Final Answer:
In river depositional environments, sand-sized sediment is transported along the stream bed and is deposited during baseflow. The characteristic sedimentary rock formed in this type of environment is sandstone.
Step-by-step explanation:
Sandstone is a sedimentary rock primarily composed of sand-sized mineral, rock, or organic particles that have been compacted and cemented together. In river depositional environments, the transportation and deposition of sand-sized sediment are influenced by the energy conditions of the flowing water. During baseflow, when the energy levels are low, the river lacks the force to transport larger particles, leading to the deposition of sand-sized sediment. Over time, as these sand particles accumulate and undergo diagenesis—processes like compaction and cementation—they transform into sandstone.
The formation of sandstone in river depositional environments is a result of the dynamic interplay between sediment transport and deposition. When rivers flow at baseflow conditions, the velocity decreases, allowing sand-sized particles to settle and accumulate on the streambed.
These deposited sediments are then subjected to subsequent geological processes that lead to the lithification of the sedimentary rock, ultimately forming sandstone. The characteristics of the sandstone, such as its grain size, composition, and structure, provide valuable insights into the depositional history and environmental conditions of the ancient river system.