Sedimentary Settings on Continental Margins — an Overview
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Continental Margin
Mass wasting
Sedimentation
Submarine canyon
A region on the U.S. East Coast exhibiting sediment instability is present on the continental margin seaward of the coast of Delaware and the Baltimore Canyon Trough area. A detailed bathymetric and seismic-reflection survey of a 7.5 by 13.0-km area, together with box, hydroplastic, and piston cores, affords an integrated study of a large submarine slide with a volume of 11 cu km on the continental slope northeast of Wilmington Canyon. The geotechnical properties and sedimentologic characteristics of the seafloor show variations that are associated with the slide. The slump block is believed to be composed of Pleistocene sediment with sediment failure occurring on the slope along a late Tertiary erosion surface which formed the gross morphology of the continental margin. he suggested mechanism for triggering the sediment failure is increased wave energy associated with a lower stand of sea level during the late Pleistocene. Mass wasting of material downslope by creep is a process which apparently still is occurring.
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Submarine canyon
Mass wasting
Continental Margin
Bathymetric chart
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The Var Canyon and the continental slope along the French Riviera were investigated using SAR, a new deeply towed high-resolution side-scan sonar and 3.5-kHz subbottom profiler package. Later on, a ground-truth operation using the CYANA submersible and Kuellenberg cores provided in-situ observations and samples. The main characteristics of this area are the narrow shelf, the steep continental slope, and very coarse superficial materials. During the Pliocene, an alluvial cone was built on the floor of a deep ria located at the present Var alluvial plain. This detritic cone overlies the Messinian erosion surface. It is totally submarine and formed by pudding stones, conglomerates, and marls. Since the early Quaternary, this large sedimentary body has been dismantled by gravity processes (mass wasting, debris flows, turbidites). The bed form at the head of the Var Valley (500 m depth) is marked by an anastomosed network eroding the spurs that give the typical herringbone facies of the canyon's flanks. Downslope from this area begins a gravel wave field extending to a water depth of 2,100 m. Wavelength and height appear to be directly controlled by the topography. Downward and according to a break in the slope, the sea floor is characterized by amore » rhythmic alternance of gravel fields and mud fields (to 2,400 m). The muddy areas are always located on relatively high points of the sea bottom. The significance of these bed forms will be discussed and related to the sedimentary processes which may have operated in this area.« less
Submarine canyon
Mass wasting
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Marl
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Slumping
Submarine canyon
Continental Margin
Deposition
Turbidity current
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Contourite
Continental Margin
Submarine canyon
Terrace (agriculture)
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Submarine canyon
Progradation
Continental Margin
Slumping
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ABSTRACT The continental terrace of Israel consists of Nile‐derived sediments. They are classified into three major groups, according to their structures: (1) irregularly to wavy laminated, coarse‐grained sediments (quartz and skeletal debris) of the flat outer shelf and upper bend of the slope (10–20% of the bulk) which are influenced by currents. These sediments are bioturbated to various degrees. Smectitic silty clays (80–90%) form two structural groups: (2) laminated, turbiditic sediments which accumulate on the slope, particularly in the canyons of the northern slope. Irregular, wavy, thickly laminated, coarse‐grained sediments of the upper slope and canyon heads merge downslope with parallel, thinly laminated, fine‐grained sediments. Toward the foot of the slope and on the adjacent deep‐sea floor lamination becomes indistinct and the sediment is visually homogeneous. (3) Slump‐generated mud lumps of various size which accumulate on the lower slope and along the transport axes of the canyons. These are the most visible evidence for large‐scale slumping mass movement. Transportational and depositional processes are far more intensive over the steep northern continental slope of Israel, and especially in its canyons than over the gentle southern slope. Very stiff overconsolidated sediments unconformably overlain by the ubiquitous recent silty‐clayey sediment were cored on steep sections of the middle continental slope and along the canyon walls. Their preconsolidation stress values suggest that these sections were formerly overlain by more than 40 m of sediment and now are exposed by slumping. The downsliding slabs usually disintegrated into small fragments although several huge fragments could be identified along the canyon axes.
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Turbidity current
Continental Margin
Terrigenous sediment
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Submarine canyon
Contourite
Seafloor Spreading
Mass wasting
Continental Margin
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Mass wasting
Submarine canyon
Turbidity current
Continental Margin
Slumping
Seafloor Spreading
Terrigenous sediment
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ABSTRACT Recent analysis of high-resolution seismic (3.5 kHz), piston core, multichannel seismic, and side-scan sonar data from the continental slope has been used to determine the distribution of acoustic facies and sediment types and to inerpret the depositional processes and their controls. Although hemipelagic drape is areally the most extensive sediment, much thicker sequences of slumps, slides, debris flows, and turbidites are concentrated in intraslope basins and troughs created by salt/shale tectonics. Sedimentation concentrated by tectonics also affects diapir tectonism producing an episodic to cyclic feedback of sediments. This tectono-sedimentary episodicity is superimposed on and interrelated to larger scale sequences resulting from glacioeustatic cycles. Submarine canyons and channels which have served as sediment pathways to the intraslope basins and Alaminos Canyon have been mapped across the continental slope. Intra-basin channels cross previously filled upper slope basins, have high relative width-to-depth ratios, and develop broad levees. Inter-basis canyons and associated channels connect intraslope basins, have low relative width-to-depth ratios, are erosional, and generally have narrow to no levees. The downslope preservation and continuity of these canyon/channel systems is related to the downslope migration of the zone of active salt through time. FIGURE 1. [Grey Scale] INTRA-BASINAL CHANNELS FIGURE 2. [Grey Scale] INTER-BASINAL CHANNELS End_of_Record - Last_Page 585-------
Contourite
Isopach map
Submarine canyon
Mass wasting
Continental Margin
Salt tectonics
Submarine landslide
Aggradation
Passive margin
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