Marine geology of the continental margin off southern Oregon

• Main Author: Spigai, Joseph John
• Other Authors: Kulm, LaVerne D., Oceanography, Oregon State University. Graduate School
• Format: Doctoral or Postdoctoral Thesis
• Language: English; unknown
• Published: Oregon State University
• Subjects: Submarine geology; Planktonic foraminifera
• Online Access: https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/2r36v139f

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 ...