Sedimentary facies on the rises and slopes of passive continental margins

1980 ◽  
Vol 294 (1409) ◽  
pp. 169-176 ◽  
Keyword(s):  
Sediment Transport ◽  
Debris Flows ◽  
Thermohaline Circulation ◽  
Dominant Role ◽  
Sedimentary Facies ◽  
Turbidity Currents ◽  
Continental Margins ◽  
Passive Margins ◽  
New Evidence

JOIDES drilling results provide new evidence concerning facies patterns on evolving passive margins that strengthens and extends hypotheses constructed from studies of morphology, seismic reflexion data and shallow samples on modern margins, and from field geologic studies of uplifted ancient margins. On the slopes and rise, gravity-controlled mechanisms - turbidity currents, debris flows, slides and the like - play the dominant role in sediment transport over the long term, but when clastic supplies are reduced, as for example during rapid transgressions, then oceanic sedimentation and the effects of thermohaline circulation become important. Sedimentary facies models used as the basis of unravelling tectonic complexities of some deformed margins, for example in the Mesozoic Tethys, may be too simplistic in the light of available data from modern continental margins.

Morphology of the continental margin

1978 ◽  
Vol 290 (1366) ◽  
pp. 75-85 ◽  
Keyword(s):  
Continental Margin ◽  
Turbidity Currents ◽  
Continental Margins ◽  
Island Arcs ◽  
Horizontal Shear ◽  
Passive Margins ◽  
Shelf Slope ◽  
Shear Motion ◽  
Continental Shelf Slope ◽  
Active Continental Margins

The continental margin is the surface morphological expression of the deeper fundamental transition between the thick low density continental igneous crust and the thin high density and chemically different oceanic igneous crust. Covering the transition are thick sediment accumulations comprising over half the total sediments of the ocean, so that the precise morphological boundaries often differ in position from those of the deeper geology. Continental margins are classified as active or passive depending on the level of seismicity. Active continental margins are divided into two categories, based on the depth distribution of earthquakes and the tectonic regime. Active transform margins, characterized by shear and shallow focus earthquakes, result from horizontal shear motion between plates. Active compressional margins are characterized by shallow, intermediate and deep earthquakes along a dipping zone, by oceanic trenches and by volcanic island arcs or mountain ranges depending on whether the margin is oceanocean or ocean-continent. Passive margins, found in the Atlantic and Indian Oceans, are formed initially by the rifting of continental crust and mark the ocean-continent boundary within the spreading plate. They are characterized by continental shelf, slope and rise physiographic provinces. Once clear of the rifting axis, they cool and subside. Sedimentation can prograde the shelf and load the edge leading to further down warping; changes of sea level lead to erosion by wave action and by ice; ocean currents and turbidity currents redistribute sediments; slumps occur in unstable areas. The passive and sediment-starved margin west of Europe is described where the following factors have been significant: (a) faulting related to initial rifting; (b) infilling and progradation by sediments; (c) slumping; (d) contour current erosion and deposition; (e)canyon erosion.

scholarly journals Channel-levee evolution in combined contour current–turbidity current flows from flume-tank experiments

Geology ◽  
2020 ◽  
Vol 48 (4) ◽  
pp. 353-357 ◽  
Author(s):  
Elda Miramontes ◽  
Joris T. Eggenhuisen ◽  
Ricardo Silva Jacinto ◽  
Giovanni Poneti ◽  
Florian Pohl ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Maximum Velocity ◽  
Turbidity Currents ◽  
Continental Margins ◽  
Synchronous Interaction ◽  
Channel Form ◽  
Stationary Front ◽  
Levee System ◽  
Current Flows

