scholarly journals Effect of channel tributaries on the evolution of submarine channel confluences (Espírito Santo Basin, SE Brazil)

2019 ◽  
Vol 132 (1-2) ◽  
pp. 263-272 ◽  
Author(s):  
Yongpeng Qin ◽  
Tiago M. Alves ◽  
José Antonio Constantine ◽  
Davide Gamboa ◽  
Shiguo Wu
Keyword(s):  
Continental Shelf ◽  
Main Channel ◽  
Turbidity Currents ◽  
Lateral Migration ◽  
Sediment Sources ◽  
The West ◽  
Multiple Channel ◽  
Channel Bend ◽  
Submarine Channel ◽  
Se Brazil

AbstractConfluences are geomorphologic features fed by distinct channel tributaries that record the contribution of multiple sediment sources. They are key features of both fluvial and submarine channels in geomorphologic and sedimentologic terms. Here, we use high-quality three-dimensional seismic data from SE Brazil to document the response of a submarine channel confluence to turbidity currents originating from a tributary. The studied channel system consists of a west tributary, an east tributary, and a postconfluence channel, with the last two comprising the main channel at present. Downstream from the confluence, changes in planform morphology and architecture were found due to the effect of turbidity currents sourced from the west tributary channel. A channel bend in the main channel curved toward the west when it was first formed but later curved toward the east, and so remains until the present day. This process led to the migration of the confluence point ∼500 m to the east, and changed the bed morphology from discordant (where the beds of tributaries and main channels meet at an unequal depth) to concordant (where the beds of tributaries and main channels meet at approximately the same depth). In addition to the channel bend near the confluence, two other bends further downstream recorded significant changes with time, increasing channel sinuosity from 1.11 to 1.72. These three channel bends near the confluence accumulated a large volume of sediment at their inner banks, generating depositional bars. Multiple channel forms within the depositional bars indicate the occurrence of large-scale lateral migration near the confluence. Hence, turbidity currents from the west tributary are shown to influence the submarine channel by promoting lateral channel migration, confluence migration, increases in channel sinuosity, and the formation of large depositional bars. These variations near the confluence reveal a change in tributary activity and a shift in sediment sources from east to west on the continental shelf. Such a shift suggests variations in sedimentary processes on the continental shelf probably due to avulsions on Doce River Delta.

Effects of extreme events on the morphology of submarine channels: the case of the Elliot hazard cascade

2021 ◽  
Author(s):  
Michael Tilston ◽  
Dan H. Shugar ◽  
Michael Clare ◽  
Maarten Heijnen ◽  
Sanem Acikalin ◽  
...  
Keyword(s):  
Extreme Event ◽  
Dynamic Equilibrium ◽  
River Mouth ◽  
Channel Morphology ◽  
Sediment Supply ◽  
Turbidity Currents ◽  
Lateral Migration ◽  
Submarine Channels ◽  
Submarine Channel ◽  
Early Results

