Final answer:
The sediment movement of the San Antonio River changes as it flows from northwest to southeast. The current slows and sediments, mainly fine materials like silt and clay, settle as the river widens. Sedimentary rocks become younger downstream, suggesting they dip towards the direction of the basin.
Step-by-step explanation:
The sediment movement in the San Antonio River, as in many river systems, tends to change as it flows from its source towards the ocean or large lakes. Near the source, rivers tend to have fast-moving water that carries sediments, primarily consisting of gravel and larger particles. However, as the river or stream flows away from the source, the channel widens, the current slows, and the water becomes more saturated with suspended sediment. The gradient decreases and the water volume increases due to the convergence of tributaries, resulting in more sedimentation. As these sediments are transported and deposited, they can form various features such as deltas at a river’s mouth, where the river meets the ocean or a large lake, and the silt settles onto the ocean bottom.
Concerning the age of sedimentary rocks, they generally become younger as one moves away from their source, which is usually located in higher elevations or mountainous areas, to lower elevations or basins. This suggests that sedimentary rocks dip in the direction of the basin, implying the direction of sediment transport. The San Antonio River may exhibit similar patterns with its surrounding sedimentary rocks.
Lastly, rivers can exhibit features like cross-bedding and ripple marks, indicative of past sediment transport directions, where sediment moves up the shallow side and is deposited on the steep side. This can be observed in various environments, including those created by moving water, from river beds to Martian outcrops as seen in the photographs captured by NASA’s Mars Rover Curiosity.