Final answer:
Coastlines and dunes can indeed be built up and eroded by weathering, erosion, and deposition, which is true. These natural processes shape the landscape and leave geological records like cross-bedding, indicating past environmental conditions.
Step-by-step explanation:
It is true that coastlines and dunes can be both built up and torn down by weathering, erosion, and deposition. These processes are dynamic and can change the landscape significantly over time.
For example, ocean waves continuously crash against coastlines, and their energy can lead to erosion, wearing away land and causing cliffs to collapse. This can pose threats to coastal communities and necessitates the study of wave interactions with beaches to construct defensive structures like breakwaters.
The erosive action of water and wind can also create ripples and dunes in sediments. Over time, these temporary structures may leave behind geological features such as cross-bedding in sedimentary rock records. Cross-bedding provides important information about the direction of wind or water flow at the time the sediments were deposited.
Beach and swamp environments in coastal areas can exhibit many sedimentary facies, including distinctive features such as layering patterns, abundance of fossils, and sedimentary structures like ripple marks. Modifications to these environments, like dredging, can have significant ecological impacts and may lead to greater storm impact and shoreline erosion.