An unconsolidated mud in estuaries, lagoons, lakes, and shallow seas, its formation depending on heavier precipitation (Rohling and Hilger (1991) Geol. Mijnbouw 70), and to variations in the Earth’s orbit—they are thus useful in reconstructing palaeoclimates (Larrasoaña et al. (2006) Phys. Earth & Planet. Interiors 156, 3–4).