It is dominated by the deposition of calcite with minor pyrite, marcasite, barite, anhydrite and gypsum.
Both Ara Group pyrite and anhydrite are characterized by highly variable [delta] 34 S values.
In the Mesozoic, and into the Paleocene, limestone and dolomite interbedded with shale, clay and anhydrite prevailed in a more restricted, shallow marine to lagoonal environment.
Calcium sulfate exists in two forms, as anhydrite and as gypsum.
Gypsum and anhydrite are closely related; both are calcium minerals and both are formed early (after carbonate) in the sequence of minerals when sea water is evaporated or in sabkha environments, as in the present-day Persian Gulf.
Small crystals of insoluble residual minerals such as anhydrite , chambersite, hilgardite, and hilgardite - 3Tc were caught up in the brines pumped back to the surface.
Resetting of the [delta] 34 S values in anhydrite and pyrite by diagenetic fluids seems unlikely in the present case, because diagenesis occurred in a largely closed system and did not involve significant fluid movement.
At depths of less than 600m (up to 1000m depending on temperature and fluid composition), gypsum forms rather than anhydrite because the gypsum-anhydrite stability boundary is crossed somewhere in this interval.
The lower, evaporitic part of each cycle contains halite, anhydrite (secondary after sedimentary gypsum), and high salts (sylvite and polyhalite).
The Bonneval gneiss is separated from the augen gneiss by a fault zone in which dolomite, cargneule, anhydrite and Bündnerschiefer occur.