Diagenetic history and porosity types of the baluti formation (UPPER TRIASSIC)‎, galley derash, Duhok Governorate, Kurdistan Region, Northern Iraq

Abstract EN

The Baluti Formation in the Galley Derash locality is comprised of 73 m brecciated dolomitic limestone in the lower part, alternating with thin bedded dolomitic limestone and dark gray shale in the middle part, then thin to medium bedded brecciated sandy limestone interbedded with dark grey shale in its upper part.

The sum of 21 thin sections of the Baluti Formation carbonates are petrographically studied using polarizing microscope.

The results show various types of skeletal grains including calcareous algae, ostracods, brachiopods, bivalves, benthonic foraminifera, gastropods, and echinoderms, while the non-skeletal grains include peloids, intraclasts, extraclasts and rare ooids.

The Baluti Formation was subjected to differed diagenetic processes such as micritization, mechanical compaction, cementation, early dolomitization, neomorphism, stylolitization, late dolomitization, dedolomitization, silisification, soulution, fracturing and pyritization.

These diagenetic modifications occurred during marine phreatic shallow burial stage and were activated during intermediate to deep burial and uplift in the late stages.

Five kinds of dolomite textures are recognized: Unimodal very fine to fine-crystalline planar-s (subhedral) mosaic, unimodal very fine to fine-crystalline planar-e (euhedral) mosaic, unimodal fine to medium crystalline planar-s (subhedral) mosaic, medium to coarsecrystalline planar to non-planar-c (cement) mosaic and polymodal planar-s (subhedral) to planar-e (euhedral) mosaic.

The petrographic study revealed that the secondary porosity is dominant.

The paragenetic history of the Baluti Formation passed through four diagenetic environments which are: marine, meteoric, burial and uplift.