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Questions and Answers
What is a turbidity current?
What is a turbidity current?
A high-velocity current that flows down gentle gradients because the sediment within it makes it denser than seawater.
What is a turbidite?
What is a turbidite?
An upward fining deposit of greywacke deposited from a turbidity current.
Where do turbidity currents occur?
Where do turbidity currents occur?
On the continental slope; flow from the continental shelf and deposited on the abyssal plain.
Why do turbidity currents occur?
Why do turbidity currents occur?
Why do turbidity currents flow quickly? How quickly do they flow?
Why do turbidity currents flow quickly? How quickly do they flow?
Where is much of turbidity current sediment deposited?
Where is much of turbidity current sediment deposited?
Why are turbidity current sediments deposited on the continental rise?
Why are turbidity current sediments deposited on the continental rise?
In a turbidity current, how are the sediments maintained in suspension?
In a turbidity current, how are the sediments maintained in suspension?
Why is sediment and water from the body forced into the head? What does this result in?
Why is sediment and water from the body forced into the head? What does this result in?
What is the Bouma sequence?
What is the Bouma sequence?
What is the sequence of sedimentary structures/rocks in a turbidite called?
What is the sequence of sedimentary structures/rocks in a turbidite called?
In a turbidite, how are the layers labelled?
In a turbidite, how are the layers labelled?
What is bed A in a turbidite?
What is bed A in a turbidite?
What sedimentary structures are found in turbidite bed A? What is the interpretation?
What sedimentary structures are found in turbidite bed A? What is the interpretation?
What is bed B of a turbidite?
What is bed B of a turbidite?
What sedimentary structures are found in turbidite bed B? What is the interpretation?
What sedimentary structures are found in turbidite bed B? What is the interpretation?
What is turbidite bed C?
What is turbidite bed C?
What sedimentary structures are found in turbidite bed C? What is the interpretation?
What sedimentary structures are found in turbidite bed C? What is the interpretation?
What is turbidite bed D?
What is turbidite bed D?
What sedimentary structures are found in turbidite bed D? What is the interpretation?
What sedimentary structures are found in turbidite bed D? What is the interpretation?
What is turbidite bed E?
What is turbidite bed E?
What sedimentary structures are found in turbidite bed E? What is the interpretation?
What sedimentary structures are found in turbidite bed E? What is the interpretation?
What is the changing grain size sequence in turbidites?
What is the changing grain size sequence in turbidites?
Why is there upwards fining in turbidite deposits?
Why is there upwards fining in turbidite deposits?
How do flute casts form in turbidity currents?
How do flute casts form in turbidity currents?
How can flute casts be used as paleocurrent indicators?
How can flute casts be used as paleocurrent indicators?
How do rip-up clasts form in turbidity currents?
How do rip-up clasts form in turbidity currents?
What are tool marks?
What are tool marks?
Why do tool marks form in turbidity currents?
Why do tool marks form in turbidity currents?
How are load casts/flame structures created in turbidity currents?
How are load casts/flame structures created in turbidity currents?
What is the pictured sedimentary structure?
What is the pictured sedimentary structure?
What is the pictured sedimentary structure?
What is the pictured sedimentary structure?
What is the pictured sedimentary structure?
What is the pictured sedimentary structure?
What are the pictured sedimentary structures?
What are the pictured sedimentary structures?
What are the names of the different beds in the Bouma sequence?
What are the names of the different beds in the Bouma sequence?
Study Notes
Turbidity Currents
- High-velocity currents that flow downhill due to increased density from suspended sediments, making them denser than seawater.
- Occur primarily on continental slopes, moving sediment from continental shelves to abyssal plains.
Turbidites
- Deposits formed from turbidity currents, characterized by upward fining of sediment size, commonly involving greywacke.
Formation and Characteristics
- Triggered by rivers depositing excess sediment or disturbances like small earthquakes, causing sediment to rush down grades.
- Travel speeds range from 70-90 km/h due to their high density and low friction against the continental slope.
Deposition Areas
- Sediment is primarily deposited in submarine fans on continental rises or within ocean basins.
- Deposited sediments slow down and settle on the continental rise due to shallow inclines (around 4°) reducing energy.
Suspended Particles
- Turbulent eddies within the current help maintain suspended sediments, allowing for sediment transportation over distances.
Sedimentary Structures
- Bouma sequence: Idealized sedimentary layer arrangement in turbidites consisting of beds A through E, applied in studies of sedimentary environments.
- Layers are labeled from A to E, with A being deposited first and representing the coarsest sediments.
Bed Characteristics
- Bed A: Coarse conglomerate, features graded bedding and an erosional base, indicative of high velocity.
- Bed B: Contains coarse to medium sandstone (greywacke) with parallel laminations showing graded bedding, reflecting decreasing energy.
- Bed C: Composed of sandstone (greywacke) with small-scale cross bedding, indicating a further decrease in current strength.
- Bed D: Fine sandstone transitioning to siltstone with ripples and cross bedding observed at low velocities.
- Bed E: Shale often containing marine fossils like graptolites, showing characteristics of interturbidite deposits with parallel laminations.
Grain Size and Fining
- Turbidite deposits exhibit upward fining, where coarser materials settle as the current loses energy, forming graded beds.
Flute Casts and Tool Marks
- Flute casts form from spiral eddies in the flow, creating elongated hollows that are preserved in the sediment.
- Tool marks are indentations created by objects carried along the bedload in high-energy flows, showcasing the dynamic nature of turbidity currents.
Load Structures
- Load casts and flame structures arise when coarser sands quickly settle into still-soft fine mud layers, resulting in unique sedimentary features.
Pictured Structures
- Identify sedimentary structures such as flute casts, rip-up clasts, tool marks, and load casts/flame structures for a comprehensive understanding of turbidity current effects.
Bouma Sequence Overview
- The arrangement of beds in a turbidite follows the Bouma sequence, named in the order from top to bottom as E, D, C, B, A, reflecting the sediment deposition process.
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Description
Test your knowledge on turbidites and turbidity currents with these flashcards. Perfect for understanding the flow dynamics and sediment deposits involved in these geological processes. Ideal for geology students and enthusiasts.
