That could be a 'reef' or an 'archipelago'.
Limestone and chalk.
Limestone is a rock formed from the accumulation of calcium carbonate derived from the remains of sea shells and marine organisms. Over time, these sedimentary deposits can become compressed and cemented to form solid rock.
Skeletal remains of many sea creatures settle on the ocean floor. Here they mix with sediments and eventually become sedimentary rock.
Sediments produced by plants and animals in the sea are called biogenic sediments. These sediments are composed of organic remains, such as shells, corals, and skeletal debris, which accumulate on the seafloor over time.
Volcanic islands are formed of igneous rock and lava. They tend to be tall, and have steep slopes. Coral islands are calcium carbonate (chemically the same as limestone) and are formed from the secretions of sea coral- an animal. They tend to be low to the water, and relatively flat.
Limestone is formed from the skeletal remains of minute sea creatures, laid down on the sea floor millions of years ago.
I have visited one in Nicobars Island. Its made from fossils of plants/animals remains on the stones, It also has stuffed animal remains and sea creatures for display.
Limestone is a rock that is formed from the skeletal remains of sea animals and plants. It is primarily composed of calcium carbonate, which is derived from the shells and skeletons of marine organisms such as coral, mollusks, and foraminifera. Over time, these remains accumulate and become compacted and cemented to form limestone rock.
sea tiny animals
limestone island is for by the accumulation of dead sea creatures
It could be called an undersea island or submarisle.
the skeletons of tiny sea animals
Islands formed from the remains of tiny soft-bodied sea animals are typically made of coral, specifically coral reefs. These reefs are constructed from the calcium carbonate skeletons of coral polyps, which are small marine invertebrates. Over time, as these organisms die and accumulate, they can form large structures that can rise above sea level, creating islands. Examples include many of the islands in the Caribbean and the Great Barrier Reef.
Limestone and chalk.
all sea animals that died eventually turned into oil.
What is an ocean ridge made up of skeletal remains of tiny sea animals
rocks formed under the sea and it was pushed up by force and over the years parts of the rocks fell back into the ocean and then it eventually became a flat surface and that it how Tybee Island was formed