Final answer:
Limestone is the type of sedimentary rock that forms when a rock with abundant marine fossils weakly reacts to dilute hydrochloric acid when powdered. It forms in marine environments where the calcium carbonate shells of marine organisms accumulate over time. The reaction to hydrochloric acid indicates the presence of calcium carbonate.
Step-by-step explanation:
The type of sedimentary rock that forms when a rock with abundant marine fossils weakly reacts to dilute hydrochloric acid when powdered is called limestone.
Limestone is a chemical sedimentary rock that forms through the precipitation of minerals from concentrated solutions in water. The abundant marine fossils suggest that the rock was formed in a marine environment where the calcium carbonate shells of marine organisms accumulated over time.
To form limestone, the marine organisms (such as shells of foraminifera or oysters) would have died and sunk to the ocean floor. Over time, layers of these organic remains would have been compacted and cemented together to form the rock. When powdered limestone is exposed to dilute hydrochloric acid, it reacts weakly, indicating the presence of calcium carbonate.