Petrograhpic study of the sarmord formation in North Zakho Area, nw Iraq

الملخص EN

The Sarmord Formation in the study area is mostly composed of dolostone rich in bituminous materials.

Due to the presence of bituminous materials, most of the rocks have dark grey to grey and black color and interbedded with fissile black shale.

The present study is mostly based on 23 samples obtained from 5 surface sections and 2 spot samples emphasizing their lithofacies, fossil contents, diagenetic processes, diagenetic environments, distribution of bitumen and environment of deposition.

Detailed petrographic examination of the rocks has led to the distinction of four main lithofacies, namely limestone, dolostone, siliceous rocks and shale.

Several diagenetic processes are observed to have affected the rocks of this formation including dolomitization, which appear to have been widespread, physical and chemical compaction, neomorphism, leaching and porosity development, cementation, silicification and calcitization (vanished evaporite).

Most of the diagenetic processes might have taken place in deep burial environment, shallow subsurface evaporatic environment and submarine environments.

Many types of bitumen accumulation can be distinguished in the studied formation.

It occurs as beds, laminae, pore filling, coating, and inclusion and as lining stylolites.

The depositional environment was so difficult to be deduced due to the severe dolomitization process, which obliterated the original texture and structures of the rocks as well as the fauna.

Nevertheless, the presence of some fauna and the remained texture and structures indicate that the deposition of the formation belongs to deep marine shelf margin environment of normal salinity