Turbidity Currents

Question 1

Turbidities

Answer 1

The deposits that turbidity currents form.

Question 2

Deep-Sea Canyons

Answer 2

• No more than river channels that are exposed when sea level is low and drowned when sea level is high.

Question 3

Describe some attributes of the Bengal Fan

Answer 3

• The largest fan system due to the Himalayas

Question 4

Draw and describe a subaqueous levee formation

Answer 4

Dominated by turbidity currents

• Starts with a flat surface (flat plain) and then a turbidity current comes through.
• This becomes unstable due to loose mud piling on top of more loose mud.
• Eventually, it will collapse.
  
  • because it is on a steep slope and because of earthquakes (in the case of the collision coasts) & monsoons.

Question 5

The Morphology of Turbidity Currents - draw a diagram and explain sediment deposits at each stage.

Answer 5

• Head: Erodes the sediment and sends into suspension (largest sediment types) (sole marks)
• Neck: Large sediments will be deposited out
• Body: Sands get deposited
• Tail: Fine grain sediments get deposited (silt/clay)

Question 6

What determines the velocity of the Turbidity Current?

Answer 6

1. Density
2. The slope

Experiences high velocity at the base and backwards movement at the top.

Question 7

Draw and describe the Bouma Sequence

Answer 7

When drawing the graph: the bar that is the longest is the coarser sediment and the bar that is the shortest is the finer sediments. Upward sequence.

• A= Head
• B= Neck – deposited in the neck region (coarse material)
• C= Body – does not rain down flat – it plumes causing it to form at an angle (cross-bedding). Think about ripples migrating.
• D= Tail – no more turbulence and rain downs so it lays flat
• E= in between turbidity currents. Calcareous Ooze potential.

Question 8

What are factors that affect the completeness of the Bouma Sequence?

Answer 8

• Where the turbidite is found and the size is based on the velocity of the turbidity current.
• Distance from the source (sediment loss is less the closer you are to the source)
• Time between events – The firs thing a turbidity current does when it comes through is that it erodes the top of the last one. If you have turbidity currents right after each other, never have a chance to create a D or E unit. Tells it was a busy time.
• Volume & types of sediment composing the turbidity current
• Position with fan (channel, levee, fan)