Geology of miocene gypsum deposits in Northern Iraq : a review

Abstract EN

Miocene Evaporates sediments of northern Iraq are basically represented by Divan (Lower Miocene) and Fat 'Formations (Middle Miocene), these two formations are found both in surface and subsurface sections.

They consists of alternating cycles of three lithofacies ; gypsum, limestone and marl.

Ecstatic sea level changes besides the vertical basement block movement play an important role in the development of cyclic sediment logical regime of Miocene sediments via the opening and closing of lagoons and coastal shallow basins.

The prevailing of arid pale climate causing the deposition of evaporates.

Gypsum rocks are of massive, nodular and selenic types.

Two types of gypsum textures are recognized ; alabstrine and porphroblastic.

The Miocene gypsum is of a secondary origin resulted from the hydration of pre-existing anhydrite.

From a mineralogical point of view, the Miocene gypsum rocks consist mainly of gypsum as dominant mineral with minor amounts of anhydrite, dolomite, celestite, bassinet, and traces of quartz.

Salinity, clay minerals contents, and digenetic proceses controlled the distribution of major, minor, and trace elements in gypsum rocks under study.

Great petro logical and geochemical similarity was documented between Lower and Middle Miocene gypsum.

Most of the economic gypsum deposits in Iraq occur in Fat'ha Formation, these deposits are generally pure (Insoluble residue 1-2 %) and suitable for many industrial uses.