marl

Carbonate-rich clay deposits formed by the weathering of impure limestones.

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 North American geology, while the term seekreide is used in European references.

The lower stratigraphic units of the chalk cliffs of Dover consist of a sequence of glauconitic marl followed by rhythmically-banded limestone and marl layers.