Dessication (shinkage) cracks that form in non-marine mudstones as they dry out in the sun, and are later filled in by sediment. Mudcracks cut across bedding in cross-sectional view, and form polygonal patterns in map view. Multiple episodes of dessication, infilling and re-wetting may be displayed as in the Tulare core below from the Maxwell 860 well. Sub-aqueous shinkage cracks can also form, and are known as syneresis cracks. These form in limey sediments during contraction of the clay minerals in response to salinity changes in the overlying water column. However, syneresis cracks tend be much more discontinous and irregular than most mudcracks.
Examples of Ancient Mudcracks
Examples of Modern Mudcracks