Final answer:
The described sandstone with oyster shells was most likely deposited in a river floodplain environment, associated with shallow marine conditions conducive to oyster life. Large-scale cross-bedding points towards desert dunes, while wavy bedding with mudcracks suggests swamp or wetlands. Coral reefs are located in shallow ocean waters.
Step-by-step explanation:
The sandstone in the photograph described was most likely deposited in a river floodplain environment, as indicated by the presence of oyster shells, which thrive in coastal and estuarine environments where they can filter feed from nutrient-rich water. Understanding depositional environments is essential for interpreting geological history. Oysters are typically found in shallow marine environments, such as estuaries and nearshore waters, indicating that the sandstone deposition occurred near such an environment. The environments best for preserving fossils are typically those with rapid burial and low oxygen conditions, such as deep marine sediments and areas where fine-grained sediments can gently accumulate and protect the remains before decomposition or scavenging occurs.
Descriptions of depositional environments provided suggest that description (A) with large-scale cross-bedding and very well-rounded sand grains corresponds to desert sand dunes, indicative of aeolian processes, whereas description (B) with mudcracks and wavy bedding suggests a more variable environment like a swamp or wetland that experiences both wet and dry conditions. Coral reefs are found in shallow ocean water where sunlight can penetrate to support the photosynthetic symbionts within the coral organisms.