Final answer:
Bedding structures in sedimentary rocks reveal historical geological processes and include environmental changes, fluid speed variations, and sediment source modifications. Graded bedding, cross-bedding, and mineral presence provide clues to the depositional history.
Step-by-step explanation:
Bedding structures in sedimentary rocks can be caused by all of the options listed: changes in the environment in which the sediment was being deposited, changes in the speed of the fluid that was transporting the sediments, and changes in the sediment source. These structures provide valuable information about the past environments and processes during the time of sediment deposition.
For example, graded bedding often indicates a decrease in energy over time in a depositional environment, as seen when water velocity in a river changes. Moreover, the presence of specific sediment types, like quartz or feldspar, can indicate the history of erosion and transport prior to deposition, speaking to the stability of mineral grains and their source proximity.
Cross-bedding is a key structure that can reveal the direction of wind or water flow during the time of sediment deposition by analyzing the angles and orientation of the layers. The comprehensive study of these bedding structures helps geologists reconstruct the geological history of an area.