Sedimentary Structures 2

Question 1

Describe the relationships between cross-bedding types and flow environments:

Answer 1

• Cross-bedding is formed on the inclined surfaces of bedforms (such as ripples and dunes) in a flowing medium, such as water or wind.
• Different types of cross-bedding can indicate specific flow environments, such as unidirectional or multidirectional flow.
• Cross-bedding structures can provide information about the flow direction and the nature of the flow regime.

Question 2

Describe the details of the various types of cross-bedding that can occur in unidirectional and multidirectional flow environments:

Answer 2

In unidirectional flow environments, cross-bedding can include tabular cross-beds (straight-crested 2D ripples/dunes), trough cross-beds (sinuous/linguoid-crested 3D ripples/dunes), climbing ripples, and antidunes.
In multidirectional flow environments, cross-bedding can include lenticular and flaser bedding, reactivation surfaces, interference ripples, herringbone (bipolar) cross-bedding, wave-generated ripples, and hummocky cross-bedding.

Question 3

Explain how wave-generated ripples are formed:

Answer 3

• Wave-generated ripples are small, symmetrical bedforms with long, relatively straight crests.
• They are primarily formed in environments with weak currents where water motion is dominated by wave oscillations.
• These ripples are typically found in tidal environments and lakes, where the water motion is mainly caused by oscillatory wave direction (wind-generated).