<p>Submarine systems where the canyon head is directly connected to the river mouth arguably provide the best setting for <em>in situ</em> studies of turbidity currents since the sediment supply propelling them arrive in periodic pulses linked to fluvial freshet events. Consequently, the frequency of, and similarity between, the turbidity currents flowing through these systems make it easier for their channel morphology to evolve towards a state of dynamic equilibrium. Therefore, if an extreme event occurs that dramatically alters the system’s sediment supply, it is reasonable to assume that submarine channels will undergo a period of rapid adjustment. This is the present scenario occurring in Bute Inlet following the recent Elliot Creek hazard cascade. Bute Inlet is one of the most actively monitored sites for turbidity currents in the world, and the extensive historical dataset that has been amassed at this site along with the rare Elliot Creek event provides the unique opportunity to study the impacts of extreme allogenic forcing mechanisms on the morphodynamics of submarine channels.</p><p>Preliminary measurements indicate that the turbidity in Elliot Creek has increased by ~40x compared to pre-slide measurements, and oceanographic measurements within a few days of the event show very high turbidity in ocean bottom water to a distance of almost 70 km from the delta. While the bathymetric survey since the landslide is so far constrained to the proximal region of the inlet, early results show that channel morphology was rapidly altered. Specifically, the submarine channel fed by Southgate River, which supplied water and sediment from the landslide and glacial outburst flood, was lowered by about 3m across the width of the channel bed. Conversely, the morphology of the channel fed by Homathko River has remained static between the 2020 and 2021 surveys. Below the confluence of these two submarine channels, the cyclic steps that once dominated the bed morphology appear to have been largely infilled by a 1-2m thick drape of sediment along the inner half of the channel bend, whereas the outer banks have laterally eroded by upwards of 50m at some points. This trend of channel widening and lateral migration appear to be propagating down the system. Importantly, the nature of the slide suggests that sediment delivery will remain elevated with respect to background conditions for decades into the future, suggesting that the submarine channel may be in the process of adapting to an entirely new flow regime rather than reacting to a singular extreme flow event.</p>

Observed variability of the West India Coastal Current on the continental shelf from 2010–2017

2021 ◽  
Vol 130 (2) ◽  
Author(s):  
Anya Chaudhuri ◽  
P Amol ◽  
D Shankar ◽  
S Mukhopadhyay ◽  
S G Aparna ◽  
...  
Keyword(s):  
Continental Shelf ◽  
Coastal Current ◽  
The West

Why no red tide was observed on the West Florida Continental Shelf in 2010

Harmful Algae ◽  
2014 ◽  
Vol 38 ◽  
pp. 119-126 ◽  
Author(s):  
Robert H. Weisberg ◽  
Lianyuan Zheng ◽  
Yonggang Liu ◽  
Chad Lembke ◽  
Jason M. Lenes ◽  
...  
Keyword(s):  
Continental Shelf ◽  
Red Tide ◽  
The West

Outer limits of the continental shelf beyond CLCS recommendations and Article 76(8) of UNCLOS: With reference to Japan’s Cabinet Order No. 302

2021 ◽  
pp. 1-19
Author(s):  
Michael Sheng-ti Gau ◽  
Si-han Zhao
Keyword(s):  
Continental Shelf ◽  
The West ◽  
Common Heritage ◽  
Common Heritage Of Mankind ◽  
Essential Questions ◽  
National Jurisdiction ◽  
The Common ◽  
United Nations Convention ◽  
Legal Consequences ◽  
The Unclos

Abstract In 2014 Japan’s Cabinet Order No. 302 declared the outer limits of its continental shelf beyond 200 nautical miles (OL) to the west and north of Oki-no-Tori Shima (Area 302). Oki-no-Tori Shima consists of two small, barren, and uninhabitable rocks in the West Pacific. The northern part of Area 302 is broader than what the 2012 recommendations of the Commission on the Limits of the Continental Shelf (CLCS) specify. A question arises whether Order No. 302 violates Article 76(8) of the United Nations Convention on the Law of the Sea (UNCLOS), which provides that the OL established by a coastal state ‘on the basis of’ the CLCS recommendations shall be final and binding. Another question is the role played by the CLCS in ‘assisting’ the coastal states to delimit their national jurisdiction so as to know where the Area (i.e., the Common Heritage of Mankind under UNCLOS Articles 1(1)(1) and 136) begins. The essential questions arising from Area 302 concern how well the UNCLOS mechanism can perform to safeguard the Common Heritage of Mankind through preventing encroachment thereupon by individual coastal states. This article looks at the context and explores the obligations implied by Article 76(8) for coastal states to ‘follow’ the recommendations in establishing the OL, with special reference to the northern part of Area 302. The article also examines legal consequences arising from a breach of these obligations.

