Sediment Transport and River Types Overview

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Questions and Answers

Which of the following describes a characteristic of braided rivers?

Steep banks with high cohesion

Low gradient with fine sediment load

High sinuosity and low sediment transport

Numerous channels separated by bars and islands (correct)

What primarily drives the lateral migration of meandering rivers?

Erosion of cohesive bank materials

Fluctuations in discharge from glaciers

Lateral channel migration (correct)

Presence of tectonic features

Which grain size significantly influences bedform stability in river systems?

Gravel

Clay

Silt

Sand (correct)

What is a common feature of river systems influenced by monsoon discharge?

Dramatic seasonal variations in discharge Signup and view all the answers

How do meandering rivers leave behind a record of their history?

Through lateral accretion surfaces in deposits Signup and view all the answers

What is a defining characteristic of meandering rivers?

They are characterized by high sinuosity and cohesive banks. Signup and view all the answers

How do meandering rivers affect their environment?

Lateral accretion occurs on the point bar with energy decreasing. Signup and view all the answers

What influences the stability of bedforms in rivers?

Grain size and flow velocity. Signup and view all the answers

What effect does topography have on rivers?

It dictates the gradients along which rivers change. Signup and view all the answers

Which river is identified as an example of a meandering river?

South Saskatchewan River Signup and view all the answers

Which characteristic is NOT typically associated with fluvial systems and their deposits?

Presence of marine trace fossils Signup and view all the answers

Which classification of delta is characterized predominantly by fluvial processes?

River-dominated delta Signup and view all the answers

What type of delta experiences enhanced sediment-transporting energy due to tidal influence?

Tide-dominated delta Signup and view all the answers

How does wave action primarily influence sediment in wave-dominated deltas?

By forming sandbars and beaches Signup and view all the answers

Which factor is crucial for delta construction?

Sediment dispersal process Signup and view all the answers

What describes

The emergence of land plants and rivers Signup and view all the answers

Which type of deltas have sediment dispersal primarily influenced by wave action?

Wave-dominated deltas Signup and view all the answers

What is a feature typical of river-dominated deltas?

Bifurcating distributary channels Signup and view all the answers

What leads to daily changes in sedimentation patterns in tidal-influenced deltas?

Rhythmic sedimentation from tidal energy Signup and view all the answers

What are deltas characterized by in terms of sedimentation?

Fluvial sediments building into a standing body of water Signup and view all the answers

Which factor does NOT influence the morphology and internal facies distribution of a delta?

Distance from urban areas Signup and view all the answers

Which type of river outflow is associated with a denser delta formation?

Hyperpycnal Signup and view all the answers

What morphological feature is typically a result of progradation and reworking in a delta?

Coarsening upward succession Signup and view all the answers

When comparing the grain size distribution in a delta, what trend is typically observed?

Distal fining of grain size is observed Signup and view all the answers

Which sediment characteristic is most likely to be found at the delta front?

Sandstone Signup and view all the answers

What type of stratigraphic succession does a classic progradational delta show?

Coarsening upward succession Signup and view all the answers

What is an example of a depositional feature that can be found in deltas?

Crevasse splay Signup and view all the answers

Study Notes

Announcements

Labs will meet at the usual location and then walk to the water tank with the TA.
No lab scheduled for next week.
First exam on September 26th, during class; will be paper-based, no phones allowed.

Class Outline (September 14, 2023)

Previous week covered siliciclastic sediment transport.
Current topics include bedform stability, environments of deposition, rivers, and deltas.
Next week’s focus: coastal environments.

River Types Overview

Rivers adapt to topography and landscape gradients.
Meandering rivers: High sinuosity and fine sediment load; cohesive banks resistant to erosion.
Braided rivers: Numerous channels separated by bars; characterized by low cohesion banks and coarser sediment load.

Meandering Rivers

Lateral accretion occurs on point bars (inner bends) and erosion on cut banks (outer bends).
Important mechanisms include helical flow and decreased energy at point bars.
Facies distribution is determined by lateral migration of the channel.
Leave behind fining-upwards deposits as they migrate.

Braided Rivers

Exhibit multiple channels with low cohesion banks, which are easily eroded.
Channels show variability in morphology and deposits.
Typically found in high gradient settings with heavy sediment loads.

Fluvial Deposits Characteristics

Absence of marine fossils; often contains roots, mudcracks, and tracks.
Typically red in color with a downstream decrease in grain size, indicating downstream flow patterns.

Coastal Environments: Deltas

Deltas form at river mouths where water and sediment meet another body of water (ocean, lake).
Major global river deltas have distinct classifications based on sediment dispersal processes: river-dominated, tide-dominated, and wave-dominated.

Delta Types and Characteristics

River-dominated deltas: Distributary channels with mouth bars (e.g., Mississippi Delta).
Tide-dominated deltas: Exhibit normal tidal channels; sediments transport bidirectionally due to tides.
Wave-dominated deltas: Sediment reworked into bars and influenced by longshore drift (e.g., Sao Francisco Delta).

Delta Formation Processes

Factors determining delta morphology include river outflow density and interaction with marine processes.
Delta environments consist of delta plain (fluvial processes), delta front (fluvial & marine), and prodelta (marine processes).
Progradation and lobe-switching are key features of delta development.

General Delta Characteristics

Deltas can vary greatly in size—from less than 1 km² to over 100,000 km².
Sediment tends to fine distally; a coarsening upward succession often observed.
Classic facies models predict lithology based on depositional environments and sea-level changes.

Key Takeaways

Bedform stability depends on grain size and flow velocity.
Understanding river dynamics is crucial in predicting sediment distribution and delta morphology.
Deltas are complex systems influenced by both fluvial and marine processes, leading to diverse sedimentary environments.

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Description

This quiz covers key concepts related to siliciclastic sediment transport and river types, including meandering and braided rivers. It explores the mechanisms of lateral accretion, erosion, and the environments of deposition. Test your understanding of these important geological processes.