Author: L. D. KulmPublisher:
ISBN:
Category : Geology
Languages : en
Pages : 33
Book Description
Oregon Continental Shelf Sedimentation
Author: L. D. KulmGold Distribution in Surface Sediments on the Continental Shelf Off Southern Oregon
Author: Hugh Edward CliftonPublisher:
ISBN:
Category : Continental shelf
Languages : en
Pages : 16
Book Description
Continental Shelf Sediments Off Oregon
Author: Continental Shelf Sediments, Columbia River to Cape Blanco, Oregon
Author: Erwin John RungePublisher:
ISBN:
Category : Coasts
Languages : en
Pages : 330
Book Description
Sediment Textures and Internal Structures
Author: Robert Cornelius RoushPublisher:
ISBN:
Category : Marine sediments
Languages : en
Pages : 150
Book Description
A study of sedimentary structures and sediment texture of beach and continental shelf sediments provides a basis for the interpretation of the recent history of sedimentation on the Oregon continental shelf. The texture of various sediment types suggests that coastal rivers supply a considerable quantity of very fine sand in addition to modern mud to the continental shelf. Relict sediments remain uncovered on areas of the shelf not under the influence of major river runoff and are mixed or covered by modern mud and very fine sand where rivers influence shelf sedimentation. Primary sedimentary structures show that sands ranging from very fine to medium in mean grain size are capable of being moved at shelf water depths from at least 38 to 88 meters. No net transport of sand, however, can be determined from these structures. Organic structures apparently are controlled by water depth and/or grain size and sediment type which determine faunal composition and concentration. At mid-shelf depths fine sand cores are characterized by shell fragments, worm tubes, and worm trails. Beyond 100 meters water depth worm tubes were not found, but worm trails become abundant, and large burrows appear in the sediment.
Continental Shelf Sediments Off Oregon
Author: John Vincent ByrnePublisher:
ISBN:
Category : Continental shelf
Languages : en
Pages : 1
Book Description
Continental Shelf Sediments in the Vicinity of Newport, Oregon
Author: David Clifford BushnellPublisher:
ISBN:
Category : Coasts
Languages : en
Pages : 214
Book Description
Sediment Transport on the Northern Oregon Continental Shelf
Author: John Charles HarlettPublisher:
ISBN:
Category : Continental shelf
Languages : en
Pages : 240
Book Description
The distribution of surface sediments on the northern Oregon continental shell is characterized by a nearshore sandy facies and an outer shelf muddy facies, separated by a mid-shelf zone of mixed sand and mud. Currents which have been measured at 130 centimeters above the bottom indicate that the distribution of the surface sediment is a reflection of the hydraulic regime. The strongest bottom currents which were measured were in the nearshore region at a depth of 36 meters. Here currents of over 40 cm/sec generated by surface waves are capable of placing the nearshore sands in suspension, where they are transported shoreward by the wave surge. At mid-shelf, in 90 meters of water, the bottom current veolcity ranges from zero to over 25 cm/sec, although the mean is normally about 10 cm/sec. The strongest currents at this depth are capable of eroding some of the fine sediments, but probably do not rework the older sediments which have been compacted. Currents which are similar in character to those at mid-shelf were observed at the shelf edge in a depth of 165 meters. A significant departure, however, is the difference in frequency where the most energy is found. At the shelf edge the dominant frequency was about four cpd whereas the dominant frequency at mid-shelf was two cpd or lower. The dominant frequencies indicate that tides are important in the generation of continental shelf bottom currents. The twelve - hour period is that of the semi-diurnal tide; the six-hour period is the second harmonic of the semi-diurnal component. No indication of surface wave influence was found at mid-shelf or shelf-edge depths. Profiles of turbidity made at four east-west transects of the continental shelf indicate suspended sediment transport occurs principally at three levels in the water column. An upper layer is at the level of the seasonal thermocline, a mid-water layer is located at the level of the permanent pycnocline, and the third layer is at the bottom. The surface layer is important in transporting suspended sediment of the Columbia River plume, although there is also a contribution to the surface layer from the surf zone by the process of diffusion of fine particles. The mid-water layer thickens vertically and becomes less intense seaward, indicating a nearshore source for the suspended material. This source is diffusion of fine particles from the surf zone at mid-water depths. The mid-water layer is located at the level of the permanent pycnocline. The layer is sub-parallel to the bottom over the shelf but becomes diffuse at the shelf edge. Sediment transport in the mid-water layer provides a mechanism by which sediment bypasses the outer shelf and upper slope area. The bottom layer receives its suspended material from erosion of the bottom, from the water column above, and from fine material moving seaward from the surf zone. The amount of eroded material contributed to the bottom layer depends on the bottom current strength and on the bottom roughness characteristics. Over a rough bottom the erosive power of a given bottom current is increased drastically. For this reason, the presence or absence of rippling is important to sediment transport on the shelf. The fine material of the bottom layer may concentrate by settling during quiescent periods, allowing low-density flows to initiate. Several time-series observations of turbidity indicate that the bottom layer thickens and thins in response to increases and decreases in current velocity. The mid-water layer migrated somewhat in a vertical direction, but its thickness and intensity remained nearly the same. The thickness and intensity of the upper layer responded to changes in the structure of the thermocline, becoming thick and dispersed when the upper part of the water column is mixed. A model of sediment transport proposes that mid-water and bottom currents transport suspended sediments diagonally across the shelf toward the south-southwest. The sediments of the Columbia River plume are also transported in a southerly direction in the surface waters. Relatively little deposition takes place on the shelf and upper slope, with the bulk of the sediments bypassing the shelf and depositing on the lower slope and continental rise.
Author: 
Author: Meredith Grant Gross