English: Modern mudcracks in a cave in Kentucky, USA.

Mudcracks are diagnostic sedimentary structures indicating subaerial exposure of sediment surfaces, with alternating wet & dry conditions. They are much more common that raindrop imprints, which indicate the same environmental setting. Mudcracks are most likely to occur in fine-grained siliciclastic sediments, fine-grained carbonate sediments, and in some evaporitic settings.

Mudcracks are distinctive and easy to identify, but they do vary in appearance. The cracks themselves vary in width, depth, and areal density. Mudcrack polygons also vary in size & shape.

The mudcracks shown above are developed in a relatively thin mud layer overlying sand in a cave passage at Mammoth Cave, Kentucky. The cave is a complex network of passages in Mississippian-aged limestones. The lowest levels are at and below the modern water table. Water flows from the deepest passages toward the Green River. During and after storms, the Green River experiences high flow, which results in water levels rising in the cave. The site shown here has been inundated many times. After flood events wane, the water table lowers and this site is exposed. The sands and muds were deposited by flood waters. The capping mud layer dried out, cracked, and the edges of the mudcrack polygons curled upward.

Locality: trailside in the Dead Sea-Lake Lethe area, south of River Hall, Mammoth Cave, near the northwestern end of Mammoth Cave Ridge, Edmonson County, western Kentucky, USA