Abstract Turbidity currents and contour currents are common sedimentary and oceanographic processes in deep-marine settings that affect continental margins worldwide. Their simultaneous interaction can form asymmetric and unidirectionally migrating channels, which can lead to opposite interpretations of paleocontour current direction: channels migrating against the contour current or in the direction of the contour current. In this study, we performed three-dimensional flume-tank experiments of the synchronous interaction between contour currents and turbidity currents to understand the effect of these combined currents on channel architecture and evolution. Our results show that contour currents with a velocity of 10–19 cm s−1 can substantially deflect the direction of turbidity currents with a maximum velocity of 76–96 cm s−1, and modify the channel-levee system architecture. A lateral and nearly stationary front formed on the levee located upstream of the contour current, reduced overspill and thus restrained the development of a levee on this side of the channel. Sediment was preferentially carried out of the channel at the flank located downstream of the contour current. An increase in contour-current velocity resulted in an increase in channel-levee asymmetry, with the development of a wider levee and more abundant bedforms downstream of the contour current. This asymmetric deposition along the channel suggests that the direction of long-term migration of the channel form should go against the direction of the contour current due to levee growth downstream of the contour current, in agreement with one of the previously proposed conceptual models.

Elevated, passive continental margins: Long-term highs or Neogene uplifts? New evidence from West Greenland

2006 ◽  
Vol 248 (1-2) ◽  
pp. 330-339 ◽  
Author(s):  
Peter Japsen ◽  
Johan M. Bonow ◽  
Paul F. Green ◽  
James A. Chalmers ◽  
Karna Lidmar-Bergström
Keyword(s):  
Continental Margins ◽  
West Greenland ◽  
New Evidence

Deepwater debrites and linked megaturbidites in confined basins: An example from the Onnuri Basin, East Sea of Korea

2021 ◽  
Vol 91 (1) ◽  
pp. 1-20
Author(s):  
Deniz Cukur ◽  
In-Kwon Um ◽  
Jong-Hwa Chun ◽  
Gwang-Soo Lee ◽  
Gee-Soo Kong ◽  
...  
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Slope Failure ◽  
Sedimentary Facies ◽  
High Amplitude ◽  
Seismic Facies ◽  
East Sea ◽  
Turbidity Currents ◽  
Radiocarbon Dates ◽  
Depositional Processes

ABSTRACT We analyzed data from seven piston cores, multi-channel seismic-reflection (MCS) and chirp profiles, and multibeam echosounder (MBES) data to study the distribution, emplacement time, sedimentary facies, and depositional processes of sediment-gravity-flow deposits in the Onnuri Basin, a confined basin in the East Sea. These data reveal that debris flows have traveled ca. 30 km downslope, forming a seismic facies consisting of stacked, wedge-shaped, transparent units separated by high-amplitude continuous reflectors. Analysis of piston cores shows three distinct sedimentary units, throughout the basin. The lowest unit, I, is a debrite containing numerous mud clasts of varying size and color distributed in a mud-rich matrix; it is absent over elevated basinal highs or ridges, such as the Onnuri Ridge, suggesting that local topography controls its distribution. The debrite forms a recognizable acoustically transparent layer on subbottom chirp profiles (av. 7 m thick), covers approximately 500 km2, and has an estimated volume of ∼ 3.5 km3. The overlying unit, II, contains normally graded beds composed of massive sand, laminated and cross-laminated sand and silt, and a thick cap of structureless mud. This unit is interpreted to be a megaturbidite deposited from turbidity currents that originated from the flow transformation of debris flows on the upper continental slope. The megaturbidite covers the entire basin (at least 650 km2), and has an average thickness of 2.8 m (maximum thickness of 4.35 m), and comprises a volume of 1.8 km3. Variations in grain size and sedimentary structures suggest that the megaturbidite was deposited by progressively waning flows that reflected off basin flanks and ridges. The thick (up to 3.65 m) structureless mud cap further indicates deposition in a confined basin. The sharp basal contact, together with the lack of hemipelagic sediments between debrite and overlying megaturbidite, suggest that both were deposited during the same flow event, likely to have originated from a single catastrophic slope failure. Collapsing slide material evolved into a debris flow, from which a turbidite formed by dilution of the debris flow. Radiocarbon dates suggest that the slope failure occurred about 13–11 ka, a time when sea level was ca. 50 m lower than at the present day. Hemipelagic sediments in the topmost unit, III-2, above the megaturbidite indicate that the basin has been stable since ca. 11 ka. We provide robust evidence that submarine slope failures evolve downslope into slides, debris flows, and finally, thick megaturbidites. This contribution highlights the importance of seafloor morphology on the distribution and stratigraphy of submarine flows in confined basins.

