The Central Oregon Continental Margin, Lines WO76-4 and WO76-55
Parke D. Snavely, Jr., Roland von Huene, Dennis M. Mann, John Miller, 1986. "The Central Oregon Continental Margin, Lines WO76-4 and WO76-55", Seismic Images of Modern Convergent Margin Tectonic Structure, Roland von Huene, Susan Vath, Christine Sperber, Bridgett Fulop, Lee Bailey, Monique Martin
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The geologic history of Cenozoic sedimentary and volcanic rocks of the Oregon continental margin is interpreted as having involved episodic periods of underthrusting, transcurrent faulting, and extension between the oceanic and North American plates. The seismic sections across this margin illustrate that both compressional and extensional forces have molded the tectonic framework (Snavely et al., 1980).
The Oregon Coast Range and inner shelf is floored by Paleocene to lower Eocene ridge basalt (see diagrammatic cross section), which is interpreted to represent eruptions in an elongate basin formed by rifting of the continental margin (Snavely, 1984). Oceanic islands and sea mounts were constructed on the basaltic ocean floor, and the volcanic flows and breccia that erupted from these centers intertongue with neritic to bathyal sedimentary rocks of early and middle Eocene age. Middle Eocene turbidite sandstone overlaps both the oceanic basalts and the pre-Tertiary rocks of the Klamath Mountains, suturing the Coast Range to North America about 50 Ma.
Oblique convergence between the oceanic and the North American plates occurred during most of post-middle Eocene time, but periods of more head-on convergence occurred in the middle late Eocene and late middle Miocene. Sedimentation, punctuated by episodes of volcanism, was virtually continuous in the forearc basin, the axis of which lay along the present inner continental shelf. More than 7000 m of sedimentary and volcanic rocks were deposited in this basin (Snavely et al., 1980), which is located east of seismic lines 4 and 5 (see diagrammatic cross section).
The principal structure
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In 1980, A. W. Bally assembled and edited an innovative three-volume “picture and work” atlas of seismic reflection record sections. This compilation of more than 130 excellent seismic section reproductions provided much new data from the earth's subsurface. For petroleum geologists, academic scientists, and students, it is the field geologist's counterpart of outcrops and type sections. The smaller collection of seismic sections presented in this Studies 26 publication was inspired by Bally's atlas, and follows his general format and philosophy. The objective is to provide a reference series of sections for the earth sciences and a vehicle for continuing scientific dialogue relating to modern convergent margins. This publication's assembled sections represent a single facet of that dialogue by bringing together a series of exceptional seismic sections from the fronts of presently active convergent margins around the Pacific.