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BLACK CHERT, AN INTERESTING PETROGRAPHIC COMPONENT WITHIN THE UPPER PART OF SARGELU FORMATION (MIDDLE JURASSIC) – NORTH AND NORTHEASTERN IRAQI KURDISTAN | ||
| Iraqi Bulletin of Geology and Mining | ||
| Article 1, Volume 2, Issue 1, 2006, Pages 77-88 | ||
| Authors | ||
| Sardar M. Balaky; Govand H. Sherwani | ||
| Abstract | ||
| Three surface sections of Sargelu Formation were chosen for the purpose of this study, Naokelekan village (near Rowanduz), Gara mountain (southern Amadia), and Banik village (northeast of Zakho) Northern Iraqi Kurdistan. At all these localities, the upper part of Sargelu Formation is characterized by interesting black chert beds. The petrographic study of chert beds was based on 25 thin sections. This study revealed fossils similar to those described in limestone units of the same formation, but with clear signs of silicification. By combination of field observations and petrographic studies, it can be concluded that chert beds are formed by diagenetic reorganization of silica, which is mostly of biogenic origin, mostly from radiolarians. Complete replacement of some thin limestone beds(or thin parts of them) by silica resulted in the development of chert beds. Dissolution of radiolarians, either within chert beds or in neighboring limestone beds, provides a major source of silica for this process. | ||
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