Define Graded Bedding In Earth Science

Graded bedding is a type of sedimentary structure that is characterized by a gradual change in the size of the particles that make up the bed. The particles are typically larger at the bottom of the bed and become smaller towards the top. This type of bedding is often found in sedimentary rocks that were deposited by currents, such as in a river or stream. The current will carry larger particles farther than smaller particles, so the larger particles will be deposited first, followed by the smaller particles.

There are a number of different factors that can cause graded bedding. One factor is the velocity of the current. A faster current will be able to carry larger particles farther than a slower current. Another factor is the distance from the source of the sediment. The farther away from the source, the smaller the particles will be. Finally, the shape of the particles can also affect graded bedding. Angular particles will be more difficult to transport than rounded particles, so they will be deposited closer to the source.

Graded bedding can be used to interpret the history of a sedimentary deposit. For example, the thickness of a graded bed can be used to determine the velocity of the current that deposited it. The distance from the source of the sediment can be determined by the size of the particles in the bed. And the shape of the particles can be used to determine the type of environment in which the sediment was deposited.

Types of Graded Bedding

There are two main types of graded bedding: normal grading and reverse grading. Normal grading is the most common type of graded bedding, and it is characterized by a gradual decrease in the size of the particles from the bottom of the bed to the top. Reverse grading is less common, and it is characterized by a gradual increase in the size of the particles from the bottom of the bed to the top.

Normal grading is typically caused by a decrease in the velocity of the current that deposited the sediment. As the current slows down, it will no longer be able to carry the larger particles, so they will be deposited first. The smaller particles will then be deposited on top of the larger particles. Reverse grading is typically caused by an increase in the velocity of the current that deposited the sediment. As the current speeds up, it will be able to carry larger particles farther, so they will be deposited on top of the smaller particles.

Significance of Graded Bedding

Graded bedding is a significant sedimentary structure because it can provide information about the history of a sedimentary deposit. The thickness of a graded bed can be used to determine the velocity of the current that deposited it. The distance from the source of the sediment can be determined by the size of the particles in the bed. And the shape of the particles can be used to determine the type of environment in which the sediment was deposited.

Graded bedding is also important because it can be used to identify the direction of sediment transport. In most cases, the graded bed will be deposited with the larger particles facing downstream. This is because the current will carry the larger particles farther downstream than the smaller particles.