Final answer:
The fastest sediment flows are known as turbidity currents, which can reach speeds up to 20 m/s, whereas the slowest sedimentation happens in calm bodies of water, with terminal speeds of about 5 µm/s for small particles. The dynamics of various sediment flows can be observed by studying sedimentary units across a geological cross-section.
Step-by-step explanation:
The question 'What are fastest and slowest types of sediment flows?' pertains to the speeds at which sediment is transported in aqueous environments. Two extreme types of sediment flows could be classified as turbidity currents for the fastest and laminar flows or settling for the slowest.
Turbidity currents are typically very fast-moving, dense flows driven by the gravity of sediment-laden water which is heavier than clear water. They can carry large amounts of sediment rapidly, often along submarine canyons, to the deep-sea. The driving force behind these is the increased density due to suspended sediments, compared to surrounding water, causing a downslope flux. Sediments in this flow can move at velocities up to 20 m/s.
On the other end of the spectrum, in the slowest types of sediment flows, such as in a lake or still environments, sedimentation occurs much more gradually as less-energetic water allows particles to settle out of suspension. The settling of sediment in a lake for small particles can have a terminal velocity of about 5 µm/s, meaning it could take days to reach the bottom layer after being released at the surface. Slow sedimentation is also influenced by the particle size, shape, and density, as well as the viscosity of the water.
To understand sedimentation rates and deposition in different settings, one could examine various sedimentary units across a cross-section, identifying the most and least continuous units based on their appearance or interruption in the geologic record. This observation points to different transport and deposition mechanisms operating over time.