Route 1

DEEP WATER EVAPORITES

Source Roger Suthren

Photograph of an ancient evaporite deposit

The basic requirements for deposits of marine evaporites are:

• a relatively arid climate, where rates of evaporation exceed rates of precipitation,

• partial isolation of the depositional basin from the open ocean, allowing brines to develop.

Deep-water evaporites are the product of the large size and volume of the brine body. An alkaline, saline brine is created, by the removal of water vapor from the surface, causing increased concentrations of dissolved ions due to evaporation.

This brine will probably have a higher density than most of the underlying water. A lack of turbulent mixing will allow the dense brine to sink and form a layer on the basin floor. In very large basins this stagnant layer can be of very high salinity and low oxygen content (8303 Ancient Environments).

Progressive water loss causes concentration in the brine to exceed solubility for each mineral and precipitation takes place. Marine basin deposits can be 100's m thick but are only seen in ancient examples such as the Permian Zechstein Basin.

Deep-water deposits are layered sequences of salts, which change in composition reflecting the progressive water loss over the basin. Creamy-yellow carbonates are overlain by pink and white sulfates and then gray or orange sodium chloride, indicating loss of highly soluble potassium bearing salts by a short lived new input of sea water, before renewed evaporation.

Locality 1

Locality 2

3.Depositional models

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This page was created by Pamela Williams

Last Modified:18/06/02