5.3 PRIMARY INORGANIC SEDIMENTARY STRUCTURES
163
Fig. 5.34. Salt pseudomorphs in hypersaline lagoonal pellet mudstone. Purbeck Beds (Upper Jurassic).
recorded in muddy sediments. They are of two types. Desiccation cracks form subaerially; synaeresis cracks form subaqueously.
Desiccation cracks, also known as sun cracks, are downward tapering cracks in mud,
which are infilled by sand. In plan view they are polygonal. Individual cracks are a centimeter or so wide. Polygons are generally about 0.5 m across (Fig. 5.35). The cracks
Fig. 5.35. Desiccation cracks in lacustrine Torridon Group (Pre-Cambrian) shales. Raasay, northwest
Scotland.
163
Fig. 5.34. Salt pseudomorphs in hypersaline lagoonal pellet mudstone. Purbeck Beds (Upper Jurassic).
recorded in muddy sediments. They are of two types. Desiccation cracks form subaerially; synaeresis cracks form subaqueously.
Desiccation cracks, also known as sun cracks, are downward tapering cracks in mud,
which are infilled by sand. In plan view they are polygonal. Individual cracks are a centimeter or so wide. Polygons are generally about 0.5 m across (Fig. 5.35). The cracks
Fig. 5.35. Desiccation cracks in lacustrine Torridon Group (Pre-Cambrian) shales. Raasay, northwest
Scotland.