The tangue has been observed as a relatively shallow-water sediment along the French Atlantic coast, and especially in Brittany. It has a very high calcium carbonate content. The tangue was originally thought to be a recent deposit, but the discovery of considerable layers of old tangue made this original hypothesis untenable. Tangue beds are characterized by thin layers reminiscent of varves.
The tangue does not conform to the traditional deposit patterns inasmuch as, if one progresses seaward, the size distribution of grains is contrary to the distribution observed normally in other sediments.