (standard deviation/mean) for elemental concentrations from cores 169, 165, and 121.…”

mentioning

confidence: 99%

Magnetite diagenesis in marine sediments from the Oregon continental margin

Karlin¹

1990

J. Geophys. Res.

172

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The magnetochemistry of sediments from the Oregon continental margin is examined to determine the effects of iron-sulfur diagenesis on the paleomagnetic record. Magnetic mineral dissolution and lxansformation into iron sulfides are a common feature in these suboxic to anoxic lutites. These processes are evidenced in rapid decreases in natural reinanent magnetization intensities and stabilities, systematic changes in other rock magnetic properties, and increases in solid phase sulfur concentrations with depth. Hysteresis measurements are used to evaluate downcore changes in magnetite concenlxation and grain size. Magnetite abundances decrease downcore from initial values of about 0.1%, and nominal grain diameters lie within a narrow pseudosingle domain range of 0.08 to 0.6 !xm. A first-order surface area reaction model, dA/dt = -kA, is proposed to explain the magnetite dissolution mechanism, where A is the total magnetite surface area and k is the rate constant. The solution of this equation predicts that the surface area and concenlxation decrease exponentially, and the concenlxation, in addition, depends on grain size. Application of this model in two cores where grain size varies with depth successfully explains the downcore profiles of both concenlxation and surface area. Despite extensive magnetite deslxuction, magnetic directions in such sediments appear to reliably record long-wavelength lxends of the geomagnetic field. Consequently, the potential for using rock magnetism as a sedimentological tool has not been fully developed. In recent years, a new generation of sediment paleomagnetic studies has begun to explore the possibilities of using rock magnetic properties as proxy indicators of climatic change to explore the expression of Milankovitch cyclicities in the sediment record as well as to delineate patterns of paleocean and paleowind circulation [Mead et al., 1986, Ledbetter and Ciesielski, 1986; Doh et al., 1988]. Since magnetic techniques are rapid, nondestructive, and very sensitive, rock magnetism is becoming increasingly important in examining long sedimentary sections such as recovered by the Ocean Drilling Program. Rock magnetic variations in sediments reflect changes in the composition, concentration, and grain size of magnetic minerals, especially magnetite. In a given section, downcore trends arise from changes in provenance of the magnetic minerals, dilution effects from other sources (particularly biogenic), depositional perturbations, and any postdepositional modifications of the original remanence due to authigenesis or diagenesis. Before the potential of rock magnetism as a paleoclimatic tool can be fully realized, the interaction of magnetic phases with physical and chemical processes in different depositional environments must be understood. Very few studies have addressed the causes of magnetic fluctuations in sediments or the biogeochemical and physical processes responsible for acquisition, fixation, and preservation of remanence. However, there is a growing realization that the amb...

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Marine geology of the continental margin off southern Oregon

Cited by 9 publications

References 17 publications

Site Survey of the Northern Oregon Continental Margin and Astoria Fan

Site Survey of the Northern Oregon Continental Margin and Astoria Fan

The California Current of the Last Glacial Maximum: Reconstruction at 42°N based on multiple proxies

Magnetite diagenesis in marine sediments from the Oregon continental margin

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