Petrology and stratigraphy of pre-Cambrian Hormuz Series outcrops in Jabal Sanam structure - the oldest surface rocks in Iraq

Abstract

Detailed geological field investigations have been done at Jabal Sanam structure Southern Iraq. More than 150 rock and mineral represented samples were collected, and 130 thin sections of these samples were prepared and examined microscopically. An accurate mineralogical study of these rocks by analysis of 15 samples with the X-ray diffraction technique was achieved. A large number of sedimentary rocks were distinguished through field observations and petrographic studies, such as gypsum, limestone, dolomite, red and green marl, sedimentary ironstones, chert, and salts. Various types of igneous and metamorphic rocks such as dolerite, schist, slate, and metamorphic sediments were found as beds or fragments intruded with the evaporite rocks of Jabal Sanam. Distinct mineralizations of hematite, pyrite, and dolomite minerals were observed in these successions. It was noted also, that these rocks were subjected to varied geological processes of different degrees that affected their original rock characteristics such as diagenesis, metamorphism, deformation, and dissolution processes. A petrological, stratigraphic, and tectonic correlation has been made with similar structures spread through the region (Iran and Arabian Peninsula) in the light of their composition which, in general; consists of infra-Cambrian evaporates of Hormuz Series. This study supports the previous geological studies on this salt structure, shows a great similarity between the rocks of Hormuz Series Complex and those of Jabal Sanam, which may be considered in terms of stratigraphy and petrology as equivalent rock units. Thus, these rocks may be suggested as the oldest rocks exposed above the earth’s surface in Iraq

Natural Radioactivity and its Hazards of Infracambrian Rocks at Jabal Sanam Structure, Southern Iraq

“…The gypsum is the predominant mineral, in addition to a minor amount of quartz and dolomite (Figure 3D). Chert rocks appeared under the microscope consisting of microcrystalline quartz and sometimes polycrystalline, with the absence of any traces of fossils, which indicates their chemical origin in their formation [31] with a clear content of iron oxides, which gave these rocks a distinguished dark brown colour in hand samples. The main igneous rock at the Jabal Sanam is dolerite.…”

“…The age of Jabal Sanam's rocks was estimated in the Infracambrian period (approximately 600 Ma), after determining the age of the igneous rocks by the dating method that was achieved by [24], which was found to be about 580 Ma. Furthermore, the age of the Jabal Sanam was concluded by comparison of the stratigraphic units of its rocks with the domes of the Infracambrian salts of Hormuz distributed in the southwestern region of Iran and the Arabian Gulf [31].…”