A Novel Hydrothermal Salt Theory and its Application to Understanding Deep-Water Salt Accumulations and Piercement Structures

Martin Hovland¹, Håkon Rueslåtten², Christine Fichler³, and Hans Konrad Johnsen^3
1Statoil, Stavanger, Norway
²Numericalrocks, Trondheim, Norway
³Statoil, Trondheim, Norway

Laboratory experiments have demonstrated that supercritical water has extremely low solubility for normal sea salts. This fact opens up the possibility for the precipitation of salt from seawater that circulates in faults and fractures close to a heat source in tectonically active basins (typically extensional pre-rifts and rift settings). Seawater attains supercritical conditions at depths exceeding 2,800 metres (corresponding to a pressure of 300 bars) and temperatures above 405 C. Salts may also precipitate by the boiling of seawater in sub-surface or submarine settings. This is demonstrated by a simple laboratory experiment. The theoretical basis for the precipitation of salts from seawater attaining supercritical condition has been examined by molecular modelling. These processes of salt precipitation constitute a new approach to the geological understanding of salt deposits, and two regions are selected to examine whether salt may have deposited under such hydrothermal conditions today: the Atlantis II Deep in the Red Sea (sub-marine setting), and Lake Asale, Dallol, Ethiopia (continental setting).
The new model can be used to understand the emplacement of deep-water salt accumulations, such as those in the abyssal Gulf of Mexico, abyssal Mediterranean, off Brazil and West Africa. Furthermore, local salt accumulation and alteration of sedimentary rocks by supercritical water at basin floors can also explain the formation of salt-cored and mud-cored piercement structures in deep-water settings.

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece