Chapter 7: Problem 8

Describe how a turbidity current forms and moves. How does it produce graded bedding?

Short Answer

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A turbidity current is an underwater, sediment-laden flow triggered by events such as earthquakes, sediment overload, or underwater landslides. The current moves down a slope due to gravity, eroding and carrying sediments along at high speeds. As the current slows, it forms graded bedding by depositing the coarse, heavy particles first, followed by lighter, finer particles. Graded bedding is a horizontally layered structure that helps geologists interpret the sediment transport and depositional environment.

Step by step solution

Defining Turbidity Current

A turbidity current is an underwater current of sediment-laden water that flows down a slope due to the pull of gravity. It consists of a mixture of water, sediments (such as sand, silt, and clay), and sometimes organic materials, which have a higher density than the surrounding water. They are common underwater geological processes responsible for transporting and depositing sediments on the ocean floor.

Formation of Turbidity Current

A turbidity current can form in many different ways, such as: 1. Earthquakes: The shaking of the earth during an earthquake can dislodge large amounts of sediments underwater, leading to a turbidity current. 2. Sediment Overload: When the rate of sediment deposition on a slope exceeds the slope's ability to hold it, a turbidity current may initiate. 3. Underwater Landslides: These can rapidly move sediments downhill, creating a turbidity current. Once the sediments are set into motion by any of these processes, they mix with the water, forming a dense, sediment-laden current that travels along the slope.

Movement of Turbidity Current

The turbidity current moves down the slope under the influence of gravity. As it moves, the suspended particles start to affect the flow of the current. The heavier, coarser particles tend to stay towards the bottom of the flow due to their density, while the lighter, finer particles remain suspended in the water. The current can travel at high speeds, sometimes exceeding 50 miles per hour, eroding the seabed and carrying along sediments as it flows. Eventually, the turbidity current loses its speed as the slope decreases or encounters a flatter area, causing the sediments to settle.

Producing Graded Bedding

Graded bedding is produced as the turbidity current slows down and the suspended particles begin to settle. The coarser and heavier particles are deposited first at the bottom, while the lighter and finer particles settle more slowly and are deposited on top of the coarser sediments. This process creates a horizontally layered bed with the coarsest sediments at the bottom and progressively finer sediments towards the top. This type of layering, or bedding, is termed as "graded bedding". It is a distinct sedimentary structure that helps geologists to understand the depositional environment and the processes responsible for the sediment transport and deposition.

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Describe how a turbidity current forms and moves. How does it produce graded bedding?

Short Answer

Step by step solution

Defining Turbidity Current

Formation of Turbidity Current

Movement of Turbidity Current

Producing Graded Bedding

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