The climate variations lead to the very dynamic nature of a sabkha. Halite is deposited on the surface of the sabkha and gypsum and aragonite precipitate in the subsurface via capillary action from brines brought up from the water table. In drier parts of the sabkha the gypsum can be altered to anhydrite and the aragonite can be dolomitized diagenetically. Thermal contraction at night and expansion during the day leads to concave polygonal pans as the edges have been upturned, in part due to growth of evaporites wedging the crack apart. Below this is a gypsum mush where nodules of anhydrite and other sulfates may develop. These might also form a “chicken wire” crystalline structure. Below this are the intertidal deposits typified by laminated, organic-rich muds formed by the microbial mats that grade downward into more bioturbated muds. The subtidal facies show carbonate grainstones and lagoonal muds.