What type of rocks are formed from the accumulation of marine organisms?

Limestone is classified as a sedimentary rock that forms from the accumulation of organic materials, primarily marine organisms such as corals, mollusks, and foraminifera. Over time, the shells and skeletal remains of these organisms accumulate on the seabed and undergo compaction and cementation, which transforms them into limestone. This rock is often found in marine environments and can also contain fossils, providing valuable information about past ecosystems.

The formation process of limestone is significant in understanding sedimentary environments, especially in shallow marine settings. As marine organisms die, their calcium carbonate shells contribute to the sediment, which, under pressure over geological time, forms limestone. This characteristic makes limestone a vital rock type in oceanography and geology as it indicates past marine conditions and biodiversity. The other types of rocks mentioned do not primarily form from the accumulation of marine organisms, which is why limestone stands out as the correct answer.