Assessing Bypassed Hydrocarbons

2021 ◽  
Author(s):  
Stanley Oifoghe ◽  
Nora Alarcon ◽  
Lucrecia Grigoletto
Keyword(s):  
Continental Shelf ◽  
Reservoir Characterization ◽  
Gamma Ray ◽  
West African ◽  
The Novel ◽  
The West ◽  
Present Case Study ◽  
Novel Model

Abstract Hydrocarbons are bypassed in known fields. This is due to reservoir heterogeneities, complex lithology, and limitations of existing technology. This paper seeks to identify the scenarios of bypassed hydrocarbons, and to highlight how advances in reservoir characterization techniques have improved assessment of bypassed hydrocarbons. The present case study is an evaluation well drilled on the continental shelf, off the West African Coastline. The targeted thin-bedded reservoir sands are of Cenomanian age. Some technologies for assessing bypassed hydrocarbon include Gamma Ray Spectralog and Thin Bed Analysis. NMR is important for accurate reservoir characterization of thinly bedded reservoirs. The measured NMR porosity was 15pu, which is 42% of the actual porosity. Using the measured values gave a permeability of 5.3mD as against the actual permeability of 234mD. The novel model presented in this paper increased the porosity by 58% and the permeability by 4315%.

Linking submarine channel-levee facies and architecture to flow structure of turbidity currents: insights from flume tank experiments

Sedimentology ◽  
2017 ◽  
Vol 65 (3) ◽  
pp. 931-951 ◽  
Author(s):  
Jan de Leeuw ◽  
Joris T. Eggenhuisen ◽  
Matthieu J. B. Cartigny
Keyword(s):  
Flow Structure ◽  
Turbidity Currents ◽  
Submarine Channel

scholarly journals Data-Driven, Multi-Model Workflow Suggests Strong Influence from Hurricanes on the Generation of Turbidity Currents in the Gulf of Mexico

2020 ◽  
Vol 8 (8) ◽  
pp. 586
Author(s):  
Courtney Harris ◽  
Jaia Syvitski ◽  
H.G. Arango ◽  
E.H. Meiburg ◽  
Sagy Cohen ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Continental Shelf ◽  
Numerical Models ◽  
Ocean Dynamics ◽  
Turbidity Currents ◽  
Regional Ocean Modeling System ◽  
Transport Pathway ◽  
Seabed Sediment ◽  
Continental Scale ◽  
Sediment Routing

Turbidity currents deliver sediment rapidly from the continental shelf to the slope and beyond; and can be triggered by processes such as shelf resuspension during oceanic storms; mass failure of slope deposits due to sediment- and wave-pressure loadings; and localized events that grow into sustained currents via self-amplifying ignition. Because these operate over multiple spatial and temporal scales, ranging from the eddy-scale to continental-scale; coupled numerical models that represent the full transport pathway have proved elusive though individual models have been developed to describe each of these processes. Toward a more holistic tool, a numerical workflow was developed to address pathways for sediment routing from terrestrial and coastal sources, across the continental shelf and ultimately down continental slope canyons of the northern Gulf of Mexico, where offshore infrastructure is susceptible to damage by turbidity currents. Workflow components included: (1) a calibrated simulator for fluvial discharge (Water Balance Model - Sediment; WBMsed); (2) domain grids for seabed sediment textures (dbSEABED); bathymetry, and channelization; (3) a simulator for ocean dynamics and resuspension (the Regional Ocean Modeling System; ROMS); (4) A simulator (HurriSlip) of seafloor failure and flow ignition; and (5) A Reynolds-averaged Navier–Stokes (RANS) turbidity current model (TURBINS). Model simulations explored physical oceanic conditions that might generate turbidity currents, and allowed the workflow to be tested for a year that included two hurricanes. Results showed that extreme storms were especially effective at delivering sediment from coastal source areas to the deep sea, at timescales that ranged from individual wave events (~hours), to the settling lag of fine sediment (~days).

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