Basinwide evaporites - No modern counterpart

Basinwide evaporites (aka megahalite, megasulphate, saline giant deposits) are made up of thick evaporite units >50–100 m thick composed of varying combinations of deepwater and shallow water evaporites (Warren, 2010). They retain textural evidence of different but synchronous local depositional settings, including mudflat, saltern, slope and basin (Figure). When basinwide evaporite deposition occurs, the whole basin hydrology is evaporitic, holomictic, and typically saturated with the same mineral phase across vast areas of the basin floor, as in the Dead Sea basin today.

The Dead Sea has a more limited lateral scale than ancient basinwides, but currently has halite forming simultaneously as; 1) decimetre-thick chevron-dominated beds on the saline-pan floor of the shallow parts around the basin edge in waters typically less than 1-10 meters deep, and 2) as coarse inclusion-poor crystal meshworks of halite on the deep basin floor that sits below a halite-saturated brine column up to hundreds of meters deep.

Thick massive salt beds usually dominate ancient basinwide successions, generally more than 100-500 m thick. Deposits tend to made up of stacked thick halite beds, but can also contain substantial volumes of thick-bedded Ca-sulphate and evaporitic carbonate, as in the intracratonic basinwide accumulations of the Delaware and Otto Fiord Basins.

Owing to the inherent purity and thickness of the deposited halite, many halite-dominant basinwide beds are also remobilised, via loading or tectonics, into various halokinetic geometries. Some basinwide systems (mostly marine-fed intracratonic settings) entrain significant accumulations of marine-fed potash salts, as in the Devonian Prairie Evaporite of western Canada. In contrast, all Quaternary examples of commercial potash deposits are accumulating in continental lacustrine systems.

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Tectonic and hydrographically isolated (marine endorheic) continent-margin situations where basinwide evaporites tend to accumulate (evaporite beds are shaded pink). Positions are tied mainly to world-scale times of continent-continent proximity and so can be linked to the various stages of the Wilson Cycle.