Structures associated with desiccation and evaporation

Images copyright © 1998-2016, John W.F. Waldron, except where otherwise stated


Mudcracks: Large sand-filled mudcracks below sandstone bed in Mabou Group at Knoydart, Nova Scotia. Notice that there is a boundary between oxidized (red) mud and reduced (green) mud that rises and falls around the mudcracks, suggesting that the cracks allowed oxygen into the sediment.


Mudcracks in laminated limestone, St. George Group, Newfoundland. These laminated dolomitic limestones must have been exposed in the supratidal or upper intertidal zone.

edgewise conglomerate

Edgewise conglomerate: Mud flakes ripped up by storms may produce flat-pebble conglomerates, considered most characteristic of the supratidal zone in carbonate shorelines. Exceptionally, the closely packed pebbles acquire a near-vertical orientation as seen in this 'edgewise' flat-pebble conglomerate. Cambrian Port au Port Group, Newfoundland.

gypsum cast

Gypsum casts. Evaporation may lead to the production of evaporite minerals. In this case the 'swallow-tail' outline of twinned gypsum crystals is clearly recognizable from these casts in limestone. Carboniferous Windsor Group, Pomquet, Nova Scotia.


Chickenwire structure. More extensive evaporite deposition, ocurring within sediments, may produce chickenwire structure, due to the coalescing of evaporite nodules. Pomquet, Nova Scotia.