Sedimentary Structures 1

Question 1

Type(s) of flow conditions and their associated environments:

Answer 1

Unidirectional flow: Rivers, alluvial fans, delta distributaries, submarine canyons, some pyroclastic flows.
Multidirectional flow: Shelf seas, tidal channels, lagoons, tidal flats, deserts.

Question 2

Migration of current ripples through unidirectional flow:

Answer 2

current ripples migrate through the following processes:
Flow contraction over the crest, leading to erosion.
Flow expansion on the stoss surface, resulting in deposition.

Question 3

Various types of bedforms in terms of shape and size:

Answer 3

Ripples: Small wave-like structures, typically less than 5 cm in height and with a wavelength of less than 30 cm.
Dunes: Larger-scale ripples, ranging from 0.05 to 20 meters in height and 0.5 to 100 meters in wavelength.
Megaripples: Also known as sand waves or larger-scale dunes.

Question 4

Relationship between bedforms and flow and sediment characteristics:

Answer 4

• Subcritical flow (Fr < 1): Associated with ripples and smaller dunes, influenced by grain size and flow velocity.
• Supercritical flow (Fr > 1): Associated with larger dunes, antidunes, and chutes and pools, characterized by high flow velocity and rapid erosion and deposition.
• Bedforms are influenced by variables such as flow velocity, mean grain size, and water depth, which are largely determined by the depositional environment