Final answer:
Sandstone is the type of rock typically found in river floodplain deposits. Large cross-bedding and well-rounded sand grains suggest a braided river, while wavy bedding and mudcracks are indicative of swamp/wetlands. Oysters in sedimentary rock hint at a shallow marine environment.
Step-by-step explanation:
In a river floodplain environment, you would typically find sedimentary rocks such as sandstone. This is because sandstone forms from the compaction and cementation of sand particles, which are commonly deposited in river environments.
Below, we can evaluate the two different environments:
- Environment A with large-scale cross-bedding and very well-rounded sand grains is indicative of a high-energy environment such as a braided river.
- Environment B with sandstone and mudstone showing wavy bedding and mudcracks could represent a swamp/wetlands area with periodic drying and wetting conditions.
Regarding tectonic environments, limestones are often associated with passive tectonic settings, while rocks like sandstones, shales, and conglomerates tend to indicate active tectonic margins. These rock types provide geologists with clues about the history of tectonic activity in an area.
Focusing on sedimentary environments, an area with sedimentary rocks containing oyster shells, such as those found in the Dom João Formation, typically indicates a shallow marine environment where oysters thrive.