scholarly journals A stratigraphic example of the architecture and evolution of shallow water mouth bars

Sedimentology ◽  
2020 ◽  
Author(s):  
Grant Cole ◽  
Rhodri Jerrett ◽  
Matthew P. Watkinson
Keyword(s):  
Shallow Water ◽  
Mouth Bars

The architecture and evolution of shallow water delta mouth bars: examples from the Lower Cretaceous of Spain

2021 ◽  
Author(s):  
Matthew Watkinson ◽  
Grant Cole ◽  
Rhodri Jerrett
Keyword(s):  
Shallow Water ◽  
Lower Cretaceous ◽  
East Central ◽  
Architectural Analysis ◽  
Rapid Flow ◽  
Flow Deceleration ◽  
Mouth Bar ◽  
Mouth Bars ◽  
Accelerated Flow ◽  
Bed Friction

<p>Improved understanding of delta mouth bar morphodynamics, and the resulting stratigraphic architectures, is important for predicting the loci of deposition of different sediment fractions, coastal geomorphic change and heterogeneity in mouth bar reservoirs. Facies and architectural analysis of exceptionally well-exposed shallow water (ca. 5 m depth) mouth bars and associated distributaries, from the Xert Formation (Lower Cretaceous), of the Maestrat Basin (east-central Spain), reveal that they grew via a succession of repeated autogenic cycles. The formation is part of a mixed clastic-carbonate succession deposited during a time of active faulting and incipient salt tectonism, but in an area away from their direct influence and where wave and tidal reworking were minimal.</p><p>An initial mouth bar accretion element forms after avulsion of a distributary into shallow standing water. Turbulent expansion of the fluvial jet and high bed friction results in rapid flow deceleration, and deposition of sediment in an aggradational to expansional bar-form. Vertical bar growth causes flattening and acceleration of the jet. The accelerated flow scours channels on the bar top, which focuses further expansion of the mouth bar at individual loci where the channels break through the front of the mouth bar. Here, new mouth bar accretion elements form, downlapping and onlapping against a readily recognizable surface of mouth bar reorganization. Vertical growth of the new mouth bar accretion elements causes flattening and re-acceleration of the jet, leading to channelization, and initiation of the next generation of mouth bar accretion elements. Thus the mouth bar grows, until bed-friction effects cause backwater deceleration and superelevation of flow in the feeding distributary. Within-channel sedimentation, choking and upstream avulsion of the feeding channel, results in mouth bar abandonment. In this study, mouth bars are formed of at least two to three accretion elements, before abandonment happened. The results of this study contrast with the notion that mouth bars form by simple vertical aggradation and radial expansion. However, the architecture and facies distributions of shallow water mouth bars are a predictable product of intrinsic processes that operate to deposit them.</p>

Hydrodynamics and deposition in lacustrine shallow-water delta front: A combination of numerical simulations and modern sedimentation measurements

2020 ◽  
Vol 8 (3) ◽  
pp. SM39-SM52
Author(s):  
Yunlong Zhang ◽  
Zhidong Bao ◽  
Luxing Dou ◽  
Li Jiang ◽  
Mingyang Wei ◽  
...  
Keyword(s):  
Shear Stress ◽  
Numerical Simulations ◽  
Shallow Water ◽  
River Flow ◽  
Oil And Gas ◽  
Bed Shear Stress ◽  
Delta Front ◽  
Sedimentary Architecture ◽  
Dip Angle ◽  
Mouth Bars

With the exploration of tight oil and gas, shallow-water deltaic reservoirs have been attracting more and more attention. The sedimentary architecture of a shallow-water delta shows distinctive differences with that of a deep-slope delta. These differences may be associated with the mechanism and characteristics of the deposition in the area where the sediments unloaded. Based on modern sedimentary research of the Poyang Lake in China, this paper focuses on the processes of river flow entering a lake with a low dip angle. We conducted six sets of numerical simulations with different initial sedimentary flow velocities using Fluent software for analyzing the hydrodynamics and the sediment transportation in the shallow-water delta. We combined the simulation results with an analysis of the geomorphology of the Gangjiang Delta to reveal the deposition along the shoreline of the lacustrine shallow-water delta. The numerical simulation shows that the shallow-water delta is dominated by bed friction with an extensive hydrodynamical boundary layer. The bed shear stress, which varies with the changes in river flux, dominated the sediment transport and deposition at the shallow-water delta front, where the effluent flow mixes with lake water. The distributary channels show characteristics of repeatedly occurred erosion, scouring, filling, and reoccupation. We argue that the depositional characteristics are associated with the changes in bed shear stress controlled by variation of flow velocity. Mouth bars are less likely to grow to a reasonable scale because of the seasonal scouring of extreme floods. Moreover, the lake flow potentially reworks the mouth bars. Consequently, mouth bar deposits were difficult to preserve as hydrocarbon reservoirs in ancient shallow-water delta.

Spatial assemblage structure of shallow-water reef fish in Southwest Australia

2020 ◽  
Vol 649 ◽  
pp. 125-140
Author(s):  
DS Goldsworthy ◽  
BJ Saunders ◽  
JRC Parker ◽  
ES Harvey
Keyword(s):  
Shallow Water ◽  
Reef Fish ◽  
Marine Environment ◽  
Fish Assemblages ◽  
Canopy Cover ◽  
Reef Fishes ◽  
Reef Fish Assemblage ◽  
Reef Type ◽  
Present Distribution ◽  
Southwest Australia

Bioregional categorisation of the Australian marine environment is essential to conserve and manage entire ecosystems, including the biota and associated habitats. It is important that these regions are optimally positioned to effectively plan for the protection of distinct assemblages. Recent climatic variation and changes to the marine environment in Southwest Australia (SWA) have resulted in shifts in species ranges and changes to the composition of marine assemblages. The goal of this study was to determine if the current bioregionalisation of SWA accurately represents the present distribution of shallow-water reef fishes across 2000 km of its subtropical and temperate coastline. Data was collected in 2015 using diver-operated underwater stereo-video surveys from 7 regions between Port Gregory (north of Geraldton) to the east of Esperance. This study indicated that (1) the shallow-water reef fish of SWA formed 4 distinct assemblages along the coast: one Midwestern, one Central and 2 Southern Assemblages; (2) differences between these fish assemblages were primarily driven by sea surface temperature, Ecklonia radiata cover, non-E. radiata (canopy) cover, understorey algae cover, reef type and reef height; and (3) each of the 4 assemblages were characterised by a high number of short-range Australian and Western Australian endemic species. The findings from this study suggest that 4, rather than the existing 3 bioregions would more effectively capture the shallow-water reef fish assemblage patterns, with boundaries having shifted southwards likely associated with ocean warming.

Low mode acoustics of shallow water waveguides

2011 ◽  
Vol 181 (11) ◽  
pp. 1222 ◽  
Author(s):  
Aleksandr G. Luchinin ◽  
Aleksandr I. Khil'ko
Keyword(s):  
Shallow Water

Analysis and Modeling of Ambient Noise in Shallow Water of Arabian Sea

2012 ◽  
Vol 2 (6) ◽  
pp. 271-272
Author(s):  
Sudhir Pal Singh Rawat ◽  
◽  
Dr. Arnab Das ◽  
Dr. H.G.Virani Dr. H.G.Virani ◽  
Dr. Y.K.Somayajulu Dr. Y.K.Somayajulu
Keyword(s):  
Shallow Water ◽  
Arabian Sea ◽  
Ambient Noise
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