DISSOLUTION-COLLAPSE BRECCIAS AND PALEOKARST RESULTING FROM DISSOLUTION OF EVAPORITE ROCKS, ESPECIALLY SULFATES

The lithological trinity of dolostone, limestone, and sulfates (anhydr ite and/or gypsum) is subject to rapid dissolution of the sulfates and leads to the development of dissolution-collapse breccias resulting f rom the withdrawal of the sulfates. The resultant features commonly in clude spectacular dissolution-collapse breccias. Owing to their mobili ty and chemical instability evaporite rocks, such as gypsum and anhydr ite, are highly soluble and can be dissolved rapidly to form karstic f eatures. When anhydrite and/or gypsum are dissolved the overlying cont inuous strata of carbonate rocks collapse, generating dissolution-coll apse breccia composed of carbonate clasts. Such dissolution-collapse b reccias as a result of dissolution of gypsum and/or anhydrite are more common worldwide than the literature suggests. Evaporite karst interf eres with human activity, including highways, buildings, canals, and a griculture. A Cretaceous deposit composed of dolostone, limestone, and anhydrite breccia set in a carbonate matrix has been interpreted as t he result of asteroid- or comet collision. An origin as evaporite pale okarst could explain the formation of this same breccia. In the Willis ton Basin of Montana anhydrites form the caps of basin-wide peritidal cycles in successions which brine upward. The supratidal cycle caps ar e zones of anhydrite leaching and creation of dissolution-collapse bre ccia. Cambro-Lower Ordovician (Sauk) platform cycles in the Appalachia n Basin are composed of peritidal upward-shallowing carbonate facies w hich show evidence of ultimate emergence. The sulfates in the cycle ca ps have entirely dissolved out and the paleokarst serves as testament to their former presence.