The Dolomitization mechanism of Pila Spi Formation (Middle- Late Eocene) in the High Folded Zone, Northern Iraq
Petrographic analysis and geochemistry of the Pila Spi Formation (Middle-late Eocene) were investigated from two outcrop sections (Gali-Zakho and Shaqlawa), within the High Folded Zone, northern Iraq. This formation consists of fine to coarsely crystalline dolomites and limestone sequences. Despite the fact that these strata have been buried and impacted by several episodes of dolomitization and dissolution, some intervals in the Pila Spi Formation have acquired porosity. Dolomicrite, dolomicrosparite, dolosparite, vein, and saddle dolomite are the five primary kinds of dolomite textures recognized based on fabric, grain size, and elemental analysis. Dolomicrite produced the sabkha model in a low-energy hypersaline sedimentary environment, since these rocks had unusually high Sr and Na values, lower Fe and Mn values. The dolomicrosparite and dolosparite developed in a shallow burial environment using the seepage-reflux model, and these rocks had a higher formation temperature, low Sr and Na levels, and a broad range of Fe and Mn values, indicating that they were impacted by meteoric water. The vein and saddle dolomite
evolved as a result of the burial model at increased temperature since these rocks had the lowest Sr and Na contents, the greatest MgO and CaO contents, and the highest Fe and Mn values. In selective dissolution processes, the early sabkha, the seepage-reflux model of dolomitization, and the synchronous cycle of meteoric freshwater, many porous intervals were formed.