Preliminary geologic interpretation of USGS S. P. Lee seismic-reflection profile WO 76-7 on the continental shelf and upper slope, northwestern Oregon

Snavely, Parke Detweiler; McClellan, P.H.

doi:10.3133/ofr87612

Cited by 5 publications

(9 citation statements)

References 14 publications

(9 reference statements)

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“…The continental shelf of Washington and the outer to midshelf of northernmost Oregon are underlain by a thick section of Eocene to middle Miocene mdlange and broken formation (Figures 1 and 3) [Snavely, 1987]. The rodlange and broken formation may also be present elsewhere on the Cascadia margin but not immediately underlying late Tertiar.• strata.…”

Section: Stratigraphy and Uplift Historymentioning

confidence: 99%

“…These Pliocene strata are, in turn, overlain by Pliocene and Pleistocene gravels [Palmer and Lingley, 1989]. Paleobathymetry [Rau, 1970;Bergen and Bird, 1972] and younger sediments thin and onlap against these aliapits, suggesting that growth began in the late Miocene [Snavely, 1987].…”

Section: Stratigraphy and Uplift Historymentioning

confidence: 99%

“…Phase 1 data were acquired using a four-gun aquapulse array and 110 foot shot Wagner, 1982] and in onshore outcrops [Rau, 1973;Orange, 1990], imply that the MBF is overpressured at depth [Snavely, 1987] The subhorizontal upper contact of the MBF on the continental shelf and upper slope suggests mobilization and redistribution of this unit, aided by gravitationally driven downslope movement. The MBF may therefore be undergoing mobilization and extension to the west, where it is apparently unconstrained, with accompanying rigid or brittle extension of the overlying younger deposits (Figures 9a and 9c) is also indicated by shaded relief bathymetry [Haugerud, 1996].…”

Section: Seismic Reflection Data Acquisition and Processingmentioning

confidence: 99%

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Listric normal faulting on the Cascadia continental margin

McNeill¹,

Piper²,

Goldfinger³

et al. 1997

J. Geophys. Res.

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Section: Stratigraphy and Uplift Historymentioning

confidence: 99%

Section: Stratigraphy and Uplift Historymentioning

confidence: 99%

Section: Seismic Reflection Data Acquisition and Processingmentioning

confidence: 99%

See 1 more Smart Citation

Listric normal faulting on the Cascadia continental margin

McNeill¹,

Piper²,

Goldfinger³

et al. 1997

J. Geophys. Res.

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“…1). The northern Oregon and Washington accretionary wedge is a broad landward-vergent thrust system with widely spaced folds, and a decollement stepping down to the basement, with virtually all incoming sediment being frontally accreted (FLUEH et al, 1996;MACKAY, 1995;GOLDFINGER, 1994;MACKAY et al, 1992;SNAVELY and MCCLELLAN, 1987;SILVER, 1972). This low-taper wedge is composed primarily of the Pleistocene Astoria and Nitinat Fans, which have been accreting outboard of a narrow, older Cenozoic accretionary complex.…”

