How are organic sedimentary rocks formed?
Organic sedimentary rocks are composed of the remains or products of plants or animals. Many limestone’s are composed mainly of the fossil shells of relatives of the oysters, clams, and other shellfish common in today’s oceans, These shells range in size from microscopic size to more than 3 feet (0.9 meters) across. Although some limestone’s in South Dakota were formed in lakes, most of the state’s limestone’s were formed during times when large inland seas covered the region. In fact, most of South Dakota’s sedimentary rocks are marine in origin, that is, they were deposited from sea water. Some organic sedimentary rocks, such as coal, were formed on land. Coal forms black layers in the hillsides of northwestern South Dakota, near Firesteel and Isabel. Careful examination of fist-sized lumps of these rocks will often reveal stems, leaves, and wood from trees and other plants that once grew in low-lying forests and swamps. How Are Chemical Sedimentary Rocks Formed? Chemical sedimentary
