Diagenetic features of some subsurface Tertiary-Cretaceous evaporites from northern Iraq

Abstract

Subsurface Cretaceous-Tertiary evaporite samples collected from selected oil boreholes in northern Iraq exhibit complicated diagenetic features that resulted from deep burial and other modifying agents. Among these features are extensive dissolution, growth of larger crystals or laths from preexisting evaporitic groundmass, widespread cementation in both evaporitic and non-evaporitic rocks, and the development of stylolites and fractures. SEM examination of evaporite-carbonate replacive contacts has shown that evaporites replace carbonates in root-like structures that gradually penetrate the carbonate structure following either capillary interstitial spaces or weakness planes. Cretaceous evaporites were deposited mainly in sabkha settings, whereas Tertiary evaporites were formed in salinas and sabkhas.