Section: Introductionmentioning

confidence: 99%

Super-scale Failure of the Southern Oregon Cascadia Margin

Goldfinger

Kulm

McNeill

et al. 2000

Pure and Applied Geophysics

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Using SeaBeam bathymetry and multichannel seismic reflection records we have identified three large submarine landslides on the southern Oregon Cascadia margin. The area enclosed by the three arcuate slide scarps is approximately 8000 km 2 , and involves an estimated 12,000 -16,000 km 3 of the accretionary wedge. The three arcuate slump escarpments are nearly coincident with the continental shelf edge on their landward margins, spanning the full width of the accretionary wedge. Debris from the slides is buried or partially buried beneath the abyssal plain, covering a subsurface area of at least 8000 km 2 . The three major slides, called the Heceta, Coos Basin and Blanco slides, display morphologic and structural features typical of submarine landslides. Bathymetry, sidescan sonar, and seismic reflection profiles reveal that regions of the continental slope enclosed by the scarps are chaotic, with poor penetration of seismic energy and numerous diffractions. These regions show little structural coherence, in strong contrast to the fold thrust belt tectonics of the adjacent northern Oregon margin. The bathymetric scarps correlate with listric detachment faults identified on reflection profiles that show large vertical separation and bathymetric relief. Reflection profiles on the adjacent abyssal plain image buried debris packages extending 20-35 km seaward of the base of the continental slope. In the case of the youngest slide, an intersection of slide debris and abyssal plain sediments, rather than a thrust fault, mark the base of slope. The age of the three major slides decreases from south to north, indicated by the progressive northward shallowing of buried debris packages, increasing sharpness of morphologic expression, and southward increase in post-slide reformation of the accretionary wedge. The ages of the events, derived from calculated sedimentation rates in overlying Pleistocene sediments, are approximately 110 ka, 450 ka, and 1210 ka. This series of slides traveled 25-70 km onto the abyssal plain in at least three probably catastrophic events, which may have been triggered by subduction earthquakes. The lack of internal structure in the slide packages, and the considerable distance traveled suggest catastrophic rather than incremental slip, although there could have been multiple events. The slides would have generated large tsunami in the Pacific basin, possibly larger than that generated by an earthquake alone. We have identified a potential future slide off southern Oregon that may be released in a subduction earthquake. The occurrence of the slides and subsequent subduction of the slide debris, along with evidence for margin subsidence implies that basal subduction erosion has occurred over at least the last 1 Ma. The massive failure of the southern Oregon slope may have been the result of the collision of a seamount province or aseismic ridge with the margin, suggested by the age progression of the slides and evidence for subducted basement highs. The lack of latitudinal offset between the oldest ...

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“…This source most likely lies within the upper one kilometer of the clastic Cenozoic deposits which apparently overlie subducted sediments from an early Cenozoic period of subduction (Figure 12) [Snavely and McClellan, 1987]. Although the seismic section is located north of the vent field.…”

Section: Source Composition and Migration Of Fluidsmentioning

confidence: 99%

Relationship between carbonate deposits and fluid venting: Oregon Accretionary Prism

Kulm¹,

Suess²

1990

J. Geophys. Res.

199

114

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Active fluid venting and its surface manifestations (Wlique animals and carbonates) occur over the accretionary prism in the Cascadia subduction zone located off central Oregon. A large variety of authigenic carbonate deposits and unique carbonate structures have been observed from submersibles and remotely operated vehicles and recovered with aid of submersibles and bonom trawls from the outennost continental shelf and lower continental slope. The carbonate deposits range from relatively thin crusts and slabs to irregularedif1ces and well-fanned circular chimneys that rise from 1 to 2m above the seafloor. Mineralogically, the carbonate cement consists of aragonite, calcite, and heavier carbon values characterize the dolomitic chimneys from the outer continental shelf. Cemented sandstones from a "window" in the accretionary complex of the lower slope (subgroup IV) are characterized by extreme &IIQ (-5.9to -5.98 %c) and moderate snc (-18.7 to -12.67%o) -depleted carbonates. This "lightn oxygen isotope composition most likely originated from the upward migration of warm hydrothermal fluids along the main d6collement, which tapped the wann subducting basaltic slab, during the early stages of formation of the accreted complex. Well-defined plumbing tubes within some carbonate chimneys on the shelf infer a single well-defined subsurface conduit with a fairly energetic fluid flow. The majority of the chimneys probably formed above the seafloor as long as the rate of carbonate precipitation exceeded the rate of detrital input during their formation. We calculate a minimum of one conduit for each 35 m2 at one vent site on the shelf. A less energetic flow i.s suggested by the chaotic plwnbing network of an irregular edifice and by the widespread occurrence of the carbonate slabs and crusts at numerous vent sites. INrRooucnoN

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Preliminary geologic interpretation of USGS S. P. Lee seismic-reflection profile WO 76-7 on the continental shelf and upper slope, northwestern Oregon

Cited by 5 publications

References 14 publications

Listric normal faulting on the Cascadia continental margin

Listric normal faulting on the Cascadia continental margin

Super-scale Failure of the Southern Oregon Cascadia Margin

Relationship between carbonate deposits and fluid venting: Oregon Accretionary Prism

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