Question

Deltas form where moving water enters standing water and a wedge of sediment is deposited. a small delta in a lake has a distinctive internal structure, described by gilbert. in the following figure, drag and drop the labels to show the different parts of the delta. (the arrow shows where the stream flows into the lake.)

A) bottomset bed B) foreset bed topset bed D) pre-delta bedrock c

Answer 1

Deltas form where rivers carrying sediment meet standing bodies of water, leading to deposition and the formation of distinct layers such as topset, foreset, and bottomset beds above the pre-delta bedrock. Features like cross-bedding and graded bedding provide insights into past environmental conditions.

Step-by-step explanation:

Deltas are landforms created where rivers deposit sediment as they enter slower-moving or standing bodies of water, such as oceans or lakes. These deposits can form characteristic layers, which were described by geologist Grove Karl Gilbert. According to the Gilbert model, deltas have a distinctive internal structure which includes topset beds, foreset beds, and bottomset beds. The topset bed contains the finest sediments and makes up the top layer of the delta, where the river starts to lose speed. The foreset bed lies beneath, marked by coarser materials that create a slanted layer as the sediments start to settle at a quicker rate. The bottomset bed is composed of the finest sediments that finally settle further out into the standing water. Beneath these layers lies the pre-delta bedrock, which forms the base the delta structure sits upon.

These structures are also associated with other sedimentary features such as cross-bedding, where geologists can determine the direction of water or wind that transported the sediments. Furthermore, graded bedding is observed where a transition in grain size is present within a single sedimentary layer, indicating variations in depositional energies.