scholarly journals Great earthquakes along the Western United States continental margin: implications for hazards, stratigraphy and turbidite lithology

2012 ◽  
Vol 12 (11) ◽  
pp. 3191-3208 ◽  
Author(s):  
C. H. Nelson ◽  
J. Gutiérrez Pastor ◽  
C. Goldfinger ◽  
C. Escutia
Keyword(s):  
Cascadia Subduction Zone ◽  
Great Earthquake ◽  
Turbidity Currents ◽  
Continental Margins ◽  
Northern California ◽  
Recurrence Times ◽  
Passive Margins ◽  
San Andreas ◽  
Great Earthquakes ◽  
Active Tectonic

Abstract. We summarize the importance of great earthquakes (Mw &amp;gtrsim; 8) for hazards, stratigraphy of basin floors, and turbidite lithology along the active tectonic continental margins of the Cascadia subduction zone and the northern San Andreas Transform Fault by utilizing studies of swath bathymetry visual core descriptions, grain size analysis, X-ray radiographs and physical properties. Recurrence times of Holocene turbidites as proxies for earthquakes on the Cascadia and northern California margins are analyzed using two methods: (1) radiometric dating (14C method), and (2) relative dating, using hemipelagic sediment thickness and sedimentation rates (H method). The H method provides (1) the best estimate of minimum recurrence times, which are the most important for seismic hazards risk analysis, and (2) the most complete dataset of recurrence times, which shows a normal distribution pattern for paleoseismic turbidite frequencies. We observe that, on these tectonically active continental margins, during the sea-level highstand of Holocene time, triggering of turbidity currents is controlled dominantly by earthquakes, and paleoseismic turbidites have an average recurrence time of ~550 yr in northern Cascadia Basin and ~200 yr along northern California margin. The minimum recurrence times for great earthquakes are approximately 300 yr for the Cascadia subduction zone and 130 yr for the northern San Andreas Fault, which indicates both fault systems are in (Cascadia) or very close (San Andreas) to the early window for another great earthquake. On active tectonic margins with great earthquakes, the volumes of mass transport deposits (MTDs) are limited on basin floors along the margins. The maximum run-out distances of MTD sheets across abyssal-basin floors along active margins are an order of magnitude less (~100 km) than on passive margins (~1000 km). The great earthquakes along the Cascadia and northern California margins cause seismic strengthening of the sediment, which results in a margin stratigraphy of minor MTDs compared to the turbidite-system deposits. In contrast, the MTDs and turbidites are equally intermixed on basin floors along passive margins with a mud-rich continental slope, such as the northern Gulf of Mexico. Great earthquakes also result in characteristic seismo-turbidite lithology. Along the Cascadia margin, the number and character of multiple coarse pulses for correlative individual turbidites generally remain constant both upstream and downstream in different channel systems for 600 km along the margin. This suggests that the earthquake shaking or aftershock signature is normally preserved, for the stronger (Mw ≥ 9) Cascadia earthquakes. In contrast, the generally weaker (Mw = or <8) California earthquakes result in upstream simple fining-up turbidites in single tributary canyons and channels; however, downstream mainly stacked turbidites result from synchronously triggered multiple turbidity currents that deposit in channels below confluences of the tributaries. Consequently, both downstream channel confluences and the strongest (Mw ≥ 9) great earthquakes contribute to multi-pulsed and stacked turbidites that are typical for seismo-turbidites generated by a single great earthquake. Earthquake triggering and multi-pulsed or stacked turbidites also become an alternative explanation for amalgamated turbidite beds in active tectonic margins, in addition to other classic explanations. The sedimentologic characteristics of turbidites triggered by great earthquakes along the Cascadia and northern California margins provide criteria to help distinguish seismo-turbidites in other active tectonic margins.

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