1. The Nature of Turbidity Currents:
* Gravity-Driven: Turbidity currents are dense, fast-moving underwater flows driven by gravity. They occur when a mixture of water and sediment is destabilized, typically on a continental slope.
* Sediment Concentration: These currents carry a high concentration of suspended sediment, ranging from fine clay to coarse sand and gravel.
2. Sediment Settling and Grading:
* Energy Loss: As the turbidity current travels, it loses energy due to friction with the seafloor and internal mixing. This energy loss causes the current to slow down.
* Sediment Settling: As the current slows, the heavier sediment particles settle out first, followed by progressively finer particles. This results in a layering of sediment with coarser material at the base and finer material at the top.
3. Graded Bedding Formation:
* Distinct Layers: The sequential settling of sediment creates distinct layers with a gradual change in grain size, forming a graded bed.
* Bouma Sequence: Graded beds in turbidites often display a characteristic sequence of layers known as the Bouma sequence, reflecting the progressive decrease in energy and sediment settling.
In summary:
* Turbidity currents are gravity-driven flows that carry a high concentration of sediment.
* As these currents lose energy, sediment particles settle out according to their size and density.
* This sequential settling leads to the formation of graded beds, where coarser sediment layers overlie finer sediment layers.
Therefore, the presence of graded beds is a strong indicator of deposition by turbidity currents and is a key characteristic of turbidite deposits.
