Effects of climatic variation on weathering intensity for the mineral composition in some Iraqi soils

This study was conducted to find out the effect of variation in the nature of climatic conditions and physiographic location on the weathering intensity of the mineral composition in some Iraqi soils. Six different locations were selected within rainfall with intensity ranged between 100-1200 mm year^-1, located in the north, west, central and southern Iraq. These locations were represented by the governorates of Erbil and Sulaymaniyah, Salah al-Din, Wasit and Dhi Qar in the locations of Joman, Halabja, Al-Sharqat, Tikrit, Al-Suwaira project, and Hor Al-Jbayish respectively. The scanning electron microscope (SEM) was used to diagnose the most important morphological features of clay minerals. Moreover, the examination results of clays in northern Iraq showed the presence of mica minerals in their irregular lamellar shape with rough surfaces containing cracks. These features reflected the exposure of mica minerals to different stages of weathering intensity of the layers. It was also exposed to the edges weathering in some of its areas. Likewise, the surfaces of these minerals seemed to contain slab elongated particles of regular geometric shape and with curled edges belonging to other minerals that are considered as impurities within the composition of the original mineral during the formation process. Besides, a transformation of part of the mica minerals appeared towards the expanded minerals 1:2 most likely to be Smectite minerals. As for the clays of the western regions of Iraq, the mica mineral particles appeared with multiple morphological appearances within the weathering of layers and edges. The surfaces of those particles appeared rough with the presence of the layers splitting accompanied by peeling, which indicates the exposure of these minerals to layers weathering. Furthermore, the results of general examination of the particles showed the absence of sharp edges rather, and some of them had irregular edges as a result of breaking the metal flakes as they were subjected to physical weathering in conjunction with chemical weathering, in addition, the presence of a shift at the edges of the mica minerals towards the expanded Smectite minerals 1:2. The latter appeared in the form of a white cloud, in addition to the presence of mica minerals with the weathered edges, but it appeared in a limited way, which reflects the extent of the decrease in the effective weathering intensity in those areas. The particles of the Palygorskite mineral appeared in an elongated shape, which reflects the appropriateness of the environmental conditions in those areas to form it, as it is a gypsum soil in nature. In the case of the clays of the central regions of Iraq, mica minerals appeared in the form of unaffected surfaces and the edges of some of them weathered which may have been weathered by transport and sedimentation processes. On the other hand, at the source, the conditions of the sampling areas do not encourage the occurrence of weathering processes, since they are dry or semi-dry areas with little rain. Similarly, it may be caused by wind weathering. In addition, chlorite minerals appeared in a pseudo hexagonal form, while Smectite minerals in a white cloudy form. At the same time, the clays of the southern regions of Iraq - Hor Al-Jbayish showed that a large part of the surfaces of their minerals were irregular. However, the surfaces of the mica minerals contained holes of different sizes and that some of those mineral surfaces appeared in a spongy form. Moreover, the holes that had been observed on the surfaces of Mica minerals can be the result of the presence of impurities from fossilized plant. Otherwise, animal remains during the synthesis of the mineral, which left a hole after the process of its complete dissolution. Similarly, it may be the result of the mineral impurity in the presence of impurities of other minerals that may differ in their geological age and degree of resistance to weathering. In general, all these morphological features are a product of what these minerals are exposed to the weathering processes, whether they are water or wind in the source
areas or during transport and deposition.