Marl

[2][3] The term is today often used to describe indurated marine deposits and lacustrine (lake) sediments which more accurately should be named 'marlstone'.

[10] Upper Cretaceous cyclic sequences in Germany and marl–opal-rich Tortonian-Messinian strata in the Sorbas Basin related to multiple sea drawdown have been correlated with Milankovitch orbital forcing.

[12][13][14] Chara, a macroalga also known as stonewort, thrives in shallow lakes with high pH and alkalinity, where its stems and fruiting bodies become calcified.

After the alga dies, the calcified stems and fruiting bodies break down into fine carbonate particles that mingle with silt and clay to produce marl.

Normal pond life is unable to survive, and skeletons of freshwater molluscs such as Sphaerium and Planorbis accumulate as part of the bottom marl.

[18] Because some marls have a very low permeability, they have been exploited for construction of the Channel Tunnel between England and France and are being investigated for the storage of nuclear waste.

[17] Marl has been used in Pamlico Sound to provide a suitable artificial substrate for oysters in a reef-like environment.

[18] It is abundant and yields better physical and mechanical properties than metakaolin as a supplementary cementitious material[30] and can be calcined at a considerably lower temperature.

[31][32] The Channel Tunnel was constructed in the West Melbury Marly Chalk, a geological formation containing marl beds.

The underlying Glauconitic Marl is easily recognizable in core samples and helped establish the right level for excavating the tunnel.

[18] However, they are regarded as ecologically important,[39] and are vulnerable to damage by silting, nutrient pollution, drainage, and invasive species.

In Britain, only the marl lakes of the more remote parts of northern Scotland are likely to remain pristine into the near future.