![]() ![]() The limestone that makes up these cave formations is known as "travertine," a chemical sedimentary rock. If droplets fall to the floor and evaporate there, stalagmites could eventually grow upwards from the cave floor. Over time, this evaporative process can result in an accumulation of icicle-shaped calcium carbonate on the cave ceiling. When the water evaporates, any calcium carbonate that was dissolved in the water will be deposited. ![]() There they might evaporate before falling to the cave floor. In a cave, droplets of water seeping down from above enter the cave through fractures or other pore spaces in the cave ceiling. Stalactites, stalagmites, and other cave formations (often called "speleothems") are examples of limestone that formed through evaporation. Limestone can also form through evaporation. This is producing an extensive deposit of calcium carbonate sediment that has already converted to limestone at depth. There, abundant corals, shellfish, algae, and other organisms produce vast amounts of calcium carbonate skeletal debris and fecal matter that completely blanket the platform. One of these areas is the Bahamas Platform, located in the Atlantic Ocean about 100 miles southeast of southern Florida (see satellite image). Limestone is forming in the Caribbean Sea, Indian Ocean, Persian Gulf, Gulf of Mexico, around Pacific Ocean islands, and within the Indonesian archipelago. Most of them are found in shallow parts of the ocean between 30 degrees north latitude and 30 degrees south latitude. Many limestone-forming environments are active on Earth today. The amount of precipitated calcium carbonate in a biological limestone can be as low as a few percent of the rock by volume, or it can be higher than 50% of the rock by volume. If the biological grains are not cemented together, a rock will not be formed. "Cementation" is an important step in the transformation of a sediment into a rock. Calcium carbonate, precipitated directly from solution, forms as a "cement" that binds the biological grains together. After the biological grains have accumulated and are buried, water that is saturated with dissolved materials moves slowly through the sediment mass. Most biological limestones contain significant amounts of directly precipitated calcium carbonate. They are thought to be less abundant than biological limestones. Limestones formed this way are chemical sedimentary rocks. Sedimentation may also occur as dissolved minerals precipitate from water solution.Some limestones form by direct precipitation of calcium carbonate from marine or fresh water. ![]() Biological detritus was formed by bodies and parts of dead aquatic organisms, as well as their fecal mass, suspended in water and slowly piling up on the floor of water bodies. The geological detritus is transported to the place of deposition by water, wind, ice or mass movement, which are called agents of denudation. The geological detritus originated from weathering and erosion of existing rocks, or from the solidification of molten lava blobs erupted by volcanoes. The particles that form a sedimentary rock are called sediment, and may be composed of geological detritus (minerals) or biological detritus. Sedimentation is the collective name for processes that cause these particles to settle in place. ![]() Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. ![]()
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