White to gray accumulation on lake bottoms caused by precipitation of calcium carbonate (CaCO3) in hard water lakes. Marl may contain many snail and clam shells, which are also calcium carbonate. While it gradually fills in lakes, marl also precipitates phosphorus, resulting in low algae populations and good water clarity. In the past, marl was recovered and used to lime agricultural fields.
A deposit of calcium carbonate resulting from biotically induced changes in the carbonate-bicarbonate balance in freshwater basins; also as a result of evaporation or abrupt changes in temperature causing the escape of carbon dioxide from soluble calcium bicarbonate and the formation of insoluble calcium carbonate.
Marls are calcium carbonate or lime-rich muds or mudstones which contain variable amounts of clays and calcite or aragonite. The term is most often used to describe lacustrine (lake) sediments but may also be used for marine deposits. The term 'marl' is widely used in English-language geology, while the term seekreide is used in European references.