Mudcracks

Mudcracks form when muddy sediment is exposed to the atmosphere and dries up. They have a characteristic polygonal shape when viewed from above. When viewed from the side, the cracks are “V”-shaped, with the wider part of the “V” toward the surface. Thus, mudcracks, when preserved in the rock record, indicate that the sediment formed in an environment that was alternately wet and dry, like a tidal flat or the flood plain of a river. The distinct "V" shape of the crack in cross-sectional view can indicate which way is up.

	Plan (map) view of cracked surface, showing polygonal shapes and curled edges.  Notice that this image shows multiple sizes of cracks, where the larger cracks are deeper than smaller cracks, suggesting that the larger cracks began forming earlier than the smaller ones.
	Cross-sectional view of mudcracks.  These are sand-filled cracks developed in carbonate.  Notice the prominent "V" shape of the cracks in cross section, where the "V" is wider at the top of the crack and narrower at the bottom.  This relationship indicates stratigraphic top (the pencil points upward also).